Provided by: libanyevent-http-perl_2.25-2_all 
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.
Note that this module will prefer an existing persistent connection, even if that connection was
made using another proxy. If you need to ensure that a new connection is made in this case, you
can either force "persistent" to false or e.g. use the proxy address in your "sessionid".
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.
sessionid => $string
The module might reuse connections to the same host internally (regardless of other settings,
such as "tcp_connect" or "proxy"). Sometimes (e.g. when using TLS or a specfic proxy), 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,
or the proxy IP) - 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.
The connections made by this hook will be treated as equivalent to connections made the built-in
way, specifically, they will be put into and taken from the persistent connection cache. If your
$tcp_connect function is incompatible with this kind of re-use, consider switching off
"persistent" connections and/or providing a "sessionid" identifier.
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 same host (i.e. identical URL scheme, hostname, port and
sessionid) 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 "sessionid" 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 2, otherwise the hash gets cleared. 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 => 2,
"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 <schmorp@schmorp.de>
http://home.schmorp.de/
With many thanks to Дмитрий Шалашов, who provided countless testcases and bugreports.
perl v5.36.0 2022-10-14 HTTP(3pm)