filter.pm

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

      return Apache2::Const::OK;
  }

Usually arguments C<$mode>, C<$block>, C<$readbytes> are the same as
passed to the filter itself.

You can see that in case of a failure, the handler returns immediately
with that failure code, which gets propagated to the downstream
filter.

If you decide not check the return code, you can write it as:

  sub filter {
      my ($f, $bb, $mode, $block, $readbytes) = @_;
      
      $f->next->get_brigade($bb, $mode, $block, $readbytes);
      
      # ... process $bb
      
      return Apache2::Const::OK;
  }

and the error checking will be done on your behalf.

You will find many more examples in C<the filter
handlers|docs::2.0::user::handlers::filters> and
C<the protocol
handlers|docs::2.0::user::handlers::protocols> tutorials.






=head2 C<pass_brigade>

This is a method to use in bucket brigade output filters.  It passes
the current bucket brigade to the downstream output filter.

  $rc = $next_f->pass_brigade($bb);

=over 4

=item obj: C<$next_f>
( C<L<Apache2::Filter object|docs::2.0::api::Apache2::Filter>> )

The next filter in the filter chain.

Inside L<output filter handlers|docs::2.0::user::handlers::filters>
it's usually C<L<$f-E<gt>next|/C_next_>>. Inside L<protocol
handlers|docs::2.0::user::handlers::protocols>:
C<L<$c-E<gt>output_filters|docs::2.0::api::Apache2::Connection/C_output_filters_>>.

=item arg1: C<$bb>
( C<L<APR::Brigade object|docs::2.0::api::APR::Brigade>> )

The bucket brigade to pass.

Inside L<output filter
handlers|docs::2.0::user::handlers::filters> it's usually the second 
argument to the filter handler (after potential manipulations).

=item ret: C<$rc> ( C<L<APR::Const status
constant|docs::2.0::api::APR::Const>> )

On success,
C<L<APR::Const::SUCCESS|docs::2.0::api::APR::Const/C_APR__Const__SUCCESS_>> is
returned.

In case of a failure -- a failure code is returned, in which case
normally it should be returned to the caller.

If the bottom-most filter doesn't write to the network, then
C<Apache2::NOBODY_WROTE> is returned (META: need to add this constant).

Also refer to the C<L<get_brigade()|/C_get_brigade_>> entry to see how
to avoid checking the errors explicitly.

=item excpt: C<L<APR::Error|docs::2.0::api::APR::Error>>

Exceptions are thrown only when this function is called in the VOID
context. Refer to the C<L<get_brigade()|/C_get_brigade_>> entry for
details.

=item since: 2.0.00

=back

The caller relinquishes ownership of the brigade (i.e. it may get
destroyed/overwritten/etc. by the callee).

Example:

Here is a fragment of a filter handler, that passes a bucket brigade
to the downstream filter (after some potential processing of the
buckets in the bucket brigade):

  use Apache2::Filter ();
  use APR::Const    -compile => qw(SUCCESS);
  use Apache2::Const -compile => qw(OK);
  sub filter {
      my ($f, $bb) = @_;
  
      # ... process $bb
  
      my $rc = $f->next->pass_brigade($bb);
      return $rc unless $rc == APR::Const::SUCCESS;
  
      return Apache2::Const::OK;
  }












=head1 Streaming Filter API

The following methods can be called from any filter, which uses the
simplified streaming functionality:





=head2 C<print>

Send the contents of C<$buffer> to the next filter in chain (via
internal buffer).

  $sent = $f->print($buffer);

=over 4

=item obj: C<$f>
( C<L<Apache2::Filter object|docs::2.0::api::Apache2::Filter>> )

=item arg1: C<$buffer> ( string )

The data to send.

=item ret: C<$sent> ( integer )

How many characters were sent. There is no need to check, since all
should go through and if something goes work an exception will be
thrown.

=item excpt: C<L<APR::Error|docs::2.0::api::APR::Error>>

=item since: 2.0.00

=back

This method should be used only in L<streaming
filters|docs::2.0::user::handlers::filters>.






=head2 C<read>

Read data from the filter

  $read = $f->read($buffer, $wanted);

=over 4

=item obj: C<$f>
( C<L<Apache2::Filter object|docs::2.0::api::Apache2::Filter>> )

=item arg1: C<$buffer> ( SCALAR )

The buffer to fill. All previous data will be lost.

=item opt arg2: C<$wanted> ( integer )

How many bytes to attempt to read.

If this optional argument is not specified -- the default 8192 will be
used.

=item ret: C<$read> ( integer )

How many bytes were actually read.

C<$buffer> gets populated with the string that is read. It will
contain an empty string if there was nothing to read.

=item excpt: C<L<APR::Error|docs::2.0::api::APR::Error>>

=item since: 2.0.00

=back

Reads at most C<$wanted> characters into C<$buffer>. The returned
value C<$read> tells exactly how many were read, making it easy to use
it in a while loop:

  while ($filter->read(my $buffer, $wanted)) {
      # transform $buffer here
      $filter->print($buffer);
  }

This is a streaming filter method, which acquires a single bucket
brigade behind the scenes and reads data from all its
buckets. Therefore it can only read from one bucket brigade per filter
invocation.

If the EOS bucket is read, the C<L<seen_eos|/C_seen_eos_>> method will
return a true value.






=head2 C<seen_eos>

This methods returns a true value when the EOS bucket is seen by the
C<L<read|/C_read_>> method.

  $ok = $f->seen_eos;

=over 4

=item obj: C<$f>
( C<L<Apache2::Filter object|docs::2.0::api::Apache2::Filter>> )

The filter to remove

=item ret: C<$ok> ( boolean )

a true value if EOS has been seen, otherwise a false value

=item since: 2.0.00

=back

This method only works in streaming filters which exhaustively
C<L<$f-E<gt>read|/C_read_>> all the incoming data in a while loop,
like so:

      while ($f->read(my $buffer, $wanted)) {
          # do something with $buffer
      }
      if ($f->seen_eos) {
          # do something
      }

The technique in this example is useful when a streaming filter wants
to append something to the very end of data, or do something at the
end of the last filter invocation. After the EOS bucket is read, the
filter should expect not to be invoked again.

If an input streaming filter doesn't consume all data in the bucket
brigade (or even in several bucket brigades), it has to generate the
EOS event by itself. So when the filter is done it has to set the EOS
flag:

  $f->seen_eos(1);

when the filter handler returns, internally mod_perl will take care of
creating and sending the EOS bucket to the upstream input filter.

A similar logic may apply for output filters.

In most other cases you shouldn't set this flag.  When this flag is
prematurely set (before the real EOS bucket has arrived) in the
current filter invocation, instead of invoking the filter again,
mod_perl will create and send the EOS bucket to the next filter,
ignoring any other bucket brigades that may have left to consume. As
mentioned earlier this special behavior is useful in writing special
tests that test abnormal situations.




=head1 Other Filter-related API

Other methods which affect filters, but called on
non-C<Apache2::Filter> objects:



=head2 C<add_input_filter>

Add C<&callback> filter handler to input request filter chain.

  $r->add_input_filter(\&callback);

Add C<&callback> filter handler to input connection filter chain.

  $c->add_input_filter(\&callback);

=over 4

=item obj: C<$c>
( C<L<Apache2::Connection object|docs::2.0::api::Apache2::Connection>> ) or C<$r>
( C<L<Apache2::RequestRec object|docs::2.0::api::Apache2::RequestRec>> )

=item arg1: C<&callback> (CODE ref)

=item ret: no return value

=item since: 2.0.00

=back

[META: It seems that you can't add a filter when another filter is
called. I've tried to add an output connection filter from the input
connection filter when it was called for the first time. It didn't
have any affect for the first request (over keepalive connection). The
only way I succeeded to do that is from that input connection filter's
filter_init handler.
In fact it does work if there is any filter additional filter of the
same kind configured from httpd.conf or via filter_init. It looks like
there is a bug in httpd, where it doesn't prepare the chain of 3rd
party filter if none were inserted before the first filter was called.]




=head2 C<add_output_filter>

Add C<&callback> filter handler to output request filter chain.

  $r->add_output_filter(\&callback);

Add C<&callback> filter handler to output connection filter chain.

  $c->add_output_filter(\&callback);

=over 4

=item obj: C<$c>
( C<L<Apache2::Connection object|docs::2.0::api::Apache2::Connection>> ) or C<$r>
( C<L<Apache2::RequestRec object|docs::2.0::api::Apache2::RequestRec>> )

=item arg1: C<&callback> (CODE ref)

=item ret: no return value

=item since: 2.0.00

=back






=head1 Filter Handler Attributes

Packages using filter attributes have to subclass C<Apache2::Filter>:

  package MyApache2::FilterCool;
  use base qw(Apache2::Filter);

Attributes are parsed during the code compilation, by the function
C<MODIFY_CODE_ATTRIBUTES>, inherited from the C<Apache2::Filter>
package.




=head2 C<FilterRequestHandler>

The C<FilterRequestHandler> attribute tells mod_perl to insert the
filter into an HTTP request filter chain. 

For example, to configure an output request filter handler, use the
C<FilterRequestHandler> attribute in the handler subroutine's
declaration:

  package MyApache2::FilterOutputReq;
  sub handler : FilterRequestHandler { ... }

and add the configuration entry:

  PerlOutputFilterHandler MyApache2::FilterOutputReq

This is the default mode. So if you are writing an HTTP request
filter, you don't have to specify this attribute.

The section L<HTTP Request vs. Connection
Filters|docs::2.0::user::handlers::filters/HTTP_Request_vs__Connection_Filters>
delves into more details.




=head2 C<FilterConnectionHandler>

The C<FilterConnectionHandler> attribute tells mod_perl to insert this
filter into a connection filter chain.

For example, to configure an output connection filter handler, use the
C<FilterConnectionHandler> attribute in the handler subroutine's
declaration:

  package MyApache2::FilterOutputCon;
  sub handler : FilterConnectionHandler { ... }

and add the configuration entry:

  PerlOutputFilterHandler MyApache2::FilterOutputCon

The section L<HTTP Request vs. Connection
Filters|docs::2.0::user::handlers::filters/HTTP_Request_vs__Connection_Filters>
delves into more details.




=head2 C<FilterInitHandler>

The attribute C<FilterInitHandler> marks the function suitable to be
used as a filter initialization callback, which is called immediately
after a filter is inserted to the filter chain and before it's
actually called.

  sub init : FilterInitHandler {
      my $f = shift;
      #...
      return Apache2::Const::OK;
  }

In order to hook this filter callback, the real filter has to assign
this callback using the
C<L<FilterHasInitHandler|/C_FilterHasInitHandler_>> which accepts a
reference to the callback function.

For further discussion and examples refer to the L<Filter
Initialization
Phase|docs::2.0::user::handlers::filters/Filter_Initialization_Phase>
tutorial section.




=head2 C<FilterHasInitHandler>

If a filter wants to run an initialization callback it can register
such using the C<FilterHasInitHandler> attribute. Similar to
C<push_handlers> the callback reference is expected, rather than a
callback name. The used callback function has to have the
C<L<FilterInitHandler|/C_FilterInitHandler_>> attribute. For example:

  package MyApache2::FilterBar;
  use base qw(Apache2::Filter);
  sub init   : FilterInitHandler { ... }
  sub filter : FilterRequestHandler FilterHasInitHandler(\&init) {
      my ($f, $bb) = @_;
      # ...
      return Apache2::Const::OK;
  }

For further discussion and examples refer to the L<Filter
Initialization
Phase|docs::2.0::user::handlers::filters/Filter_Initialization_Phase>
tutorial section.




=head1 Configuration

mod_perl 2.0 filters configuration is explained in the L<filter
handlers
tutorial|docs::2.0::user::handlers::filters/mod_perl_Filters_Declaration_and_Configuration>.



=head2 C<PerlInputFilterHandler>

See
C<L<PerlInputFilterHandler|docs::2.0::user::handlers::filters/C_PerlInputFilterHandler_>>.



=head2 C<PerlOutputFilterHandler>

See
C<L<PerlOutputFilterHandler|docs::2.0::user::handlers::filters/C_PerlOutputFilterHandler_>>.



=head2 C<PerlSetInputFilter>

See
C<L<PerlSetInputFilter|docs::2.0::user::handlers::filters/C_PerlSetInputFilter_>>.



=head2 C<PerlSetOutputFilter>


See
C<L<PerlSetInputFilter|docs::2.0::user::handlers::filters/C_PerlSetInputFilter_>>.







=head1 TIE Interface

C<Apache2::Filter> also implements a tied interface, so you can work
with the C<$f> object as a hash reference.

The TIE interface is mostly unimplemented and might be implemented
post 2.0 release.



=head2 C<TIEHANDLE>

  $ret = TIEHANDLE($stashsv, $sv);

=over 4

=item obj: C<$stashsv> ( SCALAR )

=item arg1: C<$sv> ( SCALAR )

=item ret: C<$ret> ( SCALAR )

=item since: subject to change

=back





=head2 C<PRINT>

  $ret = PRINT(...);

=over 4

=item obj: C<...> (XXX)

=item ret: C<$ret> ( integer )

=item since: subject to change

=back








=head1 See Also

L<mod_perl 2.0 documentation|docs::2.0::index>.




=head1 Copyright

mod_perl 2.0 and its core modules are copyrighted under
The Apache Software License, Version 2.0.




=head1 Authors

L<The mod_perl development team and numerous
contributors|about::contributors::people>.

=cut