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This is lzlib.info, produced by makeinfo version 4.13+ from lzlib.texi.
INFO-DIR-SECTION Compression
START-INFO-DIR-ENTRY
* Lzlib: (lzlib). Compression library for the lzip format
END-INFO-DIR-ENTRY
File: lzlib.info, Node: Top, Next: Introduction, Up: (dir)
Lzlib Manual
************
This manual is for Lzlib (version 1.13, 23 January 2022).
* Menu:
* Introduction:: Purpose and features of lzlib
* Library version:: Checking library version
* Buffering:: Sizes of lzlib's buffers
* Parameter limits:: Min / max values for some parameters
* Compression functions:: Descriptions of the compression functions
* Decompression functions:: Descriptions of the decompression functions
* Error codes:: Meaning of codes returned by functions
* Error messages:: Error messages corresponding to error codes
* Invoking minilzip:: Command line interface of the test program
* Data format:: Detailed format of the compressed data
* Examples:: A small tutorial with examples
* Problems:: Reporting bugs
* Concept index:: Index of concepts
Copyright (C) 2009-2022 Antonio Diaz Diaz.
This manual is free documentation: you have unlimited permission to copy,
distribute, and modify it.
File: lzlib.info, Node: Introduction, Next: Library version, Prev: Top, Up: Top
1 Introduction
**************
Lzlib is a data compression library providing in-memory LZMA compression and
decompression functions, including integrity checking of the decompressed
data. The compressed data format used by the library is the lzip format.
Lzlib is written in C.
The lzip file format is designed for data sharing and long-term
archiving, taking into account both data integrity and decoder availability:
* The lzip format provides very safe integrity checking and some data
recovery means. The program lziprecover can repair bit flip errors
(one of the most common forms of data corruption) in lzip files, and
provides data recovery capabilities, including error-checked merging
of damaged copies of a file. *Note Data safety: (lziprecover)Data
safety.
* The lzip format is as simple as possible (but not simpler). The lzip
manual provides the source code of a simple decompressor along with a
detailed explanation of how it works, so that with the only help of the
lzip manual it would be possible for a digital archaeologist to extract
the data from a lzip file long after quantum computers eventually
render LZMA obsolete.
* Additionally the lzip reference implementation is copylefted, which
guarantees that it will remain free forever.
A nice feature of the lzip format is that a corrupt byte is easier to
repair the nearer it is from the beginning of the file. Therefore, with the
help of lziprecover, losing an entire archive just because of a corrupt
byte near the beginning is a thing of the past.
The functions and variables forming the interface of the compression
library are declared in the file 'lzlib.h'. Usage examples of the library
are given in the files 'bbexample.c', 'ffexample.c', and 'minilzip.c' from
the source distribution.
All the library functions are thread safe. The library does not install
any signal handler. The decoder checks the consistency of the compressed
data, so the library should never crash even in case of corrupted input.
Compression/decompression is done by repeatedly calling a couple of
read/write functions until all the data have been processed by the library.
This interface is safer and less error prone than the traditional zlib
interface.
Compression/decompression is done when the read function is called. This
means the value returned by the position functions will not be updated until
a read call, even if a lot of data are written. If you want the data to be
compressed in advance, just call the read function with a SIZE equal to 0.
If all the data to be compressed are written in advance, lzlib will
automatically adjust the header of the compressed data to use the largest
dictionary size that does not exceed neither the data size nor the limit
given to 'LZ_compress_open'. This feature reduces the amount of memory
needed for decompression and allows minilzip to produce identical compressed
output as lzip.
Lzlib will correctly decompress a data stream which is the concatenation
of two or more compressed data streams. The result is the concatenation of
the corresponding decompressed data streams. Integrity testing of
concatenated compressed data streams is also supported.
Lzlib is able to compress and decompress streams of unlimited size by
automatically creating multimember output. The members so created are large,
about 2 PiB each.
In spite of its name (Lempel-Ziv-Markov chain-Algorithm), LZMA is not a
concrete algorithm; it is more like "any algorithm using the LZMA coding
scheme". For example, the option '-0' of lzip uses the scheme in almost the
simplest way possible; issuing the longest match it can find, or a literal
byte if it can't find a match. Inversely, a much more elaborated way of
finding coding sequences of minimum size than the one currently used by lzip
could be developed, and the resulting sequence could also be coded using the
LZMA coding scheme.
Lzlib currently implements two variants of the LZMA algorithm: fast
(used by option '-0' of minilzip) and normal (used by all other compression
levels).
The high compression of LZMA comes from combining two basic, well-proven
compression ideas: sliding dictionaries (LZ77/78) and markov models (the
thing used by every compression algorithm that uses a range encoder or
similar order-0 entropy coder as its last stage) with segregation of
contexts according to what the bits are used for.
The ideas embodied in lzlib are due to (at least) the following people:
Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey Markov (for the
definition of Markov chains), G.N.N. Martin (for the definition of range
encoding), Igor Pavlov (for putting all the above together in LZMA), and
Julian Seward (for bzip2's CLI).
LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never
have been compressed. Decompressed is used to refer to data which have
undergone the process of decompression.
File: lzlib.info, Node: Library version, Next: Buffering, Prev: Introduction, Up: Top
2 Library version
*****************
One goal of lzlib is to keep perfect backward compatibility with older
versions of itself down to 1.0. Any application working with an older lzlib
should work with a newer lzlib. Installing a newer lzlib should not break
anything. This chapter describes the constants and functions that the
application can use to discover the version of the library being used. All
of them are declared in 'lzlib.h'.
-- Constant: LZ_API_VERSION
This constant is defined in 'lzlib.h' and works as a version test
macro. The application should verify at compile time that
LZ_API_VERSION is greater than or equal to the version required by the
application:
#if !defined LZ_API_VERSION || LZ_API_VERSION < 1012
#error "lzlib 1.12 or newer needed."
#endif
Before version 1.8, lzlib didn't define LZ_API_VERSION.
LZ_API_VERSION was first defined in lzlib 1.8 to 1.
Since lzlib 1.12, LZ_API_VERSION is defined as (major * 1000 + minor).
NOTE: Version test macros are the library's way of announcing
functionality to the application. They should not be confused with feature
test macros, which allow the application to announce to the library its
desire to have certain symbols and prototypes exposed.
-- Function: int LZ_api_version ( void )
If LZ_API_VERSION >= 1012, this function is declared in 'lzlib.h' (else
it doesn't exist). It returns the LZ_API_VERSION of the library object
code being used. The application should verify at run time that the
value returned by 'LZ_api_version' is greater than or equal to the
version required by the application. An application may be dinamically
linked at run time with a different version of lzlib than the one it
was compiled for, and this should not break the program as long as the
library used provides the functionality required by the application.
#if defined LZ_API_VERSION && LZ_API_VERSION >= 1012
if( LZ_api_version() < 1012 )
show_error( "lzlib 1.12 or newer needed." );
#endif
-- Constant: const char * LZ_version_string
This string constant is defined in the header file 'lzlib.h' and
represents the version of the library being used at compile time.
-- Function: const char * LZ_version ( void )
This function returns a string representing the version of the library
being used at run time.
File: lzlib.info, Node: Buffering, Next: Parameter limits, Prev: Library version, Up: Top
3 Buffering
***********
Lzlib internal functions need access to a memory chunk at least as large as
the dictionary size (sliding window). For efficiency reasons, the input
buffer for compression is twice or sixteen times as large as the dictionary
size.
Finally, for safety reasons, lzlib uses two more internal buffers.
These are the four buffers used by lzlib, and their guaranteed minimum
sizes:
* Input compression buffer. Written to by the function
'LZ_compress_write'. For the normal variant of LZMA, its size is two
times the dictionary size set with the function 'LZ_compress_open' or
64 KiB, whichever is larger. For the fast variant, its size is 1 MiB.
* Output compression buffer. Read from by the function
'LZ_compress_read'. Its size is 64 KiB.
* Input decompression buffer. Written to by the function
'LZ_decompress_write'. Its size is 64 KiB.
* Output decompression buffer. Read from by the function
'LZ_decompress_read'. Its size is the dictionary size set in the header
of the member currently being decompressed or 64 KiB, whichever is
larger.
File: lzlib.info, Node: Parameter limits, Next: Compression functions, Prev: Buffering, Up: Top
4 Parameter limits
******************
These functions provide minimum and maximum values for some parameters.
Current values are shown in square brackets.
-- Function: int LZ_min_dictionary_bits ( void )
Returns the base 2 logarithm of the smallest valid dictionary size
[12].
-- Function: int LZ_min_dictionary_size ( void )
Returns the smallest valid dictionary size [4 KiB].
-- Function: int LZ_max_dictionary_bits ( void )
Returns the base 2 logarithm of the largest valid dictionary size [29].
-- Function: int LZ_max_dictionary_size ( void )
Returns the largest valid dictionary size [512 MiB].
-- Function: int LZ_min_match_len_limit ( void )
Returns the smallest valid match length limit [5].
-- Function: int LZ_max_match_len_limit ( void )
Returns the largest valid match length limit [273].
File: lzlib.info, Node: Compression functions, Next: Decompression functions, Prev: Parameter limits, Up: Top
5 Compression functions
***********************
These are the functions used to compress data. In case of error, all of
them return -1 or 0, for signed and unsigned return values respectively,
except 'LZ_compress_open' whose return value must be verified by calling
'LZ_compress_errno' before using it.
-- Function: struct LZ_Encoder * LZ_compress_open ( const int
DICTIONARY_SIZE, const int MATCH_LEN_LIMIT, const unsigned long
long MEMBER_SIZE )
Initializes the internal stream state for compression and returns a
pointer that can only be used as the ENCODER argument for the other
LZ_compress functions, or a null pointer if the encoder could not be
allocated.
The returned pointer must be verified by calling 'LZ_compress_errno'
before using it. If 'LZ_compress_errno' does not return 'LZ_ok', the
returned pointer must not be used and should be freed with
'LZ_compress_close' to avoid memory leaks.
DICTIONARY_SIZE sets the dictionary size to be used, in bytes. Valid
values range from 4 KiB to 512 MiB. Note that dictionary sizes are
quantized. If the size specified does not match one of the valid
sizes, it will be rounded upwards by adding up to
(DICTIONARY_SIZE / 8) to it.
MATCH_LEN_LIMIT sets the match length limit in bytes. Valid values
range from 5 to 273. Larger values usually give better compression
ratios but longer compression times.
If DICTIONARY_SIZE is 65535 and MATCH_LEN_LIMIT is 16, the fast
variant of LZMA is chosen, which produces identical compressed output
as 'lzip -0'. (The dictionary size used will be rounded upwards to
64 KiB).
MEMBER_SIZE sets the member size limit in bytes. Valid values range
from 4 KiB to 2 PiB. A small member size may degrade compression
ratio, so use it only when needed. To produce a single-member data
stream, give MEMBER_SIZE a value larger than the amount of data to be
produced. Values larger than 2 PiB will be reduced to 2 PiB to prevent
the uncompressed size of the member from overflowing.
-- Function: int LZ_compress_close ( struct LZ_Encoder * const ENCODER )
Frees all dynamically allocated data structures for this stream. This
function discards any unprocessed input and does not flush any pending
output. After a call to 'LZ_compress_close', ENCODER can no longer be
used as an argument to any LZ_compress function. It is safe to call
'LZ_compress_close' with a null argument.
-- Function: int LZ_compress_finish ( struct LZ_Encoder * const ENCODER )
Use this function to tell 'lzlib' that all the data for this member
have already been written (with the function 'LZ_compress_write'). It
is safe to call 'LZ_compress_finish' as many times as needed. After
all the compressed data have been read with 'LZ_compress_read' and
'LZ_compress_member_finished' returns 1, a new member can be started
with 'LZ_compress_restart_member'.
-- Function: int LZ_compress_restart_member ( struct LZ_Encoder * const
ENCODER, const unsigned long long MEMBER_SIZE )
Use this function to start a new member in a multimember data stream.
Call this function only after 'LZ_compress_member_finished' indicates
that the current member has been fully read (with the function
'LZ_compress_read'). *Note member_size::, for a description of
MEMBER_SIZE.
-- Function: int LZ_compress_sync_flush ( struct LZ_Encoder * const
ENCODER )
Use this function to make available to 'LZ_compress_read' all the data
already written with the function 'LZ_compress_write'. First call
'LZ_compress_sync_flush'. Then call 'LZ_compress_read' until it
returns 0.
This function writes at least one LZMA marker '3' ("Sync Flush" marker)
to the compressed output. Note that the sync flush marker is not
allowed in lzip files; it is a device for interactive communication
between applications using lzlib, but is useless and wasteful in a
file, and is excluded from the media type 'application/lzip'. The LZMA
marker '2' ("End Of Stream" marker) is the only marker allowed in lzip
files. *Note Data format::.
Repeated use of 'LZ_compress_sync_flush' may degrade compression
ratio, so use it only when needed. If the interval between calls to
'LZ_compress_sync_flush' is large (comparable to dictionary size),
creating a multimember data stream with 'LZ_compress_restart_member'
may be an alternative.
Combining multimember stream creation with flushing may be tricky. If
there are more bytes available than those needed to complete
MEMBER_SIZE, 'LZ_compress_restart_member' needs to be called when
'LZ_compress_member_finished' returns 1, followed by a new call to
'LZ_compress_sync_flush'.
-- Function: int LZ_compress_read ( struct LZ_Encoder * const ENCODER,
uint8_t * const BUFFER, const int SIZE )
Reads up to SIZE bytes from the stream pointed to by ENCODER, storing
the results in BUFFER. If LZ_API_VERSION >= 1012, BUFFER may be a null
pointer, in which case the bytes read are discarded.
Returns the number of bytes actually read. This might be less than
SIZE; for example, if there aren't that many bytes left in the stream
or if more bytes have to be yet written with the function
'LZ_compress_write'. Note that reading less than SIZE bytes is not an
error.
-- Function: int LZ_compress_write ( struct LZ_Encoder * const ENCODER,
uint8_t * const BUFFER, const int SIZE )
Writes up to SIZE bytes from BUFFER to the stream pointed to by
ENCODER. Returns the number of bytes actually written. This might be
less than SIZE. Note that writing less than SIZE bytes is not an error.
-- Function: int LZ_compress_write_size ( struct LZ_Encoder * const
ENCODER )
Returns the maximum number of bytes that can be immediately written
through 'LZ_compress_write'. For efficiency reasons, once the input
buffer is full and 'LZ_compress_write_size' returns 0, almost all the
buffer must be compressed before a size greater than 0 is returned
again. (This is done to minimize the amount of data that must be
copied to the beginning of the buffer before new data can be accepted).
It is guaranteed that an immediate call to 'LZ_compress_write' will
accept a SIZE up to the returned number of bytes.
-- Function: enum LZ_Errno LZ_compress_errno ( struct LZ_Encoder * const
ENCODER )
Returns the current error code for ENCODER. *Note Error codes::. It is
safe to call 'LZ_compress_errno' with a null argument, in which case
it returns 'LZ_bad_argument'.
-- Function: int LZ_compress_finished ( struct LZ_Encoder * const ENCODER )
Returns 1 if all the data have been read and 'LZ_compress_close' can
be safely called. Otherwise it returns 0. 'LZ_compress_finished'
implies 'LZ_compress_member_finished'.
-- Function: int LZ_compress_member_finished ( struct LZ_Encoder * const
ENCODER )
Returns 1 if the current member, in a multimember data stream, has been
fully read and 'LZ_compress_restart_member' can be safely called.
Otherwise it returns 0.
-- Function: unsigned long long LZ_compress_data_position ( struct
LZ_Encoder * const ENCODER )
Returns the number of input bytes already compressed in the current
member.
-- Function: unsigned long long LZ_compress_member_position ( struct
LZ_Encoder * const ENCODER )
Returns the number of compressed bytes already produced, but perhaps
not yet read, in the current member.
-- Function: unsigned long long LZ_compress_total_in_size ( struct
LZ_Encoder * const ENCODER )
Returns the total number of input bytes already compressed.
-- Function: unsigned long long LZ_compress_total_out_size ( struct
LZ_Encoder * const ENCODER )
Returns the total number of compressed bytes already produced, but
perhaps not yet read.
File: lzlib.info, Node: Decompression functions, Next: Error codes, Prev: Compression functions, Up: Top
6 Decompression functions
*************************
These are the functions used to decompress data. In case of error, all of
them return -1 or 0, for signed and unsigned return values respectively,
except 'LZ_decompress_open' whose return value must be verified by calling
'LZ_decompress_errno' before using it.
-- Function: struct LZ_Decoder * LZ_decompress_open ( void )
Initializes the internal stream state for decompression and returns a
pointer that can only be used as the DECODER argument for the other
LZ_decompress functions, or a null pointer if the decoder could not be
allocated.
The returned pointer must be verified by calling 'LZ_decompress_errno'
before using it. If 'LZ_decompress_errno' does not return 'LZ_ok', the
returned pointer must not be used and should be freed with
'LZ_decompress_close' to avoid memory leaks.
-- Function: int LZ_decompress_close ( struct LZ_Decoder * const DECODER )
Frees all dynamically allocated data structures for this stream. This
function discards any unprocessed input and does not flush any pending
output. After a call to 'LZ_decompress_close', DECODER can no longer
be used as an argument to any LZ_decompress function. It is safe to
call 'LZ_decompress_close' with a null argument.
-- Function: int LZ_decompress_finish ( struct LZ_Decoder * const DECODER )
Use this function to tell 'lzlib' that all the data for this stream
have already been written (with the function 'LZ_decompress_write').
It is safe to call 'LZ_decompress_finish' as many times as needed. It
is not required to call 'LZ_decompress_finish' if the input stream
only contains whole members, but not calling it prevents lzlib from
detecting a truncated member.
-- Function: int LZ_decompress_reset ( struct LZ_Decoder * const DECODER )
Resets the internal state of DECODER as it was just after opening it
with the function 'LZ_decompress_open'. Data stored in the internal
buffers is discarded. Position counters are set to 0.
-- Function: int LZ_decompress_sync_to_member ( struct LZ_Decoder * const
DECODER )
Resets the error state of DECODER and enters a search state that lasts
until a new member header (or the end of the stream) is found. After a
successful call to 'LZ_decompress_sync_to_member', data written with
'LZ_decompress_write' will be consumed and 'LZ_decompress_read' will
return 0 until a header is found.
This function is useful to discard any data preceding the first member,
or to discard the rest of the current member, for example in case of a
data error. If the decoder is already at the beginning of a member,
this function does nothing.
-- Function: int LZ_decompress_read ( struct LZ_Decoder * const DECODER,
uint8_t * const BUFFER, const int SIZE )
Reads up to SIZE bytes from the stream pointed to by DECODER, storing
the results in BUFFER. If LZ_API_VERSION >= 1012, BUFFER may be a null
pointer, in which case the bytes read are discarded.
Returns the number of bytes actually read. This might be less than
SIZE; for example, if there aren't that many bytes left in the stream
or if more bytes have to be yet written with the function
'LZ_decompress_write'. Note that reading less than SIZE bytes is not
an error.
'LZ_decompress_read' returns at least once per member so that
'LZ_decompress_member_finished' can be called (and trailer data
retrieved) for each member, even for empty members. Therefore,
'LZ_decompress_read' returning 0 does not mean that the end of the
stream has been reached. The increase in the value returned by
'LZ_decompress_total_in_size' can be used to tell the end of the stream
from an empty member.
In case of decompression error caused by corrupt or truncated data,
'LZ_decompress_read' does not signal the error immediately to the
application, but waits until all the bytes decoded have been read. This
allows tools like tarlz to recover as much data as possible from each
damaged member. *Note tarlz manual: (tarlz)Top.
-- Function: int LZ_decompress_write ( struct LZ_Decoder * const DECODER,
uint8_t * const BUFFER, const int SIZE )
Writes up to SIZE bytes from BUFFER to the stream pointed to by
DECODER. Returns the number of bytes actually written. This might be
less than SIZE. Note that writing less than SIZE bytes is not an error.
-- Function: int LZ_decompress_write_size ( struct LZ_Decoder * const
DECODER )
Returns the maximum number of bytes that can be immediately written
through 'LZ_decompress_write'. This number varies smoothly; each
compressed byte consumed may be overwritten immediately, increasing by
1 the value returned.
It is guaranteed that an immediate call to 'LZ_decompress_write' will
accept a SIZE up to the returned number of bytes.
-- Function: enum LZ_Errno LZ_decompress_errno ( struct LZ_Decoder * const
DECODER )
Returns the current error code for DECODER. *Note Error codes::. It is
safe to call 'LZ_decompress_errno' with a null argument, in which case
it returns 'LZ_bad_argument'.
-- Function: int LZ_decompress_finished ( struct LZ_Decoder * const
DECODER )
Returns 1 if all the data have been read and 'LZ_decompress_close' can
be safely called. Otherwise it returns 0. 'LZ_decompress_finished'
does not imply 'LZ_decompress_member_finished'.
-- Function: int LZ_decompress_member_finished ( struct LZ_Decoder * const
DECODER )
Returns 1 if the previous call to 'LZ_decompress_read' finished reading
the current member, indicating that final values for the member are
available through 'LZ_decompress_data_crc',
'LZ_decompress_data_position', and 'LZ_decompress_member_position'.
Otherwise it returns 0.
-- Function: int LZ_decompress_member_version ( struct LZ_Decoder * const
DECODER )
Returns the version of the current member, read from the member header.
-- Function: int LZ_decompress_dictionary_size ( struct LZ_Decoder * const
DECODER )
Returns the dictionary size of the current member, read from the
member header.
-- Function: unsigned LZ_decompress_data_crc ( struct LZ_Decoder * const
DECODER )
Returns the 32 bit Cyclic Redundancy Check of the data decompressed
from the current member. The value returned is valid only when
'LZ_decompress_member_finished' returns 1.
-- Function: unsigned long long LZ_decompress_data_position ( struct
LZ_Decoder * const DECODER )
Returns the number of decompressed bytes already produced, but perhaps
not yet read, in the current member.
-- Function: unsigned long long LZ_decompress_member_position ( struct
LZ_Decoder * const DECODER )
Returns the number of input bytes already decompressed in the current
member.
-- Function: unsigned long long LZ_decompress_total_in_size ( struct
LZ_Decoder * const DECODER )
Returns the total number of input bytes already decompressed.
-- Function: unsigned long long LZ_decompress_total_out_size ( struct
LZ_Decoder * const DECODER )
Returns the total number of decompressed bytes already produced, but
perhaps not yet read.
File: lzlib.info, Node: Error codes, Next: Error messages, Prev: Decompression functions, Up: Top
7 Error codes
*************
Most library functions return -1 to indicate that they have failed. But
this return value only tells you that an error has occurred. To find out
what kind of error it was, you need to verify the error code by calling
'LZ_(de)compress_errno'.
Library functions don't change the value returned by
'LZ_(de)compress_errno' when they succeed; thus, the value returned by
'LZ_(de)compress_errno' after a successful call is not necessarily LZ_ok,
and you should not use 'LZ_(de)compress_errno' to determine whether a call
failed. If the call failed, then you can examine 'LZ_(de)compress_errno'.
The error codes are defined in the header file 'lzlib.h'.
-- Constant: enum LZ_Errno LZ_ok
The value of this constant is 0 and is used to indicate that there is
no error.
-- Constant: enum LZ_Errno LZ_bad_argument
At least one of the arguments passed to the library function was
invalid.
-- Constant: enum LZ_Errno LZ_mem_error
No memory available. The system cannot allocate more virtual memory
because its capacity is full.
-- Constant: enum LZ_Errno LZ_sequence_error
A library function was called in the wrong order. For example
'LZ_compress_restart_member' was called before
'LZ_compress_member_finished' indicates that the current member is
finished.
-- Constant: enum LZ_Errno LZ_header_error
An invalid member header (one with the wrong magic bytes) was read. If
this happens at the end of the data stream it may indicate trailing
data.
-- Constant: enum LZ_Errno LZ_unexpected_eof
The end of the data stream was reached in the middle of a member.
-- Constant: enum LZ_Errno LZ_data_error
The data stream is corrupt. If 'LZ_decompress_member_position' is 6 or
less, it indicates either a format version not supported, an invalid
dictionary size, a corrupt header in a multimember data stream, or
trailing data too similar to a valid lzip header. Lziprecover can be
used to remove conflicting trailing data from a file.
-- Constant: enum LZ_Errno LZ_library_error
A bug was detected in the library. Please, report it. *Note Problems::.
File: lzlib.info, Node: Error messages, Next: Invoking minilzip, Prev: Error codes, Up: Top
8 Error messages
****************
-- Function: const char * LZ_strerror ( const enum LZ_Errno LZ_ERRNO )
Returns the standard error message for a given error code. The messages
are fairly short; there are no multi-line messages or embedded
newlines. This function makes it easy for your program to report
informative error messages about the failure of a library call.
The value of LZ_ERRNO normally comes from a call to
'LZ_(de)compress_errno'.
File: lzlib.info, Node: Invoking minilzip, Next: Data format, Prev: Error messages, Up: Top
9 Invoking minilzip
*******************
Minilzip is a test program for the compression library lzlib, fully
compatible with lzip 1.4 or newer.
Lzip is a lossless data compressor with a user interface similar to the
one of gzip or bzip2. Lzip uses a simplified form of the 'Lempel-Ziv-Markov
chain-Algorithm' (LZMA) stream format and provides a 3 factor integrity
checking to maximize interoperability and optimize safety. Lzip can compress
about as fast as gzip (lzip -0) or compress most files more than bzip2
(lzip -9). Decompression speed is intermediate between gzip and bzip2. Lzip
is better than gzip and bzip2 from a data recovery perspective. Lzip has
been designed, written, and tested with great care to replace gzip and
bzip2 as the standard general-purpose compressed format for unix-like
systems.
The format for running minilzip is:
minilzip [OPTIONS] [FILES]
If no file names are specified, minilzip compresses (or decompresses) from
standard input to standard output. A hyphen '-' used as a FILE argument
means standard input. It can be mixed with other FILES and is read just
once, the first time it appears in the command line.
minilzip supports the following options: *Note Argument syntax:
(arg_parser)Argument syntax.
'-h'
'--help'
Print an informative help message describing the options and exit.
'-V'
'--version'
Print the version number of minilzip on the standard output and exit.
This version number should be included in all bug reports.
'-a'
'--trailing-error'
Exit with error status 2 if any remaining input is detected after
decompressing the last member. Such remaining input is usually trailing
garbage that can be safely ignored.
'-b BYTES'
'--member-size=BYTES'
When compressing, set the member size limit to BYTES. It is advisable
to keep members smaller than RAM size so that they can be repaired with
lziprecover in case of corruption. A small member size may degrade
compression ratio, so use it only when needed. Valid values range from
100 kB to 2 PiB. Defaults to 2 PiB.
'-c'
'--stdout'
Compress or decompress to standard output; keep input files unchanged.
If compressing several files, each file is compressed independently.
(The output consists of a sequence of independently compressed
members). This option (or '-o') is needed when reading from a named
pipe (fifo) or from a device. Use it also to recover as much of the
decompressed data as possible when decompressing a corrupt file. '-c'
overrides '-o' and '-S'. '-c' has no effect when testing or listing.
'-d'
'--decompress'
Decompress the files specified. If a file does not exist, can't be
opened, or the destination file already exists and '--force' has not
been specified, minilzip continues decompressing the rest of the files
and exits with error status 1. If a file fails to decompress, or is a
terminal, minilzip exits immediately with error status 2 without
decompressing the rest of the files. A terminal is considered an
uncompressed file, and therefore invalid.
'-f'
'--force'
Force overwrite of output files.
'-F'
'--recompress'
When compressing, force re-compression of files whose name already has
the '.lz' or '.tlz' suffix.
'-k'
'--keep'
Keep (don't delete) input files during compression or decompression.
'-m BYTES'
'--match-length=BYTES'
When compressing, set the match length limit in bytes. After a match
this long is found, the search is finished. Valid values range from 5
to 273. Larger values usually give better compression ratios but longer
compression times.
'-o FILE'
'--output=FILE'
If '-c' has not been also specified, write the (de)compressed output to
FILE; keep input files unchanged. If compressing several files, each
file is compressed independently. (The output consists of a sequence of
independently compressed members). This option (or '-c') is needed when
reading from a named pipe (fifo) or from a device. '-o -' is
equivalent to '-c'. '-o' has no effect when testing or listing.
When compressing and splitting the output in volumes, FILE is used as
a prefix, and several files named 'FILE00001.lz', 'FILE00002.lz', etc,
are created. In this case, only one input file is allowed.
'-q'
'--quiet'
Quiet operation. Suppress all messages.
'-s BYTES'
'--dictionary-size=BYTES'
When compressing, set the dictionary size limit in bytes. Minilzip
will use for each file the largest dictionary size that does not
exceed neither the file size nor this limit. Valid values range from
4 KiB to 512 MiB. Values 12 to 29 are interpreted as powers of two,
meaning 2^12 to 2^29 bytes. Dictionary sizes are quantized so that
they can be coded in just one byte (*note coded-dict-size::). If the
size specified does not match one of the valid sizes, it will be
rounded upwards by adding up to (BYTES / 8) to it.
For maximum compression you should use a dictionary size limit as large
as possible, but keep in mind that the decompression memory requirement
is affected at compression time by the choice of dictionary size limit.
'-S BYTES'
'--volume-size=BYTES'
When compressing, and '-c' has not been also specified, split the
compressed output into several volume files with names
'original_name00001.lz', 'original_name00002.lz', etc, and set the
volume size limit to BYTES. Input files are kept unchanged. Each
volume is a complete, maybe multimember, lzip file. A small volume
size may degrade compression ratio, so use it only when needed. Valid
values range from 100 kB to 4 EiB.
'-t'
'--test'
Check integrity of the files specified, but don't decompress them. This
really performs a trial decompression and throws away the result. Use
it together with '-v' to see information about the files. If a file
fails the test, does not exist, can't be opened, or is a terminal,
minilzip continues checking the rest of the files. A final diagnostic
is shown at verbosity level 1 or higher if any file fails the test
when testing multiple files.
'-v'
'--verbose'
Verbose mode.
When compressing, show the compression ratio and size for each file
processed.
When decompressing or testing, further -v's (up to 4) increase the
verbosity level, showing status, compression ratio, dictionary size,
and trailer contents (CRC, data size, member size).
'-0 .. -9'
Compression level. Set the compression parameters (dictionary size and
match length limit) as shown in the table below. The default
compression level is '-6', equivalent to '-s8MiB -m36'. Note that '-9'
can be much slower than '-0'. These options have no effect when
decompressing or testing.
The bidimensional parameter space of LZMA can't be mapped to a linear
scale optimal for all files. If your files are large, very repetitive,
etc, you may need to use the options '--dictionary-size' and
'--match-length' directly to achieve optimal performance.
If several compression levels or '-s' or '-m' options are given, the
last setting is used. For example '-9 -s64MiB' is equivalent to
'-s64MiB -m273'
Level Dictionary size (-s) Match length limit (-m)
-0 64 KiB 16 bytes
-1 1 MiB 5 bytes
-2 1.5 MiB 6 bytes
-3 2 MiB 8 bytes
-4 3 MiB 12 bytes
-5 4 MiB 20 bytes
-6 8 MiB 36 bytes
-7 16 MiB 68 bytes
-8 24 MiB 132 bytes
-9 32 MiB 273 bytes
'--fast'
'--best'
Aliases for GNU gzip compatibility.
'--loose-trailing'
When decompressing or testing, allow trailing data whose first bytes
are so similar to the magic bytes of a lzip header that they can be
confused with a corrupt header. Use this option if a file triggers a
"corrupt header" error and the cause is not indeed a corrupt header.
'--check-lib'
Compare the version of lzlib used to compile minilzip with the version
actually being used at run time and exit. Report any differences
found. Exit with error status 1 if differences are found. A mismatch
may indicate that lzlib is not correctly installed or that a different
version of lzlib has been installed after compiling the shared version
of minilzip. Exit with error status 2 if LZ_API_VERSION and
LZ_version_string don't match. 'minilzip -v --check-lib' shows the
version of lzlib being used and the value of LZ_API_VERSION (if
defined). *Note Library version::.
Numbers given as arguments to options may be followed by a multiplier
and an optional 'B' for "byte".
Table of SI and binary prefixes (unit multipliers):
Prefix Value | Prefix Value
k kilobyte (10^3 = 1000) | Ki kibibyte (2^10 = 1024)
M megabyte (10^6) | Mi mebibyte (2^20)
G gigabyte (10^9) | Gi gibibyte (2^30)
T terabyte (10^12) | Ti tebibyte (2^40)
P petabyte (10^15) | Pi pebibyte (2^50)
E exabyte (10^18) | Ei exbibyte (2^60)
Z zettabyte (10^21) | Zi zebibyte (2^70)
Y yottabyte (10^24) | Yi yobibyte (2^80)
Exit status: 0 for a normal exit, 1 for environmental problems (file not
found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or invalid
input file, 3 for an internal consistency error (e.g., bug) which caused
minilzip to panic.
File: lzlib.info, Node: Data format, Next: Examples, Prev: Invoking minilzip, Up: Top
10 Data format
**************
Perfection is reached, not when there is no longer anything to add, but
when there is no longer anything to take away.
-- Antoine de Saint-Exupery
In the diagram below, a box like this:
+---+
| | <-- the vertical bars might be missing
+---+
represents one byte; a box like this:
+==============+
| |
+==============+
represents a variable number of bytes.
Lzip data consist of a series of independent "members" (compressed data
sets). The members simply appear one after another in the data stream, with
no additional information before, between, or after them. Each member can
encode in compressed form up to 16 EiB - 1 byte of uncompressed data. The
size of a multimember data stream is unlimited.
Each member has the following structure:
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | LZMA stream | CRC32 | Data size | Member size |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All multibyte values are stored in little endian order.
'ID string (the "magic" bytes)'
A four byte string, identifying the lzip format, with the value "LZIP"
(0x4C, 0x5A, 0x49, 0x50).
'VN (version number, 1 byte)'
Just in case something needs to be modified in the future. 1 for now.
'DS (coded dictionary size, 1 byte)'
The dictionary size is calculated by taking a power of 2 (the base
size) and subtracting from it a fraction between 0/16 and 7/16 of the
base size.
Bits 4-0 contain the base 2 logarithm of the base size (12 to 29).
Bits 7-5 contain the numerator of the fraction (0 to 7) to subtract
from the base size to obtain the dictionary size.
Example: 0xD3 = 2^19 - 6 * 2^15 = 512 KiB - 6 * 32 KiB = 320 KiB
Valid values for dictionary size range from 4 KiB to 512 MiB.
'LZMA stream'
The LZMA stream, finished by an "End Of Stream" marker. Uses default
values for encoder properties. *Note Stream format: (lzip)Stream
format, for a complete description.
Lzip only uses the LZMA marker '2' ("End Of Stream" marker). Lzlib
also uses the LZMA marker '3' ("Sync Flush" marker). *Note
sync_flush::.
'CRC32 (4 bytes)'
Cyclic Redundancy Check (CRC) of the original uncompressed data.
'Data size (8 bytes)'
Size of the original uncompressed data.
'Member size (8 bytes)'
Total size of the member, including header and trailer. This field acts
as a distributed index, allows the verification of stream integrity,
and facilitates the safe recovery of undamaged members from
multimember files. Member size should be limited to 2 PiB to prevent
the data size field from overflowing.
File: lzlib.info, Node: Examples, Next: Problems, Prev: Data format, Up: Top
11 A small tutorial with examples
*********************************
This chapter provides real code examples for the most common uses of the
library. See these examples in context in the files 'bbexample.c' and
'ffexample.c' from the source distribution of lzlib.
Note that the interface of lzlib is symmetrical. That is, the code for
normal compression and decompression is identical except because one calls
LZ_compress* functions while the other calls LZ_decompress* functions.
* Menu:
* Buffer compression:: Buffer-to-buffer single-member compression
* Buffer decompression:: Buffer-to-buffer decompression
* File compression:: File-to-file single-member compression
* File decompression:: File-to-file decompression
* File compression mm:: File-to-file multimember compression
* Skipping data errors:: Decompression with automatic resynchronization
File: lzlib.info, Node: Buffer compression, Next: Buffer decompression, Up: Examples
11.1 Buffer compression
=======================
Buffer-to-buffer single-member compression (MEMBER_SIZE > total output).
/* Compress 'insize' bytes from 'inbuf' to 'outbuf'.
Return the size of the compressed data in '*outlenp'.
In case of error, or if 'outsize' is too small, return false and do not
modify '*outlenp'.
*/
bool bbcompress( const uint8_t * const inbuf, const int insize,
const int dictionary_size, const int match_len_limit,
uint8_t * const outbuf, const int outsize,
int * const outlenp )
{
int inpos = 0, outpos = 0;
bool error = false;
struct LZ_Encoder * const encoder =
LZ_compress_open( dictionary_size, match_len_limit, INT64_MAX );
if( !encoder || LZ_compress_errno( encoder ) != LZ_ok )
{ LZ_compress_close( encoder ); return false; }
while( true )
{
int ret = LZ_compress_write( encoder, inbuf + inpos, insize - inpos );
if( ret < 0 ) { error = true; break; }
inpos += ret;
if( inpos >= insize ) LZ_compress_finish( encoder );
ret = LZ_compress_read( encoder, outbuf + outpos, outsize - outpos );
if( ret < 0 ) { error = true; break; }
outpos += ret;
if( LZ_compress_finished( encoder ) == 1 ) break;
if( outpos >= outsize ) { error = true; break; }
}
if( LZ_compress_close( encoder ) < 0 ) error = true;
if( error ) return false;
*outlenp = outpos;
return true;
}
File: lzlib.info, Node: Buffer decompression, Next: File compression, Prev: Buffer compression, Up: Examples
11.2 Buffer decompression
=========================
Buffer-to-buffer decompression.
/* Decompress 'insize' bytes from 'inbuf' to 'outbuf'.
Return the size of the decompressed data in '*outlenp'.
In case of error, or if 'outsize' is too small, return false and do not
modify '*outlenp'.
*/
bool bbdecompress( const uint8_t * const inbuf, const int insize,
uint8_t * const outbuf, const int outsize,
int * const outlenp )
{
int inpos = 0, outpos = 0;
bool error = false;
struct LZ_Decoder * const decoder = LZ_decompress_open();
if( !decoder || LZ_decompress_errno( decoder ) != LZ_ok )
{ LZ_decompress_close( decoder ); return false; }
while( true )
{
int ret = LZ_decompress_write( decoder, inbuf + inpos, insize - inpos );
if( ret < 0 ) { error = true; break; }
inpos += ret;
if( inpos >= insize ) LZ_decompress_finish( decoder );
ret = LZ_decompress_read( decoder, outbuf + outpos, outsize - outpos );
if( ret < 0 ) { error = true; break; }
outpos += ret;
if( LZ_decompress_finished( decoder ) == 1 ) break;
if( outpos >= outsize ) { error = true; break; }
}
if( LZ_decompress_close( decoder ) < 0 ) error = true;
if( error ) return false;
*outlenp = outpos;
return true;
}
File: lzlib.info, Node: File compression, Next: File decompression, Prev: Buffer decompression, Up: Examples
11.3 File compression
=====================
File-to-file compression using LZ_compress_write_size.
int ffcompress( struct LZ_Encoder * const encoder,
FILE * const infile, FILE * const outfile )
{
enum { buffer_size = 16384 };
uint8_t buffer[buffer_size];
while( true )
{
int len, ret;
int size = min( buffer_size, LZ_compress_write_size( encoder ) );
if( size > 0 )
{
len = fread( buffer, 1, size, infile );
ret = LZ_compress_write( encoder, buffer, len );
if( ret < 0 || ferror( infile ) ) break;
if( feof( infile ) ) LZ_compress_finish( encoder );
}
ret = LZ_compress_read( encoder, buffer, buffer_size );
if( ret < 0 ) break;
len = fwrite( buffer, 1, ret, outfile );
if( len < ret ) break;
if( LZ_compress_finished( encoder ) == 1 ) return 0;
}
return 1;
}
File: lzlib.info, Node: File decompression, Next: File compression mm, Prev: File compression, Up: Examples
11.4 File decompression
=======================
File-to-file decompression using LZ_decompress_write_size.
int ffdecompress( struct LZ_Decoder * const decoder,
FILE * const infile, FILE * const outfile )
{
enum { buffer_size = 16384 };
uint8_t buffer[buffer_size];
while( true )
{
int len, ret;
int size = min( buffer_size, LZ_decompress_write_size( decoder ) );
if( size > 0 )
{
len = fread( buffer, 1, size, infile );
ret = LZ_decompress_write( decoder, buffer, len );
if( ret < 0 || ferror( infile ) ) break;
if( feof( infile ) ) LZ_decompress_finish( decoder );
}
ret = LZ_decompress_read( decoder, buffer, buffer_size );
if( ret < 0 ) break;
len = fwrite( buffer, 1, ret, outfile );
if( len < ret ) break;
if( LZ_decompress_finished( decoder ) == 1 ) return 0;
}
return 1;
}
File: lzlib.info, Node: File compression mm, Next: Skipping data errors, Prev: File decompression, Up: Examples
11.5 File-to-file multimember compression
=========================================
Example 1: Multimember compression with members of fixed size
(MEMBER_SIZE < total output).
int ffmmcompress( FILE * const infile, FILE * const outfile )
{
enum { buffer_size = 16384, member_size = 4096 };
uint8_t buffer[buffer_size];
bool done = false;
struct LZ_Encoder * const encoder =
LZ_compress_open( 65535, 16, member_size );
if( !encoder || LZ_compress_errno( encoder ) != LZ_ok )
{ fputs( "ffexample: Not enough memory.\n", stderr );
LZ_compress_close( encoder ); return 1; }
while( true )
{
int len, ret;
int size = min( buffer_size, LZ_compress_write_size( encoder ) );
if( size > 0 )
{
len = fread( buffer, 1, size, infile );
ret = LZ_compress_write( encoder, buffer, len );
if( ret < 0 || ferror( infile ) ) break;
if( feof( infile ) ) LZ_compress_finish( encoder );
}
ret = LZ_compress_read( encoder, buffer, buffer_size );
if( ret < 0 ) break;
len = fwrite( buffer, 1, ret, outfile );
if( len < ret ) break;
if( LZ_compress_member_finished( encoder ) == 1 )
{
if( LZ_compress_finished( encoder ) == 1 ) { done = true; break; }
if( LZ_compress_restart_member( encoder, member_size ) < 0 ) break;
}
}
if( LZ_compress_close( encoder ) < 0 ) done = false;
return done;
}
Example 2: Multimember compression (user-restarted members). (Call
LZ_compress_open with MEMBER_SIZE > largest member).
/* Compress 'infile' to 'outfile' as a multimember stream with one member
for each line of text terminated by a newline character or by EOF.
Return 0 if success, 1 if error.
*/
int fflfcompress( struct LZ_Encoder * const encoder,
FILE * const infile, FILE * const outfile )
{
enum { buffer_size = 16384 };
uint8_t buffer[buffer_size];
while( true )
{
int len, ret;
int size = min( buffer_size, LZ_compress_write_size( encoder ) );
if( size > 0 )
{
for( len = 0; len < size; )
{
int ch = getc( infile );
if( ch == EOF || ( buffer[len++] = ch ) == '\n' ) break;
}
/* avoid writing an empty member to outfile */
if( len == 0 && LZ_compress_data_position( encoder ) == 0 ) return 0;
ret = LZ_compress_write( encoder, buffer, len );
if( ret < 0 || ferror( infile ) ) break;
if( feof( infile ) || buffer[len-1] == '\n' )
LZ_compress_finish( encoder );
}
ret = LZ_compress_read( encoder, buffer, buffer_size );
if( ret < 0 ) break;
len = fwrite( buffer, 1, ret, outfile );
if( len < ret ) break;
if( LZ_compress_member_finished( encoder ) == 1 )
{
if( feof( infile ) && LZ_compress_finished( encoder ) == 1 ) return 0;
if( LZ_compress_restart_member( encoder, INT64_MAX ) < 0 ) break;
}
}
return 1;
}
File: lzlib.info, Node: Skipping data errors, Prev: File compression mm, Up: Examples
11.6 Skipping data errors
=========================
/* Decompress 'infile' to 'outfile' with automatic resynchronization to
next member in case of data error, including the automatic removal of
leading garbage.
*/
int ffrsdecompress( struct LZ_Decoder * const decoder,
FILE * const infile, FILE * const outfile )
{
enum { buffer_size = 16384 };
uint8_t buffer[buffer_size];
while( true )
{
int len, ret;
int size = min( buffer_size, LZ_decompress_write_size( decoder ) );
if( size > 0 )
{
len = fread( buffer, 1, size, infile );
ret = LZ_decompress_write( decoder, buffer, len );
if( ret < 0 || ferror( infile ) ) break;
if( feof( infile ) ) LZ_decompress_finish( decoder );
}
ret = LZ_decompress_read( decoder, buffer, buffer_size );
if( ret < 0 )
{
if( LZ_decompress_errno( decoder ) == LZ_header_error ||
LZ_decompress_errno( decoder ) == LZ_data_error )
{ LZ_decompress_sync_to_member( decoder ); continue; }
else break;
}
len = fwrite( buffer, 1, ret, outfile );
if( len < ret ) break;
if( LZ_decompress_finished( decoder ) == 1 ) return 0;
}
return 1;
}
File: lzlib.info, Node: Problems, Next: Concept index, Prev: Examples, Up: Top
12 Reporting bugs
*****************
There are probably bugs in lzlib. There are certainly errors and omissions
in this manual. If you report them, they will get fixed. If you don't, no
one will ever know about them and they will remain unfixed for all
eternity, if not longer.
If you find a bug in lzlib, please send electronic mail to
. Include the version number, which you can find by
running 'minilzip --version' and 'minilzip -v --check-lib'.
File: lzlib.info, Node: Concept index, Prev: Problems, Up: Top
Concept index
*************
[index ]
* Menu:
* buffer compression: Buffer compression. (line 6)
* buffer decompression: Buffer decompression. (line 6)
* buffering: Buffering. (line 6)
* bugs: Problems. (line 6)
* compression functions: Compression functions. (line 6)
* data format: Data format. (line 6)
* decompression functions: Decompression functions. (line 6)
* error codes: Error codes. (line 6)
* error messages: Error messages. (line 6)
* examples: Examples. (line 6)
* file compression: File compression. (line 6)
* file decompression: File decompression. (line 6)
* getting help: Problems. (line 6)
* introduction: Introduction. (line 6)
* invoking: Invoking minilzip. (line 6)
* library version: Library version. (line 6)
* multimember compression: File compression mm. (line 6)
* options: Invoking minilzip. (line 6)
* parameter limits: Parameter limits. (line 6)
* skipping data errors: Skipping data errors. (line 6)
Tag Table:
Node: Top215
Node: Introduction1338
Node: Library version6413
Node: Buffering8957
Node: Parameter limits10182
Node: Compression functions11136
Ref: member_size12946
Ref: sync_flush14712
Node: Decompression functions19400
Node: Error codes26968
Node: Error messages29259
Node: Invoking minilzip29838
Node: Data format39786
Ref: coded-dict-size41232
Node: Examples42641
Node: Buffer compression43602
Node: Buffer decompression45122
Node: File compression46536
Node: File decompression47519
Node: File compression mm48523
Node: Skipping data errors51552
Node: Problems52862
Node: Concept index53423
End Tag Table
Local Variables:
coding: iso-8859-15
End: