/*      $NetBSD: buffer.c,v 1.7 2024/08/18 20:47:20 christos Exp $      */

/*
* Copyright (c) 2002-2007 Niels Provos <[email protected]>
* Copyright (c) 2007-2012 Niels Provos and Nick Mathewson
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
*    derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#include "event2/event-config.h"
#include "evconfig-private.h"

#ifdef _WIN32
#include <winsock2.h>
#include <windows.h>
#include <io.h>
#endif

#ifdef EVENT__HAVE_VASPRINTF
/* If we have vasprintf, we need to define _GNU_SOURCE before we include
* stdio.h.  This comes from evconfig-private.h.
*/
#endif

#include <sys/types.h>

#ifdef EVENT__HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#ifdef EVENT__HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif

#ifdef EVENT__HAVE_SYS_UIO_H
#include <sys/uio.h>
#endif

#ifdef EVENT__HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif

#ifdef EVENT__HAVE_SYS_MMAN_H
#include <sys/mman.h>
#endif

#ifdef EVENT__HAVE_SYS_SENDFILE_H
#include <sys/sendfile.h>
#endif
#ifdef EVENT__HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif


#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef EVENT__HAVE_STDARG_H
#include <stdarg.h>
#endif
#ifdef EVENT__HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <limits.h>

#include "event2/event.h"
#include "event2/buffer.h"
#include "event2/buffer_compat.h"
#include "event2/bufferevent.h"
#include "event2/bufferevent_compat.h"
#include "event2/bufferevent_struct.h"
#include "event2/thread.h"
#include "log-internal.h"
#include "mm-internal.h"
#include "util-internal.h"
#include "evthread-internal.h"
#include "evbuffer-internal.h"
#include "bufferevent-internal.h"
#include "event-internal.h"

/* some systems do not have MAP_FAILED */
#ifndef MAP_FAILED
#define MAP_FAILED      ((void *)-1)
#endif

/* send file support */
#if defined(EVENT__HAVE_SYS_SENDFILE_H) && defined(EVENT__HAVE_SENDFILE) && defined(__linux__)
#define USE_SENDFILE            1
#define SENDFILE_IS_LINUX       1
#elif defined(EVENT__HAVE_SENDFILE) && defined(__FreeBSD__)
#define USE_SENDFILE            1
#define SENDFILE_IS_FREEBSD     1
#elif defined(EVENT__HAVE_SENDFILE) && defined(__APPLE__)
#define USE_SENDFILE            1
#define SENDFILE_IS_MACOSX      1
#elif defined(EVENT__HAVE_SENDFILE) && defined(__sun__) && defined(__svr4__)
#define USE_SENDFILE            1
#define SENDFILE_IS_SOLARIS     1
#endif

/* Mask of user-selectable callback flags. */
#define EVBUFFER_CB_USER_FLAGS      0xffff
/* Mask of all internal-use-only flags. */
#define EVBUFFER_CB_INTERNAL_FLAGS  0xffff0000

/* Flag set if the callback is using the cb_obsolete function pointer  */
#define EVBUFFER_CB_OBSOLETE           0x00040000

/* evbuffer_chain support */
#define CHAIN_SPACE_PTR(ch) ((ch)->buffer + (ch)->misalign + (ch)->off)
#define CHAIN_SPACE_LEN(ch) ((ch)->flags & EVBUFFER_IMMUTABLE ? \
           0 : (ch)->buffer_len - ((ch)->misalign + (ch)->off))

#define CHAIN_PINNED(ch)  (((ch)->flags & EVBUFFER_MEM_PINNED_ANY) != 0)
#define CHAIN_PINNED_R(ch)  (((ch)->flags & EVBUFFER_MEM_PINNED_R) != 0)

/* evbuffer_ptr support */
#define PTR_NOT_FOUND(ptr) do {                 \
       (ptr)->pos = -1;                                        \
       (ptr)->internal_.chain = NULL;          \
       (ptr)->internal_.pos_in_chain = 0;      \
} while (0)

static void evbuffer_chain_align(struct evbuffer_chain *chain);
static int evbuffer_chain_should_realign(struct evbuffer_chain *chain,
   size_t datalen);
static void evbuffer_deferred_callback(struct event_callback *cb, void *arg);
static int evbuffer_ptr_memcmp(const struct evbuffer *buf,
   const struct evbuffer_ptr *pos, const char *mem, size_t len);
static struct evbuffer_chain *evbuffer_expand_singlechain(struct evbuffer *buf,
   size_t datlen);
static int evbuffer_ptr_subtract(struct evbuffer *buf, struct evbuffer_ptr *pos,
   size_t howfar);
static int evbuffer_file_segment_materialize(struct evbuffer_file_segment *seg);
static inline void evbuffer_chain_incref(struct evbuffer_chain *chain);

static struct evbuffer_chain *
evbuffer_chain_new(size_t size)
{
       struct evbuffer_chain *chain;
       size_t to_alloc;

       if (size > EVBUFFER_CHAIN_MAX - EVBUFFER_CHAIN_SIZE)
               return (NULL);

       size += EVBUFFER_CHAIN_SIZE;

       /* get the next largest memory that can hold the buffer */
       if (size < EVBUFFER_CHAIN_MAX / 2) {
               to_alloc = MIN_BUFFER_SIZE;
               while (to_alloc < size) {
                       to_alloc <<= 1;
               }
       } else {
               to_alloc = size;
       }

       /* we get everything in one chunk */
       if ((chain = mm_malloc(to_alloc)) == NULL)
               return (NULL);

       memset(chain, 0, EVBUFFER_CHAIN_SIZE);

       chain->buffer_len = to_alloc - EVBUFFER_CHAIN_SIZE;

       /* this way we can manipulate the buffer to different addresses,
        * which is required for mmap for example.
        */
       chain->buffer = EVBUFFER_CHAIN_EXTRA(unsigned char, chain);

       chain->refcnt = 1;

       return (chain);
}

static inline void
evbuffer_chain_free(struct evbuffer_chain *chain)
{
       EVUTIL_ASSERT(chain->refcnt > 0);
       if (--chain->refcnt > 0) {
               /* chain is still referenced by other chains */
               return;
       }

       if (CHAIN_PINNED(chain)) {
               /* will get freed once no longer dangling */
               chain->refcnt++;
               chain->flags |= EVBUFFER_DANGLING;
               return;
       }

       /* safe to release chain, it's either a referencing
        * chain or all references to it have been freed */
       if (chain->flags & EVBUFFER_REFERENCE) {
               struct evbuffer_chain_reference *info =
                   EVBUFFER_CHAIN_EXTRA(
                           struct evbuffer_chain_reference,
                           chain);
               if (info->cleanupfn)
                       (*info->cleanupfn)(chain->buffer,
                           chain->buffer_len,
                           info->extra);
       }
       if (chain->flags & EVBUFFER_FILESEGMENT) {
               struct evbuffer_chain_file_segment *info =
                   EVBUFFER_CHAIN_EXTRA(
                           struct evbuffer_chain_file_segment,
                           chain);
               if (info->segment) {
#ifdef _WIN32
                       if (info->segment->is_mapping)
                               UnmapViewOfFile(chain->buffer);
#endif
                       evbuffer_file_segment_free(info->segment);
               }
       }
       if (chain->flags & EVBUFFER_MULTICAST) {
               struct evbuffer_multicast_parent *info =
                   EVBUFFER_CHAIN_EXTRA(
                           struct evbuffer_multicast_parent,
                           chain);
               /* referencing chain is being freed, decrease
                * refcounts of source chain and associated
                * evbuffer (which get freed once both reach
                * zero) */
               EVUTIL_ASSERT(info->source != NULL);
               EVUTIL_ASSERT(info->parent != NULL);
               EVBUFFER_LOCK(info->source);
               evbuffer_chain_free(info->parent);
               evbuffer_decref_and_unlock_(info->source);
       }

       mm_free(chain);
}

static void
evbuffer_free_all_chains(struct evbuffer_chain *chain)
{
       struct evbuffer_chain *next;
       for (; chain; chain = next) {
               next = chain->next;
               evbuffer_chain_free(chain);
       }
}

#ifndef NDEBUG
static int
evbuffer_chains_all_empty(struct evbuffer_chain *chain)
{
       for (; chain; chain = chain->next) {
               if (chain->off)
                       return 0;
       }
       return 1;
}
#else
/* The definition is needed for EVUTIL_ASSERT, which uses sizeof to avoid
"unused variable" warnings. */
static inline int evbuffer_chains_all_empty(struct evbuffer_chain *chain) {
       return 1;
}
#endif

/* Free all trailing chains in 'buf' that are neither pinned nor empty, prior
* to replacing them all with a new chain.  Return a pointer to the place
* where the new chain will go.
*
* Internal; requires lock.  The caller must fix up buf->last and buf->first
* as needed; they might have been freed.
*/
static struct evbuffer_chain **
evbuffer_free_trailing_empty_chains(struct evbuffer *buf)
{
       struct evbuffer_chain **ch = buf->last_with_datap;
       /* Find the first victim chain.  It might be *last_with_datap */
       while ((*ch) && ((*ch)->off != 0 || CHAIN_PINNED(*ch)))
               ch = &(*ch)->next;
       if (*ch) {
               EVUTIL_ASSERT(evbuffer_chains_all_empty(*ch));
               evbuffer_free_all_chains(*ch);
               *ch = NULL;
       }
       return ch;
}

/* Add a single chain 'chain' to the end of 'buf', freeing trailing empty
* chains as necessary.  Requires lock.  Does not schedule callbacks.
*/
static void
evbuffer_chain_insert(struct evbuffer *buf,
   struct evbuffer_chain *chain)
{
       ASSERT_EVBUFFER_LOCKED(buf);
       if (*buf->last_with_datap == NULL) {
               /* There are no chains data on the buffer at all. */
               EVUTIL_ASSERT(buf->last_with_datap == &buf->first);
               EVUTIL_ASSERT(buf->first == NULL);
               buf->first = buf->last = chain;
       } else {
               struct evbuffer_chain **chp;
               chp = evbuffer_free_trailing_empty_chains(buf);
               *chp = chain;
               if (chain->off)
                       buf->last_with_datap = chp;
               buf->last = chain;
       }
       buf->total_len += chain->off;
}

static inline struct evbuffer_chain *
evbuffer_chain_insert_new(struct evbuffer *buf, size_t datlen)
{
       struct evbuffer_chain *chain;
       if ((chain = evbuffer_chain_new(datlen)) == NULL)
               return NULL;
       evbuffer_chain_insert(buf, chain);
       return chain;
}

void
evbuffer_chain_pin_(struct evbuffer_chain *chain, unsigned flag)
{
       EVUTIL_ASSERT((chain->flags & flag) == 0);
       chain->flags |= flag;
}

void
evbuffer_chain_unpin_(struct evbuffer_chain *chain, unsigned flag)
{
       EVUTIL_ASSERT((chain->flags & flag) != 0);
       chain->flags &= ~flag;
       if (chain->flags & EVBUFFER_DANGLING)
               evbuffer_chain_free(chain);
}

static inline void
evbuffer_chain_incref(struct evbuffer_chain *chain)
{
   ++chain->refcnt;
}

struct evbuffer *
evbuffer_new(void)
{
       struct evbuffer *buffer;

       buffer = mm_calloc(1, sizeof(struct evbuffer));
       if (buffer == NULL)
               return (NULL);

       LIST_INIT(&buffer->callbacks);
       buffer->refcnt = 1;
       buffer->last_with_datap = &buffer->first;

       return (buffer);
}

int
evbuffer_set_flags(struct evbuffer *buf, ev_uint64_t flags)
{
       EVBUFFER_LOCK(buf);
       buf->flags |= (ev_uint32_t)flags;
       EVBUFFER_UNLOCK(buf);
       return 0;
}

int
evbuffer_clear_flags(struct evbuffer *buf, ev_uint64_t flags)
{
       EVBUFFER_LOCK(buf);
       buf->flags &= ~(ev_uint32_t)flags;
       EVBUFFER_UNLOCK(buf);
       return 0;
}

void
evbuffer_incref_(struct evbuffer *buf)
{
       EVBUFFER_LOCK(buf);
       ++buf->refcnt;
       EVBUFFER_UNLOCK(buf);
}

void
evbuffer_incref_and_lock_(struct evbuffer *buf)
{
       EVBUFFER_LOCK(buf);
       ++buf->refcnt;
}

int
evbuffer_defer_callbacks(struct evbuffer *buffer, struct event_base *base)
{
       EVBUFFER_LOCK(buffer);
       buffer->cb_queue = base;
       buffer->deferred_cbs = 1;
       event_deferred_cb_init_(&buffer->deferred,
           event_base_get_npriorities(base) / 2,
           evbuffer_deferred_callback, buffer);
       EVBUFFER_UNLOCK(buffer);
       return 0;
}

int
evbuffer_enable_locking(struct evbuffer *buf, void *lock)
{
#ifdef EVENT__DISABLE_THREAD_SUPPORT
       return -1;
#else
       if (buf->lock)
               return -1;

       if (!lock) {
               EVTHREAD_ALLOC_LOCK(lock, EVTHREAD_LOCKTYPE_RECURSIVE);
               if (!lock)
                       return -1;
               buf->lock = lock;
               buf->own_lock = 1;
       } else {
               buf->lock = lock;
               buf->own_lock = 0;
       }

       return 0;
#endif
}

void
evbuffer_set_parent_(struct evbuffer *buf, struct bufferevent *bev)
{
       EVBUFFER_LOCK(buf);
       buf->parent = bev;
       EVBUFFER_UNLOCK(buf);
}

static void
evbuffer_run_callbacks(struct evbuffer *buffer, int running_deferred)
{
       struct evbuffer_cb_entry *cbent, *next;
       struct evbuffer_cb_info info;
       size_t new_size;
       ev_uint32_t mask, masked_val;
       int clear = 1;

       if (running_deferred) {
               mask = EVBUFFER_CB_NODEFER|EVBUFFER_CB_ENABLED;
               masked_val = EVBUFFER_CB_ENABLED;
       } else if (buffer->deferred_cbs) {
               mask = EVBUFFER_CB_NODEFER|EVBUFFER_CB_ENABLED;
               masked_val = EVBUFFER_CB_NODEFER|EVBUFFER_CB_ENABLED;
               /* Don't zero-out n_add/n_del, since the deferred callbacks
                  will want to see them. */
               clear = 0;
       } else {
               mask = EVBUFFER_CB_ENABLED;
               masked_val = EVBUFFER_CB_ENABLED;
       }

       ASSERT_EVBUFFER_LOCKED(buffer);

       if (LIST_EMPTY(&buffer->callbacks)) {
               buffer->n_add_for_cb = buffer->n_del_for_cb = 0;
               return;
       }
       if (buffer->n_add_for_cb == 0 && buffer->n_del_for_cb == 0)
               return;

       new_size = buffer->total_len;
       info.orig_size = new_size + buffer->n_del_for_cb - buffer->n_add_for_cb;
       info.n_added = buffer->n_add_for_cb;
       info.n_deleted = buffer->n_del_for_cb;
       if (clear) {
               buffer->n_add_for_cb = 0;
               buffer->n_del_for_cb = 0;
       }
       for (cbent = LIST_FIRST(&buffer->callbacks);
            cbent != LIST_END(&buffer->callbacks);
            cbent = next) {
               /* Get the 'next' pointer now in case this callback decides
                * to remove itself or something. */
               next = LIST_NEXT(cbent, next);

               if ((cbent->flags & mask) != masked_val)
                       continue;

               if ((cbent->flags & EVBUFFER_CB_OBSOLETE))
                       cbent->cb.cb_obsolete(buffer,
                           info.orig_size, new_size, cbent->cbarg);
               else
                       cbent->cb.cb_func(buffer, &info, cbent->cbarg);
       }
}

void
evbuffer_invoke_callbacks_(struct evbuffer *buffer)
{
       if (LIST_EMPTY(&buffer->callbacks)) {
               buffer->n_add_for_cb = buffer->n_del_for_cb = 0;
               return;
       }

       if (buffer->deferred_cbs) {
               if (event_deferred_cb_schedule_(buffer->cb_queue, &buffer->deferred)) {
                       evbuffer_incref_and_lock_(buffer);
                       if (buffer->parent)
                               bufferevent_incref_(buffer->parent);
                       EVBUFFER_UNLOCK(buffer);
               }
       }

       evbuffer_run_callbacks(buffer, 0);
}

static void
evbuffer_deferred_callback(struct event_callback *cb, void *arg)
{
       struct bufferevent *parent = NULL;
       struct evbuffer *buffer = arg;

       /* XXXX It would be better to run these callbacks without holding the
        * lock */
       EVBUFFER_LOCK(buffer);
       parent = buffer->parent;
       evbuffer_run_callbacks(buffer, 1);
       evbuffer_decref_and_unlock_(buffer);
       if (parent)
               bufferevent_decref_(parent);
}

static void
evbuffer_remove_all_callbacks(struct evbuffer *buffer)
{
       struct evbuffer_cb_entry *cbent;

       while ((cbent = LIST_FIRST(&buffer->callbacks))) {
               LIST_REMOVE(cbent, next);
               mm_free(cbent);
       }
}

void
evbuffer_decref_and_unlock_(struct evbuffer *buffer)
{
       struct evbuffer_chain *chain, *next;
       ASSERT_EVBUFFER_LOCKED(buffer);

       EVUTIL_ASSERT(buffer->refcnt > 0);

       if (--buffer->refcnt > 0) {
               EVBUFFER_UNLOCK(buffer);
               return;
       }

       for (chain = buffer->first; chain != NULL; chain = next) {
               next = chain->next;
               evbuffer_chain_free(chain);
       }
       evbuffer_remove_all_callbacks(buffer);
       if (buffer->deferred_cbs)
               event_deferred_cb_cancel_(buffer->cb_queue, &buffer->deferred);

       EVBUFFER_UNLOCK(buffer);
       if (buffer->own_lock)
               EVTHREAD_FREE_LOCK(buffer->lock, EVTHREAD_LOCKTYPE_RECURSIVE);
       mm_free(buffer);
}

void
evbuffer_free(struct evbuffer *buffer)
{
       EVBUFFER_LOCK(buffer);
       evbuffer_decref_and_unlock_(buffer);
}

void
evbuffer_lock(struct evbuffer *buf)
{
       EVBUFFER_LOCK(buf);
}

void
evbuffer_unlock(struct evbuffer *buf)
{
       EVBUFFER_UNLOCK(buf);
}

size_t
evbuffer_get_length(const struct evbuffer *buffer)
{
       size_t result;

       EVBUFFER_LOCK(buffer);

       result = (buffer->total_len);

       EVBUFFER_UNLOCK(buffer);

       return result;
}

size_t
evbuffer_get_contiguous_space(const struct evbuffer *buf)
{
       struct evbuffer_chain *chain;
       size_t result;

       EVBUFFER_LOCK(buf);
       chain = buf->first;
       result = (chain != NULL ? chain->off : 0);
       EVBUFFER_UNLOCK(buf);

       return result;
}

size_t
evbuffer_add_iovec(struct evbuffer * buf, struct evbuffer_iovec * vec, int n_vec) {
       int n;
       size_t res;
       size_t to_alloc;

       EVBUFFER_LOCK(buf);

       res = to_alloc = 0;

       for (n = 0; n < n_vec; n++) {
               to_alloc += vec[n].iov_len;
       }

       if (evbuffer_expand_fast_(buf, to_alloc, 2) < 0) {
               goto done;
       }

       for (n = 0; n < n_vec; n++) {
               /* XXX each 'add' call here does a bunch of setup that's
                * obviated by evbuffer_expand_fast_, and some cleanup that we
                * would like to do only once.  Instead we should just extract
                * the part of the code that's needed. */

               if (evbuffer_add(buf, vec[n].iov_base, vec[n].iov_len) < 0) {
                       goto done;
               }

               res += vec[n].iov_len;
       }

done:
   EVBUFFER_UNLOCK(buf);
   return res;
}

int
evbuffer_reserve_space(struct evbuffer *buf, ev_ssize_t size,
   struct evbuffer_iovec *vec, int n_vecs)
{
       struct evbuffer_chain *chain, **chainp;
       int n = -1;

       EVBUFFER_LOCK(buf);
       if (buf->freeze_end)
               goto done;
       if (n_vecs < 1)
               goto done;
       if (n_vecs == 1) {
               if ((chain = evbuffer_expand_singlechain(buf, size)) == NULL)
                       goto done;

               vec[0].iov_base = (void *)CHAIN_SPACE_PTR(chain);
               vec[0].iov_len = (size_t)CHAIN_SPACE_LEN(chain);
               EVUTIL_ASSERT(size<0 || (size_t)vec[0].iov_len >= (size_t)size);
               n = 1;
       } else {
               if (evbuffer_expand_fast_(buf, size, n_vecs)<0)
                       goto done;
               n = evbuffer_read_setup_vecs_(buf, size, vec, n_vecs,
                               &chainp, 0);
       }

done:
       EVBUFFER_UNLOCK(buf);
       return n;

}

static int
advance_last_with_data(struct evbuffer *buf)
{
       int n = 0;
       struct evbuffer_chain **chainp = buf->last_with_datap;

       ASSERT_EVBUFFER_LOCKED(buf);

       if (!*chainp)
               return 0;

       while ((*chainp)->next) {
               chainp = &(*chainp)->next;
               if ((*chainp)->off)
                       buf->last_with_datap = chainp;
               ++n;
       }
       return n;
}

int
evbuffer_commit_space(struct evbuffer *buf,
   struct evbuffer_iovec *vec, int n_vecs)
{
       struct evbuffer_chain *chain, **firstchainp, **chainp;
       int result = -1;
       size_t added = 0;
       int i;

       EVBUFFER_LOCK(buf);

       if (buf->freeze_end)
               goto done;
       if (n_vecs == 0) {
               result = 0;
               goto done;
       } else if (n_vecs == 1 &&
           (buf->last && vec[0].iov_base == (void *)CHAIN_SPACE_PTR(buf->last))) {
               /* The user only got or used one chain; it might not
                * be the first one with space in it. */
               if ((size_t)vec[0].iov_len > (size_t)CHAIN_SPACE_LEN(buf->last))
                       goto done;
               buf->last->off += vec[0].iov_len;
               added = vec[0].iov_len;
               if (added)
                       advance_last_with_data(buf);
               goto okay;
       }

       /* Advance 'firstchain' to the first chain with space in it. */
       firstchainp = buf->last_with_datap;
       if (!*firstchainp)
               goto done;
       if (CHAIN_SPACE_LEN(*firstchainp) == 0) {
               firstchainp = &(*firstchainp)->next;
       }

       chain = *firstchainp;
       /* pass 1: make sure that the pointers and lengths of vecs[] are in
        * bounds before we try to commit anything. */
       for (i=0; i<n_vecs; ++i) {
               if (!chain)
                       goto done;
               if (vec[i].iov_base != (void *)CHAIN_SPACE_PTR(chain) ||
                   (size_t)vec[i].iov_len > CHAIN_SPACE_LEN(chain))
                       goto done;
               chain = chain->next;
       }
       /* pass 2: actually adjust all the chains. */
       chainp = firstchainp;
       for (i=0; i<n_vecs; ++i) {
               (*chainp)->off += vec[i].iov_len;
               added += vec[i].iov_len;
               if (vec[i].iov_len) {
                       buf->last_with_datap = chainp;
               }
               chainp = &(*chainp)->next;
       }

okay:
       buf->total_len += added;
       buf->n_add_for_cb += added;
       result = 0;
       evbuffer_invoke_callbacks_(buf);

done:
       EVBUFFER_UNLOCK(buf);
       return result;
}

static inline int
HAS_PINNED_R(struct evbuffer *buf)
{
       return (buf->last && CHAIN_PINNED_R(buf->last));
}

static inline void
ZERO_CHAIN(struct evbuffer *dst)
{
       ASSERT_EVBUFFER_LOCKED(dst);
       dst->first = NULL;
       dst->last = NULL;
       dst->last_with_datap = &(dst)->first;
       dst->total_len = 0;
}

/* Prepares the contents of src to be moved to another buffer by removing
* read-pinned chains. The first pinned chain is saved in first, and the
* last in last. If src has no read-pinned chains, first and last are set
* to NULL. */
static int
PRESERVE_PINNED(struct evbuffer *src, struct evbuffer_chain **first,
               struct evbuffer_chain **last)
{
       struct evbuffer_chain *chain, **pinned;

       ASSERT_EVBUFFER_LOCKED(src);

       if (!HAS_PINNED_R(src)) {
               *first = *last = NULL;
               return 0;
       }

       pinned = src->last_with_datap;
       if (!CHAIN_PINNED_R(*pinned))
               pinned = &(*pinned)->next;
       EVUTIL_ASSERT(CHAIN_PINNED_R(*pinned));
       chain = *first = *pinned;
       *last = src->last;

       /* If there's data in the first pinned chain, we need to allocate
        * a new chain and copy the data over. */
       if (chain->off) {
               struct evbuffer_chain *tmp;

               EVUTIL_ASSERT(pinned == src->last_with_datap);
               tmp = evbuffer_chain_new(chain->off);
               if (!tmp)
                       return -1;
               memcpy(tmp->buffer, chain->buffer + chain->misalign,
                       chain->off);
               tmp->off = chain->off;
               *src->last_with_datap = tmp;
               src->last = tmp;
               chain->misalign += chain->off;
               chain->off = 0;
       } else {
               src->last = *src->last_with_datap;
               *pinned = NULL;
       }

       return 0;
}

static inline void
RESTORE_PINNED(struct evbuffer *src, struct evbuffer_chain *pinned,
               struct evbuffer_chain *last)
{
       ASSERT_EVBUFFER_LOCKED(src);

       if (!pinned) {
               ZERO_CHAIN(src);
               return;
       }

       src->first = pinned;
       src->last = last;
       src->last_with_datap = &src->first;
       src->total_len = 0;
}

static inline void
COPY_CHAIN(struct evbuffer *dst, struct evbuffer *src)
{
       ASSERT_EVBUFFER_LOCKED(dst);
       ASSERT_EVBUFFER_LOCKED(src);
       dst->first = src->first;
       if (src->last_with_datap == &src->first)
               dst->last_with_datap = &dst->first;
       else
               dst->last_with_datap = src->last_with_datap;
       dst->last = src->last;
       dst->total_len = src->total_len;
}

static void
APPEND_CHAIN(struct evbuffer *dst, struct evbuffer *src)
{
       struct evbuffer_chain **chp;

       ASSERT_EVBUFFER_LOCKED(dst);
       ASSERT_EVBUFFER_LOCKED(src);

       chp = evbuffer_free_trailing_empty_chains(dst);
       *chp = src->first;

       if (src->last_with_datap == &src->first)
               dst->last_with_datap = chp;
       else
               dst->last_with_datap = src->last_with_datap;
       dst->last = src->last;
       dst->total_len += src->total_len;
}

static inline void
APPEND_CHAIN_MULTICAST(struct evbuffer *dst, struct evbuffer *src)
{
       struct evbuffer_chain *tmp;
       struct evbuffer_chain *chain = src->first;
       struct evbuffer_multicast_parent *extra;

       ASSERT_EVBUFFER_LOCKED(dst);
       ASSERT_EVBUFFER_LOCKED(src);

       for (; chain; chain = chain->next) {
               if (!chain->off || chain->flags & EVBUFFER_DANGLING) {
                       /* skip empty chains */
                       continue;
               }

               tmp = evbuffer_chain_new(sizeof(struct evbuffer_multicast_parent));
               if (!tmp) {
                       event_warn("%s: out of memory", __func__);
                       return;
               }
               extra = EVBUFFER_CHAIN_EXTRA(struct evbuffer_multicast_parent, tmp);
               /* reference evbuffer containing source chain so it
                * doesn't get released while the chain is still
                * being referenced to */
               evbuffer_incref_(src);
               extra->source = src;
               /* reference source chain which now becomes immutable */
               evbuffer_chain_incref(chain);
               extra->parent = chain;
               chain->flags |= EVBUFFER_IMMUTABLE;
               tmp->buffer_len = chain->buffer_len;
               tmp->misalign = chain->misalign;
               tmp->off = chain->off;
               tmp->flags |= EVBUFFER_MULTICAST|EVBUFFER_IMMUTABLE;
               tmp->buffer = chain->buffer;
               evbuffer_chain_insert(dst, tmp);
       }
}

static void
PREPEND_CHAIN(struct evbuffer *dst, struct evbuffer *src)
{
       ASSERT_EVBUFFER_LOCKED(dst);
       ASSERT_EVBUFFER_LOCKED(src);
       src->last->next = dst->first;
       dst->first = src->first;
       dst->total_len += src->total_len;
       if (*dst->last_with_datap == NULL) {
               if (src->last_with_datap == &(src)->first)
                       dst->last_with_datap = &dst->first;
               else
                       dst->last_with_datap = src->last_with_datap;
       } else if (dst->last_with_datap == &dst->first) {
               dst->last_with_datap = &src->last->next;
       }
}

int
evbuffer_add_buffer(struct evbuffer *outbuf, struct evbuffer *inbuf)
{
       struct evbuffer_chain *pinned, *last;
       size_t in_total_len, out_total_len;
       int result = 0;

       EVBUFFER_LOCK2(inbuf, outbuf);
       in_total_len = inbuf->total_len;
       out_total_len = outbuf->total_len;

       if (in_total_len == 0 || outbuf == inbuf)
               goto done;

       if (outbuf->freeze_end || inbuf->freeze_start) {
               result = -1;
               goto done;
       }

       if (PRESERVE_PINNED(inbuf, &pinned, &last) < 0) {
               result = -1;
               goto done;
       }

       if (out_total_len == 0) {
               /* There might be an empty chain at the start of outbuf; free
                * it. */
               evbuffer_free_all_chains(outbuf->first);
               COPY_CHAIN(outbuf, inbuf);
       } else {
               APPEND_CHAIN(outbuf, inbuf);
       }

       RESTORE_PINNED(inbuf, pinned, last);

       inbuf->n_del_for_cb += in_total_len;
       outbuf->n_add_for_cb += in_total_len;

       evbuffer_invoke_callbacks_(inbuf);
       evbuffer_invoke_callbacks_(outbuf);

done:
       EVBUFFER_UNLOCK2(inbuf, outbuf);
       return result;
}

int
evbuffer_add_buffer_reference(struct evbuffer *outbuf, struct evbuffer *inbuf)
{
       size_t in_total_len, out_total_len;
       struct evbuffer_chain *chain;
       int result = 0;

       EVBUFFER_LOCK2(inbuf, outbuf);
       in_total_len = inbuf->total_len;
       out_total_len = outbuf->total_len;
       chain = inbuf->first;

       if (in_total_len == 0)
               goto done;

       if (outbuf->freeze_end || outbuf == inbuf) {
               result = -1;
               goto done;
       }

       for (; chain; chain = chain->next) {
               if ((chain->flags & (EVBUFFER_FILESEGMENT|EVBUFFER_SENDFILE|EVBUFFER_MULTICAST)) != 0) {
                       /* chain type can not be referenced */
                       result = -1;
                       goto done;
               }
       }

       if (out_total_len == 0) {
               /* There might be an empty chain at the start of outbuf; free
                * it. */
               evbuffer_free_all_chains(outbuf->first);
       }
       APPEND_CHAIN_MULTICAST(outbuf, inbuf);

       outbuf->n_add_for_cb += in_total_len;
       evbuffer_invoke_callbacks_(outbuf);

done:
       EVBUFFER_UNLOCK2(inbuf, outbuf);
       return result;
}

int
evbuffer_prepend_buffer(struct evbuffer *outbuf, struct evbuffer *inbuf)
{
       struct evbuffer_chain *pinned, *last;
       size_t in_total_len, out_total_len;
       int result = 0;

       EVBUFFER_LOCK2(inbuf, outbuf);

       in_total_len = inbuf->total_len;
       out_total_len = outbuf->total_len;

       if (!in_total_len || inbuf == outbuf)
               goto done;

       if (outbuf->freeze_start || inbuf->freeze_start) {
               result = -1;
               goto done;
       }

       if (PRESERVE_PINNED(inbuf, &pinned, &last) < 0) {
               result = -1;
               goto done;
       }

       if (out_total_len == 0) {
               /* There might be an empty chain at the start of outbuf; free
                * it. */
               evbuffer_free_all_chains(outbuf->first);
               COPY_CHAIN(outbuf, inbuf);
       } else {
               PREPEND_CHAIN(outbuf, inbuf);
       }

       RESTORE_PINNED(inbuf, pinned, last);

       inbuf->n_del_for_cb += in_total_len;
       outbuf->n_add_for_cb += in_total_len;

       evbuffer_invoke_callbacks_(inbuf);
       evbuffer_invoke_callbacks_(outbuf);
done:
       EVBUFFER_UNLOCK2(inbuf, outbuf);
       return result;
}

int
evbuffer_drain(struct evbuffer *buf, size_t len)
{
       struct evbuffer_chain *chain, *next;
       size_t remaining, old_len;
       int result = 0;

       EVBUFFER_LOCK(buf);
       old_len = buf->total_len;

       if (old_len == 0)
               goto done;

       if (buf->freeze_start) {
               result = -1;
               goto done;
       }

       if (len >= old_len && !HAS_PINNED_R(buf)) {
               len = old_len;
               for (chain = buf->first; chain != NULL; chain = next) {
                       next = chain->next;
                       evbuffer_chain_free(chain);
               }

               ZERO_CHAIN(buf);
       } else {
               if (len >= old_len)
                       len = old_len;

               buf->total_len -= len;
               remaining = len;
               for (chain = buf->first;
                    remaining >= chain->off;
                    chain = next) {
                       next = chain->next;
                       remaining -= chain->off;

                       if (chain == *buf->last_with_datap) {
                               buf->last_with_datap = &buf->first;
                       }
                       if (&chain->next == buf->last_with_datap)
                               buf->last_with_datap = &buf->first;

                       if (CHAIN_PINNED_R(chain)) {
                               EVUTIL_ASSERT(remaining == 0);
                               chain->misalign += chain->off;
                               chain->off = 0;
                               break;
                       } else
                               evbuffer_chain_free(chain);
               }

               buf->first = chain;
               EVUTIL_ASSERT(remaining <= chain->off);
               chain->misalign += remaining;
               chain->off -= remaining;
       }

       buf->n_del_for_cb += len;
       /* Tell someone about changes in this buffer */
       evbuffer_invoke_callbacks_(buf);

done:
       EVBUFFER_UNLOCK(buf);
       return result;
}

/* Reads data from an event buffer and drains the bytes read */
int
evbuffer_remove(struct evbuffer *buf, void *data_out, size_t datlen)
{
       ev_ssize_t n;
       EVBUFFER_LOCK(buf);
       n = evbuffer_copyout_from(buf, NULL, data_out, datlen);
       if (n > 0) {
               if (evbuffer_drain(buf, n)<0)
                       n = -1;
       }
       EVBUFFER_UNLOCK(buf);
       return (int)n;
}

ev_ssize_t
evbuffer_copyout(struct evbuffer *buf, void *data_out, size_t datlen)
{
       return evbuffer_copyout_from(buf, NULL, data_out, datlen);
}

ev_ssize_t
evbuffer_copyout_from(struct evbuffer *buf, const struct evbuffer_ptr *pos,
   void *data_out, size_t datlen)
{
       /*XXX fails badly on sendfile case. */
       struct evbuffer_chain *chain;
       char *data = data_out;
       size_t nread;
       ev_ssize_t result = 0;
       size_t pos_in_chain;

       EVBUFFER_LOCK(buf);

       if (pos) {
               if (datlen > (size_t)(EV_SSIZE_MAX - pos->pos)) {
                       result = -1;
                       goto done;
               }
               chain = pos->internal_.chain;
               pos_in_chain = pos->internal_.pos_in_chain;
               if (datlen + pos->pos > buf->total_len)
                       datlen = buf->total_len - pos->pos;
       } else {
               chain = buf->first;
               pos_in_chain = 0;
               if (datlen > buf->total_len)
                       datlen = buf->total_len;
       }


       if (datlen == 0)
               goto done;

       if (buf->freeze_start) {
               result = -1;
               goto done;
       }

       nread = datlen;

       while (datlen && datlen >= chain->off - pos_in_chain) {
               size_t copylen = chain->off - pos_in_chain;
               memcpy(data,
                   chain->buffer + chain->misalign + pos_in_chain,
                   copylen);
               data += copylen;
               datlen -= copylen;

               chain = chain->next;
               pos_in_chain = 0;
               EVUTIL_ASSERT(chain || datlen==0);
       }

       if (datlen) {
               EVUTIL_ASSERT(chain);
               EVUTIL_ASSERT(datlen+pos_in_chain <= chain->off);

               memcpy(data, chain->buffer + chain->misalign + pos_in_chain,
                   datlen);
       }

       result = nread;
done:
       EVBUFFER_UNLOCK(buf);
       return result;
}

/* reads data from the src buffer to the dst buffer, avoids memcpy as
* possible. */
/*  XXXX should return ev_ssize_t */
int
evbuffer_remove_buffer(struct evbuffer *src, struct evbuffer *dst,
   size_t datlen)
{
       /*XXX We should have an option to force this to be zero-copy.*/

       /*XXX can fail badly on sendfile case. */
       struct evbuffer_chain *chain, *previous;
       size_t nread = 0;
       int result;

       EVBUFFER_LOCK2(src, dst);

       chain = previous = src->first;

       if (datlen == 0 || dst == src) {
               result = 0;
               goto done;
       }

       if (dst->freeze_end || src->freeze_start) {
               result = -1;
               goto done;
       }

       /* short-cut if there is no more data buffered */
       if (datlen >= src->total_len) {
               datlen = src->total_len;
               evbuffer_add_buffer(dst, src);
               result = (int)datlen; /*XXXX should return ev_ssize_t*/
               goto done;
       }

       /* removes chains if possible */
       while (chain->off <= datlen) {
               /* We can't remove the last with data from src unless we
                * remove all chains, in which case we would have done the if
                * block above */
               EVUTIL_ASSERT(chain != *src->last_with_datap);
               nread += chain->off;
               datlen -= chain->off;
               previous = chain;
               if (src->last_with_datap == &chain->next)
                       src->last_with_datap = &src->first;
               chain = chain->next;
       }

       if (chain != src->first) {
               /* we can remove the chain */
               struct evbuffer_chain **chp;
               chp = evbuffer_free_trailing_empty_chains(dst);

               if (dst->first == NULL) {
                       dst->first = src->first;
               } else {
                       *chp = src->first;
               }
               dst->last = previous;
               previous->next = NULL;
               src->first = chain;
               advance_last_with_data(dst);

               dst->total_len += nread;
               dst->n_add_for_cb += nread;
       }

       /* we know that there is more data in the src buffer than
        * we want to read, so we manually drain the chain */
       evbuffer_add(dst, chain->buffer + chain->misalign, datlen);
       chain->misalign += datlen;
       chain->off -= datlen;
       nread += datlen;

       /* You might think we would want to increment dst->n_add_for_cb
        * here too.  But evbuffer_add above already took care of that.
        */
       src->total_len -= nread;
       src->n_del_for_cb += nread;

       if (nread) {
               evbuffer_invoke_callbacks_(dst);
               evbuffer_invoke_callbacks_(src);
       }
       result = (int)nread;/*XXXX should change return type */

done:
       EVBUFFER_UNLOCK2(src, dst);
       return result;
}

unsigned char *
evbuffer_pullup(struct evbuffer *buf, ev_ssize_t size)
{
       struct evbuffer_chain *chain, *next, *tmp, *last_with_data;
       unsigned char *buffer, *result = NULL;
       ev_ssize_t remaining;
       int removed_last_with_data = 0;
       int removed_last_with_datap = 0;

       EVBUFFER_LOCK(buf);

       chain = buf->first;

       if (size < 0)
               size = buf->total_len;
       /* if size > buf->total_len, we cannot guarantee to the user that she
        * is going to have a long enough buffer afterwards; so we return
        * NULL */
       if (size == 0 || (size_t)size > buf->total_len)
               goto done;

       /* No need to pull up anything; the first size bytes are
        * already here. */
       if (chain->off >= (size_t)size) {
               result = chain->buffer + chain->misalign;
               goto done;
       }

       /* Make sure that none of the chains we need to copy from is pinned. */
       remaining = size - chain->off;
       EVUTIL_ASSERT(remaining >= 0);
       for (tmp=chain->next; tmp; tmp=tmp->next) {
               if (CHAIN_PINNED(tmp))
                       goto done;
               if (tmp->off >= (size_t)remaining)
                       break;
               remaining -= tmp->off;
       }

       if (CHAIN_PINNED(chain)) {
               size_t old_off = chain->off;
               if (CHAIN_SPACE_LEN(chain) < size - chain->off) {
                       /* not enough room at end of chunk. */
                       goto done;
               }
               buffer = CHAIN_SPACE_PTR(chain);
               tmp = chain;
               tmp->off = size;
               size -= old_off;
               chain = chain->next;
       } else if (chain->buffer_len - chain->misalign >= (size_t)size) {
               /* already have enough space in the first chain */
               size_t old_off = chain->off;
               buffer = chain->buffer + chain->misalign + chain->off;
               tmp = chain;
               tmp->off = size;
               size -= old_off;
               chain = chain->next;
       } else {
               if ((tmp = evbuffer_chain_new(size)) == NULL) {
                       event_warn("%s: out of memory", __func__);
                       goto done;
               }
               buffer = tmp->buffer;
               tmp->off = size;
               buf->first = tmp;
       }

       /* TODO(niels): deal with buffers that point to NULL like sendfile */

       /* Copy and free every chunk that will be entirely pulled into tmp */
       last_with_data = *buf->last_with_datap;
       for (; chain != NULL && (size_t)size >= chain->off; chain = next) {
               next = chain->next;

               if (chain->buffer) {
                       memcpy(buffer, chain->buffer + chain->misalign, chain->off);
                       size -= chain->off;
                       buffer += chain->off;
               }
               if (chain == last_with_data)
                       removed_last_with_data = 1;
               if (&chain->next == buf->last_with_datap)
                       removed_last_with_datap = 1;

               evbuffer_chain_free(chain);
       }

       if (chain != NULL) {
               memcpy(buffer, chain->buffer + chain->misalign, size);
               chain->misalign += size;
               chain->off -= size;
       } else {
               buf->last = tmp;
       }

       tmp->next = chain;

       if (removed_last_with_data) {
               buf->last_with_datap = &buf->first;
       } else if (removed_last_with_datap) {
               if (buf->first->next && buf->first->next->off)
                       buf->last_with_datap = &buf->first->next;
               else
                       buf->last_with_datap = &buf->first;
       }

       result = (tmp->buffer + tmp->misalign);

done:
       EVBUFFER_UNLOCK(buf);
       return result;
}

/*
* Reads a line terminated by either '\r\n', '\n\r' or '\r' or '\n'.
* The returned buffer needs to be freed by the called.
*/
char *
evbuffer_readline(struct evbuffer *buffer)
{
       return evbuffer_readln(buffer, NULL, EVBUFFER_EOL_ANY);
}

static inline ev_ssize_t
evbuffer_strchr(struct evbuffer_ptr *it, const char chr)
{
       struct evbuffer_chain *chain = it->internal_.chain;
       size_t i = it->internal_.pos_in_chain;
       while (chain != NULL) {
               char *buffer = (char *)chain->buffer + chain->misalign;
               char *cp = memchr(buffer+i, chr, chain->off-i);
               if (cp) {
                       it->internal_.chain = chain;
                       it->internal_.pos_in_chain = cp - buffer;
                       it->pos += (cp - buffer - i);
                       return it->pos;
               }
               it->pos += chain->off - i;
               i = 0;
               chain = chain->next;
       }

       return (-1);
}

static inline char *
find_eol_char(char *s, size_t len)
{
#define CHUNK_SZ 128
       /* Lots of benchmarking found this approach to be faster in practice
        * than doing two memchrs over the whole buffer, doin a memchr on each
        * char of the buffer, or trying to emulate memchr by hand. */
       char *s_end, *cr, *lf;
       s_end = s+len;
       while (s < s_end) {
               size_t chunk = (s + CHUNK_SZ < s_end) ? CHUNK_SZ : (s_end - s);
               cr = memchr(s, '\r', chunk);
               lf = memchr(s, '\n', chunk);
               if (cr) {
                       if (lf && lf < cr)
                               return lf;
                       return cr;
               } else if (lf) {
                       return lf;
               }
               s += CHUNK_SZ;
       }

       return NULL;
#undef CHUNK_SZ
}

static ev_ssize_t
evbuffer_find_eol_char(struct evbuffer_ptr *it)
{
       struct evbuffer_chain *chain = it->internal_.chain;
       size_t i = it->internal_.pos_in_chain;
       while (chain != NULL) {
               char *buffer = (char *)chain->buffer + chain->misalign;
               char *cp = find_eol_char(buffer+i, chain->off-i);
               if (cp) {
                       it->internal_.chain = chain;
                       it->internal_.pos_in_chain = cp - buffer;
                       it->pos += (cp - buffer) - i;
                       return it->pos;
               }
               it->pos += chain->off - i;
               i = 0;
               chain = chain->next;
       }

       return (-1);
}

static inline size_t
evbuffer_strspn(
       struct evbuffer_ptr *ptr, const char *chrset)
{
       size_t count = 0;
       struct evbuffer_chain *chain = ptr->internal_.chain;
       size_t i = ptr->internal_.pos_in_chain;

       if (!chain)
               return 0;

       while (1) {
               char *buffer = (char *)chain->buffer + chain->misalign;
               for (; i < chain->off; ++i) {
                       const char *p = chrset;
                       while (*p) {
                               if (buffer[i] == *p++)
                                       goto next;
                       }
                       ptr->internal_.chain = chain;
                       ptr->internal_.pos_in_chain = i;
                       ptr->pos += count;
                       return count;
               next:
                       ++count;
               }
               i = 0;

               if (! chain->next) {
                       ptr->internal_.chain = chain;
                       ptr->internal_.pos_in_chain = i;
                       ptr->pos += count;
                       return count;
               }

               chain = chain->next;
       }
}


static inline int
evbuffer_getchr(struct evbuffer_ptr *it)
{
       struct evbuffer_chain *chain = it->internal_.chain;
       size_t off = it->internal_.pos_in_chain;

       if (chain == NULL)
               return -1;

       return (unsigned char)chain->buffer[chain->misalign + off];
}

struct evbuffer_ptr
evbuffer_search_eol(struct evbuffer *buffer,
   struct evbuffer_ptr *start, size_t *eol_len_out,
   enum evbuffer_eol_style eol_style)
{
       struct evbuffer_ptr it, it2;
       size_t extra_drain = 0;
       int ok = 0;

       /* Avoid locking in trivial edge cases */
       if (start && start->internal_.chain == NULL) {
               PTR_NOT_FOUND(&it);
               if (eol_len_out)
                       *eol_len_out = extra_drain;
               return it;
       }

       EVBUFFER_LOCK(buffer);

       if (start) {
               memcpy(&it, start, sizeof(it));
       } else {
               it.pos = 0;
               it.internal_.chain = buffer->first;
               it.internal_.pos_in_chain = 0;
       }

       /* the eol_style determines our first stop character and how many
        * characters we are going to drain afterwards. */
       switch (eol_style) {
       case EVBUFFER_EOL_ANY:
               if (evbuffer_find_eol_char(&it) < 0)
                       goto done;
               memcpy(&it2, &it, sizeof(it));
               extra_drain = evbuffer_strspn(&it2, "\r\n");
               break;
       case EVBUFFER_EOL_CRLF_STRICT: {
               it = evbuffer_search(buffer, "\r\n", 2, &it);
               if (it.pos < 0)
                       goto done;
               extra_drain = 2;
               break;
       }
       case EVBUFFER_EOL_CRLF: {
               ev_ssize_t start_pos = it.pos;
               /* Look for a LF ... */
               if (evbuffer_strchr(&it, '\n') < 0)
                       goto done;
               extra_drain = 1;
               /* ... optionally preceeded by a CR. */
               if (it.pos == start_pos)
                       break; /* If the first character is \n, don't back up */
               /* This potentially does an extra linear walk over the first
                * few chains.  Probably, that's not too expensive unless you
                * have a really pathological setup. */
               memcpy(&it2, &it, sizeof(it));
               if (evbuffer_ptr_subtract(buffer, &it2, 1)<0)
                       break;
               if (evbuffer_getchr(&it2) == '\r') {
                       memcpy(&it, &it2, sizeof(it));
                       extra_drain = 2;
               }
               break;
       }
       case EVBUFFER_EOL_LF:
               if (evbuffer_strchr(&it, '\n') < 0)
                       goto done;
               extra_drain = 1;
               break;
       case EVBUFFER_EOL_NUL:
               if (evbuffer_strchr(&it, '\0') < 0)
                       goto done;
               extra_drain = 1;
               break;
       default:
               goto done;
       }

       ok = 1;
done:
       EVBUFFER_UNLOCK(buffer);

       if (!ok)
               PTR_NOT_FOUND(&it);
       if (eol_len_out)
               *eol_len_out = extra_drain;

       return it;
}

char *
evbuffer_readln(struct evbuffer *buffer, size_t *n_read_out,
               enum evbuffer_eol_style eol_style)
{
       struct evbuffer_ptr it;
       char *line;
       size_t n_to_copy=0, extra_drain=0;
       char *result = NULL;

       EVBUFFER_LOCK(buffer);

       if (buffer->freeze_start) {
               goto done;
       }

       it = evbuffer_search_eol(buffer, NULL, &extra_drain, eol_style);
       if (it.pos < 0)
               goto done;
       n_to_copy = it.pos;

       if ((line = mm_malloc(n_to_copy+1)) == NULL) {
               event_warn("%s: out of memory", __func__);
               goto done;
       }

       evbuffer_remove(buffer, line, n_to_copy);
       line[n_to_copy] = '\0';

       evbuffer_drain(buffer, extra_drain);
       result = line;
done:
       EVBUFFER_UNLOCK(buffer);

       if (n_read_out)
               *n_read_out = result ? n_to_copy : 0;

       return result;
}

#define EVBUFFER_CHAIN_MAX_AUTO_SIZE 4096

/* Adds data to an event buffer */

int
evbuffer_add(struct evbuffer *buf, const void *data_in, size_t datlen)
{
       struct evbuffer_chain *chain, *tmp;
       const unsigned char *data = data_in;
       size_t remain, to_alloc;
       int result = -1;

       EVBUFFER_LOCK(buf);

       if (buf->freeze_end) {
               goto done;
       }
       /* Prevent buf->total_len overflow */
       if (datlen > EV_SIZE_MAX - buf->total_len) {
               goto done;
       }

       if (*buf->last_with_datap == NULL) {
               chain = buf->last;
       } else {
               chain = *buf->last_with_datap;
       }

       /* If there are no chains allocated for this buffer, allocate one
        * big enough to hold all the data. */
       if (chain == NULL) {
               chain = evbuffer_chain_new(datlen);
               if (!chain)
                       goto done;
               evbuffer_chain_insert(buf, chain);
       }

       if ((chain->flags & EVBUFFER_IMMUTABLE) == 0) {
               /* Always true for mutable buffers */
               EVUTIL_ASSERT(chain->misalign >= 0 &&
                   (ev_uint64_t)chain->misalign <= EVBUFFER_CHAIN_MAX);
               remain = chain->buffer_len - (size_t)chain->misalign - chain->off;
               if (remain >= datlen) {
                       /* there's enough space to hold all the data in the
                        * current last chain */
                       memcpy(chain->buffer + chain->misalign + chain->off,
                           data, datlen);
                       chain->off += datlen;
                       buf->total_len += datlen;
                       buf->n_add_for_cb += datlen;
                       goto out;
               } else if (!CHAIN_PINNED(chain) &&
                   evbuffer_chain_should_realign(chain, datlen)) {
                       /* we can fit the data into the misalignment */
                       evbuffer_chain_align(chain);

                       memcpy(chain->buffer + chain->off, data, datlen);
                       chain->off += datlen;
                       buf->total_len += datlen;
                       buf->n_add_for_cb += datlen;
                       goto out;
               }
       } else {
               /* we cannot write any data to the last chain */
               remain = 0;
       }

       /* we need to add another chain */
       to_alloc = chain->buffer_len;
       if (to_alloc <= EVBUFFER_CHAIN_MAX_AUTO_SIZE/2)
               to_alloc <<= 1;
       if (datlen > to_alloc)
               to_alloc = datlen;
       tmp = evbuffer_chain_new(to_alloc);
       if (tmp == NULL)
               goto done;

       if (remain) {
               memcpy(chain->buffer + chain->misalign + chain->off,
                   data, remain);
               chain->off += remain;
               buf->total_len += remain;
               buf->n_add_for_cb += remain;
       }

       data += remain;
       datlen -= remain;

       memcpy(tmp->buffer, data, datlen);
       tmp->off = datlen;
       evbuffer_chain_insert(buf, tmp);
       buf->n_add_for_cb += datlen;

out:
       evbuffer_invoke_callbacks_(buf);
       result = 0;
done:
       EVBUFFER_UNLOCK(buf);
       return result;
}

int
evbuffer_prepend(struct evbuffer *buf, const void *data, size_t datlen)
{
       struct evbuffer_chain *chain, *tmp;
       int result = -1;

       EVBUFFER_LOCK(buf);

       if (datlen == 0) {
               result = 0;
               goto done;
       }
       if (buf->freeze_start) {
               goto done;
       }
       if (datlen > EV_SIZE_MAX - buf->total_len) {
               goto done;
       }

       chain = buf->first;

       if (chain == NULL) {
               chain = evbuffer_chain_new(datlen);
               if (!chain)
                       goto done;
               evbuffer_chain_insert(buf, chain);
       }

       /* we cannot touch immutable buffers */
       if ((chain->flags & EVBUFFER_IMMUTABLE) == 0) {
               /* Always true for mutable buffers */
               EVUTIL_ASSERT(chain->misalign >= 0 &&
                   (ev_uint64_t)chain->misalign <= EVBUFFER_CHAIN_MAX);

               /* If this chain is empty, we can treat it as
                * 'empty at the beginning' rather than 'empty at the end' */
               if (chain->off == 0)
                       chain->misalign = chain->buffer_len;

               if ((size_t)chain->misalign >= datlen) {
                       /* we have enough space to fit everything */
                       memcpy(chain->buffer + chain->misalign - datlen,
                           data, datlen);
                       chain->off += datlen;
                       chain->misalign -= datlen;
                       buf->total_len += datlen;
                       buf->n_add_for_cb += datlen;
                       goto out;
               } else if (chain->misalign) {
                       /* we can only fit some of the data. */
                       memcpy(chain->buffer,
                           (char*)data + datlen - chain->misalign,
                           (size_t)chain->misalign);
                       chain->off += (size_t)chain->misalign;
                       buf->total_len += (size_t)chain->misalign;
                       buf->n_add_for_cb += (size_t)chain->misalign;
                       datlen -= (size_t)chain->misalign;
                       chain->misalign = 0;
               }
       }

       /* we need to add another chain */
       if ((tmp = evbuffer_chain_new(datlen)) == NULL)
               goto done;
       buf->first = tmp;
       if (buf->last_with_datap == &buf->first && chain->off)
               buf->last_with_datap = &tmp->next;

       tmp->next = chain;

       tmp->off = datlen;
       EVUTIL_ASSERT(datlen <= tmp->buffer_len);
       tmp->misalign = tmp->buffer_len - datlen;

       memcpy(tmp->buffer + tmp->misalign, data, datlen);
       buf->total_len += datlen;
       buf->n_add_for_cb += datlen;

out:
       evbuffer_invoke_callbacks_(buf);
       result = 0;
done:
       EVBUFFER_UNLOCK(buf);
       return result;
}

/** Helper: realigns the memory in chain->buffer so that misalign is 0. */
static void
evbuffer_chain_align(struct evbuffer_chain *chain)
{
       EVUTIL_ASSERT(!(chain->flags & EVBUFFER_IMMUTABLE));
       EVUTIL_ASSERT(!(chain->flags & EVBUFFER_MEM_PINNED_ANY));
       memmove(chain->buffer, chain->buffer + chain->misalign, chain->off);
       chain->misalign = 0;
}

#define MAX_TO_COPY_IN_EXPAND 4096
#define MAX_TO_REALIGN_IN_EXPAND 2048

/** Helper: return true iff we should realign chain to fit datalen bytes of
   data in it. */
static int
evbuffer_chain_should_realign(struct evbuffer_chain *chain,
   size_t datlen)
{
       return chain->buffer_len - chain->off >= datlen &&
           (chain->off < chain->buffer_len / 2) &&
           (chain->off <= MAX_TO_REALIGN_IN_EXPAND);
}

/* Expands the available space in the event buffer to at least datlen, all in
* a single chunk.  Return that chunk. */
static struct evbuffer_chain *
evbuffer_expand_singlechain(struct evbuffer *buf, size_t datlen)
{
       struct evbuffer_chain *chain, **chainp;
       struct evbuffer_chain *result = NULL;
       ASSERT_EVBUFFER_LOCKED(buf);

       chainp = buf->last_with_datap;

       /* XXX If *chainp is no longer writeable, but has enough space in its
        * misalign, this might be a bad idea: we could still use *chainp, not
        * (*chainp)->next. */
       if (*chainp && CHAIN_SPACE_LEN(*chainp) == 0)
               chainp = &(*chainp)->next;

       /* 'chain' now points to the first chain with writable space (if any)
        * We will either use it, realign it, replace it, or resize it. */
       chain = *chainp;

       if (chain == NULL ||
           (chain->flags & (EVBUFFER_IMMUTABLE|EVBUFFER_MEM_PINNED_ANY))) {
               /* We can't use the last_with_data chain at all.  Just add a
                * new one that's big enough. */
               goto insert_new;
       }

       /* If we can fit all the data, then we don't have to do anything */
       if (CHAIN_SPACE_LEN(chain) >= datlen) {
               result = chain;
               goto ok;
       }

       /* If the chain is completely empty, just replace it by adding a new
        * empty chain. */
       if (chain->off == 0) {
               goto insert_new;
       }

       /* If the misalignment plus the remaining space fulfills our data
        * needs, we could just force an alignment to happen.  Afterwards, we
        * have enough space.  But only do this if we're saving a lot of space
        * and not moving too much data.  Otherwise the space savings are
        * probably offset by the time lost in copying.
        */
       if (evbuffer_chain_should_realign(chain, datlen)) {
               evbuffer_chain_align(chain);
               result = chain;
               goto ok;
       }

       /* At this point, we can either resize the last chunk with space in
        * it, use the next chunk after it, or   If we add a new chunk, we waste
        * CHAIN_SPACE_LEN(chain) bytes in the former last chunk.  If we
        * resize, we have to copy chain->off bytes.
        */

       /* Would expanding this chunk be affordable and worthwhile? */
       if (CHAIN_SPACE_LEN(chain) < chain->buffer_len / 8 ||
           chain->off > MAX_TO_COPY_IN_EXPAND ||
               datlen >= (EVBUFFER_CHAIN_MAX - chain->off)) {
               /* It's not worth resizing this chain. Can the next one be
                * used? */
               if (chain->next && CHAIN_SPACE_LEN(chain->next) >= datlen) {
                       /* Yes, we can just use the next chain (which should
                        * be empty. */
                       result = chain->next;
                       goto ok;
               } else {
                       /* No; append a new chain (which will free all
                        * terminal empty chains.) */
                       goto insert_new;
               }
       } else {
               /* Okay, we're going to try to resize this chain: Not doing so
                * would waste at least 1/8 of its current allocation, and we
                * can do so without having to copy more than
                * MAX_TO_COPY_IN_EXPAND bytes. */
               /* figure out how much space we need */
               size_t length = chain->off + datlen;
               struct evbuffer_chain *tmp = evbuffer_chain_new(length);
               if (tmp == NULL)
                       goto err;

               /* copy the data over that we had so far */
               tmp->off = chain->off;
               memcpy(tmp->buffer, chain->buffer + chain->misalign,
                   chain->off);
               /* fix up the list */
               EVUTIL_ASSERT(*chainp == chain);
               result = *chainp = tmp;

               if (buf->last == chain)
                       buf->last = tmp;

               tmp->next = chain->next;
               evbuffer_chain_free(chain);
               goto ok;
       }

insert_new:
       result = evbuffer_chain_insert_new(buf, datlen);
       if (!result)
               goto err;
ok:
       EVUTIL_ASSERT(result);
       EVUTIL_ASSERT(CHAIN_SPACE_LEN(result) >= datlen);
err:
       return result;
}

/* Make sure that datlen bytes are available for writing in the last n
* chains.  Never copies or moves data. */
int
evbuffer_expand_fast_(struct evbuffer *buf, size_t datlen, int n)
{
       struct evbuffer_chain *chain = buf->last, *tmp, *next;
       size_t avail;
       int used;

       ASSERT_EVBUFFER_LOCKED(buf);
       EVUTIL_ASSERT(n >= 2);

       if (chain == NULL || (chain->flags & EVBUFFER_IMMUTABLE)) {
               /* There is no last chunk, or we can't touch the last chunk.
                * Just add a new chunk. */
               chain = evbuffer_chain_new(datlen);
               if (chain == NULL)
                       return (-1);

               evbuffer_chain_insert(buf, chain);
               return (0);
       }

       used = 0; /* number of chains we're using space in. */
       avail = 0; /* how much space they have. */
       /* How many bytes can we stick at the end of buffer as it is?  Iterate
        * over the chains at the end of the buffer, tring to see how much
        * space we have in the first n. */
       for (chain = *buf->last_with_datap; chain; chain = chain->next) {
               if (chain->off) {
                       size_t space = (size_t) CHAIN_SPACE_LEN(chain);
                       EVUTIL_ASSERT(chain == *buf->last_with_datap);
                       if (space) {
                               avail += space;
                               ++used;
                       }
               } else {
                       /* No data in chain; realign it. */
                       chain->misalign = 0;
                       avail += chain->buffer_len;
                       ++used;
               }
               if (avail >= datlen) {
                       /* There is already enough space.  Just return */
                       return (0);
               }
               if (used == n)
                       break;
       }

       /* There wasn't enough space in the first n chains with space in
        * them. Either add a new chain with enough space, or replace all
        * empty chains with one that has enough space, depending on n. */
       if (used < n) {
               /* The loop ran off the end of the chains before it hit n
                * chains; we can add another. */
               EVUTIL_ASSERT(chain == NULL);

               tmp = evbuffer_chain_new(datlen - avail);
               if (tmp == NULL)
                       return (-1);

               buf->last->next = tmp;
               buf->last = tmp;
               /* (we would only set last_with_data if we added the first
                * chain. But if the buffer had no chains, we would have
                * just allocated a new chain earlier) */
               return (0);
       } else {
               /* Nuke _all_ the empty chains. */
               int rmv_all = 0; /* True iff we removed last_with_data. */
               chain = *buf->last_with_datap;
               if (!chain->off) {
                       EVUTIL_ASSERT(chain == buf->first);
                       rmv_all = 1;
                       avail = 0;
               } else {
                       /* can't overflow, since only mutable chains have
                        * huge misaligns. */
                       avail = (size_t) CHAIN_SPACE_LEN(chain);
                       chain = chain->next;
               }


               for (; chain; chain = next) {
                       next = chain->next;
                       EVUTIL_ASSERT(chain->off == 0);
                       evbuffer_chain_free(chain);
               }
               EVUTIL_ASSERT(datlen >= avail);
               tmp = evbuffer_chain_new(datlen - avail);
               if (tmp == NULL) {
                       if (rmv_all) {
                               ZERO_CHAIN(buf);
                       } else {
                               buf->last = *buf->last_with_datap;
                               (*buf->last_with_datap)->next = NULL;
                       }
                       return (-1);
               }

               if (rmv_all) {
                       buf->first = buf->last = tmp;
                       buf->last_with_datap = &buf->first;
               } else {
                       (*buf->last_with_datap)->next = tmp;
                       buf->last = tmp;
               }
               return (0);
       }
}

int
evbuffer_expand(struct evbuffer *buf, size_t datlen)
{
       struct evbuffer_chain *chain;

       EVBUFFER_LOCK(buf);
       chain = evbuffer_expand_singlechain(buf, datlen);
       EVBUFFER_UNLOCK(buf);
       return chain ? 0 : -1;
}

/*
* Reads data from a file descriptor into a buffer.
*/

#if defined(EVENT__HAVE_SYS_UIO_H) || defined(_WIN32)
#define USE_IOVEC_IMPL
#endif

#ifdef USE_IOVEC_IMPL

#ifdef EVENT__HAVE_SYS_UIO_H
/* number of iovec we use for writev, fragmentation is going to determine
* how much we end up writing */

#define DEFAULT_WRITE_IOVEC 128

#if defined(UIO_MAXIOV) && UIO_MAXIOV < DEFAULT_WRITE_IOVEC
#define NUM_WRITE_IOVEC UIO_MAXIOV
#elif defined(IOV_MAX) && IOV_MAX < DEFAULT_WRITE_IOVEC
#define NUM_WRITE_IOVEC IOV_MAX
#else
#define NUM_WRITE_IOVEC DEFAULT_WRITE_IOVEC
#endif

#define IOV_TYPE struct iovec
#define IOV_PTR_FIELD iov_base
#define IOV_LEN_FIELD iov_len
#define IOV_LEN_TYPE size_t
#else
#define NUM_WRITE_IOVEC 16
#define IOV_TYPE WSABUF
#define IOV_PTR_FIELD buf
#define IOV_LEN_FIELD len
#define IOV_LEN_TYPE unsigned long
#endif
#endif
#define NUM_READ_IOVEC 4

#define EVBUFFER_MAX_READ       4096

/** Helper function to figure out which space to use for reading data into
   an evbuffer.  Internal use only.

   @param buf The buffer to read into
   @param howmuch How much we want to read.
   @param vecs An array of two or more iovecs or WSABUFs.
   @param n_vecs_avail The length of vecs
   @param chainp A pointer to a variable to hold the first chain we're
     reading into.
   @param exact Boolean: if true, we do not provide more than 'howmuch'
     space in the vectors, even if more space is available.
   @return The number of buffers we're using.
*/
int
evbuffer_read_setup_vecs_(struct evbuffer *buf, ev_ssize_t howmuch,
   struct evbuffer_iovec *vecs, int n_vecs_avail,
   struct evbuffer_chain ***chainp, int exact)
{
       struct evbuffer_chain *chain;
       struct evbuffer_chain **firstchainp;
       size_t so_far;
       int i;
       ASSERT_EVBUFFER_LOCKED(buf);

       if (howmuch < 0)
               return -1;

       so_far = 0;
       /* Let firstchain be the first chain with any space on it */
       firstchainp = buf->last_with_datap;
       EVUTIL_ASSERT(*firstchainp);
       if (CHAIN_SPACE_LEN(*firstchainp) == 0) {
               firstchainp = &(*firstchainp)->next;
       }

       chain = *firstchainp;
       EVUTIL_ASSERT(chain);
       for (i = 0; i < n_vecs_avail && so_far < (size_t)howmuch; ++i) {
               size_t avail = (size_t) CHAIN_SPACE_LEN(chain);
               if (avail > (howmuch - so_far) && exact)
                       avail = howmuch - so_far;
               vecs[i].iov_base = (void *)CHAIN_SPACE_PTR(chain);
               vecs[i].iov_len = avail;
               so_far += avail;
               chain = chain->next;
       }

       *chainp = firstchainp;
       return i;
}

static int
get_n_bytes_readable_on_socket(evutil_socket_t fd)
{
#if defined(FIONREAD) && defined(_WIN32)
       unsigned long lng = EVBUFFER_MAX_READ;
       if (ioctlsocket(fd, FIONREAD, &lng) < 0)
               return -1;
       /* Can overflow, but mostly harmlessly. XXXX */
       return (int)lng;
#elif defined(FIONREAD)
       int n = EVBUFFER_MAX_READ;
       if (ioctl(fd, FIONREAD, &n) < 0)
               return -1;
       return n;
#else
       return EVBUFFER_MAX_READ;
#endif
}

/* TODO(niels): should this function return ev_ssize_t and take ev_ssize_t
* as howmuch? */
int
evbuffer_read(struct evbuffer *buf, evutil_socket_t fd, int howmuch)
{
       struct evbuffer_chain **chainp;
       int n;
       int result;

#ifdef USE_IOVEC_IMPL
       int nvecs, i, remaining;
#else
       struct evbuffer_chain *chain;
       unsigned char *p;
#endif

       EVBUFFER_LOCK(buf);

       if (buf->freeze_end) {
               result = -1;
               goto done;
       }

       n = get_n_bytes_readable_on_socket(fd);
       if (n <= 0 || n > EVBUFFER_MAX_READ)
               n = EVBUFFER_MAX_READ;
       if (howmuch < 0 || howmuch > n)
               howmuch = n;

#ifdef USE_IOVEC_IMPL
       /* Since we can use iovecs, we're willing to use the last
        * NUM_READ_IOVEC chains. */
       if (evbuffer_expand_fast_(buf, howmuch, NUM_READ_IOVEC) == -1) {
               result = -1;
               goto done;
       } else {
               IOV_TYPE vecs[NUM_READ_IOVEC];
#ifdef EVBUFFER_IOVEC_IS_NATIVE_
               nvecs = evbuffer_read_setup_vecs_(buf, howmuch, vecs,
                   NUM_READ_IOVEC, &chainp, 1);
#else
               /* We aren't using the native struct iovec.  Therefore,
                  we are on win32. */
               struct evbuffer_iovec ev_vecs[NUM_READ_IOVEC];
               nvecs = evbuffer_read_setup_vecs_(buf, howmuch, ev_vecs, 2,
                   &chainp, 1);

               for (i=0; i < nvecs; ++i)
                       WSABUF_FROM_EVBUFFER_IOV(&vecs[i], &ev_vecs[i]);
#endif

#ifdef _WIN32
               {
                       DWORD bytesRead;
                       DWORD flags=0;
                       if (WSARecv(fd, vecs, nvecs, &bytesRead, &flags, NULL, NULL)) {
                               /* The read failed. It might be a close,
                                * or it might be an error. */
                               if (WSAGetLastError() == WSAECONNABORTED)
                                       n = 0;
                               else
                                       n = -1;
                       } else
                               n = bytesRead;
               }
#else
               n = readv(fd, vecs, nvecs);
#endif
       }

#else /*!USE_IOVEC_IMPL*/
       /* If we don't have FIONREAD, we might waste some space here */
       /* XXX we _will_ waste some space here if there is any space left
        * over on buf->last. */
       if ((chain = evbuffer_expand_singlechain(buf, howmuch)) == NULL) {
               result = -1;
               goto done;
       }

       /* We can append new data at this point */
       p = chain->buffer + chain->misalign + chain->off;

#ifndef _WIN32
       n = read(fd, p, howmuch);
#else
       n = recv(fd, p, howmuch, 0);
#endif
#endif /* USE_IOVEC_IMPL */

       if (n == -1) {
               result = -1;
               goto done;
       }
       if (n == 0) {
               result = 0;
               goto done;
       }

#ifdef USE_IOVEC_IMPL
       remaining = n;
       for (i=0; i < nvecs; ++i) {
               /* can't overflow, since only mutable chains have
                * huge misaligns. */
               size_t space = (size_t) CHAIN_SPACE_LEN(*chainp);
               /* XXXX This is a kludge that can waste space in perverse
                * situations. */
               if (space > EVBUFFER_CHAIN_MAX)
                       space = EVBUFFER_CHAIN_MAX;
               if ((ev_ssize_t)space < remaining) {
                       (*chainp)->off += space;
                       remaining -= (int)space;
               } else {
                       (*chainp)->off += remaining;
                       buf->last_with_datap = chainp;
                       break;
               }
               chainp = &(*chainp)->next;
       }
#else
       chain->off += n;
       advance_last_with_data(buf);
#endif
       buf->total_len += n;
       buf->n_add_for_cb += n;

       /* Tell someone about changes in this buffer */
       evbuffer_invoke_callbacks_(buf);
       result = n;
done:
       EVBUFFER_UNLOCK(buf);
       return result;
}

#ifdef USE_IOVEC_IMPL
static inline int
evbuffer_write_iovec(struct evbuffer *buffer, evutil_socket_t fd,
   ev_ssize_t howmuch)
{
       IOV_TYPE iov[NUM_WRITE_IOVEC];
       struct evbuffer_chain *chain = buffer->first;
       int n, i = 0;

       if (howmuch < 0)
               return -1;

       ASSERT_EVBUFFER_LOCKED(buffer);
       /* XXX make this top out at some maximal data length?  if the
        * buffer has (say) 1MB in it, split over 128 chains, there's
        * no way it all gets written in one go. */
       while (chain != NULL && i < NUM_WRITE_IOVEC && howmuch) {
#ifdef USE_SENDFILE
               /* we cannot write the file info via writev */
               if (chain->flags & EVBUFFER_SENDFILE)
                       break;
#endif
               iov[i].IOV_PTR_FIELD = (void *) (chain->buffer + chain->misalign);
               if ((size_t)howmuch >= chain->off) {
                       /* XXXcould be problematic when windows supports mmap*/
                       iov[i++].IOV_LEN_FIELD = (IOV_LEN_TYPE)chain->off;
                       howmuch -= chain->off;
               } else {
                       /* XXXcould be problematic when windows supports mmap*/
                       iov[i++].IOV_LEN_FIELD = (IOV_LEN_TYPE)howmuch;
                       break;
               }
               chain = chain->next;
       }
       if (! i)
               return 0;

#ifdef _WIN32
       {
               DWORD bytesSent;
               if (WSASend(fd, iov, i, &bytesSent, 0, NULL, NULL))
                       n = -1;
               else
                       n = bytesSent;
       }
#else
       n = writev(fd, iov, i);
#endif
       return (n);
}
#endif

#ifdef USE_SENDFILE
static inline int
evbuffer_write_sendfile(struct evbuffer *buffer, evutil_socket_t dest_fd,
   ev_ssize_t howmuch)
{
       struct evbuffer_chain *chain = buffer->first;
       struct evbuffer_chain_file_segment *info =
           EVBUFFER_CHAIN_EXTRA(struct evbuffer_chain_file_segment,
               chain);
       const int source_fd = info->segment->fd;
#if defined(SENDFILE_IS_MACOSX) || defined(SENDFILE_IS_FREEBSD)
       int res;
       ev_off_t len = chain->off;
#elif defined(SENDFILE_IS_LINUX) || defined(SENDFILE_IS_SOLARIS)
       ev_ssize_t res;
       off_t offset = chain->misalign;
#endif

       ASSERT_EVBUFFER_LOCKED(buffer);

#if defined(SENDFILE_IS_MACOSX)
       res = sendfile(source_fd, dest_fd, chain->misalign, &len, NULL, 0);
       if (res == -1 && !EVUTIL_ERR_RW_RETRIABLE(errno))
               return (-1);

       return (len);
#elif defined(SENDFILE_IS_FREEBSD)
       res = sendfile(source_fd, dest_fd, chain->misalign, chain->off, NULL, &len, 0);
       if (res == -1 && !EVUTIL_ERR_RW_RETRIABLE(errno))
               return (-1);

       return (len);
#elif defined(SENDFILE_IS_LINUX)
       /* TODO(niels): implement splice */
       res = sendfile(dest_fd, source_fd, &offset, chain->off);
       if (res == -1 && EVUTIL_ERR_RW_RETRIABLE(errno)) {
               /* if this is EAGAIN or EINTR return 0; otherwise, -1 */
               return (0);
       }
       return (res);
#elif defined(SENDFILE_IS_SOLARIS)
       {
               const off_t offset_orig = offset;
               res = sendfile(dest_fd, source_fd, &offset, chain->off);
               if (res == -1 && EVUTIL_ERR_RW_RETRIABLE(errno)) {
                       if (offset - offset_orig)
                               return offset - offset_orig;
                       /* if this is EAGAIN or EINTR and no bytes were
                        * written, return 0 */
                       return (0);
               }
               return (res);
       }
#endif
}
#endif

int
evbuffer_write_atmost(struct evbuffer *buffer, evutil_socket_t fd,
   ev_ssize_t howmuch)
{
       int n = -1;

       EVBUFFER_LOCK(buffer);

       if (buffer->freeze_start) {
               goto done;
       }

       if (howmuch < 0 || (size_t)howmuch > buffer->total_len)
               howmuch = buffer->total_len;

       if (howmuch > 0) {
#ifdef USE_SENDFILE
               struct evbuffer_chain *chain = buffer->first;
               if (chain != NULL && (chain->flags & EVBUFFER_SENDFILE))
                       n = evbuffer_write_sendfile(buffer, fd, howmuch);
               else {
#endif
#ifdef USE_IOVEC_IMPL
               n = evbuffer_write_iovec(buffer, fd, howmuch);
#elif defined(_WIN32)
               /* XXX(nickm) Don't disable this code until we know if
                * the WSARecv code above works. */
               void *p = evbuffer_pullup(buffer, howmuch);
               EVUTIL_ASSERT(p || !howmuch);
               n = send(fd, p, howmuch, 0);
#else
               void *p = evbuffer_pullup(buffer, howmuch);
               EVUTIL_ASSERT(p || !howmuch);
               n = write(fd, p, howmuch);
#endif
#ifdef USE_SENDFILE
               }
#endif
       }

       if (n > 0)
               evbuffer_drain(buffer, n);

done:
       EVBUFFER_UNLOCK(buffer);
       return (n);
}

int
evbuffer_write(struct evbuffer *buffer, evutil_socket_t fd)
{
       return evbuffer_write_atmost(buffer, fd, -1);
}

unsigned char *
evbuffer_find(struct evbuffer *buffer, const unsigned char *what, size_t len)
{
       unsigned char *search;
       struct evbuffer_ptr ptr;

       EVBUFFER_LOCK(buffer);

       ptr = evbuffer_search(buffer, (const char *)what, len, NULL);
       if (ptr.pos < 0) {
               search = NULL;
       } else {
               search = evbuffer_pullup(buffer, ptr.pos + len);
               if (search)
                       search += ptr.pos;
       }
       EVBUFFER_UNLOCK(buffer);
       return search;
}

/* Subract <b>howfar</b> from the position of <b>pos</b> within
* <b>buf</b>. Returns 0 on success, -1 on failure.
*
* This isn't exposed yet, because of potential inefficiency issues.
* Maybe it should be. */
static int
evbuffer_ptr_subtract(struct evbuffer *buf, struct evbuffer_ptr *pos,
   size_t howfar)
{
       if (pos->pos < 0)
               return -1;
       if (howfar > (size_t)pos->pos)
               return -1;
       if (pos->internal_.chain && howfar <= pos->internal_.pos_in_chain) {
               pos->internal_.pos_in_chain -= howfar;
               pos->pos -= howfar;
               return 0;
       } else {
               const size_t newpos = pos->pos - howfar;
               /* Here's the inefficient part: it walks over the
                * chains until we hit newpos. */
               return evbuffer_ptr_set(buf, pos, newpos, EVBUFFER_PTR_SET);
       }
}

int
evbuffer_ptr_set(struct evbuffer *buf, struct evbuffer_ptr *pos,
   size_t position, enum evbuffer_ptr_how how)
{
       size_t left = position;
       struct evbuffer_chain *chain = NULL;
       int result = 0;

       EVBUFFER_LOCK(buf);

       switch (how) {
       case EVBUFFER_PTR_SET:
               chain = buf->first;
               pos->pos = position;
               position = 0;
               break;
       case EVBUFFER_PTR_ADD:
               /* this avoids iterating over all previous chains if
                  we just want to advance the position */
               if (pos->pos < 0 || EV_SIZE_MAX - position < (size_t)pos->pos) {
                       EVBUFFER_UNLOCK(buf);
                       return -1;
               }
               chain = pos->internal_.chain;
               pos->pos += position;
               position = pos->internal_.pos_in_chain;
               break;
       }

       EVUTIL_ASSERT(EV_SIZE_MAX - left >= position);
       while (chain && position + left >= chain->off) {
               left -= chain->off - position;
               chain = chain->next;
               position = 0;
       }
       if (chain) {
               pos->internal_.chain = chain;
               pos->internal_.pos_in_chain = position + left;
       } else if (left == 0) {
               /* The first byte in the (nonexistent) chain after the last chain */
               pos->internal_.chain = NULL;
               pos->internal_.pos_in_chain = 0;
       } else {
               PTR_NOT_FOUND(pos);
               result = -1;
       }

       EVBUFFER_UNLOCK(buf);

       return result;
}

/**
  Compare the bytes in buf at position pos to the len bytes in mem.  Return
  less than 0, 0, or greater than 0 as memcmp.
*/
static int
evbuffer_ptr_memcmp(const struct evbuffer *buf, const struct evbuffer_ptr *pos,
   const char *mem, size_t len)
{
       struct evbuffer_chain *chain;
       size_t position;
       int r;

       ASSERT_EVBUFFER_LOCKED(buf);

       if (pos->pos < 0 ||
           EV_SIZE_MAX - len < (size_t)pos->pos ||
           pos->pos + len > buf->total_len)
               return -1;

       chain = pos->internal_.chain;
       position = pos->internal_.pos_in_chain;
       while (len && chain) {
               size_t n_comparable;
               if (len + position > chain->off)
                       n_comparable = chain->off - position;
               else
                       n_comparable = len;
               r = memcmp(chain->buffer + chain->misalign + position, mem,
                   n_comparable);
               if (r)
                       return r;
               mem += n_comparable;
               len -= n_comparable;
               position = 0;
               chain = chain->next;
       }

       return 0;
}

struct evbuffer_ptr
evbuffer_search(struct evbuffer *buffer, const char *what, size_t len, const struct evbuffer_ptr *start)
{
       return evbuffer_search_range(buffer, what, len, start, NULL);
}

struct evbuffer_ptr
evbuffer_search_range(struct evbuffer *buffer, const char *what, size_t len, const struct evbuffer_ptr *start, const struct evbuffer_ptr *end)
{
       struct evbuffer_ptr pos;
       struct evbuffer_chain *chain, *last_chain = NULL;
       const unsigned char *p;
       char first;

       EVBUFFER_LOCK(buffer);

       if (start) {
               memcpy(&pos, start, sizeof(pos));
               chain = pos.internal_.chain;
       } else {
               pos.pos = 0;
               chain = pos.internal_.chain = buffer->first;
               pos.internal_.pos_in_chain = 0;
       }

       if (end)
               last_chain = end->internal_.chain;

       if (!len || len > EV_SSIZE_MAX)
               goto done;

       first = what[0];

       while (chain) {
               const unsigned char *start_at =
                   chain->buffer + chain->misalign +
                   pos.internal_.pos_in_chain;
               p = memchr(start_at, first,
                   chain->off - pos.internal_.pos_in_chain);
               if (p) {
                       pos.pos += p - start_at;
                       pos.internal_.pos_in_chain += p - start_at;
                       if (!evbuffer_ptr_memcmp(buffer, &pos, what, len)) {
                               if (end && pos.pos + (ev_ssize_t)len > end->pos)
                                       goto not_found;
                               else
                                       goto done;
                       }
                       ++pos.pos;
                       ++pos.internal_.pos_in_chain;
                       if (pos.internal_.pos_in_chain == chain->off) {
                               chain = pos.internal_.chain = chain->next;
                               pos.internal_.pos_in_chain = 0;
                       }
               } else {
                       if (chain == last_chain)
                               goto not_found;
                       pos.pos += chain->off - pos.internal_.pos_in_chain;
                       chain = pos.internal_.chain = chain->next;
                       pos.internal_.pos_in_chain = 0;
               }
       }

not_found:
       PTR_NOT_FOUND(&pos);
done:
       EVBUFFER_UNLOCK(buffer);
       return pos;
}

int
evbuffer_peek(struct evbuffer *buffer, ev_ssize_t len,
   struct evbuffer_ptr *start_at,
   struct evbuffer_iovec *vec, int n_vec)
{
       struct evbuffer_chain *chain;
       int idx = 0;
       ev_ssize_t len_so_far = 0;

       /* Avoid locking in trivial edge cases */
       if (start_at && start_at->internal_.chain == NULL)
               return 0;

       EVBUFFER_LOCK(buffer);

       if (start_at) {
               chain = start_at->internal_.chain;
               len_so_far = chain->off
                   - start_at->internal_.pos_in_chain;
               idx = 1;
               if (n_vec > 0) {
                       vec[0].iov_base = (void *)(chain->buffer + chain->misalign
                           + start_at->internal_.pos_in_chain);
                       vec[0].iov_len = len_so_far;
               }
               chain = chain->next;
       } else {
               chain = buffer->first;
       }

       if (n_vec == 0 && len < 0) {
               /* If no vectors are provided and they asked for "everything",
                * pretend they asked for the actual available amount. */
               len = buffer->total_len;
               if (start_at) {
                       len -= start_at->pos;
               }
       }

       while (chain) {
               if (len >= 0 && len_so_far >= len)
                       break;
               if (idx<n_vec) {
                       vec[idx].iov_base = (void *)(chain->buffer + chain->misalign);
                       vec[idx].iov_len = chain->off;
               } else if (len<0) {
                       break;
               }
               ++idx;
               len_so_far += chain->off;
               chain = chain->next;
       }

       EVBUFFER_UNLOCK(buffer);

       return idx;
}


int
evbuffer_add_vprintf(struct evbuffer *buf, const char *fmt, va_list ap)
{
       char *buffer;
       size_t space;
       int sz, result = -1;
       va_list aq;
       struct evbuffer_chain *chain;


       EVBUFFER_LOCK(buf);

       if (buf->freeze_end) {
               goto done;
       }

       /* make sure that at least some space is available */
       if ((chain = evbuffer_expand_singlechain(buf, 64)) == NULL)
               goto done;

       for (;;) {
#if 0
               size_t used = chain->misalign + chain->off;
               buffer = (char *)chain->buffer + chain->misalign + chain->off;
               EVUTIL_ASSERT(chain->buffer_len >= used);
               space = chain->buffer_len - used;
#endif
               buffer = (char*) CHAIN_SPACE_PTR(chain);
               space = (size_t) CHAIN_SPACE_LEN(chain);

#ifndef va_copy
#define va_copy(dst, src)       memcpy(&(dst), &(src), sizeof(va_list))
#endif
               va_copy(aq, ap);

               sz = evutil_vsnprintf(buffer, space, fmt, aq);

               va_end(aq);

               if (sz < 0)
                       goto done;
               if (INT_MAX >= EVBUFFER_CHAIN_MAX &&
                   (size_t)sz >= EVBUFFER_CHAIN_MAX)
                       goto done;
               if ((size_t)sz < space) {
                       chain->off += sz;
                       buf->total_len += sz;
                       buf->n_add_for_cb += sz;

                       advance_last_with_data(buf);
                       evbuffer_invoke_callbacks_(buf);
                       result = sz;
                       goto done;
               }
               if ((chain = evbuffer_expand_singlechain(buf, sz + 1)) == NULL)
                       goto done;
       }
       /* NOTREACHED */

done:
       EVBUFFER_UNLOCK(buf);
       return result;
}

int
evbuffer_add_printf(struct evbuffer *buf, const char *fmt, ...)
{
       int res = -1;
       va_list ap;

       va_start(ap, fmt);
       res = evbuffer_add_vprintf(buf, fmt, ap);
       va_end(ap);

       return (res);
}

int
evbuffer_add_reference(struct evbuffer *outbuf,
   const void *data, size_t datlen,
   evbuffer_ref_cleanup_cb cleanupfn, void *extra)
{
       struct evbuffer_chain *chain;
       struct evbuffer_chain_reference *info;
       int result = -1;

       chain = evbuffer_chain_new(sizeof(struct evbuffer_chain_reference));
       if (!chain)
               return (-1);
       chain->flags |= EVBUFFER_REFERENCE | EVBUFFER_IMMUTABLE;
       chain->buffer = (unsigned char *)data;
       chain->buffer_len = datlen;
       chain->off = datlen;

       info = EVBUFFER_CHAIN_EXTRA(struct evbuffer_chain_reference, chain);
       info->cleanupfn = cleanupfn;
       info->extra = extra;

       EVBUFFER_LOCK(outbuf);
       if (outbuf->freeze_end) {
               /* don't call chain_free; we do not want to actually invoke
                * the cleanup function */
               mm_free(chain);
               goto done;
       }
       evbuffer_chain_insert(outbuf, chain);
       outbuf->n_add_for_cb += datlen;

       evbuffer_invoke_callbacks_(outbuf);

       result = 0;
done:
       EVBUFFER_UNLOCK(outbuf);

       return result;
}

/* TODO(niels): we may want to add to automagically convert to mmap, in
* case evbuffer_remove() or evbuffer_pullup() are being used.
*/
struct evbuffer_file_segment *
evbuffer_file_segment_new(
       int fd, ev_off_t offset, ev_off_t length, unsigned flags)
{
       struct evbuffer_file_segment *seg =
           mm_calloc(sizeof(struct evbuffer_file_segment), 1);
       if (!seg)
               return NULL;
       seg->refcnt = 1;
       seg->fd = fd;
       seg->flags = flags;
       seg->file_offset = offset;
       seg->cleanup_cb = NULL;
       seg->cleanup_cb_arg = NULL;
#ifdef _WIN32
#ifndef lseek
#define lseek _lseeki64
#endif
#ifndef fstat
#define fstat _fstat
#endif
#ifndef stat
#define stat _stat
#endif
#endif
       if (length == -1) {
               struct stat st;
               if (fstat(fd, &st) < 0)
                       goto err;
               length = st.st_size;
       }
       seg->length = length;

       if (offset < 0 || length < 0 ||
           ((ev_uint64_t)length > EVBUFFER_CHAIN_MAX) ||
           (ev_uint64_t)offset > (ev_uint64_t)(EVBUFFER_CHAIN_MAX - length))
               goto err;

#if defined(USE_SENDFILE)
       if (!(flags & EVBUF_FS_DISABLE_SENDFILE)) {
               seg->can_sendfile = 1;
               goto done;
       }
#endif

       if (evbuffer_file_segment_materialize(seg)<0)
               goto err;

#if defined(USE_SENDFILE)
done:
#endif
       if (!(flags & EVBUF_FS_DISABLE_LOCKING)) {
               EVTHREAD_ALLOC_LOCK(seg->lock, 0);
       }
       return seg;
err:
       mm_free(seg);
       return NULL;
}

#ifdef EVENT__HAVE_MMAP
static long
get_page_size(void)
{
#ifdef SC_PAGE_SIZE
       return sysconf(SC_PAGE_SIZE);
#elif defined(_SC_PAGE_SIZE)
       return sysconf(_SC_PAGE_SIZE);
#else
       return 1;
#endif
}
#endif

/* DOCDOC */
/* Requires lock */
static int
evbuffer_file_segment_materialize(struct evbuffer_file_segment *seg)
{
       const unsigned flags = seg->flags;
       const int fd = seg->fd;
       const ev_off_t length = seg->length;
       const ev_off_t offset = seg->file_offset;

       if (seg->contents)
               return 0; /* already materialized */

#if defined(EVENT__HAVE_MMAP)
       if (!(flags & EVBUF_FS_DISABLE_MMAP)) {
               off_t offset_rounded = 0, offset_leftover = 0;
               void *mapped;
               if (offset) {
                       /* mmap implementations don't generally like us
                        * to have an offset that isn't a round  */
                       long page_size = get_page_size();
                       if (page_size == -1)
                               goto err;
                       offset_leftover = offset % page_size;
                       offset_rounded = offset - offset_leftover;
               }
               mapped = mmap(NULL, length + offset_leftover,
                   PROT_READ,
#ifdef MAP_NOCACHE
                   MAP_NOCACHE | /* ??? */
#endif
#ifdef MAP_FILE
                   MAP_FILE |
#endif
                   MAP_PRIVATE,
                   fd, offset_rounded);
               if (mapped == MAP_FAILED) {
                       event_warn("%s: mmap(%d, %d, %zu) failed",
                           __func__, fd, 0, (size_t)(offset + length));
               } else {
                       seg->mapping = mapped;
                       seg->contents = (char*)mapped+offset_leftover;
                       seg->mmap_offset = 0;
                       seg->is_mapping = 1;
                       goto done;
               }
       }
#endif
#ifdef _WIN32
       if (!(flags & EVBUF_FS_DISABLE_MMAP)) {
               intptr_t h = _get_osfhandle(fd);
               HANDLE m;
               ev_uint64_t total_size = length+offset;
               if ((HANDLE)h == INVALID_HANDLE_VALUE)
                       goto err;
               m = CreateFileMapping((HANDLE)h, NULL, PAGE_READONLY,
                   (total_size >> 32), total_size & 0xfffffffful,
                   NULL);
               if (m != INVALID_HANDLE_VALUE) { /* Does h leak? */
                       seg->mapping_handle = m;
                       seg->mmap_offset = offset;
                       seg->is_mapping = 1;
                       goto done;
               }
       }
#endif
       {
               ev_off_t start_pos = lseek(fd, 0, SEEK_CUR), pos;
               ev_off_t read_so_far = 0;
               char *mem;
               int e;
               ev_ssize_t n = 0;
               if (!(mem = mm_malloc(length)))
                       goto err;
               if (start_pos < 0) {
                       mm_free(mem);
                       goto err;
               }
               if (lseek(fd, offset, SEEK_SET) < 0) {
                       mm_free(mem);
                       goto err;
               }
               while (read_so_far < length) {
                       n = read(fd, mem+read_so_far, length-read_so_far);
                       if (n <= 0)
                               break;
                       read_so_far += n;
               }

               e = errno;
               pos = lseek(fd, start_pos, SEEK_SET);
               if (n < 0 || (n == 0 && length > read_so_far)) {
                       mm_free(mem);
                       errno = e;
                       goto err;
               } else if (pos < 0) {
                       mm_free(mem);
                       goto err;
               }

               seg->contents = mem;
       }

done:
       return 0;
err:
       return -1;
}

void evbuffer_file_segment_add_cleanup_cb(struct evbuffer_file_segment *seg,
       evbuffer_file_segment_cleanup_cb cb, void* arg)
{
       EVUTIL_ASSERT(seg->refcnt > 0);
       seg->cleanup_cb = cb;
       seg->cleanup_cb_arg = arg;
}

void
evbuffer_file_segment_free(struct evbuffer_file_segment *seg)
{
       int refcnt;
       EVLOCK_LOCK(seg->lock, 0);
       refcnt = --seg->refcnt;
       EVLOCK_UNLOCK(seg->lock, 0);
       if (refcnt > 0)
               return;
       EVUTIL_ASSERT(refcnt == 0);

       if (seg->is_mapping) {
#ifdef _WIN32
               CloseHandle(seg->mapping_handle);
#elif defined (EVENT__HAVE_MMAP)
               off_t offset_leftover;
               offset_leftover = seg->file_offset % get_page_size();
               if (munmap(seg->mapping, seg->length + offset_leftover) == -1)
                       event_warn("%s: munmap failed", __func__);
#endif
       } else if (seg->contents) {
               mm_free(seg->contents);
       }

       if ((seg->flags & EVBUF_FS_CLOSE_ON_FREE) && seg->fd >= 0) {
               close(seg->fd);
       }

       if (seg->cleanup_cb) {
               (*seg->cleanup_cb)((struct evbuffer_file_segment const*)seg,
                   seg->flags, seg->cleanup_cb_arg);
               seg->cleanup_cb = NULL;
               seg->cleanup_cb_arg = NULL;
       }

       EVTHREAD_FREE_LOCK(seg->lock, 0);
       mm_free(seg);
}

int
evbuffer_add_file_segment(struct evbuffer *buf,
   struct evbuffer_file_segment *seg, ev_off_t offset, ev_off_t length)
{
       struct evbuffer_chain *chain;
       struct evbuffer_chain_file_segment *extra;
       int can_use_sendfile = 0;

       EVBUFFER_LOCK(buf);
       EVLOCK_LOCK(seg->lock, 0);
       if (buf->flags & EVBUFFER_FLAG_DRAINS_TO_FD) {
               can_use_sendfile = 1;
       } else {
               if (!seg->contents) {
                       if (evbuffer_file_segment_materialize(seg)<0) {
                               EVLOCK_UNLOCK(seg->lock, 0);
                               EVBUFFER_UNLOCK(buf);
                               return -1;
                       }
               }
       }
       EVLOCK_UNLOCK(seg->lock, 0);

       if (buf->freeze_end)
               goto err;

       if (length < 0) {
               if (offset > seg->length)
                       goto err;
               length = seg->length - offset;
       }

       /* Can we actually add this? */
       if (offset+length > seg->length)
               goto err;

       chain = evbuffer_chain_new(sizeof(struct evbuffer_chain_file_segment));
       if (!chain)
               goto err;
       extra = EVBUFFER_CHAIN_EXTRA(struct evbuffer_chain_file_segment, chain);

       chain->flags |= EVBUFFER_IMMUTABLE|EVBUFFER_FILESEGMENT;
       if (can_use_sendfile && seg->can_sendfile) {
               chain->flags |= EVBUFFER_SENDFILE;
               chain->misalign = seg->file_offset + offset;
               chain->off = length;
               chain->buffer_len = chain->misalign + length;
       } else if (seg->is_mapping) {
#ifdef _WIN32
               ev_uint64_t total_offset = seg->mmap_offset+offset;
               ev_uint64_t offset_rounded=0, offset_remaining=0;
               LPVOID data;
               if (total_offset) {
                       SYSTEM_INFO si;
                       memset(&si, 0, sizeof(si)); /* cargo cult */
                       GetSystemInfo(&si);
                       offset_remaining = total_offset % si.dwAllocationGranularity;
                       offset_rounded = total_offset - offset_remaining;
               }
               data = MapViewOfFile(
                       seg->mapping_handle,
                       FILE_MAP_READ,
                       offset_rounded >> 32,
                       offset_rounded & 0xfffffffful,
                       length + offset_remaining);
               if (data == NULL) {
                       mm_free(chain);
                       goto err;
               }
               chain->buffer = (unsigned char*) data;
               chain->buffer_len = length+offset_remaining;
               chain->misalign = offset_remaining;
               chain->off = length;
#else
               chain->buffer = (unsigned char*)(seg->contents + offset);
               chain->buffer_len = length;
               chain->off = length;
#endif
       } else {
               chain->buffer = (unsigned char*)(seg->contents + offset);
               chain->buffer_len = length;
               chain->off = length;
       }

       EVLOCK_LOCK(seg->lock, 0);
       ++seg->refcnt;
       EVLOCK_UNLOCK(seg->lock, 0);
       extra->segment = seg;
       buf->n_add_for_cb += length;
       evbuffer_chain_insert(buf, chain);

       evbuffer_invoke_callbacks_(buf);

       EVBUFFER_UNLOCK(buf);

       return 0;
err:
       EVBUFFER_UNLOCK(buf);
       evbuffer_file_segment_free(seg); /* Lowers the refcount */
       return -1;
}

int
evbuffer_add_file(struct evbuffer *buf, int fd, ev_off_t offset, ev_off_t length)
{
       struct evbuffer_file_segment *seg;
       unsigned flags = EVBUF_FS_CLOSE_ON_FREE;
       int r;

       seg = evbuffer_file_segment_new(fd, offset, length, flags);
       if (!seg)
               return -1;
       r = evbuffer_add_file_segment(buf, seg, 0, length);
       if (r == 0)
               evbuffer_file_segment_free(seg);
       return r;
}

int
evbuffer_setcb(struct evbuffer *buffer, evbuffer_cb cb, void *cbarg)
{
       EVBUFFER_LOCK(buffer);

       if (!LIST_EMPTY(&buffer->callbacks))
               evbuffer_remove_all_callbacks(buffer);

       if (cb) {
               struct evbuffer_cb_entry *ent =
                   evbuffer_add_cb(buffer, NULL, cbarg);
               if (!ent) {
                       EVBUFFER_UNLOCK(buffer);
                       return -1;
               }
               ent->cb.cb_obsolete = cb;
               ent->flags |= EVBUFFER_CB_OBSOLETE;
       }
       EVBUFFER_UNLOCK(buffer);
       return 0;
}

struct evbuffer_cb_entry *
evbuffer_add_cb(struct evbuffer *buffer, evbuffer_cb_func cb, void *cbarg)
{
       struct evbuffer_cb_entry *e;
       if (! (e = mm_calloc(1, sizeof(struct evbuffer_cb_entry))))
               return NULL;
       EVBUFFER_LOCK(buffer);
       e->cb.cb_func = cb;
       e->cbarg = cbarg;
       e->flags = EVBUFFER_CB_ENABLED;
       LIST_INSERT_HEAD(&buffer->callbacks, e, next);
       EVBUFFER_UNLOCK(buffer);
       return e;
}

int
evbuffer_remove_cb_entry(struct evbuffer *buffer,
                        struct evbuffer_cb_entry *ent)
{
       EVBUFFER_LOCK(buffer);
       LIST_REMOVE(ent, next);
       EVBUFFER_UNLOCK(buffer);
       mm_free(ent);
       return 0;
}

int
evbuffer_remove_cb(struct evbuffer *buffer, evbuffer_cb_func cb, void *cbarg)
{
       struct evbuffer_cb_entry *cbent;
       int result = -1;
       EVBUFFER_LOCK(buffer);
       LIST_FOREACH(cbent, &buffer->callbacks, next) {
               if (cb == cbent->cb.cb_func && cbarg == cbent->cbarg) {
                       result = evbuffer_remove_cb_entry(buffer, cbent);
                       goto done;
               }
       }
done:
       EVBUFFER_UNLOCK(buffer);
       return result;
}

int
evbuffer_cb_set_flags(struct evbuffer *buffer,
                     struct evbuffer_cb_entry *cb, ev_uint32_t flags)
{
       /* the user isn't allowed to mess with these. */
       flags &= ~EVBUFFER_CB_INTERNAL_FLAGS;
       EVBUFFER_LOCK(buffer);
       cb->flags |= flags;
       EVBUFFER_UNLOCK(buffer);
       return 0;
}

int
evbuffer_cb_clear_flags(struct evbuffer *buffer,
                     struct evbuffer_cb_entry *cb, ev_uint32_t flags)
{
       /* the user isn't allowed to mess with these. */
       flags &= ~EVBUFFER_CB_INTERNAL_FLAGS;
       EVBUFFER_LOCK(buffer);
       cb->flags &= ~flags;
       EVBUFFER_UNLOCK(buffer);
       return 0;
}

int
evbuffer_freeze(struct evbuffer *buffer, int start)
{
       EVBUFFER_LOCK(buffer);
       if (start)
               buffer->freeze_start = 1;
       else
               buffer->freeze_end = 1;
       EVBUFFER_UNLOCK(buffer);
       return 0;
}

int
evbuffer_unfreeze(struct evbuffer *buffer, int start)
{
       EVBUFFER_LOCK(buffer);
       if (start)
               buffer->freeze_start = 0;
       else
               buffer->freeze_end = 0;
       EVBUFFER_UNLOCK(buffer);
       return 0;
}

#if 0
void
evbuffer_cb_suspend(struct evbuffer *buffer, struct evbuffer_cb_entry *cb)
{
       if (!(cb->flags & EVBUFFER_CB_SUSPENDED)) {
               cb->size_before_suspend = evbuffer_get_length(buffer);
               cb->flags |= EVBUFFER_CB_SUSPENDED;
       }
}

void
evbuffer_cb_unsuspend(struct evbuffer *buffer, struct evbuffer_cb_entry *cb)
{
       if ((cb->flags & EVBUFFER_CB_SUSPENDED)) {
               unsigned call = (cb->flags & EVBUFFER_CB_CALL_ON_UNSUSPEND);
               size_t sz = cb->size_before_suspend;
               cb->flags &= ~(EVBUFFER_CB_SUSPENDED|
                              EVBUFFER_CB_CALL_ON_UNSUSPEND);
               cb->size_before_suspend = 0;
               if (call && (cb->flags & EVBUFFER_CB_ENABLED)) {
                       cb->cb(buffer, sz, evbuffer_get_length(buffer), cb->cbarg);
               }
       }
}
#endif

int
evbuffer_get_callbacks_(struct evbuffer *buffer, struct event_callback **cbs,
   int max_cbs)
{
       int r = 0;
       EVBUFFER_LOCK(buffer);
       if (buffer->deferred_cbs) {
               if (max_cbs < 1) {
                       r = -1;
                       goto done;
               }
               cbs[0] = &buffer->deferred;
               r = 1;
       }
done:
       EVBUFFER_UNLOCK(buffer);
       return r;
}