BUILD::mod_perl-2.0.2:UserBUILD::mod_perl-2.0.2::docs::api::Apache2::Filter(3)NAMEApache2::Filter - Perl API for Apache 2.0 Filtering
Synopsis
use Apache2::Filter ();
# filter attributes
my $c = $f->c;
my $r = $f->r;
my $frec = $f->frec();
my $next_f = $f->next;
my $ctx = $f->ctx;
$f->ctx($ctx);
# bucket brigade filtering API
$rc = $f->next->get_brigade($bb, $mode, $block, $readbytes);
$rc = $f->next->pass_brigade($bb);
$rc = $f->fflush($bb);
# streaming filtering API
while ($filter->read(my $buffer, $wanted)) {
# transform $buffer here
$filter->print($buffer);
}
if ($f->seen_eos) {
$filter->print("filter signature");
}
# filter manipulations
$r->add_input_filter(\&callback);
$c->add_input_filter(\&callback);
$r->add_output_filter(\&callback);
$c->add_output_filter(\&callback);
$f->remove;
Description
"Apache2::Filter" provides Perl API for Apache 2.0 filtering framework.
Make sure to read "the Filtering tutorial⎪docs::2.0::user::han‐
dlers::filters".
Common Filter API
The following methods can be called from any filter handler:
"c"
Get the current connection object from a connection or a request fil‐
ter:
$c = $f->c;
obj: $f ( "Apache2::Filter object" )
ret: $c ( "Apache2::Connection object" )
since: 2.0.00
"ctx"
Get/set the filter context data.
$ctx = $f->ctx;
$f->ctx($ctx);
obj: $f ( "Apache2::Filter object" )
opt arg2: $ctx ( SCALAR )
next context
ret: $ctx ( SCALAR )
current context
since: 2.0.00
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 pre‐
served 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.
Besides its primary purpose of storing context data across multiple
filter invocations, this method is also useful when used as a flag. For
example here is how to ensure that something happens only once during
the filter's life:
unless ($f->ctx) {
do_something_once();
$f->ctx(1);
}
"frec"
Get/set the "Apache2::FilterRec" (filter record) object.
$frec = $f->frec();
obj: $f ( "Apache2::Filter object" )
ret: $frec ( "Apache2::FilterRec object" )
since: 2.0.00
For example you can call "$frec->name" to get filter's name.
"next"
Return the "Apache2::Filter" object of the next filter in chain.
$next_f = $f->next;
obj: $f ( "Apache2::Filter object" )
The current filter object
ret: $next_f ( "Apache2::Filter object" )
The next filter object in chain
since: 2.0.00
Since Apache inserts several core filters at the end of each chain,
normally this method always returns an object. However if it's not a
mod_perl filter handler, you can call only the following methods on it:
"get_brigade", "pass_brigade", "c", "r", "frec" and "next". If you call
other methods the behavior is undefined.
The next filter can be a mod_perl one or not, it's easy to tell which
one is that by calling "$f->frec->name".
"r"
Inside an HTTP request filter retrieve the current request object:
$r = $f->r;
obj: $f ( "Apache2::Filter object" )
ret: $r ( "Apache2::RequestRec object" )
since: 2.0.00
If a sub-request adds filters, then that sub-request object is associ‐
ated with the filter.
"remove"
Remove the current filter from the filter chain (for the current
request or connection).
$f->remove;
obj: $f ( "Apache2::Filter object" )
ret: no return value
since: 2.0.00
Notice that you should either complete the current filter invocation
normally (by calling "get_brigade" or "pass_brigade" depending on the
filter kind) or if nothing was done, return "Apache2::Const::DECLINED"
and mod_perl will take care of passing the current bucket brigade
through unmodified to the next filter in chain.
Note: calling remove() on the very top connection filter doesn't affect
the filter chain due to a bug in Apache 2.0 (which may be fixed in
2.1). So don't use it with connection filters, till it gets fixed in
Apache and then make sure to require the minimum Apache version if you
rely on.
Remember that if the connection is "$c->keepalive" ) and the connection
filter is removed, it won't be added until the connection is closed.
Which may happen after many HTTP requests. You may want to keep the
filter in place and pass the data through unmodified, by returning
"Apache2::Const::DECLINED". If you need to reset the whole or parts of
the filter context between requests, use the technique based on
"$c->keepalives" counting.
This method works for native Apache (non-mod_perl) filters too.
Bucket Brigade Filter API
The following methods can be called from any filter, directly manipu‐
lating bucket brigades:
"fflush"
Flush a bucket brigade down the filter stack.
$rc = $f->fflush($bb);
obj: $f ( "Apache2::Filter object" )
The current filter
arg1: $bb ( "Apache2::Brigade object" )
The brigade to flush
ret: $rc ( "APR::Const status constant" )
Refer to the "pass_brigade()" entry.
excpt: "APR::Error"
Exceptions are thrown only when this function is called in the VOID
context. Refer to the "get_brigade()" entry for details.
since: 2.0.00
"fflush" is a shortcut method. So instead of doing:
my $b = APR::Bucket::flush_create($f->c->bucket_alloc);
$bb->insert_tail($b);
$f->pass_brigade($bb);
one can just write:
$f->fflush($bb);
"get_brigade"
This is a method to use in bucket brigade input filters. It acquires a
bucket brigade from the upstream input filter.
$rc = $next_f->get_brigade($bb, $mode, $block, $readbytes);
$rc = $next_f->get_brigade($bb, $mode, $block);
$rc = $next_f->get_brigade($bb, $mode)
$rc = $next_f->get_brigade($bb);
obj: $next_f ( "Apache2::Filter object" )
The next filter in the filter chain.
Inside filter handlers it's usually "$f->next". Inside protocol
handlers: "$c->input_filters".
arg1: $bb ( "APR::Brigade object" )
The original bucket brigade passed to "get_brigade()", which must
be empty.
Inside input filter handlers it's usually the second argument to
the filter handler.
Otherwise it should be created:
my $bb = APR::Brigade->new($c->pool, $c->bucket_alloc);
On return it gets populated with the next bucket brigade. That
brigade may contain nothing if there was no more data to read. The
return status tells the outcome.
opt arg2: $mode ( "Apache2::Const :input_mode constant" )
The filter mode in which the data should be read.
If inside the filter handler, you should normally pass the same
mode that was passed to the filter handler (the third argument).
At the end of this section the available modes are presented.
If the argument $mode is not passed, "Apache2::Const::MODE_READ‐
BYTES" is used as a default value.
opt arg3: $block ( "APR::Const :read_type constant" )
You may ask the reading operation to be blocking:
"APR::Const::BLOCK_READ", or nonblocking: "APR::Const::NON‐
BLOCK_READ".
If inside the filter handler, you should normally pass the same
blocking mode argument that was passed to the filter handler (the
forth argument).
If the argument $block is not passed, "APR::Const::BLOCK_READ" is
used as a default value.
opt arg4: $readbytes ( integer )
How many bytes to read from the next filter.
If inside the filter handler, you may want the same number of
bytes, as the upstream filter, i.e. the argument that was passed to
the filter handler (the fifth argument).
If the argument $block is not passed, 8192 is used as a default
value.
ret: $rc ( "APR::Const status constant" )
On success, "APR::Const::SUCCESS" is returned and $bb is populated
(see the $bb entry).
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 read from the network, then
"Apache2::NOBODY_READ" is returned (META: need to add this con‐
stant).
Inside protocol handlers the return code can also be
"APR::Const::EOF", which is success as well.
excpt: "APR::Error"
You don't have to ask for the return value. If this function is
called in the VOID context, e.g.:
$f->next->get_brigade($bb, $mode, $block, $readbytes);
mod_perl will do the error checking on your behalf, and if the
return code is not "APR::Const::SUCCESS", an "APR::Error exception"
will be thrown. The only time you want to do the error checking
yourself, is when return codes besides "APR::Const::SUCCESS" are
considered as successful and you want to manage them by yourself.
since: 2.0.00
Available input filter modes (the optional second argument $mode) are:
* "Apache2::Const::MODE_READBYTES"
The filter should return at most readbytes data
* "Apache2::Const::MODE_GETLINE"
The filter should return at most one line of CRLF data. (If a
potential line is too long or no CRLF is found, the filter may
return partial data).
* "Apache2::Const::MODE_EATCRLF"
The filter should implicitly eat any CRLF pairs that it sees.
* "Apache2::Const::MODE_SPECULATIVE"
The filter read should be treated as speculative and any returned
data should be stored for later retrieval in another mode.
* "Apache2::Const::MODE_EXHAUSTIVE"
The filter read should be exhaustive and read until it can not read
any more. Use this mode with extreme caution.
* "Apache2::Const::MODE_INIT"
The filter should initialize the connection if needed, NNTP or FTP
over SSL for example.
Either compile all these constants with:
use Apache2::Const -compile => qw(:input_mode);
But it's a bit more efficient to compile only those constants that you
need.
Example:
Here is a fragment of a filter handler, that receives a bucket brigade
from the upstream filter:
use Apache2::Filter ();
use APR::Const -compile => qw(SUCCESS);
use Apache2::Const -compile => qw(OK);
sub filter {
my ($f, $bb, $mode, $block, $readbytes) = @_;
my $rc = $f->next->get_brigade($bb, $mode, $block, $readbytes);
return $rc unless $rc == APR::Const::SUCCESS;
# ... process $bb
return Apache2::Const::OK;
}
Usually arguments $mode, $block, $readbytes are the same as passed to
the filter itself.
You can see that in case of a failure, the handler returns immediately
with that failure code, which gets propagated to the downstream filter.
If you decide not check the return code, you can write it as:
sub filter {
my ($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 "the filter han‐
dlers⎪docs::2.0::user::handlers::filters" and "the protocol han‐
dlers⎪docs::2.0::user::handlers::protocols" tutorials.
"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);
obj: $next_f ( "Apache2::Filter object" )
The next filter in the filter chain.
Inside output filter handlers it's usually "$f->next". Inside pro‐
tocol handlers: "$c->output_filters".
arg1: $bb ( "APR::Brigade object" )
The bucket brigade to pass.
Inside output filter handlers it's usually the second argument to
the filter handler (after potential manipulations).
ret: $rc ( "APR::Const status constant" )
On success, "APR::Const::SUCCESS" is returned.
In case of a failure -- a failure code is returned, in which case
normally it should be returned to the caller.
If the bottom-most filter doesn't write to the network, then
"Apache2::NOBODY_WROTE" is returned (META: need to add this con‐
stant).
Also refer to the "get_brigade()" entry to see how to avoid check‐
ing the errors explicitly.
excpt: "APR::Error"
Exceptions are thrown only when this function is called in the VOID
context. Refer to the "get_brigade()" entry for details.
since: 2.0.00
The caller relinquishes ownership of the brigade (i.e. it may get
destroyed/overwritten/etc. by the callee).
Example:
Here is a fragment of a filter handler, that passes a bucket brigade to
the downstream filter (after some potential processing of the buckets
in the bucket brigade):
use Apache2::Filter ();
use APR::Const -compile => qw(SUCCESS);
use Apache2::Const -compile => qw(OK);
sub filter {
my ($f, $bb) = @_;
# ... process $bb
my $rc = $f->next->pass_brigade($bb);
return $rc unless $rc == APR::Const::SUCCESS;
return Apache2::Const::OK;
}
Streaming Filter API
The following methods can be called from any filter, which uses the
simplified streaming functionality:
"print"
Send the contents of $buffer to the next filter in chain (via internal
buffer).
$sent = $f->print($buffer);
obj: $f ( "Apache2::Filter object" )
arg1: $buffer ( string )
The data to send.
ret: $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.
excpt: "APR::Error"
since: 2.0.00
This method should be used only in streaming filters.
"read"
Read data from the filter
$read = $f->read($buffer, $wanted);
obj: $f ( "Apache2::Filter object" )
arg1: $buffer ( SCALAR )
The buffer to fill. All previous data will be lost.
opt arg2: $wanted ( integer )
How many bytes to attempt to read.
If this optional argument is not specified -- the default 8192 will
be used.
ret: $read ( integer )
How many bytes were actually read.
$buffer gets populated with the string that is read. It will con‐
tain an empty string if there was nothing to read.
excpt: "APR::Error"
since: 2.0.00
Reads at most $wanted characters into $buffer. The returned value $read
tells exactly how many were read, making it easy to use it in a while
loop:
while ($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. There‐
fore it can only read from one bucket brigade per filter invocation.
If the EOS bucket is read, the "seen_eos" method will return a true
value.
"seen_eos"
This methods returns a true value when the EOS bucket is seen by the
"read" method.
$ok = $f->seen_eos;
obj: $f ( "Apache2::Filter object" )
The filter to remove
ret: $ok ( boolean )
a true value if EOS has been seen, otherwise a false value
since: 2.0.00
This method only works in streaming filters which exhaustively
"$f->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.
Other Filter-related API
Other methods which affect filters, but called on non-"Apache2::Filter"
objects:
"add_input_filter"
Add &callback filter handler to input request filter chain.
$r->add_input_filter(\&callback);
Add &callback filter handler to input connection filter chain.
$c->add_input_filter(\&callback);
obj: $c ( "Apache2::Connection object" ) or $r ( "Apache2::RequestRec
object" )
arg1: &callback (CODE ref)
ret: no return value
since: 2.0.00
[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 fil‐
ter_init handler. In fact it does work if there is any filter addi‐
tional filter of the same kind configured from httpd.conf or via fil‐
ter_init. It looks like there is a bug in httpd, where it doesn't pre‐
pare the chain of 3rd party filter if none were inserted before the
first filter was called.]
"add_output_filter"
Add &callback filter handler to output request filter chain.
$r->add_output_filter(\&callback);
Add &callback filter handler to output connection filter chain.
$c->add_output_filter(\&callback);
obj: $c ( "Apache2::Connection object" ) or $r ( "Apache2::RequestRec
object" )
arg1: &callback (CODE ref)
ret: no return value
since: 2.0.00
Filter Handler Attributes
Packages using filter attributes have to subclass "Apache2::Filter":
package MyApache2::FilterCool;
use base qw(Apache2::Filter);
Attributes are parsed during the code compilation, by the function
"MODIFY_CODE_ATTRIBUTES", inherited from the "Apache2::Filter" package.
"FilterRequestHandler"
The "FilterRequestHandler" attribute tells mod_perl to insert the fil‐
ter into an HTTP request filter chain.
For example, to configure an output request filter handler, use the
"FilterRequestHandler" attribute in the handler subroutine's declara‐
tion:
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 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 decla‐
ration:
package MyApache2::FilterOutputCon;
sub handler : FilterConnectionHandler { ... }
and add the configuration entry:
PerlOutputFilterHandler MyApache2::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 $f = shift;
#...
return Apache2::Const::OK;
}
In order to hook this filter callback, the real filter has to assign
this callback using the "FilterHasInitHandler" which accepts a refer‐
ence to the callback function.
For further discussion and examples refer to the Filter Initialization
Phase tutorial section.
"FilterHasInitHandler"
If a filter wants to run an initialization callback it can register
such using the "FilterHasInitHandler" attribute. Similar to "push_han‐
dlers" the callback reference is expected, rather than a callback name.
The used callback function has to have the "FilterInitHandler"
attribute. For example:
package MyApache2::FilterBar;
use base qw(Apache2::Filter);
sub init : FilterInitHandler { ... }
sub filter : FilterRequestHandler FilterHasInitHandler(\&init) {
my ($f, $bb) = @_;
# ...
return Apache2::Const::OK;
}
For further discussion and examples refer to the Filter Initialization
Phase tutorial section.
Configuration
mod_perl 2.0 filters configuration is explained in the filter handlers
tutorial.
"PerlInputFilterHandler"
See "PerlInputFilterHandler".
"PerlOutputFilterHandler"
See "PerlOutputFilterHandler".
"PerlSetInputFilter"
See "PerlSetInputFilter".
"PerlSetOutputFilter"
See "PerlSetInputFilter".
TIE Interface
"Apache2::Filter" also implements a tied interface, so you can work
with the $f object as a hash reference.
The TIE interface is mostly unimplemented and might be implemented post
2.0 release.
"TIEHANDLE"
$ret = TIEHANDLE($stashsv, $sv);
obj: $stashsv ( SCALAR )
arg1: $sv ( SCALAR )
ret: $ret ( SCALAR )
since: subject to change
"PRINT"
$ret = PRINT(...);
obj: "..." (XXX)
ret: $ret ( integer )
since: subject to change
See Also
mod_perl 2.0 documentation.
Copyright
mod_perl 2.0 and its core modules are copyrighted under The Apache
Software License, Version 2.0.
Authors
The mod_perl development team and numerous contributors.
perl v5.8.8BUILD::mod_perl-2.0.2::docs::api::Apache2::Filter(3)