APR::Bucket - Perl API for manipulating APR Buckets
use APR::Bucket (); my $ba = $c->bucket_alloc; $b1 = APR::Bucket->new($ba, "aaa"); $b2 = APR::Bucket::eos_create($ba); $b3 = APR::Bucket::flush_create($ba); $b2->is_eos; $b3->is_flush; $len = $b1->length; $len = $b1->read($data); $type = $b1->type; $b1->insert_after($b2); $b1->insert_before($b3); $b1->remove; $b1->destroy; $b2->delete; # remove+destroy $b4 = APR::Bucket->new($ba, "to be setaside"); $b4->setaside($pool);
APR::Bucket allows you to create, manipulate and delete APR buckets.
APR::Bucket
You will probably find the various insert methods confusing, the tip is to read the function right to left. The following code sample helps to visualize the operations:
my $bb = APR::Brigade->new($r->pool, $ba); my $d1 = APR::Bucket->new($ba, "d1"); my $d2 = APR::Bucket->new($ba, "d2"); my $f1 = APR::Bucket::flush_create($ba); my $f2 = APR::Bucket::flush_create($ba); my $e1 = APR::Bucket::eos_create($ba); # head->tail $bb->insert_head( $d1); # head->d1->tail $d1->insert_after( $d2); # head->d1->d2->tail $d2->insert_before($f1); # head->d1->f1->d2->tail $d2->insert_after( $f2); # head->d1->f1->d2->f2->tail $bb->insert_tail( $e1); # head->d1->f1->d2->f2->e1->tail
APR::Bucket provides the following functions and/or methods:
delete
Tell the bucket to remove itself from the bucket brigade it belongs to, and destroy itself.
$bucket->delete();
$bucket
APR::Bucket object
If the bucket is not attached to any bucket brigade then this operation just destroys the bucket.
delete is a convenience wrapper, internally doing:
$b->remove; $b->destroy;
Examples:
Assuming that $bb already exists and filled with buckets, replace the existing data buckets with new buckets with upcased data;
$bb
for (my $b = $bb->first; $b; $b = $bb->next($b)) { if ($b->read(my $data)) { my $nb = APR::Bucket->new($bb->bucket_alloc, uc $data); $b->insert_before($nb); $b->delete; $b = $nb; } }
destroy
Free the resources used by a bucket. If multiple buckets refer to the same resource it is freed when the last one goes away.
$bucket->destroy();
A bucket needs to be destroyed if it was removed from a bucket brigade, to avoid memory leak.
If a bucket is linked to a bucket brigade, it needs to be removed from it, before it can be destroyed.
Usually instead of calling:
it's better to call delete which does exactly that.
eos_create
Create an EndOfStream bucket.
$b = APR::Bucket::eos_create($ba);
$ba
APR::BucketAlloc object
The freelist from which this bucket should be allocated
$b
The new bucket
This bucket type indicates that there is no more data coming from down the filter stack. All filters should flush any buffered data at this point.
Example:
use APR::Bucket (); use Apache::Connection (); my $ba = $c->bucket_alloc; my $eos_b = APR::Bucket::eos_create($ba);
flush_create
Create a flush bucket.
$b = APR::Bucket::flush_create($ba);
This bucket type indicates that filters should flush their data. There is no guarantee that they will flush it, but this is the best we can do.
insert_after
Insert a list of buckets after a specified bucket
$after_bucket->insert_after($add_bucket);
$after_bucket
The bucket to insert after
$add_bucket
The buckets to insert. It says buckets, since $add_bucket may have more buckets attached after itself.
insert_before
Insert a list of buckets before a specified bucket
$before_bucket->insert_before($add_bucket);
$before_bucket
The bucket to insert before
is_eos
Determine if a bucket is an EOS bucket
$ret = $bucket->is_eos();
$ret
is_flush
Determine if a bucket is a FLUSH bucket
$ret = $bucket->is_flush();
length
Get the length of the data in the bucket.
$len = $b->length;
$len
If the length is unknown, $len value will be -1.
new
Create a new bucket and initialize it with data:
$nb = APR::Bucket->new($ba, $data); $nb = $b->new($ba, $data); $nb = APR::Bucket->new($ba, $data, $offset); $nb = APR::Bucket->new($ba, $data, $offset, $len);
APR::Bucket object or class
$data
The data to initialize with.
Important: in order to avoid unnecessary data copying the variable is stored in the bucket object. That means that if you modify $data after passing it to new() you will modify the data in the bucket as well. To avoid that pass to new() a copy which you won't modify.
new()
$offset
Optional offset inside $data. Default: 0.
Optional partial length to read.
If $offset is specified, then:
length $buffer - $offset;
will be used. Otherwise the default is to use:
length $buffer;
$nb
a newly created bucket object
Create a new bucket using a whole string:
use APR::Bucket (); my $data = "my data"; my $b = APR::Bucket->new($ba, $data);
now the bucket contains the string 'my data'.
Create a new bucket using a sub-string:
use APR::Bucket (); my $data = "my data"; my $offset = 3; my $b = APR::Bucket->new($ba, $data, $offset);
now the bucket contains the string 'data'.
Create a new bucket not using the whole length and starting from an offset:
use APR::Bucket (); my $data = "my data"; my $offset = 3; my $len = 3; my $b = APR::Bucket->new($ba, $data, $offset, $len);
now the bucket contains the string 'dat'.
read
Read the data from the bucket.
$len = $b->read($buffer); $len = $b->read($buffer, $block);
The bucket to read from
$buffer
The buffer to fill. All previous data will be lost.
$block
APR::Const :read_type constant
optional reading mode constant.
By default the read is blocking, via APR::BLOCK_READ constant.
APR::BLOCK_READ constant
How many bytes were actually read
$buffer gets populated with the string that is read. It will contain an empty string if there was nothing to read.
APR::Error
It's important to know that certain bucket types (e.g. file bucket), may perform a split and insert extra buckets following the current one. Therefore never call $b->remove, before calling $b->read, or you may lose data.
$b->remove
$b->read
Blocking read:
my $len = $b->read(my $buffer);
Non-blocking read:
use APR::Const -compile 'NONBLOCK_READ'; my $len = $b->read(my $buffer, APR::NONBLOCK_READ);
remove
Tell the bucket to remove itself from the bucket brigade it belongs to.
$bucket->remove();
If the bucket is not attached to any bucket brigade then this operation doesn't do anything.
When the bucket is removed, it's not not destroyed. Usually this is done in order to move the bucket to another bucket brigade. Or to copy the data way before destroying the bucket. If the bucket wasn't moved to another bucket brigade it must be destroyed.
Assuming that $bb1 already exists and filled with buckets, move every odd bucket number to $bb2 and every even to $bb3:
$bb1
$bb2
$bb3
my $bb2 = APR::Brigade->new($c->pool, $c->bucket_alloc); my $bb3 = APR::Brigade->new($c->pool, $c->bucket_alloc); my $count = 0; while (my $bucket = $bb->first) { $count++; $bucket->remove; $count % 2 ? $bb2->insert_tail($bucket) : $bb3->insert_tail($bucket); }
setaside
Ensure the bucket's data lasts at least as long as the given pool:
my $status = $b->setaside($pool);
$pool
APR::Pool object
APR::Const status constant
On success, APR::SUCCESS is returned. Otherwise a failure code is returned.
APR::SUCCESS
when your code deals only with mod_perl buckets, you don't have to ask for the return value. If this method is called in the VOID context, i.e.:
VOID
$b->setaside($pool);
mod_perl will do the error checking on your behalf, and if the return code is not APR::SUCCESS, an APR::Error exception will be thrown.
APR::Error exception
However if your code doesn't know which bucket types it may need to setaside, you may want to check the return code and deal with any errors. For example one of the possible error codes is APR::ENOTIMPL. As of this writing the pipe and socket buckets can't setaside(), in which case you may want to look at the ap_save_brigade() implementation.
APR::ENOTIMPL
setaside()
ap_save_brigade()
Usually setaside is called by certain output filters, in order to buffer socket writes of smaller buckets into a single write. This method works on all bucket types (not only the mod_perl bucket type), but as explained in the exceptions section, not all bucket types implement this method.
When a mod_perl bucket is setaside, its data is detached from the original perl scalar and copied into a pool bucket. That allows downstream filters to deal with the data originally owned by a Perl interpreter, making it possible for that interpreter to go away and do other things, or be destroyed.
type
Get the type of the data in the bucket.
$type = $b->type;
$type
APR::BucketType object
You need to invoke APR::BucketType methods to access the data.
APR::BucketType
Create a flush bucket and read its type's name:
use APR::Bucket (); use APR::BucketType (); my $b = APR::Bucket::flush_create($ba); my $type = $b->type; my $type_name = $type->name; # FLUSH
The type name will be 'FLUSH' in this example.
APR::Socket also provides auto-generated Perl interface for a few other methods which aren't tested at the moment and therefore their API is a subject to change. These methods will be finalized later as a need arises. If you want to rely on any of the following methods please contact the the mod_perl development mailing list so we can help each other take the steps necessary to shift the method to an officially supported API.
APR::Socket
data
$data = $b->data;
Gives a C pointer to the address of the data in the bucket. I can't see what use can be done of it in Perl.
start
$start = $b->start;
It gives the offset to when a new bucket is created with a non-zero offset value:
my $b = APR::Bucket->new($ba, $data, $offset, $len);
So if the offset was 3. $start will be 3 too.
$start
I fail to see what it can be useful for to the end user (it's mainly used internally).
mod_perl 2.0 documentation.
mod_perl 2.0 and its core modules are copyrighted under The Apache Software License, Version 2.0.
The mod_perl development team and numerous contributors.
To install mod_perl, copy and paste the appropriate command in to your terminal.
cpanm
cpanm mod_perl
CPAN shell
perl -MCPAN -e shell install mod_perl
For more information on module installation, please visit the detailed CPAN module installation guide.