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Man Pages


Manual Reference Pages  -  AL (3)

NAME

OSSP al - Assembly Line

CONTENTS

VERSION

OSSP al 0.9.2 (03-Oct-2005)

SYNOPSIS

Abstract Data Types: al_rc_t, al_t, al_tx_t, al_td_t, al_chunk_t.
Assembly Line Operations: al_create, al_destroy, al_append_bytes, al_prepend_bytes, al_attach_buffer, al_splice, al_setlabel, al_bytes.
Traversal Operations: al_txalloc, al_txfree, al_traverse, al_traverse_next, al_traverse_end, al_traverse_cb.
Convenience Operations: al_flatten, al_copy, al_firstlabel, al_spanlabel.
Chunk Operations: al_chunk_len, al_chunk_span, al_chunk_label, al_same_label, al_chunk_ptr.
Error Handling: al_error.

DESCRIPTION

OSSP al defines an abstract data type of a data buffer that can assemble, move and truncate chunks of data in a stream but avoids actual copying. It was built to deal efficiently with communication streams between software modules. It especially provides flexible semantical data attribution through by-chunk labeling. It also has convenient chunk traversal methods and optional OSSP ex based exception handling.

DATA TYPES

OSSP al uses six data types in its API:
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



al_t (Assembly Line Type) This is an opaque data type representing a data buffer. Only pointers to this abstract data type are used in the API.
al_label_t (Label Type) This is an opaque pointer type representing a specific data flavour. You can restrict traversal operations to data that was marked with the specific flavour. Usually you would cast a pointer to the object that maintains the data to al_label_t. You may use NULL as a label but on traversal NULL matches any label.
al_tx_t (Traversal Context Type) This is an opaque data type representing the state of a buffer traversal operation. Only pointers to this abstract data type are used in the API.
al_td_t (Traversal Direction Type) This is an exported enumerated integer type with the following possible values:



 AL_FORWARD        traverse assembly line from beginning to end
 AL_BACKWARD       traverse assembly line from end to beginning
 AL_FORWARD_SPAN   like AL_FORWARD, but stop when label does not match
 AL_BACKWARD_SPAN  like AL_BACKWARD, but stop when label does not match



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 al_chunk_t type is used to generate a pointer and byte count to access the data in the buffer.

FUNCTIONS

OSSP al provides a bunch of API functions, all modelled after the same prototype: "al_rc_t al_name(al_[chunk]_t *, ...)". This means every function returns al_rc_t to indicate its success (AL_OK) or failure (AL_ERR_XXX) by returning a return code (the corresponding describing text can be determined by passing this return code to al_error). Each function name starts with the common prefix al_ and receives a al_t (or al_chunk_t) object on which it operates as its first argument.

Assembly Line Operations

al_rc_t al_create(al_t **alp); Create an assembly line abstraction object. The object is stored in alp on success.

Example: al_t *al; al_create(&al);

al_rc_t al_destroy(al_t *al); Destroy an assembly line abstraction object. The object al is invalid after this call succeeded.

Example: al_destroy(al);

al_rc_t al_append_bytes(al_t *al, const char *src, size_t n, al_label_t label); Append n bytes from a storage array at src to the assembly line. The bytes are copied, memory is allocated as necessary. The data is tagged with label.

Example: al_append_bytes(al, "Goodbye cruel world\n", 20, NULL);

al_rc_t al_prepend_bytes(al_t *al, const char *src, size_t n, al_label_t label); Prepend n bytes from a storage array at src to the assembly line. The bytes are copied, memory is allocated as necessary.

Example: al_prepend_bytes(al, "Hello world\n", 12, NULL);

al_rc_t al_attach_buffer(al_t *al, char *p, size_t n, al_label_t label, void (*freemem)(char *, size_t, void *), void *u); Attach the storage array starting at p with size n at the end of the assembly line. Its content becomes part of the assembly line and is subject to assembly line operations. The storage array must stay in scope until it is no longer referenced by the assembly line. When this happens the function freemem is called with the original pointer p, size n and an arbitrary pointer u. Passing a NULL pointer for freemem is valid, then no callback takes place, which might be appropriate for static buffers.

Example: char store[] = "foo\n"; al_attach_buffer(al, store, sizeof(store), NULL, NULL, NULL);

al_rc_t al_splice(al_t *al, size_t off, size_t n, al_t *nal, al_t *tal); This is the general data move operation modelled after the perl operator splice.

off and n are byte counts that define a span of bytes within the source assembly line al. These bytes are moved to the target assembly line tal while the content of the new assembly line 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 assembly line tal appends the data to its end. The move from the new assembly line nal removes the data from its origin.

The target assembly line tal may be NULL, the data bytes that would be moved to the target are then discarded. This avoids creation and destruction of a dummy target.

The new assembly line nal may be NULL, then nothing is inserted into the source. This avoids creation and destruction of an empty assembly line.

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, NULL);
 al_append_bytes(insertion, "Goodbye cruel", 13, NULL);





 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, NULL);
 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, NULL);
 al_splice(source, 0, 8, NULL, buffer);
 al_splice(source, 0, 1, insertion, NULL);
 al_append_bytes(insertion, "\n", 1, NULL);
 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.

al_rc_t al_setlabel(al_t *al, size_t off, size_t n, al_label_t oldlabel, al_label_t newlabel); off and n are byte counts that define a span of bytes within the source assembly line al. The bytes within that span that match oldlabel are tagged with newlabel, any existing labels for these bytes are overwritten.
size_t al_bytes(const al_t *al); Returns the number of bytes stored in the assembly line.

Example: al_t *al; size_t count; count = al_bytes(al);

Traversal Operations

al_rc_t al_txalloc(al_t *al, al_tx_t **txp); Allocate a traversal context.

Example: al_tx_t *tx; al_txalloc(&tx);

al_rc_t al_txfree(al_t *al, al_tx_t *tx); Free a traversal context.

Example: al_tx_t *tx; al_txfree(tx);

al_rc_t al_traverse(al_t *al, size_t off, size_t n, al_td_t dir, al_label_t label, al_tx_t *tx); Start traversing the assembly line al beginning at byte offset off for up to n bytes in direction dir. If label is not NULL then you will see only data that was tagged with label. The state of the traversal is stored in the supplied context tx.

This function fails when the offset is outside the assembly line bounds.

al_rc_t al_traverse_next(al_t *al, al_tx_t *tx, al_chunk_t **alcp); Complete a traversal step on the assembly line al using the initialized context tx. In each step a chunk descriptor is filled and stored in 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 assembly line.

al_rc_t al_traverse_end(al_t *al, al_tx_t *tx, int final); Clean up internal state of traversal. If final is zero, you may continue the traversal later by calling al_traverse_next. If final is non-zero you need to start a new traversal. It is mandatory that every traversal that was started is finished by a call to al_traverse_end with final set to a non-zero value.
al_rc_t al_traverse_cb(al_t *al, size_t off, size_t n, al_td_t dir, al_label_t label, al_rc_t (*cb)(al_chunk_t *, void *), void *u); al_traverse_cb is a wrapper function that does a full assembly line traversal in a single call. In every step a chunk descriptor is passed to the callback function cb together with a user supplied pointer u. When the callback function returns AL_OK the traversal continues, when it returns AL_ERR_EOF the traversal is aborted and AL_OK is returned to the original caller. Any other return code returned by the callback is passed to the original caller verbatim.

Convenience Operations

al_rc_t al_flatten(al_t *al, size_t off, size_t n, al_td_t dir, char *dst, size_t *lenp); off and n are byte counts that define a span of bytes with the assembly line al. These bytes are copied to the storage array dst which must be sized appropriately. off must be a valid offset, n must be positive but may exceed the size of the assembly line. The actual number of bytes that is copied to the destination is stored in lenp. If dst is NULL then no data is copied but the number of bytes is still counted in lenp. This can be used to precalculate the size of the needed storage array by passing an arbitrary high maximum size as n. If dir denotes a backwards traversal the storage array is filled from its end.

Example:



 al_t *al;
 char buffer[42];
 size_t actual;





 al_flatten(al, 500, 42, AL_FORWARD, buffer, &actual);



al_rc_t al_copy(al_t *al, size_t off, size_t n, al_td_t dir, al_t *tal); off and n are byte counts that define a span of bytes within the assembly line al. These bytes are appended to the target assembly line tal, memory is allocated as necessary. off must be a valid offset, n must be positive but may exceed the size of the assembly line.

Example:



 al_t *al;
 al_t *tal;





 al_create(&tal);
 al_flatten(al, 500, 42, tal);



al_rc_t al_firstlabel(al_t *al, size_t off, size_t n, al_td_t dir, al_label_t *labelp); off and n are byte counts that define a span of bytes within the assembly line al. The label that was attached to the first byte within the defined span is stored in labelp, otherwise al_firstlabel returns an error.
al_rc_t al_spanlabel(al_t *al, size_t off, size_t n, al_label_t *label, size_t *<offp>, size_t *<spanp>); off and n are byte counts that define a span of bytes within the assembly line al. This span is searched for data tagged with the label. The absolute byte offset of the first byte matching the label and the length of the span of the same label is returned in offp and spanp respectively.

Chunk Operations

size_t al_chunk_len(al_chunk_t *alc); Returns the number of bytes in a chunk.
size_t al_chunk_span(al_chunk_t *alc, size_t off, size_t n); off and n are byte counts that define a span of bytes. al_chunk_span returns the number of bytes that are stored in the chunk. off must be a valid offset, n must be positive but may exceed the size of the chunk.
al_label_t al_chunk_label(al_chunk_t *alc); Return the label that was used to tag the data in alc. This can be NULL.
int al_same_label(al_chunk_t *alc, al_label_t *label); Return true if label matches the label that was used to tag the data in alc. A NULL label matches everything.
char *al_chunk_ptr(al_chunk_t *alc, size_t off); Returns the pointer to the byte at offset off within the chunk alc. 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;



Error Handling

const char *al_error(al_rc_t rv); Retrieve a string that describes the return code rv in english.

SEE ALSO

HISTORY

OSSP al was invented in October 2002 by Michael van Elst <mlelstv@serpens.de> under contract with Cable & Wireless Germany <http://www.cw.com/de> for use inside the OSSP project <http://www.ossp.org/>.

AUTHORS



 Michael van Elst
 mlelstv@serpens.de



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03-Oct-2005 AL (3) OSSP al 0.9.2

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