ossp-pkg/sio/al.pod
1.1
##
## OSSP al - Assembly Lists
## Copyright (c) 2002 Michael van Elst <mlelstv@dev.de.cw.net>
## Copyright (c) 2002 The OSSP Project <http://www.ossp.org/>
## Copyright (c) 2002 Cable & Wireless Deutschland <http://www.cw.com/de/>
##
## This file is part of OSSP al, an abstract datatype of a data buffer
## that can assemble, move and truncate data but avoids actual copying.
##
## Permission to use, copy, modify, and distribute this software for
## any purpose with or without fee is hereby granted, provided that
## the above copyright notice and this permission notice appear in all
## copies.
##
## THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
## WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
## MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
## IN NO EVENT SHALL THE AUTHORS AND COPYRIGHT HOLDERS AND THEIR
## CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
## SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
## LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
## USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
## ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
## OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
## OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
## SUCH DAMAGE.
##
## al.pod: assembly lists library manual page
##
=pod
=head1 NAME
B<OSSP al> - Assembly Lists
=head1 VERSION
B<OSSP al AL_VERSION_STR>
=head1 SYNOPSIS
=over 4
=item B<Abstract Data Types>:
al_rc_t,
al_t,
al_tx_t,
al_td_t,
al_chunk_t.
=item B<Assembly List Operations>:
al_create,
al_destroy,
al_append_bytes,
al_prepend_bytes,
al_attach_buffer,
al_splice,
al_bytes.
=item B<Traversal Operations>:
al_txalloc,
al_txfree,
al_traverse,
al_traverse_next,
al_traverse_cb.
=item B<Convenience Operations>:
al_flatten,
al_copy.
=item B<Chunk Operations>:
al_chunk_len,
al_chunk_span,
al_chunk_ptr.
=item B<Error Handling>:
al_error.
=back
=head1 DESCRIPTION
B<OSSP al> defines an abstract type of a data buffer that can
assemble, move and truncate data but avoids actual copying.
It provides the following key features:
=over 4
=back
=head1 DATA TYPES
B<OSSP al> uses five data types in its API:
=over 4
=item B<al_rc_t> (Return Code Type)
This is an exported enumerated integer type with the following possible
values:
AL_OK Everything Ok
AL_ERR_ARG Invalid Argument
AL_ERR_MEM Not Enough Memory
AL_ERR_EOF End Of Communication
AL_ERR_INT Internal Error
=item B<al_t> (Assembly List Type)
This is an opaque data type representing a data buffer.
Only pointers to this abstract data type are used in the API.
=item B<al_tx_t> (Traversal Context Type)
This is an opaque data type representing a the state of a buffer
traversal operation. Only pointers to this abstract data type are
used in the API.
=item B<al_td_t> (Traversal Direction Type)
This is an exported enumerated integer type with the following possible
values:
AL_FORWARD traverse list from beginning to end
AL_BACKWARD traverse list from end to beginning
=item B<al_chunk_t> (Chunk Type)
This is an opaque data type representing a chunk of a buffer during
a traversal operation. Only pointers to this abstract data type are
used in the API. The B<al_chunk_t> type is used to generate a pointer
and byte count to access the data in the buffer.
=back
=head1 FUNCTIONS
B<OSSP al> provides a bunch of API functions, all modelled after the
same prototype: "C<al_rc_t> C<al_>I<name>C<(al_>[C<chunk>]C<_t *,>
...C<)>". This means every function returns C<al_rc_t> to indicate its
success (C<AL_OK>) or failure (C<AL_ERR_XXX>) by returning a return code
(the corresponding describing text can be determined by passing this
return code to C<al_error>). Each function name starts with the common
prefix C<al_> and receives a C<al_t> (or C<al_chunk_t>) object on which
it operates as its first argument.
=head2 Assembly List Operations
=over 4
=item al_rc_t B<al_create>(al_t **I<alp>);
Create an assembly list abstraction object.
The object is stored in I<alp> on success.
Example: C<al_t *al; sa_create(&al);>
=item al_rc_t B<al_destroy>(al_t *I<al>);
Destroy an assembly list abstraction object.
The object I<al> is invalid after this call succeeded.
Example: C<al_destroy(al);>
=item al_rc_t B<al_append_bytes>(al_t *I<al>, const char *I<src>, size_t I<n>);
Append I<n> bytes from a storage array at I<src> to the assembly list, the
bytes are copied, memory is allocated as necessary.
Example: C<al_append_bytes(al, "Goodbye cruel world\n", 20);>
=item al_rc_t B<al_prepend_bytes>(al_t *I<al>, const char *I<src>, size_t I<n>);
Prepend I<n> bytes from a storage array at I<src> to the assembly list, the
bytes are copied, memory is allocated as necessary.
Example: C<al_prepend_bytes(al, "Hello world\n", 12);>
=item al_rc_t B<al_attach_buffer>(al_t *I<al>, char *I<p>, size_t I<n>);
Attach the storage array starting at I<p> with size <n> at the end of
the assembly list. Its content will become part of the assembly list
and is subject to assembly list operations. The storage array must stay
in scope for the whole life time of the assembly list, there is no way
to detach it from the assembly list.
Example: C<char store[] = "foo\n"; al_attach_buffer(al, store, sizeof(store));>
=item al_rc_t B<al_splice>(al_t *I<al>, size_t I<off>, size_t I<n>, al_t *I<nal>, al_t *I<tal>);
This is the general data move operation modelled after the perl operator
B<splice>.
I<off> and I<n> are byte counts that define a span of bytes within the
source assembly list I<al>. These bytes are moved to the target list
I<tal> while the content of the new list I<nal> is moved to the source
to replace the selected span.
There are two deviations from the perl operator to avoid copying:
The move to the target list I<tal> appends the data to its end.
The move from the new list I<nal> removes the data from its origin.
The target list I<tal> may be B<NULL>, the data bytes that would
be moved to the target are then discard. This avoids creation
and destruction of a dummy target.
The new list I<nal> may be B<NULL>, then nothing is inserted into
the source. This avoids creation and destruction of an empty list.
Examples:
al_t *source;
al_t *insertion;
al_t *buffer;
al_create(&source);
al_create(&insertion);
al_create(&buffer);
al_append_bytes(source, "Hello world\n", 12);
al_append_bytes(insertion, "Goodbye cruel", 13);
al_splice(source, 0, 5, insertion, buffer);
The buffer now holds the string "Hello".
The source now holds the string "Goodbye cruel world\n".
The insertion is now empty.
al_append_bytes(insertion, "brave", 5);
al_splice(source, 8, 5, insertion, NULL);
The source now holds the string "Goodbye brave world\n".
The insertion is now empty.
al_append_bytes(insertion, "B", 1);
al_splice(source, 0, 8, NULL, buffer);
al_splice(source, 0, 1, insertion, NULL);
al_append_bytes(insertion, "\n", 1);
al_splice(buffer, al_bytes(buffer)-1, 1, insertion, NULL),
The source now holds the string "Brave world\n".
The buffer now holds the string "HelloGoodbye\n".
The insertion is empty.
=item size_t B<al_bytes>(const al_t *I<al>);
Returns the number of bytes stored in the assembly list.
Example: C<al_t *al; size_t count; count = al_bytes(al);>
=back
=head2 Traversal Operations
=over 4
=item al_rc_t B<al_txalloc>(al_t *I<al>, al_tx_t **txp);
Allocate a traversal context.
Example: C<al_tx_t *tx; al_txalloc(&tx);>
=item al_rc_t B<al_free>(al_t *I<al>, al_tx_t *tx);
Free a traversal context.
Example: C<al_tx_t *tx; al_txfree(tx);>
=item al_rc_t B<al_traverse>(al_t *I<al>, size_t I<off>, size_t I<n>, al_td_t I<dir>, al_tx_t *I<tx>);
Start traversing the assembly list I<al> beginning at byte offset I<off>
for up to I<n> bytes in direction I<dir>. The state of the traversal is
stored in the supplied context I<tx>.
This function fails when the offset is outside the assembly list bounds.
=item al_rc_t B<al_traverse_next>(al_t *I<al>, al_tx_t *I<tx>, al_chunk_t **I<alcp>);
Complete a traversal step on the assembly list I<al> using the initialized
context I<tx>. In each step a chunk descriptor is filled and stored in
I<alcp>. All bytes of the chunk are guaranteed to be stored in a flat
array and can be accessed through the chunk operations described below.
The function returns AL_ERR_EOF when it passes the end (or beginning
in case of backward traversal) of the list.
=item al_rc_t B<al_traverse_cb>(al_t *I<al>, size_t I<off>, size_t I<n>, al_td_t I<dir>, al_rc_t (*I<cb>)(al_chunk_t *, void *), void *u);
B<al_traverse_cb> is a wrapper function that does a full list traversal in
a single call. In every step a chunk descriptor is passed to the callback
function I<cb> together with a user supplied pointer I<u>. When the
callback function returns anything but AL_OK the traversal is aborted
and B<al_traverse_cb> returns with that result code.
=back
=head2 Convenience Operations
=over 4
=item al_rc_t B<al_flatten>(al_t *I<al>, size_t I<off>, size_t I<n>, char *I<dst>, size_t *I<lenp>);
I<off> and I<n> are byte counts that define a span of bytes with the
assembly list I<al>. These bytes are copied to the storage array I<dst>
which must be sized appropriately.
I<off> must be a valid offset, I<n> must be positive but may exceed
the size of the assembly list.
The actual number of bytes that is copied to the destination is stored
in I<lenp>.
Example:
al_t *al;
char buffer[42];
size_t actual;
al_flatten(al, 500, 42, buffer, &actual);
=item al_rc_t B<al_copy>(al_t *I<al>, size_t I<off>, size_t I<n>, al_t *I<tal);
I<off> and I<n> are byte counts that define a span of bytes within the
assembly list I<al>. These bytes are appended to the target list I<tal>,
memory is allocated as necessary.
I<off> must be a valid offset, I<n> must be positive but may exceed
the size of the assembly list.
Example:
al_t *al;
al_t *tal;
al_create(&tal);
al_flatten(al, 500, 42, tal);
=back
=head2 Chunk Operations
=over 4
=item size_t B<al_chunk_len>(al_chunk_t *I<alc>);
Returns the number of bytes in a chunk.
=item size_t B<al_chunk_span>(al_chunk_t *I<alc>, size_t I<off>, size_t I<n>);
I<off> and I<n> are byte counts that define a span of bytes.
B<al_chunk_span> returns the number of bytes that are stored in the chunk.
I<off> must be a valid offset, I<n> must be positive but may exceed
the size of the chunk.
=item char *B<al_chunk_ptr>(al_chunk_t *I<alc>, size_t I<off>);
Returns the pointer to the byte at offset I<off> within the chunk I<alc>.
I<off> must be positive and must not exceed the size of the chunk.
Since all bytes of the chunk are guaranteed to be stored in a flat
array the pointer can be used to reference every byte within the chunk.
Example:
al_chunk_t *alc;
char *start, *end;
start = al_chunk_ptr(alc, 0);
end = start + al_chunk_len(alc) - 1;
=back
=head2 Error Handling
=over 4
=item const char *B<al_error>(al_rc_t I<rv>);
=back
=head1 SEE ALSO
=head1 HISTORY
B<OSSP al> was invented in October 2002 by Michael van Elst
E<lt>mlelstv@dev.de.cw.netE<gt> for use inside the OSSP project.
=head1 AUTHORS
Michael van Elst
mlelstv@dev.de.cw.net
=cut
