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Apache::Filter -- A Perl API for Apache 2.0 Filtering | ||||
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c
Inside a connection or a request filter the current connection object can be retrieved with:
my $c = $f->c;
ctx
A filter context is created before the filter is called for the first
time and it's destroyed at the end of the request. The context is
preserved between filter invocations of the same request. So if a
filter needs to store some data between invocations it should use the
filter context for that. The filter context is initialized with the
undef
value.
The ctx
method accepts a single SCALAR argument. Therefore if you
want to store any other perl datastructure you should use a reference
to it.
For example you can store a hash reference:
$f->ctx({ foo => 'bar' });
and then access it:
$foo = $f->ctx->{foo};
if you access the context more than once it's more efficient to copy it's value before using it:
my $ctx = $f->ctx; $foo = $ctx->{foo};
to avoid redundant method calls. As of this writing $ctx
is not a
tied variable, so if you modify it need to store it at the end:
$f->ctx($ctx);
META: later we might make it a TIEd-variable interface, so it'll be stored automatically.
This method is useful when it's acting as a flag which ensures that something happens only once. For example:
unless ($f->ctx) { do_something_once(); $f->ctx(1); }
next
$f->next;
Returns the Apache::Filter
object of the next filter in chain.
Since Apache inserts several core filters at the end of each chain,
normally this method always returns an object. However if it's not a
mod_perl filter handler, you can call only the following methods on
it: get_brigade
,
pass_brigade
, c
, r
,
frec
and next
. If you call other methods
the behavior is undefined.
META: I doubt anybody will ever need to mess with other filters, from
within a mod_perl filter. but if the need arises it's easy to tell a
mod_perl filter from non-mod_perl one by calling
$f->frec->name
(it'll return one of the following four
names: modperl_request_output, modperl_request_input,
modperl_connection_output or modperl_connection_input).
remove
$f->remove;
Remove the current filter from the filter chain (for the current request).
Notice that you should either complete the current filter invocation
normally (by calling get_brigade
or
pass_brigade
depending on the filter kind) or
if nothing was done, return Apache::DECLINED
and mod_perl will take
care of passing the current bucket brigade through unmodified to the
next filter in chain.
note: calling remove() on the very top connection filter doesn't affect the filter chain due to a bug in Apache 2.0.46 and lower (may be fixed in 2.0.47). So don't use it with connection filters, till it gets fixed in Apache and then make sure to require the minimum Apache version if you rely on it.
The following methods can be called from any filter, directly manipulating bucket brigades:
get_brigade
sub filter { my($f, $bb, $mode, $block, $readbytes) = @_; my $rv = $f->next->get_brigade($bb, $mode, $block, $readbytes); return $rv unless $rv == APR::SUCCESS; # ... process $bb return Apache::OK; }
This is a method to use in bucket brigade input filters. It acquires a bucket brigade from the upstream input filter.
Normally arguments $mode
, $block
, $readbytes
are the same as
passed to the filter itself.
It returns APR::SUCCESS
on success, otherwise a failure code, in
which case it should be returned to the caller.
pass_brigade
sub filter { my($f, $bb) = @_; # ... process $bb my $rv = $f->next->pass_brigade($bb); return $rv unless $rv == APR::SUCCESS; # process $bb return Apache::OK; }
This is a method to use in bucket brigade output filters. It passes the current bucket brigade to the downstream output filter.
It returns APR::SUCCESS
on success, otherwise a failure code, in
which case it should be returned to the caller.
The following methods can be called from any filter, which uses the simplified streaming functionality:
seen_eos
$f->seen_eos;
This methods returns a true value when the EOS bucket is seen by the
read
method. This only works in streaming filters which
exhaustively $f->read
all the incoming data in a
while loop, like so:
while ($f->read(my $buffer, $read_len)) { # do something with $buffer } if ($f->seen_eos) { # do something }
This method 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.
read
$f->read(my $buffer, $read_len);
Reads at most $read_len
characters into $buffer
. It returns a
true value as long as it had something to read, and a false value
otherwise.
This is a streaming filter method, which acquires the bucket brigade
behind the scenes and reads data from all buckets. If the EOS bucket
is read, the seen_eos
method will return a true
value.
print
$f->print($buffer);
Sends the contents of $buffer
to the next filter in chain (via
internal buffer).
This method should be used only in streaming filters.
Other methods which affect filters, but called on
non-Apache::Filter
objects:
add_input_filter
$r->add_input_filter(\&callback);
Adds &callback
filter handler to input request filter chain.
$c->add_input_filter(\&callback);
Adds &callback
filter handler to input connection filter chain.
add_output_filter
$r->add_output_filter(\&callback);
Adds &callback
filter handler to output request filter chain.
$c->add_output_filter(\&callback);
Adds &callback
filter handler to output connection filter chain.
Packages using filter attributes have to subclass Apache::Filter
:
package MyApache::FilterCool; use base qw(Apache::Filter);
Attributes are parsed during the code compilation, by the function
MODIFY_CODE_ATTRIBUTES
, inherited from the Apache::Filter
package.
FilterRequestHandler
The 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
FilterRequestHandler
attribute in the handler subroutine's
declaration:
package MyApache::FilterOutputReq; sub handler : FilterRequestHandler { ... }
and add the configuration entry:
PerlOutputFilterHandler MyApache::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 HTTP Request vs. Connection Filters delves into more details.
FilterConnectionHandler
The 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
FilterConnectionHandler
attribute in the handler subroutine's
declaration:
package MyApache::FilterOutputCon; sub handler : FilterConnectionHandler { ... }
and add the configuration entry:
PerlOutputFilterHandler MyApache::FilterOutputCon
The section HTTP Request vs. Connection Filters delves into more details.
FilterInitHandler
The attribute 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 $f = shift; #... return Apache::OK; }
In order to hook this filter callback, the real filter has to assign
this callback using the
FilterHasInitHandler
which accepts a
reference to the callback function.
For further discussion and examples refer to the Filter Initialization Phase tutorial section.
FilterHasInitHandler
If a filter wants to run an initialization callback it can register
such using the FilterHasInitHandler
attribute. Similar to
push_handlers
the callback reference is expected, rather than a
callback name. The used callback function has to have the
FilterInitHandler
attribute. For example:
package MyApache::FilterBar; use base qw(Apache::Filter); sub init : FilterInitHandler { ... } sub filter : FilterRequestHandler FilterHasInitHandler(\&init) { my ($f, $bb) = @_; # ... return Apache::OK; }
For further discussion and examples refer to the Filter Initialization Phase tutorial section.
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