/*      $NetBSD: evrpc.c,v 1.6 2024/08/18 20:47:21 christos Exp $       */

/*
* Copyright (c) 2000-2007 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
#define WIN32_LEAN_AND_MEAN
#include <winsock2.h>
#include <windows.h>
#undef WIN32_LEAN_AND_MEAN
#endif

#include <sys/types.h>
#ifndef _WIN32
#include <sys/socket.h>
#endif
#ifdef EVENT__HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#include <sys/queue.h>
#include <stdio.h>
#include <stdlib.h>
#ifndef _WIN32
#include <unistd.h>
#endif
#include <errno.h>
#include <signal.h>
#include <string.h>

#include <sys/queue.h>

#include "event2/event.h"
#include "event2/event_struct.h"
#include "event2/rpc.h"
#include "event2/rpc_struct.h"
#include "evrpc-internal.h"
#include "event2/http.h"
#include "event2/buffer.h"
#include "event2/tag.h"
#include "event2/http_struct.h"
#include "event2/http_compat.h"
#include "event2/util.h"
#include "util-internal.h"
#include "log-internal.h"
#include "mm-internal.h"

struct evrpc_base *
evrpc_init(struct evhttp *http_server)
{
       struct evrpc_base* base = mm_calloc(1, sizeof(struct evrpc_base));
       if (base == NULL)
               return (NULL);

       /* we rely on the tagging sub system */
       evtag_init();

       TAILQ_INIT(&base->registered_rpcs);
       TAILQ_INIT(&base->input_hooks);
       TAILQ_INIT(&base->output_hooks);

       TAILQ_INIT(&base->paused_requests);

       base->http_server = http_server;

       return (base);
}

void
evrpc_free(struct evrpc_base *base)
{
       struct evrpc *rpc;
       struct evrpc_hook *hook;
       struct evrpc_hook_ctx *pause;
       int r;

       while ((rpc = TAILQ_FIRST(&base->registered_rpcs)) != NULL) {
               r = evrpc_unregister_rpc(base, rpc->uri);
               EVUTIL_ASSERT(r == 0);
       }
       while ((pause = TAILQ_FIRST(&base->paused_requests)) != NULL) {
               TAILQ_REMOVE(&base->paused_requests, pause, next);
               mm_free(pause);
       }
       while ((hook = TAILQ_FIRST(&base->input_hooks)) != NULL) {
               r = evrpc_remove_hook(base, EVRPC_INPUT, hook);
               EVUTIL_ASSERT(r);
       }
       while ((hook = TAILQ_FIRST(&base->output_hooks)) != NULL) {
               r = evrpc_remove_hook(base, EVRPC_OUTPUT, hook);
               EVUTIL_ASSERT(r);
       }
       mm_free(base);
}

void *
evrpc_add_hook(void *vbase,
   enum EVRPC_HOOK_TYPE hook_type,
   int (*cb)(void *, struct evhttp_request *, struct evbuffer *, void *),
   void *cb_arg)
{
       struct evrpc_hooks_ *base = vbase;
       struct evrpc_hook_list *head = NULL;
       struct evrpc_hook *hook = NULL;
       switch (hook_type) {
       case EVRPC_INPUT:
               head = &base->in_hooks;
               break;
       case EVRPC_OUTPUT:
               head = &base->out_hooks;
               break;
       default:
               EVUTIL_ASSERT(hook_type == EVRPC_INPUT || hook_type == EVRPC_OUTPUT);
       }

       hook = mm_calloc(1, sizeof(struct evrpc_hook));
       EVUTIL_ASSERT(hook != NULL);

       hook->process = cb;
       hook->process_arg = cb_arg;
       TAILQ_INSERT_TAIL(head, hook, next);

       return (hook);
}

static int
evrpc_remove_hook_internal(struct evrpc_hook_list *head, void *handle)
{
       struct evrpc_hook *hook = NULL;
       TAILQ_FOREACH(hook, head, next) {
               if (hook == handle) {
                       TAILQ_REMOVE(head, hook, next);
                       mm_free(hook);
                       return (1);
               }
       }

       return (0);
}

/*
* remove the hook specified by the handle
*/

int
evrpc_remove_hook(void *vbase, enum EVRPC_HOOK_TYPE hook_type, void *handle)
{
       struct evrpc_hooks_ *base = vbase;
       struct evrpc_hook_list *head = NULL;
       switch (hook_type) {
       case EVRPC_INPUT:
               head = &base->in_hooks;
               break;
       case EVRPC_OUTPUT:
               head = &base->out_hooks;
               break;
       default:
               EVUTIL_ASSERT(hook_type == EVRPC_INPUT || hook_type == EVRPC_OUTPUT);
       }

       return (evrpc_remove_hook_internal(head, handle));
}

static int
evrpc_process_hooks(struct evrpc_hook_list *head, void *ctx,
   struct evhttp_request *req, struct evbuffer *evbuf)
{
       struct evrpc_hook *hook;
       TAILQ_FOREACH(hook, head, next) {
               int res = hook->process(ctx, req, evbuf, hook->process_arg);
               if (res != EVRPC_CONTINUE)
                       return (res);
       }

       return (EVRPC_CONTINUE);
}

static void evrpc_pool_schedule(struct evrpc_pool *pool);
static void evrpc_request_cb(struct evhttp_request *, void *);

/*
* Registers a new RPC with the HTTP server.   The evrpc object is expected
* to have been filled in via the EVRPC_REGISTER_OBJECT macro which in turn
* calls this function.
*/

static char *
evrpc_construct_uri(const char *uri)
{
       char *constructed_uri;
       size_t constructed_uri_len;

       constructed_uri_len = strlen(EVRPC_URI_PREFIX) + strlen(uri) + 1;
       if ((constructed_uri = mm_malloc(constructed_uri_len)) == NULL)
               event_err(1, "%s: failed to register rpc at %s",
                   __func__, uri);
       memcpy(constructed_uri, EVRPC_URI_PREFIX, strlen(EVRPC_URI_PREFIX));
       memcpy(constructed_uri + strlen(EVRPC_URI_PREFIX), uri, strlen(uri));
       constructed_uri[constructed_uri_len - 1] = '\0';

       return (constructed_uri);
}

int
evrpc_register_rpc(struct evrpc_base *base, struct evrpc *rpc,
   void (*cb)(struct evrpc_req_generic *, void *), void *cb_arg)
{
       char *constructed_uri = evrpc_construct_uri(rpc->uri);

       rpc->base = base;
       rpc->cb = cb;
       rpc->cb_arg = cb_arg;

       TAILQ_INSERT_TAIL(&base->registered_rpcs, rpc, next);

       evhttp_set_cb(base->http_server,
           constructed_uri,
           evrpc_request_cb,
           rpc);

       mm_free(constructed_uri);

       return (0);
}

int
evrpc_unregister_rpc(struct evrpc_base *base, const char *name)
{
       char *registered_uri = NULL;
       struct evrpc *rpc;
       int r;

       /* find the right rpc; linear search might be slow */
       TAILQ_FOREACH(rpc, &base->registered_rpcs, next) {
               if (strcmp(rpc->uri, name) == 0)
                       break;
       }
       if (rpc == NULL) {
               /* We did not find an RPC with this name */
               return (-1);
       }
       TAILQ_REMOVE(&base->registered_rpcs, rpc, next);

       registered_uri = evrpc_construct_uri(name);

       /* remove the http server callback */
       r = evhttp_del_cb(base->http_server, registered_uri);
       EVUTIL_ASSERT(r == 0);

       mm_free(registered_uri);

       mm_free((char *)rpc->uri);
       mm_free(rpc);
       return (0);
}

static int evrpc_pause_request(void *vbase, void *ctx,
   void (*cb)(void *, enum EVRPC_HOOK_RESULT));
static void evrpc_request_cb_closure(void *, enum EVRPC_HOOK_RESULT);

static void
evrpc_request_cb(struct evhttp_request *req, void *arg)
{
       struct evrpc *rpc = arg;
       struct evrpc_req_generic *rpc_state = NULL;

       /* let's verify the outside parameters */
       if (req->type != EVHTTP_REQ_POST ||
           evbuffer_get_length(req->input_buffer) <= 0)
               goto error;

       rpc_state = mm_calloc(1, sizeof(struct evrpc_req_generic));
       if (rpc_state == NULL)
               goto error;
       rpc_state->rpc = rpc;
       rpc_state->http_req = req;
       rpc_state->rpc_data = NULL;

       if (TAILQ_FIRST(&rpc->base->input_hooks) != NULL) {
               int hook_res;

               evrpc_hook_associate_meta_(&rpc_state->hook_meta, req->evcon);

               /*
                * allow hooks to modify the outgoing request
                */
               hook_res = evrpc_process_hooks(&rpc->base->input_hooks,
                   rpc_state, req, req->input_buffer);
               switch (hook_res) {
               case EVRPC_TERMINATE:
                       goto error;
               case EVRPC_PAUSE:
                       evrpc_pause_request(rpc->base, rpc_state,
                           evrpc_request_cb_closure);
                       return;
               case EVRPC_CONTINUE:
                       break;
               default:
                       EVUTIL_ASSERT(hook_res == EVRPC_TERMINATE ||
                           hook_res == EVRPC_CONTINUE ||
                           hook_res == EVRPC_PAUSE);
               }
       }

       evrpc_request_cb_closure(rpc_state, EVRPC_CONTINUE);
       return;

error:
       if (rpc_state)
               evrpc_reqstate_free_(rpc_state);
       evhttp_send_error(req, HTTP_SERVUNAVAIL, NULL);
       return;
}

static void
evrpc_request_cb_closure(void *arg, enum EVRPC_HOOK_RESULT hook_res)
{
       struct evrpc_req_generic *rpc_state = arg;
       struct evrpc *rpc;
       struct evhttp_request *req;

       EVUTIL_ASSERT(rpc_state);
       rpc = rpc_state->rpc;
       req = rpc_state->http_req;

       if (hook_res == EVRPC_TERMINATE)
               goto error;

       /* let's check that we can parse the request */
       rpc_state->request = rpc->request_new(rpc->request_new_arg);
       if (rpc_state->request == NULL)
               goto error;

       if (rpc->request_unmarshal(
                   rpc_state->request, req->input_buffer) == -1) {
               /* we failed to parse the request; that's a bummer */
               goto error;
       }

       /* at this point, we have a well formed request, prepare the reply */

       rpc_state->reply = rpc->reply_new(rpc->reply_new_arg);
       if (rpc_state->reply == NULL)
               goto error;

       /* give the rpc to the user; they can deal with it */
       rpc->cb(rpc_state, rpc->cb_arg);

       return;

error:
       evrpc_reqstate_free_(rpc_state);
       evhttp_send_error(req, HTTP_SERVUNAVAIL, NULL);
       return;
}


void
evrpc_reqstate_free_(struct evrpc_req_generic* rpc_state)
{
       struct evrpc *rpc;
       EVUTIL_ASSERT(rpc_state != NULL);
       rpc = rpc_state->rpc;

       /* clean up all memory */
       if (rpc_state->hook_meta != NULL)
               evrpc_hook_context_free_(rpc_state->hook_meta);
       if (rpc_state->request != NULL)
               rpc->request_free(rpc_state->request);
       if (rpc_state->reply != NULL)
               rpc->reply_free(rpc_state->reply);
       if (rpc_state->rpc_data != NULL)
               evbuffer_free(rpc_state->rpc_data);
       mm_free(rpc_state);
}

static void
evrpc_request_done_closure(void *, enum EVRPC_HOOK_RESULT);

void
evrpc_request_done(struct evrpc_req_generic *rpc_state)
{
       struct evhttp_request *req;
       struct evrpc *rpc;

       EVUTIL_ASSERT(rpc_state);

       req = rpc_state->http_req;
       rpc = rpc_state->rpc;

       if (rpc->reply_complete(rpc_state->reply) == -1) {
               /* the reply was not completely filled in.  error out */
               goto error;
       }

       if ((rpc_state->rpc_data = evbuffer_new()) == NULL) {
               /* out of memory */
               goto error;
       }

       /* serialize the reply */
       rpc->reply_marshal(rpc_state->rpc_data, rpc_state->reply);

       if (TAILQ_FIRST(&rpc->base->output_hooks) != NULL) {
               int hook_res;

               evrpc_hook_associate_meta_(&rpc_state->hook_meta, req->evcon);

               /* do hook based tweaks to the request */
               hook_res = evrpc_process_hooks(&rpc->base->output_hooks,
                   rpc_state, req, rpc_state->rpc_data);
               switch (hook_res) {
               case EVRPC_TERMINATE:
                       goto error;
               case EVRPC_PAUSE:
                       if (evrpc_pause_request(rpc->base, rpc_state,
                               evrpc_request_done_closure) == -1)
                               goto error;
                       return;
               case EVRPC_CONTINUE:
                       break;
               default:
                       EVUTIL_ASSERT(hook_res == EVRPC_TERMINATE ||
                           hook_res == EVRPC_CONTINUE ||
                           hook_res == EVRPC_PAUSE);
               }
       }

       evrpc_request_done_closure(rpc_state, EVRPC_CONTINUE);
       return;

error:
       evrpc_reqstate_free_(rpc_state);
       evhttp_send_error(req, HTTP_SERVUNAVAIL, NULL);
       return;
}

void *
evrpc_get_request(struct evrpc_req_generic *req)
{
       return req->request;
}

void *
evrpc_get_reply(struct evrpc_req_generic *req)
{
       return req->reply;
}

static void
evrpc_request_done_closure(void *arg, enum EVRPC_HOOK_RESULT hook_res)
{
       struct evrpc_req_generic *rpc_state = arg;
       struct evhttp_request *req;
       EVUTIL_ASSERT(rpc_state);
       req = rpc_state->http_req;

       if (hook_res == EVRPC_TERMINATE)
               goto error;

       /* on success, we are going to transmit marshaled binary data */
       if (evhttp_find_header(req->output_headers, "Content-Type") == NULL) {
               evhttp_add_header(req->output_headers,
                   "Content-Type", "application/octet-stream");
       }
       evhttp_send_reply(req, HTTP_OK, "OK", rpc_state->rpc_data);

       evrpc_reqstate_free_(rpc_state);

       return;

error:
       evrpc_reqstate_free_(rpc_state);
       evhttp_send_error(req, HTTP_SERVUNAVAIL, NULL);
       return;
}


/* Client implementation of RPC site */

static int evrpc_schedule_request(struct evhttp_connection *connection,
   struct evrpc_request_wrapper *ctx);

struct evrpc_pool *
evrpc_pool_new(struct event_base *base)
{
       struct evrpc_pool *pool = mm_calloc(1, sizeof(struct evrpc_pool));
       if (pool == NULL)
               return (NULL);

       TAILQ_INIT(&pool->connections);
       TAILQ_INIT(&pool->requests);

       TAILQ_INIT(&pool->paused_requests);

       TAILQ_INIT(&pool->input_hooks);
       TAILQ_INIT(&pool->output_hooks);

       pool->base = base;
       pool->timeout = -1;

       return (pool);
}

static void
evrpc_request_wrapper_free(struct evrpc_request_wrapper *request)
{
       if (request->hook_meta != NULL)
               evrpc_hook_context_free_(request->hook_meta);
       mm_free(request->name);
       mm_free(request);
}

void
evrpc_pool_free(struct evrpc_pool *pool)
{
       struct evhttp_connection *connection;
       struct evrpc_request_wrapper *request;
       struct evrpc_hook_ctx *pause;
       struct evrpc_hook *hook;
       int r;

       while ((request = TAILQ_FIRST(&pool->requests)) != NULL) {
               TAILQ_REMOVE(&pool->requests, request, next);
               evrpc_request_wrapper_free(request);
       }

       while ((pause = TAILQ_FIRST(&pool->paused_requests)) != NULL) {
               TAILQ_REMOVE(&pool->paused_requests, pause, next);
               mm_free(pause);
       }

       while ((connection = TAILQ_FIRST(&pool->connections)) != NULL) {
               TAILQ_REMOVE(&pool->connections, connection, next);
               evhttp_connection_free(connection);
       }

       while ((hook = TAILQ_FIRST(&pool->input_hooks)) != NULL) {
               r = evrpc_remove_hook(pool, EVRPC_INPUT, hook);
               EVUTIL_ASSERT(r);
       }

       while ((hook = TAILQ_FIRST(&pool->output_hooks)) != NULL) {
               r = evrpc_remove_hook(pool, EVRPC_OUTPUT, hook);
               EVUTIL_ASSERT(r);
       }

       mm_free(pool);
}

/*
* Add a connection to the RPC pool.   A request scheduled on the pool
* may use any available connection.
*/

void
evrpc_pool_add_connection(struct evrpc_pool *pool,
   struct evhttp_connection *connection)
{
       EVUTIL_ASSERT(connection->http_server == NULL);
       TAILQ_INSERT_TAIL(&pool->connections, connection, next);

       /*
        * associate an event base with this connection
        */
       if (pool->base != NULL)
               evhttp_connection_set_base(connection, pool->base);

       /*
        * unless a timeout was specifically set for a connection,
        * the connection inherits the timeout from the pool.
        */
       if (!evutil_timerisset(&connection->timeout))
               evhttp_connection_set_timeout(connection, pool->timeout);

       /*
        * if we have any requests pending, schedule them with the new
        * connections.
        */

       if (TAILQ_FIRST(&pool->requests) != NULL) {
               struct evrpc_request_wrapper *request =
                   TAILQ_FIRST(&pool->requests);
               TAILQ_REMOVE(&pool->requests, request, next);
               evrpc_schedule_request(connection, request);
       }
}

void
evrpc_pool_remove_connection(struct evrpc_pool *pool,
   struct evhttp_connection *connection)
{
       TAILQ_REMOVE(&pool->connections, connection, next);
}

void
evrpc_pool_set_timeout(struct evrpc_pool *pool, int timeout_in_secs)
{
       struct evhttp_connection *evcon;
       TAILQ_FOREACH(evcon, &pool->connections, next) {
               evhttp_connection_set_timeout(evcon, timeout_in_secs);
       }
       pool->timeout = timeout_in_secs;
}


static void evrpc_reply_done(struct evhttp_request *, void *);
static void evrpc_request_timeout(evutil_socket_t, short, void *);

/*
* Finds a connection object associated with the pool that is currently
* idle and can be used to make a request.
*/
static struct evhttp_connection *
evrpc_pool_find_connection(struct evrpc_pool *pool)
{
       struct evhttp_connection *connection;
       TAILQ_FOREACH(connection, &pool->connections, next) {
               if (TAILQ_FIRST(&connection->requests) == NULL)
                       return (connection);
       }

       return (NULL);
}

/*
* Prototypes responsible for evrpc scheduling and hooking
*/

static void evrpc_schedule_request_closure(void *ctx, enum EVRPC_HOOK_RESULT);

/*
* We assume that the ctx is no longer queued on the pool.
*/
static int
evrpc_schedule_request(struct evhttp_connection *connection,
   struct evrpc_request_wrapper *ctx)
{
       struct evhttp_request *req = NULL;
       struct evrpc_pool *pool = ctx->pool;
       struct evrpc_status status;

       if ((req = evhttp_request_new(evrpc_reply_done, ctx)) == NULL)
               goto error;

       /* serialize the request data into the output buffer */
       ctx->request_marshal(req->output_buffer, ctx->request);

       /* we need to know the connection that we might have to abort */
       ctx->evcon = connection;

       /* if we get paused we also need to know the request */
       ctx->req = req;

       if (TAILQ_FIRST(&pool->output_hooks) != NULL) {
               int hook_res;

               evrpc_hook_associate_meta_(&ctx->hook_meta, connection);

               /* apply hooks to the outgoing request */
               hook_res = evrpc_process_hooks(&pool->output_hooks,
                   ctx, req, req->output_buffer);

               switch (hook_res) {
               case EVRPC_TERMINATE:
                       goto error;
               case EVRPC_PAUSE:
                       /* we need to be explicitly resumed */
                       if (evrpc_pause_request(pool, ctx,
                               evrpc_schedule_request_closure) == -1)
                               goto error;
                       return (0);
               case EVRPC_CONTINUE:
                       /* we can just continue */
                       break;
               default:
                       EVUTIL_ASSERT(hook_res == EVRPC_TERMINATE ||
                           hook_res == EVRPC_CONTINUE ||
                           hook_res == EVRPC_PAUSE);
               }
       }

       evrpc_schedule_request_closure(ctx, EVRPC_CONTINUE);
       return (0);

error:
       memset(&status, 0, sizeof(status));
       status.error = EVRPC_STATUS_ERR_UNSTARTED;
       (*ctx->cb)(&status, ctx->request, ctx->reply, ctx->cb_arg);
       evrpc_request_wrapper_free(ctx);
       return (-1);
}

static void
evrpc_schedule_request_closure(void *arg, enum EVRPC_HOOK_RESULT hook_res)
{
       struct evrpc_request_wrapper *ctx = arg;
       struct evhttp_connection *connection = ctx->evcon;
       struct evhttp_request *req = ctx->req;
       struct evrpc_pool *pool = ctx->pool;
       struct evrpc_status status;
       char *uri = NULL;
       int res = 0;

       if (hook_res == EVRPC_TERMINATE)
               goto error;

       uri = evrpc_construct_uri(ctx->name);
       if (uri == NULL)
               goto error;

       if (pool->timeout > 0) {
               /*
                * a timeout after which the whole rpc is going to be aborted.
                */
               struct timeval tv;
               evutil_timerclear(&tv);
               tv.tv_sec = pool->timeout;
               evtimer_add(&ctx->ev_timeout, &tv);
       }

       /* start the request over the connection */
       res = evhttp_make_request(connection, req, EVHTTP_REQ_POST, uri);
       mm_free(uri);

       if (res == -1)
               goto error;

       return;

error:
       memset(&status, 0, sizeof(status));
       status.error = EVRPC_STATUS_ERR_UNSTARTED;
       (*ctx->cb)(&status, ctx->request, ctx->reply, ctx->cb_arg);
       evrpc_request_wrapper_free(ctx);
}

/* we just queue the paused request on the pool under the req object */
static int
evrpc_pause_request(void *vbase, void *ctx,
   void (*cb)(void *, enum EVRPC_HOOK_RESULT))
{
       struct evrpc_hooks_ *base = vbase;
       struct evrpc_hook_ctx *pause = mm_malloc(sizeof(*pause));
       if (pause == NULL)
               return (-1);

       pause->ctx = ctx;
       pause->cb = cb;

       TAILQ_INSERT_TAIL(&base->pause_requests, pause, next);
       return (0);
}

int
evrpc_resume_request(void *vbase, void *ctx, enum EVRPC_HOOK_RESULT res)
{
       struct evrpc_hooks_ *base = vbase;
       struct evrpc_pause_list *head = &base->pause_requests;
       struct evrpc_hook_ctx *pause;

       TAILQ_FOREACH(pause, head, next) {
               if (pause->ctx == ctx)
                       break;
       }

       if (pause == NULL)
               return (-1);

       (*pause->cb)(pause->ctx, res);
       TAILQ_REMOVE(head, pause, next);
       mm_free(pause);
       return (0);
}

int
evrpc_make_request(struct evrpc_request_wrapper *ctx)
{
       struct evrpc_pool *pool = ctx->pool;

       /* initialize the event structure for this rpc */
       evtimer_assign(&ctx->ev_timeout, pool->base, evrpc_request_timeout, ctx);

       /* we better have some available connections on the pool */
       EVUTIL_ASSERT(TAILQ_FIRST(&pool->connections) != NULL);

       /*
        * if no connection is available, we queue the request on the pool,
        * the next time a connection is empty, the rpc will be send on that.
        */
       TAILQ_INSERT_TAIL(&pool->requests, ctx, next);

       evrpc_pool_schedule(pool);

       return (0);
}


struct evrpc_request_wrapper *
evrpc_make_request_ctx(
       struct evrpc_pool *pool, void *request, void *reply,
       const char *rpcname,
       void (*req_marshal)(struct evbuffer*, void *),
       void (*rpl_clear)(void *),
       int (*rpl_unmarshal)(void *, struct evbuffer *),
       void (*cb)(struct evrpc_status *, void *, void *, void *),
       void *cbarg)
{
       struct evrpc_request_wrapper *ctx = (struct evrpc_request_wrapper *)
           mm_malloc(sizeof(struct evrpc_request_wrapper));
       if (ctx == NULL)
               return (NULL);

       ctx->pool = pool;
       ctx->hook_meta = NULL;
       ctx->evcon = NULL;
       ctx->name = mm_strdup(rpcname);
       if (ctx->name == NULL) {
               mm_free(ctx);
               return (NULL);
       }
       ctx->cb = cb;
       ctx->cb_arg = cbarg;
       ctx->request = request;
       ctx->reply = reply;
       ctx->request_marshal = req_marshal;
       ctx->reply_clear = rpl_clear;
       ctx->reply_unmarshal = rpl_unmarshal;

       return (ctx);
}

static void
evrpc_reply_done_closure(void *, enum EVRPC_HOOK_RESULT);

static void
evrpc_reply_done(struct evhttp_request *req, void *arg)
{
       struct evrpc_request_wrapper *ctx = arg;
       struct evrpc_pool *pool = ctx->pool;
       int hook_res = EVRPC_CONTINUE;

       /* cancel any timeout we might have scheduled */
       event_del(&ctx->ev_timeout);

       ctx->req = req;

       /* we need to get the reply now */
       if (req == NULL) {
               evrpc_reply_done_closure(ctx, EVRPC_CONTINUE);
               return;
       }

       if (TAILQ_FIRST(&pool->input_hooks) != NULL) {
               evrpc_hook_associate_meta_(&ctx->hook_meta, ctx->evcon);

               /* apply hooks to the incoming request */
               hook_res = evrpc_process_hooks(&pool->input_hooks,
                   ctx, req, req->input_buffer);

               switch (hook_res) {
               case EVRPC_TERMINATE:
               case EVRPC_CONTINUE:
                       break;
               case EVRPC_PAUSE:
                       /*
                        * if we get paused we also need to know the
                        * request.  unfortunately, the underlying
                        * layer is going to free it.  we need to
                        * request ownership explicitly
                        */
                       evhttp_request_own(req);

                       evrpc_pause_request(pool, ctx,
                           evrpc_reply_done_closure);
                       return;
               default:
                       EVUTIL_ASSERT(hook_res == EVRPC_TERMINATE ||
                           hook_res == EVRPC_CONTINUE ||
                           hook_res == EVRPC_PAUSE);
               }
       }

       evrpc_reply_done_closure(ctx, hook_res);

       /* http request is being freed by underlying layer */
}

static void
evrpc_reply_done_closure(void *arg, enum EVRPC_HOOK_RESULT hook_res)
{
       struct evrpc_request_wrapper *ctx = arg;
       struct evhttp_request *req = ctx->req;
       struct evrpc_pool *pool = ctx->pool;
       struct evrpc_status status;
       int res = -1;

       memset(&status, 0, sizeof(status));
       status.http_req = req;

       /* we need to get the reply now */
       if (req == NULL) {
               status.error = EVRPC_STATUS_ERR_TIMEOUT;
       } else if (hook_res == EVRPC_TERMINATE) {
               status.error = EVRPC_STATUS_ERR_HOOKABORTED;
       } else {
               res = ctx->reply_unmarshal(ctx->reply, req->input_buffer);
               if (res == -1)
                       status.error = EVRPC_STATUS_ERR_BADPAYLOAD;
       }

       if (res == -1) {
               /* clear everything that we might have written previously */
               ctx->reply_clear(ctx->reply);
       }

       (*ctx->cb)(&status, ctx->request, ctx->reply, ctx->cb_arg);

       evrpc_request_wrapper_free(ctx);

       /* the http layer owned the original request structure, but if we
        * got paused, we asked for ownership and need to free it here. */
       if (req != NULL && evhttp_request_is_owned(req))
               evhttp_request_free(req);

       /* see if we can schedule another request */
       evrpc_pool_schedule(pool);
}

static void
evrpc_pool_schedule(struct evrpc_pool *pool)
{
       struct evrpc_request_wrapper *ctx = TAILQ_FIRST(&pool->requests);
       struct evhttp_connection *evcon;

       /* if no requests are pending, we have no work */
       if (ctx == NULL)
               return;

       if ((evcon = evrpc_pool_find_connection(pool)) != NULL) {
               TAILQ_REMOVE(&pool->requests, ctx, next);
               evrpc_schedule_request(evcon, ctx);
       }
}

static void
evrpc_request_timeout(evutil_socket_t fd, short what, void *arg)
{
       struct evrpc_request_wrapper *ctx = arg;
       struct evhttp_connection *evcon = ctx->evcon;
       EVUTIL_ASSERT(evcon != NULL);

       evhttp_connection_fail_(evcon, EVREQ_HTTP_TIMEOUT);
}

/*
* frees potential meta data associated with a request.
*/

static void
evrpc_meta_data_free(struct evrpc_meta_list *meta_data)
{
       struct evrpc_meta *entry;
       EVUTIL_ASSERT(meta_data != NULL);

       while ((entry = TAILQ_FIRST(meta_data)) != NULL) {
               TAILQ_REMOVE(meta_data, entry, next);
               mm_free(entry->key);
               mm_free(entry->data);
               mm_free(entry);
       }
}

static struct evrpc_hook_meta *
evrpc_hook_meta_new_(void)
{
       struct evrpc_hook_meta *ctx;
       ctx = mm_malloc(sizeof(struct evrpc_hook_meta));
       EVUTIL_ASSERT(ctx != NULL);

       TAILQ_INIT(&ctx->meta_data);
       ctx->evcon = NULL;

       return (ctx);
}

static void
evrpc_hook_associate_meta_(struct evrpc_hook_meta **pctx,
   struct evhttp_connection *evcon)
{
       struct evrpc_hook_meta *ctx = *pctx;
       if (ctx == NULL)
               *pctx = ctx = evrpc_hook_meta_new_();
       ctx->evcon = evcon;
}

static void
evrpc_hook_context_free_(struct evrpc_hook_meta *ctx)
{
       evrpc_meta_data_free(&ctx->meta_data);
       mm_free(ctx);
}

/* Adds meta data */
void
evrpc_hook_add_meta(void *ctx, const char *key,
   const void *data, size_t data_size)
{
       struct evrpc_request_wrapper *req = ctx;
       struct evrpc_hook_meta *store = NULL;
       struct evrpc_meta *meta = NULL;

       if ((store = req->hook_meta) == NULL)
               store = req->hook_meta = evrpc_hook_meta_new_();

       meta = mm_malloc(sizeof(struct evrpc_meta));
       EVUTIL_ASSERT(meta != NULL);
       meta->key = mm_strdup(key);
       EVUTIL_ASSERT(meta->key != NULL);
       meta->data_size = data_size;
       meta->data = mm_malloc(data_size);
       EVUTIL_ASSERT(meta->data != NULL);
       memcpy(meta->data, data, data_size);

       TAILQ_INSERT_TAIL(&store->meta_data, meta, next);
}

int
evrpc_hook_find_meta(void *ctx, const char *key, void **data, size_t *data_size)
{
       struct evrpc_request_wrapper *req = ctx;
       struct evrpc_meta *meta = NULL;

       if (req->hook_meta == NULL)
               return (-1);

       TAILQ_FOREACH(meta, &req->hook_meta->meta_data, next) {
               if (strcmp(meta->key, key) == 0) {
                       *data = meta->data;
                       *data_size = meta->data_size;
                       return (0);
               }
       }

       return (-1);
}

struct evhttp_connection *
evrpc_hook_get_connection(void *ctx)
{
       struct evrpc_request_wrapper *req = ctx;
       return (req->hook_meta != NULL ? req->hook_meta->evcon : NULL);
}

int
evrpc_send_request_generic(struct evrpc_pool *pool,
   void *request, void *reply,
   void (*cb)(struct evrpc_status *, void *, void *, void *),
   void *cb_arg,
   const char *rpcname,
   void (*req_marshal)(struct evbuffer *, void *),
   void (*rpl_clear)(void *),
   int (*rpl_unmarshal)(void *, struct evbuffer *))
{
       struct evrpc_status status;
       struct evrpc_request_wrapper *ctx;
       ctx = evrpc_make_request_ctx(pool, request, reply,
           rpcname, req_marshal, rpl_clear, rpl_unmarshal, cb, cb_arg);
       if (ctx == NULL)
               goto error;
       return (evrpc_make_request(ctx));
error:
       memset(&status, 0, sizeof(status));
       status.error = EVRPC_STATUS_ERR_UNSTARTED;
       (*(cb))(&status, request, reply, cb_arg);
       return (-1);
}

/** Takes a request object and fills it in with the right magic */
static struct evrpc *
evrpc_register_object(const char *name,
   void *(*req_new)(void*), void *req_new_arg, void (*req_free)(void *),
   int (*req_unmarshal)(void *, struct evbuffer *),
   void *(*rpl_new)(void*), void *rpl_new_arg, void (*rpl_free)(void *),
   int (*rpl_complete)(void *),
   void (*rpl_marshal)(struct evbuffer *, void *))
{
       struct evrpc* rpc = (struct evrpc *)mm_calloc(1, sizeof(struct evrpc));
       if (rpc == NULL)
               return (NULL);
       rpc->uri = mm_strdup(name);
       if (rpc->uri == NULL) {
               mm_free(rpc);
               return (NULL);
       }
       rpc->request_new = req_new;
       rpc->request_new_arg = req_new_arg;
       rpc->request_free = req_free;
       rpc->request_unmarshal = req_unmarshal;
       rpc->reply_new = rpl_new;
       rpc->reply_new_arg = rpl_new_arg;
       rpc->reply_free = rpl_free;
       rpc->reply_complete = rpl_complete;
       rpc->reply_marshal = rpl_marshal;
       return (rpc);
}

int
evrpc_register_generic(struct evrpc_base *base, const char *name,
   void (*callback)(struct evrpc_req_generic *, void *), void *cbarg,
   void *(*req_new)(void *), void *req_new_arg, void (*req_free)(void *),
   int (*req_unmarshal)(void *, struct evbuffer *),
   void *(*rpl_new)(void *), void *rpl_new_arg, void (*rpl_free)(void *),
   int (*rpl_complete)(void *),
   void (*rpl_marshal)(struct evbuffer *, void *))
{
       struct evrpc* rpc =
           evrpc_register_object(name, req_new, req_new_arg, req_free, req_unmarshal,
               rpl_new, rpl_new_arg, rpl_free, rpl_complete, rpl_marshal);
       if (rpc == NULL)
               return (-1);
       evrpc_register_rpc(base, rpc,
           (void (*)(struct evrpc_req_generic*, void *))callback, cbarg);
       return (0);
}

/** accessors for obscure and undocumented functionality */
struct evrpc_pool *
evrpc_request_get_pool(struct evrpc_request_wrapper *ctx)
{
       return (ctx->pool);
}

void
evrpc_request_set_pool(struct evrpc_request_wrapper *ctx,
   struct evrpc_pool *pool)
{
       ctx->pool = pool;
}

void
evrpc_request_set_cb(struct evrpc_request_wrapper *ctx,
   void (*cb)(struct evrpc_status*, void *request, void *reply, void *arg),
   void *cb_arg)
{
       ctx->cb = cb;
       ctx->cb_arg = cb_arg;
}

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