How It Works

All of the request-parsing and I/O marshalling is done using C or XS code. HTTP parsing is done by picohttpparser, which is the core of HTTP::Parser::XS. The network I/O is done via the libev library. This is made possible by "EV::MakeMaker", which allows extension writers to link against the same libev that "EV" is using. This means that one can write an evented app using "EV" or AnyEvent from Perl that completely co-operates with the server's event loop.

Since the Perl "app" (handler) is executed in the same thread as the event loop, one need to be careful to not block this thread. Standard techniques include using AnyEvent or EV idle and timer watchers, using Coro to multitask, and using sub-processes to do heavy lifting (e.g. AnyEvent::Worker and AnyEvent::DBI).

Feersum also attempts to do as little copying of data as possible. Feersum uses the low-level "writev" system call to avoid having to copy data into a buffer. For response data, references to scalars are kept in order to avoid copying the string values (once the data is written to the socket, the reference is dropped and the data is garbage collected).

A trivial hello-world handler can process in excess of 5000 requests per second on a 4-core Intel(R) Xeon(R) E5335 @ 2.00GHz using TCPv4 on the loopback interface, OS Ubuntu 6.06LTS, Perl 5.8.7. Your mileage will likely vary.

For even faster results, Feersum can support very simple pre-forking (See feersum, Feersum::Runner or Plack::Handler::Feersum for details).

PSGI interface

Feersum fully supports the PSGI 1.03 spec including "psgi.streaming".

See also Plack::Handler::Feersum, which provides a way to use Feersum with plackup and Plack::Runner.

Call "psgi_request_handler($app)" to register $app as a PSGI handler.

    my $app = do $filename;
    Feersum->endjinn->psgi_request_handler($app);

The env hash passed in will always have the following keys in addition to dynamic ones:

    psgi.version      => [1,0],
    psgi.nonblocking  => 1,
    psgi.multithread  => '', # i.e. false
    psgi.multiprocess => '',
    psgi.streaming    => 1,
    psgi.errors       => \*STDERR,
    SCRIPT_NAME       => "",

Feersum adds these extensions (see below for info)

    psgix.input.buffered   => 1,
    psgix.output.buffered  => 1,
    psgix.body.scalar_refs => 1,
    psgix.output.guard     => 1,
    psgix.io               => \$magical_io_socket,

Note that SCRIPT_NAME is always blank (but defined). PATH_INFO will contain the path part of the requested URI.

For requests with a body (e.g. POST) "psgi.input" will contain a valid file-handle. Feersum currently passes "undef" for psgi.input when there is no body to avoid unnecessary work.

    my $r = delete $env->{'psgi.input'};
    $r->read($body, $env->{CONTENT_LENGTH});
    # optional: choose to stop receiving further input, discard buffers:
    $r->close();

The "psgi.streaming" interface is fully supported, including the writer-object "poll_cb" callback feature defined in PSGI 1.03. Note that poll_cb is removed from the preliminary PSGI 1.1 spec. Feersum calls the poll_cb callback after all data has been flushed out and the socket is write-ready. The data is buffered until the callback returns at which point it will be immediately flushed to the socket.

    my $app = sub {
        my $env = shift;
        return sub {
            my $respond = shift;
            my $w = $respond->([
                200, ['Content-Type' => 'application/json']
            ]);
            my $n = 0;
            $w->poll_cb(sub {
                $_[0]->write(get_next_chunk());
                # will also unset the poll_cb:
                $_[0]->close if ($n++ >= 100);
            });
        };
    };

Note that "$w->close()" will be called when the last reference to the writer is dropped.

PSGI extensions

psgix.body.scalar_refs

Scalar refs in the response body are supported, and is indicated as an via the psgix.body.scalar_refs env variable. Passing by reference is significantly faster than copying a value onto the return stack or into an array. It's also very useful when broadcasting a message to many connected clients. This is a Feersum-native feature exposed to PSGI apps; very few other PSGI handlers will support this.

psgix.output.buffered

Calls to "$w->write()" will never block. This behaviour is indicated by psgix.output.buffered in the PSGI env hash.

psgix.input.buffered

"psgix.input.buffered" is defined as part of PSGI 1.1. It means that calls to read on the input handle will never block because the complete input has been buffered in some way.

Feersum currently buffers the entire input in memory calling the callback.

Feersum's input behaviour MAY eventually change to not be psgix.input.buffered! Likely, a "poll_cb()" method similar to how the writer handle works could be registered to have input "pushed" to the app.

psgix.output.guard

The streaming responder has a "response_guard()" method that can be used to attach a guard to the request. When the request completes (all data has been written to the socket and the socket has been closed) the guard will trigger. This is an alternate means to doing a "write completion" callback via "poll_cb()" that should be more efficient. An analogy is the "on_drain" handler in AnyEvent::Handle.

A "guard" in this context is some object that will do something interesting in its DESTROY/DEMOLISH method. For example, Guard.

psgix.io

The raw socket extension psgix.io is provided in order to support Web::Hippie and websockets. "psgix.io" is defined as part of PSGI 1.1. To obtain the IO::Socket corresponding to this connection, read this environment variable.

The underlying file descriptor will have "O_NONBLOCK", "TCP_NODELAY", "SO_OOBINLINE" enabled and "SO_LINGER" disabled.

PSGI apps MUST use a "psgi.streaming" response so that Feersum doesn't try to flush and close the connection. Additionally, the "respond" parameter to the streaming callback MUST NOT be called for the same reason.

    my $env = shift;
    return sub {
        my $fh = $env->{'psgix.io'};
        syswrite $fh, 
    };
    

The Feersum-native interface

The Feersum-native interface is inspired by PSGI, but is inherently incompatible with it. Apps written against this API will not work as a PSGI app.

This interface may have removals and is not stable until Feersum reaches version 1.0, at which point the interface API will become stable and will only change for bug fixes or new additions. The "stable" and will retain backwards compatibility until at least the next major release.

The main entry point is a sub-ref passed to "request_handler". This sub is passed a reference to an object that represents an HTTP connection. Currently the request_handler is called during the "check" and "idle" phases of the EV event loop. The handler is always called after request headers have been read. Currently, the handler will only be called after a full request entity has been received for POST/PUT/etc.

The simplest way to send a response is to use "send_response":

    my $req = shift;
    $req->send_response(200, \@headers, ["body ", \"parts"]);

Or, if the app has everything packed into a single scalar already, just pass it in by reference.

    my $req = shift;
    $req->send_response(200, \@headers, \"whole body");

Both of the above will generate "Content-Length" header (replacing any that were pre-defined in @headers).

An environment hash is easy to obtain, but is a method call instead of a parameter to the callback. (In PSGI, there is no $req object; the env hash is the first parameter to the callback). The hash contains the same items as it would for a PSGI handler (see above for those).

    my $req = shift;
    my $env = $req->env();

To read input from a POST/PUT, use the "psgi.input" item of the env hash.

    if ($req->{REQUEST_METHOD} eq 'POST') {
        my $body = '';
        my $r = delete $env->{'psgi.input'};
        $r->read($body, $env->{CONTENT_LENGTH});
        # optional:
        $r->close();
    }

Starting a response in stream mode enables the "write()" method (which really acts more like a buffered 'print'). Calls to "write()" will never block.

    my $req = shift;
    my $w = $req->start_streaming(200, \@headers);
    $w->write(\"this is a reference to some shared chunk\n");
    $w->write("regular scalars are OK too\n");
    $w->close(); # close off the stream

The writer object supports "poll_cb" as also specified in PSGI 1.03. Feersum will call the callback only when all data has been flushed out at the socket level. Use "close()" or unset the handler ("$w->poll_cb(undef)") to stop the callback from getting called.

    my $req = shift;
    my $w = $req->start_streaming(
        "200 OK", ['Content-Type' => 'application/json']);
    my $n = 0;
    $w->poll_cb(sub {
        # $_[0] is a copy of $w so a closure doesn't need to be made
        $_[0]->write(get_next_chunk());
        $_[0]->close if ($n++ >= 100);
    });

Note that "$w->close()" will be called when the last reference to the writer is dropped.

Compile Time Options

There are a number of constants at the top of Feersum.xs. If you change any of these, be sure to note that in any bug reports.

MAX_HEADERS

Defaults to 64. Controls how many headers can be present in an HTTP request.

If a request exceeds this limit, a 400 response is given and the app handler does not run.

MAX_HEADER_NAME_LEN

Defaults to 128. Controls how long the name of each header can be.

If a request exceeds this limit, a 400 response is given and the app handler does not run.

MAX_BODY_LEN

Defaults to ~2GB. Controls how large the body of a POST/PUT/etc. can be when that request has a "Content-Length" header.

If a request exceeds this limit, a 413 response is given and the app handler does not run.

See also BUGS

READ_BUFSZ

READ_INIT_FACTOR

READ_GROW_FACTOR

READ_BUFSZ defaults to 4096, READ_INIT_FACTOR 2 and READ_GROW_FACTOR 8.

Together, these tune how data is read for a request.

Read buffers start out at READ_INIT_FACTOR * READ_BUFSZ bytes. If another read is needed and the buffer is under READ_BUFSZ bytes then the buffer gets an additional READ_GROW_FACTOR * READ_BUFSZ bytes. The trade-off with the grow factor is memory usage vs. system calls.

AUTOCORK_WRITES

Controls how response data is written to sockets. If enabled (the default) the event loop is used to wait until the socket is writable, otherwise a write is performed immediately. In either case, non-blocking writes are used. Using the event loop is "nicer" but perhaps introduces latency, hence this option.

FLASH_SOCKET_POLICY_SUPPORT

FLASH_SOCKET_POLICY

FLASH_SOCKET_POLICY_SUPPORT defaults to disabled.

When it's enabled, Feersum will detect a Flash "<policy-file-request/>" packet and respond with the FLASH_SOCKET_POLICY string.

The default FLASH_SOCKET_POLICY string looks like this:

    <?xml version="1.0"?>
    <!DOCTYPE cross-domain-policy SYSTEM "/xml/dtds/cross-domain-policy.dtd">
    <cross-domain-policy>
      <site-control permitted-cross-domain-policies="master-only"/>
      <allow-access-from domain="*" to-ports="*" secure="false"/>
    </cross-domain-policy>
    

Since that's fairly wide-open, you may not wish to enable FLASH_SOCKET_POLICY_SUPPORT.

Note that this feature likely won't work if you use a front-end HTTP server (e.g. nginx) since the request isn't valid HTTP.

FEERSUM_IOMATRIX_SIZE

Controls the size of the main write-buffer structure in Feersum. Making this value lower will use slightly less memory per connection at the cost of speed (and vice-versa for raising the value). The effect is most noticeable when you're app is making a lot of sparce writes. The default of 64 generally keeps usage under 4k per connection on full 64-bit platforms when you take into account the other connection and request structures.

NOTE: FEERSUM_IOMATRIX_SIZE cannot exceed your OS's defined IOV_MAX or UIO_MAXIOV constant. Solaris defines IOV_MAX to be 16, making it the default on that platform. Linux and OSX seem to set this at 1024.

FEERSUM_STEAL

For non-threaded perls >= 5.12.0, this defaults to enabled.

When enabled, Feersum will "steal" the contents of temporary lexical scalars used for response bodies. The scalars become "undef" as a result, but due to them being temps they likely aren't used again anyway. Stealing saves the time and memory needed to make a copy of that scalar, resulting in a mild to moderate performance boost.

This egregious hack only extends to non-magical, string, "PADTMP" scalars.

If it breaks for your new version of perl, please send stash a note (or a pull request!) on github.

Worth noting is that a similar zero-copy effect can be achieved by using the "psgix.body.scalar_refs" feature.