NAME

NAME
AnyEvent::HTTP - simple but non-blocking HTTP/HTTPS client

SYNOPSIS
use AnyEvent::HTTP;

http_get "http://www.nethype.de/", sub { print $_[1] };

# ... do something else here

DESCRIPTION
This module is an AnyEvent user, you need to make sure that you use and
run a supported event loop.

This module implements a simple, stateless and non-blocking HTTP client.
It supports GET, POST and other request methods, cookies and more, all
on a very low level. It can follow redirects, supports proxies, and
automatically limits the number of connections to the values specified
in the RFC.

It should generally be a "good client" that is enough for most HTTP
tasks. Simple tasks should be simple, but complex tasks should still be
possible as the user retains control over request and response headers.

The caller is responsible for authentication management, cookies (if the
simplistic implementation in this module doesn't suffice), referer and
other high-level protocol details for which this module offers only
limited support.

METHODS
http_get $url, key => value..., $cb->($data, $headers)
Executes an HTTP-GET request. See the http_request function for
details on additional parameters and the return value.

http_head $url, key => value..., $cb->($data, $headers)
Executes an HTTP-HEAD request. See the http_request function for
details on additional parameters and the return value.

http_post $url, $body, key => value..., $cb->($data, $headers)
Executes an HTTP-POST request with a request body of $body. See the
http_request function for details on additional parameters and the
return value.

http_request $method => $url, key => value..., $cb->($data, $headers)
Executes a HTTP request of type $method (e.g. "GET", "POST"). The
URL must be an absolute http or https URL.

When called in void context, nothing is returned. In other contexts,
"http_request" returns a "cancellation guard" - you have to keep the
object at least alive until the callback get called. If the object
gets destroyed before the callback is called, the request will be
cancelled.

The callback will be called with the response body data as first
argument (or "undef" if an error occurred), and a hash-ref with
response headers (and trailers) as second argument.

All the headers in that hash are lowercased. In addition to the
response headers, the "pseudo-headers" (uppercase to avoid clashing
with possible response headers) "HTTPVersion", "Status" and "Reason"
contain the three parts of the HTTP Status-Line of the same name. If
an error occurs during the body phase of a request, then the
original "Status" and "Reason" values from the header are available
as "OrigStatus" and "OrigReason".

The pseudo-header "URL" contains the actual URL (which can differ
from the requested URL when following redirects - for example, you
might get an error that your URL scheme is not supported even though
your URL is a valid http URL because it redirected to an ftp URL, in
which case you can look at the URL pseudo header).

The pseudo-header "Redirect" only exists when the request was a
result of an internal redirect. In that case it is an array
reference with the "($data, $headers)" from the redirect response.
Note that this response could in turn be the result of a redirect
itself, and "$headers->{Redirect}[1]{Redirect}" will then contain
the original response, and so on.

If the server sends a header multiple times, then their contents
will be joined together with a comma (","), as per the HTTP spec.

If an internal error occurs, such as not being able to resolve a
hostname, then $data will be "undef", "$headers->{Status}" will be
590-599 and the "Reason" pseudo-header will contain an error
message. Currently the following status codes are used:

595 - errors during connection establishment, proxy handshake.
596 - errors during TLS negotiation, request sending and header
processing.
597 - errors during body receiving or processing.
598 - user aborted request via "on_header" or "on_body".
599 - other, usually nonretryable, errors (garbled URL etc.).

A typical callback might look like this:

sub {
my ($body, $hdr) = @_;

if ($hdr->{Status} =~ /^2/) {
... everything should be ok
} else {
print "error, $hdr->{Status} $hdr->{Reason}\n";
}
}

Additional parameters are key-value pairs, and are fully optional.
They include:

recurse => $count (default: $MAX_RECURSE)
Whether to recurse requests or not, e.g. on redirects,
authentication and other retries and so on, and how often to do
so.

Only redirects to http and https URLs are supported. While most
common redirection forms are handled entirely within this
module, some require the use of the optional URI module. If it
is required but missing, then the request will fail with an
error.

headers => hashref
The request headers to use. Currently, "http_request" may
provide its own "Host:", "Content-Length:", "Connection:" and
"Cookie:" headers and will provide defaults at least for "TE:",
"Referer:" and "User-Agent:" (this can be suppressed by using
"undef" for these headers in which case they won't be sent at
all).

You really should provide your own "User-Agent:" header value
that is appropriate for your program - I wouldn't be surprised
if the default AnyEvent string gets blocked by webservers sooner
or later.

Also, make sure that your headers names and values do not
contain any embedded newlines.

timeout => $seconds
The time-out to use for various stages - each connect attempt
will reset the timeout, as will read or write activity, i.e.
this is not an overall timeout.

Default timeout is 5 minutes.

proxy => [$host, $port[, $scheme]] or undef
Use the given http proxy for all requests, or no proxy if
"undef" is used.

$scheme must be either missing or must be "http" for HTTP.

If not specified, then the default proxy is used (see
"AnyEvent::HTTP::set_proxy").

Currently, if your proxy requires authorization, you have to
specify an appropriate "Proxy-Authorization" header in every
request.

body => $string
The request body, usually empty. Will be sent as-is (future
versions of this module might offer more options).

cookie_jar => $hash_ref
Passing this parameter enables (simplified) cookie-processing,
loosely based on the original netscape specification.

The $hash_ref must be an (initially empty) hash reference which
will get updated automatically. It is possible to save the
cookie jar to persistent storage with something like JSON or
Storable - see the "AnyEvent::HTTP::cookie_jar_expire" function
if you wish to remove expired or session-only cookies, and also
for documentation on the format of the cookie jar.

Note that this cookie implementation is not meant to be
complete. If you want complete cookie management you have to do
that on your own. "cookie_jar" is meant as a quick fix to get
most cookie-using sites working. Cookies are a privacy disaster,
do not use them unless required to.

When cookie processing is enabled, the "Cookie:" and
"Set-Cookie:" headers will be set and handled by this module,
otherwise they will be left untouched.

tls_ctx => $scheme | $tls_ctx
Specifies the AnyEvent::TLS context to be used for https
connections. This parameter follows the same rules as the
"tls_ctx" parameter to AnyEvent::Handle, but additionally, the
two strings "low" or "high" can be specified, which give you a
predefined low-security (no verification, highest compatibility)
and high-security (CA and common-name verification) TLS context.

The default for this option is "low", which could be interpreted
as "give me the page, no matter what".

See also the "sessionid" parameter.

session => $string
The module might reuse connections to the same host internally.
Sometimes (e.g. when using TLS), you do not want to reuse
connections from other sessions. This can be achieved by setting
this parameter to some unique ID (such as the address of an
object storing your state data, or the TLS context) - only
connections using the same unique ID will be reused.

on_prepare => $callback->($fh)
In rare cases you need to "tune" the socket before it is used to
connect (for example, to bind it on a given IP address). This
parameter overrides the prepare callback passed to
"AnyEvent::Socket::tcp_connect" and behaves exactly the same way
(e.g. it has to provide a timeout). See the description for the
$prepare_cb argument of "AnyEvent::Socket::tcp_connect" for
details.

tcp_connect => $callback->($host, $service, $connect_cb,
$prepare_cb)
In even rarer cases you want total control over how
AnyEvent::HTTP establishes connections. Normally it uses
AnyEvent::Socket::tcp_connect to do this, but you can provide
your own "tcp_connect" function - obviously, it has to follow
the same calling conventions, except that it may always return a
connection guard object.

There are probably lots of weird uses for this function,
starting from tracing the hosts "http_request" actually tries to
connect, to (inexact but fast) host => IP address caching or
even socks protocol support.

on_header => $callback->($headers)
When specified, this callback will be called with the header
hash as soon as headers have been successfully received from the
remote server (not on locally-generated errors).

It has to return either true (in which case AnyEvent::HTTP will
continue), or false, in which case AnyEvent::HTTP will cancel
the download (and call the finish callback with an error code of
598).

This callback is useful, among other things, to quickly reject
unwanted content, which, if it is supposed to be rare, can be
faster than first doing a "HEAD" request.

The downside is that cancelling the request makes it impossible
to re-use the connection. Also, the "on_header" callback will
not receive any trailer (headers sent after the response body).

Example: cancel the request unless the content-type is
"text/html".

on_header => sub {
$_[0]{"content-type"} =~ /^text\/html\s*(?:;|$)/
},

on_body => $callback->($partial_body, $headers)
When specified, all body data will be passed to this callback
instead of to the completion callback. The completion callback
will get the empty string instead of the body data.

It has to return either true (in which case AnyEvent::HTTP will
continue), or false, in which case AnyEvent::HTTP will cancel
the download (and call the completion callback with an error
code of 598).

The downside to cancelling the request is that it makes it
impossible to re-use the connection.

This callback is useful when the data is too large to be held in
memory (so the callback writes it to a file) or when only some
information should be extracted, or when the body should be
processed incrementally.

It is usually preferred over doing your own body handling via
"want_body_handle", but in case of streaming APIs, where HTTP is
only used to create a connection, "want_body_handle" is the
better alternative, as it allows you to install your own event
handler, reducing resource usage.

want_body_handle => $enable
When enabled (default is disabled), the behaviour of
AnyEvent::HTTP changes considerably: after parsing the headers,
and instead of downloading the body (if any), the completion
callback will be called. Instead of the $body argument
containing the body data, the callback will receive the
AnyEvent::Handle object associated with the connection. In error
cases, "undef" will be passed. When there is no body (e.g.
status 304), the empty string will be passed.

The handle object might or might not be in TLS mode, might be
connected to a proxy, be a persistent connection, use chunked
transfer encoding etc., and configured in unspecified ways. The
user is responsible for this handle (it will not be used by this
module anymore).

This is useful with some push-type services, where, after the
initial headers, an interactive protocol is used (typical
example would be the push-style twitter API which starts a
JSON/XML stream).

If you think you need this, first have a look at "on_body", to
see if that doesn't solve your problem in a better way.

persistent => $boolean
Try to create/reuse a persistent connection. When this flag is
set (default: true for idempotent requests, false for all
others), then "http_request" tries to re-use an existing
(previously-created) persistent connection to the host and,
failing that, tries to create a new one.

Requests failing in certain ways will be automatically retried
once, which is dangerous for non-idempotent requests, which is
why it defaults to off for them. The reason for this is because
the bozos who designed HTTP/1.1 made it impossible to
distinguish between a fatal error and a normal connection
timeout, so you never know whether there was a problem with your
request or not.

When reusing an existent connection, many parameters (such as
TLS context) will be ignored. See the "session" parameter for a
workaround.

keepalive => $boolean
Only used when "persistent" is also true. This parameter decides
whether "http_request" tries to handshake a HTTP/1.0-style
keep-alive connection (as opposed to only a HTTP/1.1 persistent
connection).

The default is true, except when using a proxy, in which case it
defaults to false, as HTTP/1.0 proxies cannot support this in a
meaningful way.

handle_params => { key => value ... }
The key-value pairs in this hash will be passed to any
AnyEvent::Handle constructor that is called - not all requests
will create a handle, and sometimes more than one is created, so
this parameter is only good for setting hints.

Example: set the maximum read size to 4096, to potentially
conserve memory at the cost of speed.

handle_params => {
max_read_size => 4096,
},

Example: do a simple HTTP GET request for http://www.nethype.de/ and
print the response body.

http_request GET => "http://www.nethype.de/", sub {
my ($body, $hdr) = @_;
print "$body\n";
};

Example: do a HTTP HEAD request on https://www.google.com/, use a
timeout of 30 seconds.

http_request
HEAD => "https://www.google.com",
headers => { "user-agent" => "MySearchClient 1.0" },
timeout => 30,
sub {
my ($body, $hdr) = @_;
use Data::Dumper;
print Dumper $hdr;
}
;

Example: do another simple HTTP GET request, but immediately try to
cancel it.

my $request = http_request GET => "http://www.nethype.de/", sub {
my ($body, $hdr) = @_;
print "$body\n";
};

undef $request;

DNS CACHING
AnyEvent::HTTP uses the AnyEvent::Socket::tcp_connect function for the
actual connection, which in turn uses AnyEvent::DNS to resolve
hostnames. The latter is a simple stub resolver and does no caching on
its own. If you want DNS caching, you currently have to provide your own
default resolver (by storing a suitable resolver object in
$AnyEvent::DNS::RESOLVER) or your own "tcp_connect" callback.

GLOBAL FUNCTIONS AND VARIABLES
AnyEvent::HTTP::set_proxy "proxy-url"
Sets the default proxy server to use. The proxy-url must begin with
a string of the form "http://host:port", croaks otherwise.

To clear an already-set proxy, use "undef".

When AnyEvent::HTTP is loaded for the first time it will query the
default proxy from the operating system, currently by looking at
"$ENV{http_proxy"}.

AnyEvent::HTTP::cookie_jar_expire $jar[, $session_end]
Remove all cookies from the cookie jar that have been expired. If
$session_end is given and true, then additionally remove all session
cookies.

You should call this function (with a true $session_end) before you
save cookies to disk, and you should call this function after
loading them again. If you have a long-running program you can
additionally call this function from time to time.

A cookie jar is initially an empty hash-reference that is managed by
this module. Its format is subject to change, but currently it is as
follows:

The key "version" has to contain 1, otherwise the hash gets emptied.
All other keys are hostnames or IP addresses pointing to
hash-references. The key for these inner hash references is the
server path for which this cookie is meant, and the values are again
hash-references. Each key of those hash-references is a cookie name,
and the value, you guessed it, is another hash-reference, this time
with the key-value pairs from the cookie, except for "expires" and
"max-age", which have been replaced by a "_expires" key that
contains the cookie expiry timestamp. Session cookies are indicated
by not having an "_expires" key.

Here is an example of a cookie jar with a single cookie, so you have
a chance of understanding the above paragraph:

{
version => 1,
"10.0.0.1" => {
"/" => {
"mythweb_id" => {
_expires => 1293917923,
value => "ooRung9dThee3ooyXooM1Ohm",
},
},
},
}

$date = AnyEvent::HTTP::format_date $timestamp
Takes a POSIX timestamp (seconds since the epoch) and formats it as
a HTTP Date (RFC 2616).

$timestamp = AnyEvent::HTTP::parse_date $date
Takes a HTTP Date (RFC 2616) or a Cookie date (netscape cookie spec)
or a bunch of minor variations of those, and returns the
corresponding POSIX timestamp, or "undef" if the date cannot be
parsed.

$AnyEvent::HTTP::MAX_RECURSE
The default value for the "recurse" request parameter (default: 10).

$AnyEvent::HTTP::TIMEOUT
The default timeout for connection operations (default: 300).

$AnyEvent::HTTP::USERAGENT
The default value for the "User-Agent" header (the default is
"Mozilla/5.0 (compatible; U; AnyEvent-HTTP/$VERSION;
+http://software.schmorp.de/pkg/AnyEvent)").

$AnyEvent::HTTP::MAX_PER_HOST
The maximum number of concurrent connections to the same host
(identified by the hostname). If the limit is exceeded, then
additional requests are queued until previous connections are
closed. Both persistent and non-persistent connections are counted
in this limit.

The default value for this is 4, and it is highly advisable to not
increase it much.

For comparison: the RFC's recommend 4 non-persistent or 2 persistent
connections, older browsers used 2, newer ones (such as firefox 3)
typically use 6, and Opera uses 8 because like, they have the
fastest browser and give a shit for everybody else on the planet.

$AnyEvent::HTTP::PERSISTENT_TIMEOUT
The time after which idle persistent connections get closed by
AnyEvent::HTTP (default: 3).

$AnyEvent::HTTP::ACTIVE
The number of active connections. This is not the number of
currently running requests, but the number of currently open and
non-idle TCP connections. This number can be useful for
load-leveling.

SHOWCASE
This section contains some more elaborate "real-world" examples or code
snippets.

HTTP/1.1 FILE DOWNLOAD
Downloading files with HTTP can be quite tricky, especially when
something goes wrong and you want to resume.

Here is a function that initiates and resumes a download. It uses the
last modified time to check for file content changes, and works with
many HTTP/1.0 servers as well, and usually falls back to a complete
re-download on older servers.

It calls the completion callback with either "undef", which means a
nonretryable error occurred, 0 when the download was partial and should
be retried, and 1 if it was successful.

use AnyEvent::HTTP;

sub download($$$) {
my ($url, $file, $cb) = @_;

open my $fh, "+<", $file
or die "$file: $!";

my %hdr;
my $ofs = 0;

if (stat $fh and -s _) {
$ofs = -s _;
warn "-s is ", $ofs;
$hdr{"if-unmodified-since"} = AnyEvent::HTTP::format_date +(stat _)[9];
$hdr{"range"} = "bytes=$ofs-";
}

http_get $url,
headers => \%hdr,
on_header => sub {
my ($hdr) = @_;

if ($hdr->{Status} == 200 && $ofs) {
# resume failed
truncate $fh, $ofs = 0;
}

sysseek $fh, $ofs, 0;

1
},
on_body => sub {
my ($data, $hdr) = @_;

if ($hdr->{Status} =~ /^2/) {
length $data == syswrite $fh, $data
or return; # abort on write errors
}

1
},
sub {
my (undef, $hdr) = @_;

my $status = $hdr->{Status};

if (my $time = AnyEvent::HTTP::parse_date $hdr->{"last-modified"}) {
utime $time, $time, $fh;
}

if ($status == 200 || $status == 206 || $status == 416) {
# download ok || resume ok || file already fully downloaded
$cb->(1, $hdr);

} elsif ($status == 412) {
# file has changed while resuming, delete and retry
unlink $file;
$cb->(0, $hdr);

} elsif ($status == 500 or $status == 503 or $status =~ /^59/) {
# retry later
$cb->(0, $hdr);

} else {
$cb->(undef, $hdr);
}
}
;
}

download "http://server/somelargefile", "/tmp/somelargefile", sub {
if ($_[0]) {
print "OK!\n";
} elsif (defined $_[0]) {
print "please retry later\n";
} else {
print "ERROR\n";
}
};

SOCKS PROXIES
Socks proxies are not directly supported by AnyEvent::HTTP. You can
compile your perl to support socks, or use an external program such as
socksify (dante) or tsocks to make your program use a socks proxy
transparently.

Alternatively, for AnyEvent::HTTP only, you can use your own
"tcp_connect" function that does the proxy handshake - here is an
example that works with socks4a proxies:

use Errno;
use AnyEvent::Util;
use AnyEvent::Socket;
use AnyEvent::Handle;

# host, port and username of/for your socks4a proxy
my $socks_host = "10.0.0.23";
my $socks_port = 9050;
my $socks_user = "";

sub socks4a_connect {
my ($host, $port, $connect_cb, $prepare_cb) = @_;

my $hdl = new AnyEvent::Handle
connect => [$socks_host, $socks_port],
on_prepare => sub { $prepare_cb->($_[0]{fh}) },
on_error => sub { $connect_cb->() },
;

$hdl->push_write (pack "CCnNZ*Z*", 4, 1, $port, 1, $socks_user, $host);

$hdl->push_read (chunk => 8, sub {
my ($hdl, $chunk) = @_;
my ($status, $port, $ipn) = unpack "xCna4", $chunk;

if ($status == 0x5a) {
$connect_cb->($hdl->{fh}, (format_address $ipn) . ":$port");
} else {
$! = Errno::ENXIO; $connect_cb->();
}
});

$hdl
}

Use "socks4a_connect" instead of "tcp_connect" when doing
"http_request"s, possibly after switching off other proxy types:

AnyEvent::HTTP::set_proxy undef; # usually you do not want other proxies

http_get 'http://www.google.com', tcp_connect => \&socks4a_connect, sub {
my ($data, $headers) = @_;
...
};

SEE ALSO
AnyEvent.

AUTHOR
Marc Lehmann <[email protected]>
http://home.schmorp.de/

With many thanks to Дмитрий Шалашов, who provided countless testcases
and bugreports.