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libbzip2
This chapter describes the programming interface to libbzip2.
For general background information, particularly about memory use and performance aspects, you'd be well advised to read Chapter 2 as well.
libbzip2 is a flexible library for compressing and decompressing
data in the bzip2 data format. Although packaged as a single
entity, it helps to regard the library as three separate parts: the low
level interface, and the high level interface, and some utility
functions.
The structure of libbzip2's interfaces is similar to
that of Jean-loup Gailly's and Mark Adler's excellent zlib
library.
All externally visible symbols have names beginning BZ2_.
This is new in version 1.0. The intention is to minimise pollution
of the namespaces of library clients.
This interface provides services for compressing and decompressing
data in memory. There's no provision for dealing with files, streams
or any other I/O mechanisms, just straight memory-to-memory work.
In fact, this part of the library can be compiled without inclusion
of stdio.h, which may be helpful for embedded applications.
The low-level part of the library has no global variables and is therefore thread-safe.
Six routines make up the low level interface:
BZ2_bzCompressInit, BZ2_bzCompress, and
BZ2_bzCompressEnd
for compression,
and a corresponding trio BZ2_bzDecompressInit,
BZ2_bzDecompress
and BZ2_bzDecompressEnd for decompression.
The *Init functions allocate
memory for compression/decompression and do other
initialisations, whilst the *End functions close down operations
and release memory.
The real work is done by BZ2_bzCompress and BZ2_bzDecompress.
These compress and decompress data from a user-supplied input buffer
to a user-supplied output buffer. These buffers can be any size;
arbitrary quantities of data are handled by making repeated calls
to these functions. This is a flexible mechanism allowing a
consumer-pull style of activity, or producer-push, or a mixture of
both.
This interface provides some handy wrappers around the low-level
interface to facilitate reading and writing bzip2 format
files (.bz2 files). The routines provide hooks to facilitate
reading files in which the bzip2 data stream is embedded
within some larger-scale file structure, or where there are
multiple bzip2 data streams concatenated end-to-end.
For reading files, BZ2_bzReadOpen, BZ2_bzRead,
BZ2_bzReadClose and
BZ2_bzReadGetUnused are supplied. For
writing files, BZ2_bzWriteOpen, BZ2_bzWrite and
BZ2_bzWriteFinish are available.
As with the low-level library, no global variables are used
so the library is per se thread-safe. However, if I/O errors
occur whilst reading or writing the underlying compressed files,
you may have to consult errno to determine the cause of
the error. In that case, you'd need a C library which correctly
supports errno in a multithreaded environment.
To make the library a little simpler and more portable,
BZ2_bzReadOpen and BZ2_bzWriteOpen require you to pass them file
handles (FILE*s) which have previously been opened for reading or
writing respectively. That avoids portability problems associated with
file operations and file attributes, whilst not being much of an
imposition on the programmer.
For very simple needs, BZ2_bzBuffToBuffCompress and
BZ2_bzBuffToBuffDecompress are provided. These compress
data in memory from one buffer to another buffer in a single
function call. You should assess whether these functions
fulfill your memory-to-memory compression/decompression
requirements before investing effort in understanding the more
general but more complex low-level interface.
Yoshioka Tsuneo (QWF00133@niftyserve.or.jp /
tsuneo-y@is.aist-nara.ac.jp) has contributed some functions to
give better zlib compatibility. These functions are
BZ2_bzopen, BZ2_bzread, BZ2_bzwrite, BZ2_bzflush,
BZ2_bzclose,
BZ2_bzerror and BZ2_bzlibVersion. You may find these functions
more convenient for simple file reading and writing, than those in the
high-level interface. These functions are not (yet) officially part of
the library, and are minimally documented here. If they break, you
get to keep all the pieces. I hope to document them properly when time
permits.
Yoshioka also contributed modifications to allow the library to be built as a Windows DLL.
The library is designed to recover cleanly in all situations, including the worst-case situation of decompressing random data. I'm not 100% sure that it can always do this, so you might want to add a signal handler to catch segmentation violations during decompression if you are feeling especially paranoid. I would be interested in hearing more about the robustness of the library to corrupted compressed data.
Version 1.0 is much more robust in this respect than 0.9.0 or 0.9.5. Investigations with Checker (a tool for detecting problems with memory management, similar to Purify) indicate that, at least for the few files I tested, all single-bit errors in the decompressed data are caught properly, with no segmentation faults, no reads of uninitialised data and no out of range reads or writes. So it's certainly much improved, although I wouldn't claim it to be totally bombproof.
The file bzlib.h contains all definitions needed to use
the library. In particular, you should definitely not include
bzlib_private.h.
In bzlib.h, the various return values are defined. The following
list is not intended as an exhaustive description of the circumstances
in which a given value may be returned -- those descriptions are given
later. Rather, it is intended to convey the rough meaning of each
return value. The first five actions are normal and not intended to
denote an error situation.
BZ_OK
BZ_RUN_OK
BZ_FLUSH_OK
BZ_FINISH_OK
BZ2_bzCompress, the requested flush/finish/nothing-special action
was completed successfully.
BZ_STREAM_END
The following return values indicate an error of some kind.
BZ_CONFIG_ERROR
sizeof(char), sizeof(short) and sizeof(int)
are not 1, 2 and 4 respectively, as they should be. Note that the
library should still work properly on 64-bit platforms which follow
the LP64 programming model -- that is, where sizeof(long)
and sizeof(void*) are 8. Under LP64, sizeof(int) is
still 4, so libbzip2, which doesn't use the long type,
is OK.
BZ_SEQUENCE_ERROR
libbzip2 checks as much as it can to ensure this is
happening, and returns BZ_SEQUENCE_ERROR if not. Code which
complies precisely with the function semantics, as detailed below,
should never receive this value; such an event denotes buggy code
which you should investigate.
BZ_PARAM_ERROR
BZ_SEQUENCE_ERROR,
this denotes a bug in the client code. The distinction between
BZ_PARAM_ERROR and BZ_SEQUENCE_ERROR is a bit hazy, but still worth
making.
BZ_MEM_ERROR
BZ2_bzDecompress and
BZ2_bzRead may return BZ_MEM_ERROR even though some of
the compressed data has been read. The same is not true for
compression; once BZ2_bzCompressInit or BZ2_bzWriteOpen have
successfully completed, BZ_MEM_ERROR cannot occur.
BZ_DATA_ERROR
BZ_DATA_ERROR_MAGIC
BZ_DATA_ERROR, it is sometimes useful to
know when the compressed stream does not start with the correct
magic bytes ('B' 'Z' 'h').
BZ_IO_ERROR
BZ2_bzRead and BZ2_bzWrite when there is an error
reading or writing in the compressed file, and by BZ2_bzReadOpen
and BZ2_bzWriteOpen for attempts to use a file for which the
error indicator (viz, ferror(f)) is set.
On receipt of BZ_IO_ERROR, the caller should consult
errno and/or perror to acquire operating-system
specific information about the problem.
BZ_UNEXPECTED_EOF
BZ2_bzRead when the compressed file finishes
before the logical end of stream is detected.
BZ_OUTBUFF_FULL
BZ2_bzBuffToBuffCompress and
BZ2_bzBuffToBuffDecompress to indicate that the output data
will not fit into the output buffer provided.
BZ2_bzCompressInit
typedef
struct {
char *next_in;
unsigned int avail_in;
unsigned int total_in_lo32;
unsigned int total_in_hi32;
char *next_out;
unsigned int avail_out;
unsigned int total_out_lo32;
unsigned int total_out_hi32;
void *state;
void *(*bzalloc)(void *,int,int);
void (*bzfree)(void *,void *);
void *opaque;
}
bz_stream;
int BZ2_bzCompressInit ( bz_stream *strm,
int blockSize100k,
int verbosity,
int workFactor );
Prepares for compression. The bz_stream structure
holds all data pertaining to the compression activity.
A bz_stream structure should be allocated and initialised
prior to the call.
The fields of bz_stream
comprise the entirety of the user-visible data. state
is a pointer to the private data structures required for compression.
Custom memory allocators are supported, via fields bzalloc,
bzfree,
and opaque. The value
opaque is passed to as the first argument to
all calls to bzalloc and bzfree, but is
otherwise ignored by the library.
The call bzalloc ( opaque, n, m ) is expected to return a
pointer p to
n * m bytes of memory, and bzfree ( opaque, p )
should free
that memory.
If you don't want to use a custom memory allocator, set bzalloc,
bzfree and
opaque to NULL,
and the library will then use the standard malloc/free
routines.
Before calling BZ2_bzCompressInit, fields bzalloc,
bzfree and opaque should
be filled appropriately, as just described. Upon return, the internal
state will have been allocated and initialised, and total_in_lo32,
total_in_hi32, total_out_lo32 and
total_out_hi32 will have been set to zero.
These four fields are used by the library
to inform the caller of the total amount of data passed into and out of
the library, respectively. You should not try to change them.
As of version 1.0, 64-bit counts are maintained, even on 32-bit
platforms, using the _hi32 fields to store the upper 32 bits
of the count. So, for example, the total amount of data in
is (total_in_hi32 << 32) + total_in_lo32.
Parameter blockSize100k specifies the block size to be used for
compression. It should be a value between 1 and 9 inclusive, and the
actual block size used is 100000 x this figure. 9 gives the best
compression but takes most memory.
Parameter verbosity should be set to a number between 0 and 4
inclusive. 0 is silent, and greater numbers give increasingly verbose
monitoring/debugging output. If the library has been compiled with
-DBZ_NO_STDIO, no such output will appear for any verbosity
setting.
Parameter workFactor controls how the compression phase behaves
when presented with worst case, highly repetitive, input data. If
compression runs into difficulties caused by repetitive data, the
library switches from the standard sorting algorithm to a fallback
algorithm. The fallback is slower than the standard algorithm by
perhaps a factor of three, but always behaves reasonably, no matter how
bad the input.
Lower values of workFactor reduce the amount of effort the
standard algorithm will expend before resorting to the fallback. You
should set this parameter carefully; too low, and many inputs will be
handled by the fallback algorithm and so compress rather slowly, too
high, and your average-to-worst case compression times can become very
large. The default value of 30 gives reasonable behaviour over a wide
range of circumstances.
Allowable values range from 0 to 250 inclusive. 0 is a special case, equivalent to using the default value of 30.
Note that the compressed output generated is the same regardless of whether or not the fallback algorithm is used.
Be aware also that this parameter may disappear entirely in future versions of the library. In principle it should be possible to devise a good way to automatically choose which algorithm to use. Such a mechanism would render the parameter obsolete.
Possible return values:
BZ_CONFIG_ERROR
if the library has been mis-compiled
BZ_PARAM_ERROR
if strm is NULL
or blockSize < 1 or blockSize > 9
or verbosity < 0 or verbosity > 4
or workFactor < 0 or workFactor > 250
BZ_MEM_ERROR
if not enough memory is available
BZ_OK
otherwise
Allowable next actions:
BZ2_bzCompress
if BZ_OK is returned
no specific action needed in case of error
BZ2_bzCompressint BZ2_bzCompress ( bz_stream *strm, int action );
Provides more input and/or output buffer space for the library. The
caller maintains input and output buffers, and calls BZ2_bzCompress to
transfer data between them.
Before each call to BZ2_bzCompress, next_in should point at
the data to be compressed, and avail_in should indicate how many
bytes the library may read. BZ2_bzCompress updates next_in,
avail_in and total_in to reflect the number of bytes it
has read.
Similarly, next_out should point to a buffer in which the
compressed data is to be placed, with avail_out indicating how
much output space is available. BZ2_bzCompress updates
next_out, avail_out and total_out to reflect the
number of bytes output.
You may provide and remove as little or as much data as you like on each
call of BZ2_bzCompress. In the limit, it is acceptable to supply and
remove data one byte at a time, although this would be terribly
inefficient. You should always ensure that at least one byte of output
space is available at each call.
A second purpose of BZ2_bzCompress is to request a change of mode of the
compressed stream.
Conceptually, a compressed stream can be in one of four states: IDLE,
RUNNING, FLUSHING and FINISHING. Before initialisation
(BZ2_bzCompressInit) and after termination (BZ2_bzCompressEnd), a
stream is regarded as IDLE.
Upon initialisation (BZ2_bzCompressInit), the stream is placed in the
RUNNING state. Subsequent calls to BZ2_bzCompress should pass
BZ_RUN as the requested action; other actions are illegal and
will result in BZ_SEQUENCE_ERROR.
At some point, the calling program will have provided all the input data
it wants to. It will then want to finish up -- in effect, asking the
library to process any data it might have buffered internally. In this
state, BZ2_bzCompress will no longer attempt to read data from
next_in, but it will want to write data to next_out.
Because the output buffer supplied by the user can be arbitrarily small,
the finishing-up operation cannot necessarily be done with a single call
of BZ2_bzCompress.
Instead, the calling program passes BZ_FINISH as an action to
BZ2_bzCompress. This changes the stream's state to FINISHING. Any
remaining input (ie, next_in[0 .. avail_in-1]) is compressed and
transferred to the output buffer. To do this, BZ2_bzCompress must be
called repeatedly until all the output has been consumed. At that
point, BZ2_bzCompress returns BZ_STREAM_END, and the stream's
state is set back to IDLE. BZ2_bzCompressEnd should then be
called.
Just to make sure the calling program does not cheat, the library makes
a note of avail_in at the time of the first call to
BZ2_bzCompress which has BZ_FINISH as an action (ie, at the
time the program has announced its intention to not supply any more
input). By comparing this value with that of avail_in over
subsequent calls to BZ2_bzCompress, the library can detect any
attempts to slip in more data to compress. Any calls for which this is
detected will return BZ_SEQUENCE_ERROR. This indicates a
programming mistake which should be corrected.
Instead of asking to finish, the calling program may ask
BZ2_bzCompress to take all the remaining input, compress it and
terminate the current (Burrows-Wheeler) compression block. This could
be useful for error control purposes. The mechanism is analogous to
that for finishing: call BZ2_bzCompress with an action of
BZ_FLUSH, remove output data, and persist with the
BZ_FLUSH action until the value BZ_RUN is returned. As
with finishing, BZ2_bzCompress detects any attempt to provide more
input data once the flush has begun.
Once the flush is complete, the stream returns to the normal RUNNING state.
This all sounds pretty complex, but isn't really. Here's a table
which shows which actions are allowable in each state, what action
will be taken, what the next state is, and what the non-error return
values are. Note that you can't explicitly ask what state the
stream is in, but nor do you need to -- it can be inferred from the
values returned by BZ2_bzCompress.
IDLE/anyIllegal. IDLE state only exists afterBZ2_bzCompressEndor beforeBZ2_bzCompressInit. Return value =BZ_SEQUENCE_ERRORRUNNING/BZ_RUNCompress fromnext_intonext_outas much as possible. Next state = RUNNING Return value =BZ_RUN_OKRUNNING/BZ_FLUSHRemember current value ofnext_in. Compress fromnext_intonext_outas much as possible, but do not accept any more input. Next state = FLUSHING Return value =BZ_FLUSH_OKRUNNING/BZ_FINISHRemember current value ofnext_in. Compress fromnext_intonext_outas much as possible, but do not accept any more input. Next state = FINISHING Return value =BZ_FINISH_OKFLUSHING/BZ_FLUSHCompress fromnext_intonext_outas much as possible, but do not accept any more input. If all the existing input has been used up and all compressed output has been removed Next state = RUNNING; Return value =BZ_RUN_OKelse Next state = FLUSHING; Return value =BZ_FLUSH_OKFLUSHING/other Illegal. Return value =BZ_SEQUENCE_ERRORFINISHING/BZ_FINISHCompress fromnext_intonext_outas much as possible, but to not accept any more input. If all the existing input has been used up and all compressed output has been removed Next state = IDLE; Return value =BZ_STREAM_ENDelse Next state = FINISHING; Return value =BZ_FINISHINGFINISHING/other Illegal. Return value =BZ_SEQUENCE_ERROR
That still looks complicated? Well, fair enough. The usual sequence of calls for compressing a load of data is:
BZ2_bzCompressInit.
BZ2_bzCompress with action = BZ_RUN.
BZ2_bzCompress with action = BZ_FINISH,
copying out the compressed output, until BZ_STREAM_END is returned.
BZ2_bzCompressEnd.
If the data you want to compress fits into your input buffer all
at once, you can skip the calls of BZ2_bzCompress ( ..., BZ_RUN ) and
just do the BZ2_bzCompress ( ..., BZ_FINISH ) calls.
All required memory is allocated by BZ2_bzCompressInit. The
compression library can accept any data at all (obviously). So you
shouldn't get any error return values from the BZ2_bzCompress calls.
If you do, they will be BZ_SEQUENCE_ERROR, and indicate a bug in
your programming.
Trivial other possible return values:
BZ_PARAM_ERROR
if strm is NULL, or strm->s is NULL
BZ2_bzCompressEndint BZ2_bzCompressEnd ( bz_stream *strm );
Releases all memory associated with a compression stream.
Possible return values:
BZ_PARAM_ERRORifstrmisNULLorstrm->sisNULLBZ_OKotherwise
BZ2_bzDecompressInitint BZ2_bzDecompressInit ( bz_stream *strm, int verbosity, int small );
Prepares for decompression. As with BZ2_bzCompressInit, a
bz_stream record should be allocated and initialised before the
call. Fields bzalloc, bzfree and opaque should be
set if a custom memory allocator is required, or made NULL for
the normal malloc/free routines. Upon return, the internal
state will have been initialised, and total_in and
total_out will be zero.
For the meaning of parameter verbosity, see BZ2_bzCompressInit.
If small is nonzero, the library will use an alternative
decompression algorithm which uses less memory but at the cost of
decompressing more slowly (roughly speaking, half the speed, but the
maximum memory requirement drops to around 2300k). See Chapter 2 for
more information on memory management.
Note that the amount of memory needed to decompress
a stream cannot be determined until the stream's header has been read,
so even if BZ2_bzDecompressInit succeeds, a subsequent
BZ2_bzDecompress could fail with BZ_MEM_ERROR.
Possible return values:
BZ_CONFIG_ERROR
if the library has been mis-compiled
BZ_PARAM_ERROR
if (small != 0 && small != 1)
or (verbosity < 0 || verbosity > 4)
BZ_MEM_ERROR
if insufficient memory is available
Allowable next actions:
BZ2_bzDecompress
if BZ_OK was returned
no specific action required in case of error
BZ2_bzDecompressint BZ2_bzDecompress ( bz_stream *strm );
Provides more input and/out output buffer space for the library. The
caller maintains input and output buffers, and uses BZ2_bzDecompress
to transfer data between them.
Before each call to BZ2_bzDecompress, next_in
should point at the compressed data,
and avail_in should indicate how many bytes the library
may read. BZ2_bzDecompress updates next_in, avail_in
and total_in
to reflect the number of bytes it has read.
Similarly, next_out should point to a buffer in which the uncompressed
output is to be placed, with avail_out indicating how much output space
is available. BZ2_bzCompress updates next_out,
avail_out and total_out to reflect
the number of bytes output.
You may provide and remove as little or as much data as you like on
each call of BZ2_bzDecompress.
In the limit, it is acceptable to
supply and remove data one byte at a time, although this would be
terribly inefficient. You should always ensure that at least one
byte of output space is available at each call.
Use of BZ2_bzDecompress is simpler than BZ2_bzCompress.
You should provide input and remove output as described above, and
repeatedly call BZ2_bzDecompress until BZ_STREAM_END is
returned. Appearance of BZ_STREAM_END denotes that
BZ2_bzDecompress has detected the logical end of the compressed
stream. BZ2_bzDecompress will not produce BZ_STREAM_END until
all output data has been placed into the output buffer, so once
BZ_STREAM_END appears, you are guaranteed to have available all
the decompressed output, and BZ2_bzDecompressEnd can safely be
called.
If case of an error return value, you should call BZ2_bzDecompressEnd
to clean up and release memory.
Possible return values:
BZ_PARAM_ERROR
if strm is NULL or strm->s is NULL
or strm->avail_out < 1
BZ_DATA_ERROR
if a data integrity error is detected in the compressed stream
BZ_DATA_ERROR_MAGIC
if the compressed stream doesn't begin with the right magic bytes
BZ_MEM_ERROR
if there wasn't enough memory available
BZ_STREAM_END
if the logical end of the data stream was detected and all
output in has been consumed, eg s->avail_out > 0
BZ_OK
otherwise
Allowable next actions:
BZ2_bzDecompress
if BZ_OK was returned
BZ2_bzDecompressEnd
otherwise
BZ2_bzDecompressEndint BZ2_bzDecompressEnd ( bz_stream *strm );
Releases all memory associated with a decompression stream.
Possible return values:
BZ_PARAM_ERROR
if strm is NULL or strm->s is NULL
BZ_OK
otherwise
Allowable next actions:
None.
This interface provides functions for reading and writing
bzip2 format files. First, some general points.
int* first argument,
bzerror.
After each call, bzerror should be consulted first to determine
the outcome of the call. If bzerror is BZ_OK,
the call completed
successfully, and only then should the return value of the function
(if any) be consulted. If bzerror is BZ_IO_ERROR,
there was an error
reading/writing the underlying compressed file, and you should
then consult errno/perror to determine the
cause of the difficulty.
bzerror may also be set to various other values; precise details are
given on a per-function basis below.
bzerror indicates an error
(ie, anything except BZ_OK and BZ_STREAM_END),
you should immediately call BZ2_bzReadClose (or BZ2_bzWriteClose,
depending on whether you are attempting to read or to write)
to free up all resources associated
with the stream. Once an error has been indicated, behaviour of all calls
except BZ2_bzReadClose (BZ2_bzWriteClose) is undefined.
The implication is that (1) bzerror should
be checked after each call, and (2) if bzerror indicates an error,
BZ2_bzReadClose (BZ2_bzWriteClose) should then be called to clean up.
FILE* arguments passed to
BZ2_bzReadOpen/BZ2_bzWriteOpen
should be set to binary mode.
Most Unix systems will do this by default, but other platforms,
including Windows and Mac, will not. If you omit this, you may
encounter problems when moving code to new platforms.
malloc/free.
At present
there is no facility for user-defined memory allocators in the file I/O
functions (could easily be added, though).
BZ2_bzReadOpen
typedef void BZFILE;
BZFILE *BZ2_bzReadOpen ( int *bzerror, FILE *f,
int small, int verbosity,
void *unused, int nUnused );
Prepare to read compressed data from file handle f. f
should refer to a file which has been opened for reading, and for which
the error indicator (ferror(f))is not set. If small is 1,
the library will try to decompress using less memory, at the expense of
speed.
For reasons explained below, BZ2_bzRead will decompress the
nUnused bytes starting at unused, before starting to read
from the file f. At most BZ_MAX_UNUSED bytes may be
supplied like this. If this facility is not required, you should pass
NULL and 0 for unused and nUnused
respectively.
For the meaning of parameters small and verbosity,
see BZ2_bzDecompressInit.
The amount of memory needed to decompress a file cannot be determined
until the file's header has been read. So it is possible that
BZ2_bzReadOpen returns BZ_OK but a subsequent call of
BZ2_bzRead will return BZ_MEM_ERROR.
Possible assignments to bzerror:
BZ_CONFIG_ERROR
if the library has been mis-compiled
BZ_PARAM_ERROR
if f is NULL
or small is neither 0 nor 1
or (unused == NULL && nUnused != 0)
or (unused != NULL && !(0 <= nUnused <= BZ_MAX_UNUSED))
BZ_IO_ERROR
if ferror(f) is nonzero
BZ_MEM_ERROR
if insufficient memory is available
BZ_OK
otherwise.
Possible return values:
Pointer to an abstract BZFILE
if bzerror is BZ_OK
NULL
otherwise
Allowable next actions:
BZ2_bzRead
if bzerror is BZ_OK
BZ2_bzClose
otherwise
BZ2_bzReadint BZ2_bzRead ( int *bzerror, BZFILE *b, void *buf, int len );
Reads up to len (uncompressed) bytes from the compressed file
b into
the buffer buf. If the read was successful,
bzerror is set to BZ_OK
and the number of bytes read is returned. If the logical end-of-stream
was detected, bzerror will be set to BZ_STREAM_END,
and the number
of bytes read is returned. All other bzerror values denote an error.
BZ2_bzRead will supply len bytes,
unless the logical stream end is detected
or an error occurs. Because of this, it is possible to detect the
stream end by observing when the number of bytes returned is
less than the number
requested. Nevertheless, this is regarded as inadvisable; you should
instead check bzerror after every call and watch out for
BZ_STREAM_END.
Internally, BZ2_bzRead copies data from the compressed file in chunks
of size BZ_MAX_UNUSED bytes
before decompressing it. If the file contains more bytes than strictly
needed to reach the logical end-of-stream, BZ2_bzRead will almost certainly
read some of the trailing data before signalling BZ_SEQUENCE_END.
To collect the read but unused data once BZ_SEQUENCE_END has
appeared, call BZ2_bzReadGetUnused immediately before BZ2_bzReadClose.
Possible assignments to bzerror:
BZ_PARAM_ERROR
if b is NULL or buf is NULL or len < 0
BZ_SEQUENCE_ERROR
if b was opened with BZ2_bzWriteOpen
BZ_IO_ERROR
if there is an error reading from the compressed file
BZ_UNEXPECTED_EOF
if the compressed file ended before the logical end-of-stream was detected
BZ_DATA_ERROR
if a data integrity error was detected in the compressed stream
BZ_DATA_ERROR_MAGIC
if the stream does not begin with the requisite header bytes (ie, is not
a bzip2 data file). This is really a special case of BZ_DATA_ERROR.
BZ_MEM_ERROR
if insufficient memory was available
BZ_STREAM_END
if the logical end of stream was detected.
BZ_OK
otherwise.
Possible return values:
number of bytes read
if bzerror is BZ_OK or BZ_STREAM_END
undefined
otherwise
Allowable next actions:
collect data from buf, then BZ2_bzRead or BZ2_bzReadClose
if bzerror is BZ_OK
collect data from buf, then BZ2_bzReadClose or BZ2_bzReadGetUnused
if bzerror is BZ_SEQUENCE_END
BZ2_bzReadClose
otherwise
BZ2_bzReadGetUnused
void BZ2_bzReadGetUnused ( int* bzerror, BZFILE *b,
void** unused, int* nUnused );
Returns data which was read from the compressed file but was not needed
to get to the logical end-of-stream. *unused is set to the address
of the data, and *nUnused to the number of bytes. *nUnused will
be set to a value between 0 and BZ_MAX_UNUSED inclusive.
This function may only be called once BZ2_bzRead has signalled
BZ_STREAM_END but before BZ2_bzReadClose.
Possible assignments to bzerror:
BZ_PARAM_ERROR
if b is NULL
or unused is NULL or nUnused is NULL
BZ_SEQUENCE_ERROR
if BZ_STREAM_END has not been signalled
or if b was opened with BZ2_bzWriteOpen
BZ_OK
otherwise
Allowable next actions:
BZ2_bzReadClose
BZ2_bzReadClosevoid BZ2_bzReadClose ( int *bzerror, BZFILE *b );
Releases all memory pertaining to the compressed file b.
BZ2_bzReadClose does not call fclose on the underlying file
handle, so you should do that yourself if appropriate.
BZ2_bzReadClose should be called to clean up after all error
situations.
Possible assignments to bzerror:
BZ_SEQUENCE_ERROR
if b was opened with BZ2_bzOpenWrite
BZ_OK
otherwise
Allowable next actions:
none
BZ2_bzWriteOpen
BZFILE *BZ2_bzWriteOpen ( int *bzerror, FILE *f,
int blockSize100k, int verbosity,
int workFactor );
Prepare to write compressed data to file handle f.
f should refer to
a file which has been opened for writing, and for which the error
indicator (ferror(f))is not set.
For the meaning of parameters blockSize100k,
verbosity and workFactor, see
BZ2_bzCompressInit.
All required memory is allocated at this stage, so if the call
completes successfully, BZ_MEM_ERROR cannot be signalled by a
subsequent call to BZ2_bzWrite.
Possible assignments to bzerror:
BZ_CONFIG_ERROR
if the library has been mis-compiled
BZ_PARAM_ERROR
if f is NULL
or blockSize100k < 1 or blockSize100k > 9
BZ_IO_ERROR
if ferror(f) is nonzero
BZ_MEM_ERROR
if insufficient memory is available
BZ_OK
otherwise
Possible return values:
Pointer to an abstract BZFILE
if bzerror is BZ_OK
NULL
otherwise
Allowable next actions:
BZ2_bzWrite
if bzerror is BZ_OK
(you could go directly to BZ2_bzWriteClose, but this would be pretty pointless)
BZ2_bzWriteClose
otherwise
BZ2_bzWritevoid BZ2_bzWrite ( int *bzerror, BZFILE *b, void *buf, int len );
Absorbs len bytes from the buffer buf, eventually to be
compressed and written to the file.
Possible assignments to bzerror:
BZ_PARAM_ERROR
if b is NULL or buf is NULL or len < 0
BZ_SEQUENCE_ERROR
if b was opened with BZ2_bzReadOpen
BZ_IO_ERROR
if there is an error writing the compressed file.
BZ_OK
otherwise
BZ2_bzWriteClose
void BZ2_bzWriteClose ( int *bzerror, BZFILE* f,
int abandon,
unsigned int* nbytes_in,
unsigned int* nbytes_out );
void BZ2_bzWriteClose64 ( int *bzerror, BZFILE* f,
int abandon,
unsigned int* nbytes_in_lo32,
unsigned int* nbytes_in_hi32,
unsigned int* nbytes_out_lo32,
unsigned int* nbytes_out_hi32 );
Compresses and flushes to the compressed file all data so far supplied
by BZ2_bzWrite. The logical end-of-stream markers are also written, so
subsequent calls to BZ2_bzWrite are illegal. All memory associated
with the compressed file b is released.
fflush is called on the
compressed file, but it is not fclose'd.
If BZ2_bzWriteClose is called to clean up after an error, the only
action is to release the memory. The library records the error codes
issued by previous calls, so this situation will be detected
automatically. There is no attempt to complete the compression
operation, nor to fflush the compressed file. You can force this
behaviour to happen even in the case of no error, by passing a nonzero
value to abandon.
If nbytes_in is non-null, *nbytes_in will be set to be the
total volume of uncompressed data handled. Similarly, nbytes_out
will be set to the total volume of compressed data written. For
compatibility with older versions of the library, BZ2_bzWriteClose
only yields the lower 32 bits of these counts. Use
BZ2_bzWriteClose64 if you want the full 64 bit counts. These
two functions are otherwise absolutely identical.
Possible assignments to bzerror:
BZ_SEQUENCE_ERROR
if b was opened with BZ2_bzReadOpen
BZ_IO_ERROR
if there is an error writing the compressed file
BZ_OK
otherwise
The high-level library facilitates use of
bzip2 data streams which form some part of a surrounding, larger
data stream.
fflushes it but does not fclose it.
The calling application can write its own data before and after the
compressed data stream, using that same file handle.
BZ2_bzRead reads from the compressed file in blocks of size
BZ_MAX_UNUSED bytes, and in doing so probably will overshoot
the logical end of compressed stream.
To recover this data once decompression has
ended, call BZ2_bzReadGetUnused after the last call of BZ2_bzRead
(the one returning BZ_STREAM_END) but before calling
BZ2_bzReadClose.
This mechanism makes it easy to decompress multiple bzip2
streams placed end-to-end. As the end of one stream, when BZ2_bzRead
returns BZ_STREAM_END, call BZ2_bzReadGetUnused to collect the
unused data (copy it into your own buffer somewhere).
That data forms the start of the next compressed stream.
To start uncompressing that next stream, call BZ2_bzReadOpen again,
feeding in the unused data via the unused/nUnused
parameters.
Keep doing this until BZ_STREAM_END return coincides with the
physical end of file (feof(f)). In this situation
BZ2_bzReadGetUnused
will of course return no data.
This should give some feel for how the high-level interface can be used. If you require extra flexibility, you'll have to bite the bullet and get to grips with the low-level interface.
Here's how you'd write data to a compressed file:
FILE* f;
BZFILE* b;
int nBuf;
char buf[ /* whatever size you like */ ];
int bzerror;
int nWritten;
f = fopen ( "myfile.bz2", "w" );
if (!f) {
/* handle error */
}
b = BZ2_bzWriteOpen ( &bzerror, f, 9 );
if (bzerror != BZ_OK) {
BZ2_bzWriteClose ( b );
/* handle error */
}
while ( /* condition */ ) {
/* get data to write into buf, and set nBuf appropriately */
nWritten = BZ2_bzWrite ( &bzerror, b, buf, nBuf );
if (bzerror == BZ_IO_ERROR) {
BZ2_bzWriteClose ( &bzerror, b );
/* handle error */
}
}
BZ2_bzWriteClose ( &bzerror, b );
if (bzerror == BZ_IO_ERROR) {
/* handle error */
}
And to read from a compressed file:
FILE* f;
BZFILE* b;
int nBuf;
char buf[ /* whatever size you like */ ];
int bzerror;
int nWritten;
f = fopen ( "myfile.bz2", "r" );
if (!f) {
/* handle error */
}
b = BZ2_bzReadOpen ( &bzerror, f, 0, NULL, 0 );
if (bzerror != BZ_OK) {
BZ2_bzReadClose ( &bzerror, b );
/* handle error */
}
bzerror = BZ_OK;
while (bzerror == BZ_OK && /* arbitrary other conditions */) {
nBuf = BZ2_bzRead ( &bzerror, b, buf, /* size of buf */ );
if (bzerror == BZ_OK) {
/* do something with buf[0 .. nBuf-1] */
}
}
if (bzerror != BZ_STREAM_END) {
BZ2_bzReadClose ( &bzerror, b );
/* handle error */
} else {
BZ2_bzReadClose ( &bzerror );
}
BZ2_bzBuffToBuffCompress
int BZ2_bzBuffToBuffCompress( char* dest,
unsigned int* destLen,
char* source,
unsigned int sourceLen,
int blockSize100k,
int verbosity,
int workFactor );
Attempts to compress the data in source[0 .. sourceLen-1]
into the destination buffer, dest[0 .. *destLen-1].
If the destination buffer is big enough, *destLen is
set to the size of the compressed data, and BZ_OK is
returned. If the compressed data won't fit, *destLen
is unchanged, and BZ_OUTBUFF_FULL is returned.
Compression in this manner is a one-shot event, done with a single call
to this function. The resulting compressed data is a complete
bzip2 format data stream. There is no mechanism for making
additional calls to provide extra input data. If you want that kind of
mechanism, use the low-level interface.
For the meaning of parameters blockSize100k, verbosity
and workFactor,
see BZ2_bzCompressInit.
To guarantee that the compressed data will fit in its buffer, allocate an output buffer of size 1% larger than the uncompressed data, plus six hundred extra bytes.
BZ2_bzBuffToBuffDecompress will not write data at or
beyond dest[*destLen], even in case of buffer overflow.
Possible return values:
BZ_CONFIG_ERROR
if the library has been mis-compiled
BZ_PARAM_ERROR
if dest is NULL or destLen is NULL
or blockSize100k < 1 or blockSize100k > 9
or verbosity < 0 or verbosity > 4
or workFactor < 0 or workFactor > 250
BZ_MEM_ERROR
if insufficient memory is available
BZ_OUTBUFF_FULL
if the size of the compressed data exceeds *destLen
BZ_OK
otherwise
BZ2_bzBuffToBuffDecompress
int BZ2_bzBuffToBuffDecompress ( char* dest,
unsigned int* destLen,
char* source,
unsigned int sourceLen,
int small,
int verbosity );
Attempts to decompress the data in source[0 .. sourceLen-1]
into the destination buffer, dest[0 .. *destLen-1].
If the destination buffer is big enough, *destLen is
set to the size of the uncompressed data, and BZ_OK is
returned. If the compressed data won't fit, *destLen
is unchanged, and BZ_OUTBUFF_FULL is returned.
source is assumed to hold a complete bzip2 format
data stream.
BZ2_bzBuffToBuffDecompress tries to decompress
the entirety of the stream into the output buffer.
For the meaning of parameters small and verbosity,
see BZ2_bzDecompressInit.
Because the compression ratio of the compressed data cannot be known in advance, there is no easy way to guarantee that the output buffer will be big enough. You may of course make arrangements in your code to record the size of the uncompressed data, but such a mechanism is beyond the scope of this library.
BZ2_bzBuffToBuffDecompress will not write data at or
beyond dest[*destLen], even in case of buffer overflow.
Possible return values:
BZ_CONFIG_ERROR
if the library has been mis-compiled
BZ_PARAM_ERROR
if dest is NULL or destLen is NULL
or small != 0 && small != 1
or verbosity < 0 or verbosity > 4
BZ_MEM_ERROR
if insufficient memory is available
BZ_OUTBUFF_FULL
if the size of the compressed data exceeds *destLen
BZ_DATA_ERROR
if a data integrity error was detected in the compressed data
BZ_DATA_ERROR_MAGIC
if the compressed data doesn't begin with the right magic bytes
BZ_UNEXPECTED_EOF
if the compressed data ends unexpectedly
BZ_OK
otherwise
zlib compatibility functions
Yoshioka Tsuneo has contributed some functions to
give better zlib compatibility. These functions are
BZ2_bzopen, BZ2_bzread, BZ2_bzwrite, BZ2_bzflush,
BZ2_bzclose,
BZ2_bzerror and BZ2_bzlibVersion.
These functions are not (yet) officially part of
the library. If they break, you get to keep all the pieces.
Nevertheless, I think they work ok.
typedef void BZFILE; const char * BZ2_bzlibVersion ( void );
Returns a string indicating the library version.
BZFILE * BZ2_bzopen ( const char *path, const char *mode ); BZFILE * BZ2_bzdopen ( int fd, const char *mode );
Opens a .bz2 file for reading or writing, using either its name
or a pre-existing file descriptor.
Analogous to fopen and fdopen.
int BZ2_bzread ( BZFILE* b, void* buf, int len ); int BZ2_bzwrite ( BZFILE* b, void* buf, int len );
Reads/writes data from/to a previously opened BZFILE.
Analogous to fread and fwrite.
int BZ2_bzflush ( BZFILE* b ); void BZ2_bzclose ( BZFILE* b );
Flushes/closes a BZFILE. BZ2_bzflush doesn't actually do
anything. Analogous to fflush and fclose.
const char * BZ2_bzerror ( BZFILE *b, int *errnum )
Returns a string describing the more recent error status of
b, and also sets *errnum to its numerical value.
stdio-free environmentstdio
In a deeply embedded application, you might want to use just
the memory-to-memory functions. You can do this conveniently
by compiling the library with preprocessor symbol BZ_NO_STDIO
defined. Doing this gives you a library containing only the following
eight functions:
BZ2_bzCompressInit, BZ2_bzCompress, BZ2_bzCompressEnd
BZ2_bzDecompressInit, BZ2_bzDecompress, BZ2_bzDecompressEnd
BZ2_bzBuffToBuffCompress, BZ2_bzBuffToBuffDecompress
When compiled like this, all functions will ignore verbosity
settings.
libbzip2 contains a number of internal assertion checks which
should, needless to say, never be activated. Nevertheless, if an
assertion should fail, behaviour depends on whether or not the library
was compiled with BZ_NO_STDIO set.
For a normal compile, an assertion failure yields the message
bzip2/libbzip2: internal error number N. This is a bug in bzip2/libbzip2, 1.0 of 21-Mar-2000. Please report it to me at: jseward@acm.org. If this happened when you were using some program which uses libbzip2 as a component, you should also report this bug to the author(s) of that program. Please make an effort to report this bug; timely and accurate bug reports eventually lead to higher quality software. Thanks. Julian Seward, 21 March 2000.
where N is some error code number. exit(3)
is then called.
For a stdio-free library, assertion failures result
in a call to a function declared as:
extern void bz_internal_error ( int errcode );
The relevant code is passed as a parameter. You should supply such a function.
In either case, once an assertion failure has occurred, any
bz_stream records involved can be regarded as invalid.
You should not attempt to resume normal operation with them.
You may, of course, change critical error handling to suit your needs. As I said above, critical errors indicate bugs in the library and should not occur. All "normal" error situations are indicated via error return codes from functions, and can be recovered from.
Everything related to Windows has been contributed by Yoshioka Tsuneo
(QWF00133@niftyserve.or.jp /
tsuneo-y@is.aist-nara.ac.jp), so you should send your queries to
him (but perhaps Cc: me, jseward@acm.org).
My vague understanding of what to do is: using Visual C++ 5.0,
open the project file libbz2.dsp, and build. That's all.
If you can't
open the project file for some reason, make a new one, naming these files:
blocksort.c, bzlib.c, compress.c,
crctable.c, decompress.c, huffman.c,
randtable.c and libbz2.def. You will also need
to name the header files bzlib.h and bzlib_private.h.
If you don't use VC++, you may need to define the proprocessor symbol
_WIN32.
Finally, dlltest.c is a sample program using the DLL. It has a
project file, dlltest.dsp.
If you just want a makefile for Visual C, have a look at
makefile.msc.
Be aware that if you compile bzip2 itself on Win32, you must set
BZ_UNIX to 0 and BZ_LCCWIN32 to 1, in the file
bzip2.c, before compiling. Otherwise the resulting binary won't
work correctly.
I haven't tried any of this stuff myself, but it all looks plausible.
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