[ViewVC] Diff of: cvs/AnyEvent/lib/AnyEvent/Handle.pm

Comparing AnyEvent/lib/AnyEvent/Handle.pm (file contents):
Revision 1.206 by root, Mon Nov 15 19:49:31 2010 UTC vs.
Revision 1.214 by root, Sun Jan 16 17:12:27 2011 UTC

 =over 4
 =item on_prepare => $cb->($handle)
 This (rarely used) callback is called before a new connection is
-attempted, but after the file handle has been created. It could be used to
+attempted, but after the file handle has been created (you can access that
+file handle via C<< $handle->{fh} >>). It could be used to prepare the
-prepare the file handle with parameters required for the actual connect
+file handle with parameters required for the actual connect (as opposed to
-(as opposed to settings that can be changed when the connection is already
+settings that can be changed when the connection is already established).
-established).
 The return value of this callback should be the connect timeout value in
 seconds (or C<0>, or C<undef>, or the empty list, to indicate that the
 default timeout is to be used).
 For example, a server accepting connections from untrusted sources should
 be configured to accept only so-and-so much data that it cannot act on
 (for example, when expecting a line, an attacker could send an unlimited
 amount of data without a callback ever being called as long as the line
 isn't finished).
+=item wbuf_max => <bytes>
+If defined, then a fatal error will be raised (with C<$!> set to C<ENOSPC>)
+when the write buffer ever (strictly) exceeds this size. This is useful to
+avoid some forms of denial-of-service attacks.
+Although the units of this parameter is bytes, this is the I<raw> number
+of bytes not yet accepted by the kernel. This can make a difference when
+you e.g. use TLS, as TLS typically makes your write data larger (but it
+can also make it smaller due to compression).
+As an example of when this limit is useful, take a chat server that sends
+chat messages to a client. If the client does not read those in a timely
+manner then the send buffer in the server would grow unbounded.
 =item autocork => <boolean>
 When disabled (the default), C<push_write> will try to immediately
 write the data to the handle if possible. This avoids having to register
 Use the C<< ->starttls >> method if you need to start TLS negotiation later.
 =item tls_ctx => $anyevent_tls
 Use the given C<AnyEvent::TLS> object to create the new TLS connection
-(unless a connection object was specified directly). If this parameter is
+(unless a connection object was specified directly). If this
-missing, then AnyEvent::Handle will use C<AnyEvent::Handle::TLS_CTX>.
+parameter is missing (or C<undef>), then AnyEvent::Handle will use
+C<AnyEvent::Handle::TLS_CTX>.
 Instead of an object, you can also specify a hash reference with C<< key
 => value >> pairs. Those will be passed to L<AnyEvent::TLS> to create a
 new TLS context object.
                },
                sub {
                   local $self->{fh} = $_[0];
                   $self->{on_prepare}
-                     ?  $self->{on_prepare}->($self)
+                     ? $self->{on_prepare}->($self)
                      : ()
                }
             );
       }
 =item $handle->rbuf_max ($max_octets)
 Configures the C<rbuf_max> setting (C<undef> disables it).
+=item $handle->wbuf_max ($max_octets)
+Configures the C<wbuf_max> setting (C<undef> disables it).
 =cut
 sub rbuf_max {
    $_[0]{rbuf_max} = $_[1];
+}
+sub rbuf_max {
+   $_[0]{wbuf_max} = $_[1];
 }
 #############################################################################
 =item $handle->timeout ($seconds)
       if $cb && $self->{low_water_mark} >= (length $self->{wbuf}) + (length $self->{_tls_wbuf});
 }
 =item $handle->push_write ($data)
-Queues the given scalar to be written. You can push as much data as you
+Queues the given scalar to be written. You can push as much data as
-want (only limited by the available memory), as C<AnyEvent::Handle>
+you want (only limited by the available memory and C<wbuf_max>), as
-buffers it independently of the kernel.
+C<AnyEvent::Handle> buffers it independently of the kernel.
 This method may invoke callbacks (and therefore the handle might be
 destroyed after it returns).
 =cut
       $cb->() unless $self->{autocork};
       # if still data left in wbuf, we need to poll
       $self->{_ww} = AE::io $self->{fh}, 1, $cb
          if length $self->{wbuf};
+      if (
+         defined $self->{wbuf_max}
+         && $self->{wbuf_max} < length $self->{wbuf}
+      ) {
+         $self->_error (Errno::ENOSPC, 1), return;
+      }
    };
 }
 our %WH;
 before it was actually written. One way to do that is to replace your
 C<on_drain> handler by a callback that shuts down the socket (and set
 C<low_water_mark> to C<0>). This method is a shorthand for just that, and
 replaces the C<on_drain> callback with:
-   sub { shutdown $_[0]{fh}, 1 }    # for push_shutdown
+   sub { shutdown $_[0]{fh}, 1 }
 This simply shuts down the write side and signals an EOF condition to the
 the peer.
 You can rely on the normal read queue and C<on_eof> handling
 Note that AnyEvent::Handle will automatically C<start_read> for you when
 you change the C<on_read> callback or push/unshift a read callback, and it
 will automatically C<stop_read> for you when neither C<on_read> is set nor
 there are any read requests in the queue.
-These methods will have no effect when in TLS mode (as TLS doesn't support
+In older versions of this module (<= 5.3), these methods had no effect,
-half-duplex connections).
+as TLS does not support half-duplex connections. In current versions they
+work as expected, as this behaviour is required to avoid certain resource
+attacks, where the program would be forced to read (and buffer) arbitrary
+amounts of data before being able to send some data. The drawback is that
+some readings of the the SSL/TLS specifications basically require this
+attack to be working, as SSL/TLS implementations might stall sending data
+during a rehandshake.
+As a guideline, during the initial handshake, you should not stop reading,
+and as a client, it might cause problems, depending on your applciation.
 =cut
 sub stop_read {
    my ($self) = @_;
-   delete $self->{_rw} unless $self->{tls};
+   delete $self->{_rw};
 }
 sub start_read {
    my ($self) = @_;
 It is only safe to "forget" the reference inside EOF or error callbacks,
 from within all other callbacks, you need to explicitly call the C<<
 ->destroy >> method.
+=item Why is my C<on_eof> callback never called?
+Probably because your C<on_error> callback is being called instead: When
+you have outstanding requests in your read queue, then an EOF is
+considered an error as you clearly expected some data.
+To avoid this, make sure you have an empty read queue whenever your handle
+is supposed to be "idle" (i.e. connection closes are O.K.). You cna set
+an C<on_read> handler that simply pushes the first read requests in the
+queue.
+See also the next question, which explains this in a bit more detail.
+=item How can I serve requests in a loop?
+Most protocols consist of some setup phase (authentication for example)
+followed by a request handling phase, where the server waits for requests
+and handles them, in a loop.
+There are two important variants: The first (traditional, better) variant
+handles requests until the server gets some QUIT command, causing it to
+close the connection first (highly desirable for a busy TCP server). A
+client dropping the connection is an error, which means this variant can
+detect an unexpected detection close.
+To handle this case, always make sure you have a on-empty read queue, by
+pushing the "read request start" handler on it:
+   # we assume a request starts with a single line
+   my @start_request; @start_request = (line => sub {
+      my ($hdl, $line) = @_;
+      ... handle request
+      # push next request read, possibly from a nested callback
+      $hdl->push_read (@start_request);
+   });
+   # auth done, now go into request handling loop
+   # now push the first @start_request
+   $hdl->push_read (@start_request);
+By always having an outstanding C<push_read>, the handle always expects
+some data and raises the C<EPIPE> error when the connction is dropped
+unexpectedly.
+The second variant is a protocol where the client can drop the connection
+at any time. For TCP, this means that the server machine may run out of
+sockets easier, and in general, it means you cnanot distinguish a protocl
+failure/client crash from a normal connection close. Nevertheless, these
+kinds of protocols are common (and sometimes even the best solution to the
+problem).
+Having an outstanding read request at all times is possible if you ignore
+C<EPIPE> errors, but this doesn't help with when the client drops the
+connection during a request, which would still be an error.
+A better solution is to push the initial request read in an C<on_read>
+callback. This avoids an error, as when the server doesn't expect data
+(i.e. is idly waiting for the next request, an EOF will not raise an
+error, but simply result in an C<on_eof> callback. It is also a bit slower
+and simpler:
+   # auth done, now go into request handling loop
+   $hdl->on_read (sub {
+      my ($hdl) = @_;
+      # called each time we receive data but the read queue is empty
+      # simply start read the request
+      $hdl->push_read (line => sub {
+         my ($hdl, $line) = @_;
+         ... handle request
+         # do nothing special when the request has been handled, just
+         # let the request queue go empty.
+      });
+   });
 =item I get different callback invocations in TLS mode/Why can't I pause
 reading?
 Unlike, say, TCP, TLS connections do not consist of two independent
 communication channels, one for each direction. Or put differently, the

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Comparing AnyEvent/lib/AnyEvent/Handle.pm (file contents): Revision 1.206 by root, Mon Nov 15 19:49:31 2010 UTC vs. Revision 1.214 by root, Sun Jan 16 17:12:27 2011 UTC

Diff Legend

Comparing AnyEvent/lib/AnyEvent/Handle.pm (file contents):
Revision 1.206 by root, Mon Nov 15 19:49:31 2010 UTC vs.
Revision 1.214 by root, Sun Jan 16 17:12:27 2011 UTC