[ViewVC] Annotation of: cvs/AnyEvent-HTTP/README

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.

Revision:	1.28
Committed:	Mon Apr 27 12:14:12 2020 UTC (4 years ago) by root
Branch:	MAIN
CVS Tags:	rel-2_25, HEAD
Changes since 1.27:	+29 -13 lines
Log Message:	2.25