path: root/doc/lzlib.texi

\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename lzlib.info
@documentencoding ISO-8859-15
@settitle Lzlib Manual
@finalout
@c %**end of header

@set UPDATED 23 January 2022
@set VERSION 1.13

@dircategory Compression
@direntry
* Lzlib: (lzlib).               Compression library for the lzip format
@end direntry


@ifnothtml
@titlepage
@title Lzlib
@subtitle Compression library for the lzip format
@subtitle for Lzlib version @value{VERSION}, @value{UPDATED}
@author by Antonio Diaz Diaz

@page
@vskip 0pt plus 1filll
@end titlepage

@contents
@end ifnothtml

@ifnottex
@node Top
@top

This manual is for Lzlib (version @value{VERSION}, @value{UPDATED}).

@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
@end menu

@sp 1
Copyright @copyright{} 2009-2022 Antonio Diaz Diaz.

This manual is free documentation: you have unlimited permission to copy,
distribute, and modify it.
@end ifnottex


@node Introduction
@chapter Introduction
@cindex introduction

@uref{http://www.nongnu.org/lzip/lzlib.html,,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:

@itemize @bullet
@item
The lzip format provides very safe integrity checking and some data
recovery means. The program
@uref{http://www.nongnu.org/lzip/manual/lziprecover_manual.html#Data-safety,,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.
@ifnothtml
@xref{Data safety,,,lziprecover}.
@end ifnothtml

@item
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.

@item
Additionally the lzip reference implementation is copylefted, which
guarantees that it will remain free forever.
@end itemize

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 @samp{lzlib.h}. Usage examples of the library are
given in the files @samp{bbexample.c}, @samp{ffexample.c}, and
@samp{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 @var{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 @samp{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 @w{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 @samp{-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 @samp{-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.


@node Library version
@chapter Library version
@cindex 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 @samp{lzlib.h}.

@defvr Constant LZ_API_VERSION
This constant is defined in @samp{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:

@example
#if !defined LZ_API_VERSION || LZ_API_VERSION < 1012
#error "lzlib 1.12 or newer needed."
#endif
@end example

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).
@end defvr

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.

@deftypefun int LZ_api_version ( void )
If LZ_API_VERSION >= 1012, this function is declared in @samp{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 @code{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.

@example
#if defined LZ_API_VERSION && LZ_API_VERSION >= 1012
  if( LZ_api_version() < 1012 )
    show_error( "lzlib 1.12 or newer needed." );
#endif
@end example
@end deftypefun

@deftypevr Constant {const char *} LZ_version_string
This string constant is defined in the header file @samp{lzlib.h} and
represents the version of the library being used at compile time.
@end deftypevr

@deftypefun {const char *} LZ_version ( void )
This function returns a string representing the version of the library being
used at run time.
@end deftypefun


@node Buffering
@chapter Buffering
@cindex 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:

@itemize @bullet
@item Input compression buffer. Written to by the function
@samp{LZ_compress_write}. For the normal variant of LZMA, its size is two
times the dictionary size set with the function @samp{LZ_compress_open} or
@w{64 KiB}, whichever is larger. For the fast variant, its size is @w{1 MiB}.

@item Output compression buffer. Read from by the function
@samp{LZ_compress_read}. Its size is @w{64 KiB}.

@item Input decompression buffer. Written to by the function
@samp{LZ_decompress_write}. Its size is @w{64 KiB}.

@item Output decompression buffer. Read from by the function
@samp{LZ_decompress_read}. Its size is the dictionary size set in the header
of the member currently being decompressed or @w{64 KiB}, whichever is larger.
@end itemize


@node Parameter limits
@chapter Parameter limits
@cindex parameter limits

These functions provide minimum and maximum values for some parameters.
Current values are shown in square brackets.

@deftypefun int LZ_min_dictionary_bits ( void )
Returns the base 2 logarithm of the smallest valid dictionary size [12].
@end deftypefun

@deftypefun int LZ_min_dictionary_size ( void )
Returns the smallest valid dictionary size [4 KiB].
@end deftypefun

@deftypefun int LZ_max_dictionary_bits ( void )
Returns the base 2 logarithm of the largest valid dictionary size [29].
@end deftypefun

@deftypefun int LZ_max_dictionary_size ( void )
Returns the largest valid dictionary size [512 MiB].
@end deftypefun

@deftypefun int LZ_min_match_len_limit ( void )
Returns the smallest valid match length limit [5].
@end deftypefun

@deftypefun int LZ_max_match_len_limit ( void )
Returns the largest valid match length limit [273].
@end deftypefun


@node Compression functions
@chapter Compression functions
@cindex 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 @samp{LZ_compress_open} whose return value must be verified by
calling @samp{LZ_compress_errno} before using it.


@deftypefun {struct LZ_Encoder *} LZ_compress_open ( const int @var{dictionary_size}, const int @var{match_len_limit}, const unsigned long long @var{member_size} )
Initializes the internal stream state for compression and returns a
pointer that can only be used as the @var{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
@samp{LZ_compress_errno} before using it. If @samp{LZ_compress_errno}
does not return @samp{LZ_ok}, the returned pointer must not be used and
should be freed with @samp{LZ_compress_close} to avoid memory leaks.

@var{dictionary_size} sets the dictionary size to be used, in bytes.
Valid values range from @w{4 KiB} to @w{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
@w{(@var{dictionary_size} / 8)} to it.

@var{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 @var{dictionary_size} is 65535 and @var{match_len_limit} is 16, the fast
variant of LZMA is chosen, which produces identical compressed output as
@w{@samp{lzip -0}}. (The dictionary size used will be rounded upwards to
@w{64 KiB}).

@anchor{member_size}
@var{member_size} sets the member size limit in bytes. Valid values range
from @w{4 KiB} to @w{2 PiB}. A small member size may degrade compression
ratio, so use it only when needed. To produce a single-member data stream,
give @var{member_size} a value larger than the amount of data to be
produced. Values larger than @w{2 PiB} will be reduced to @w{2 PiB} to
prevent the uncompressed size of the member from overflowing.
@end deftypefun


@deftypefun int LZ_compress_close ( struct LZ_Encoder * const @var{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 @samp{LZ_compress_close}, @var{encoder} can no
longer be used as an argument to any LZ_compress function.
It is safe to call @samp{LZ_compress_close} with a null argument.
@end deftypefun


@deftypefun int LZ_compress_finish ( struct LZ_Encoder * const @var{encoder} )
Use this function to tell @samp{lzlib} that all the data for this member
have already been written (with the function @samp{LZ_compress_write}).
It is safe to call @samp{LZ_compress_finish} as many times as needed.
After all the compressed data have been read with @samp{LZ_compress_read}
and @samp{LZ_compress_member_finished} returns 1, a new member can be
started with @samp{LZ_compress_restart_member}.
@end deftypefun


@deftypefun int LZ_compress_restart_member ( struct LZ_Encoder * const @var{encoder}, const unsigned long long @var{member_size} )
Use this function to start a new member in a multimember data stream. Call
this function only after @samp{LZ_compress_member_finished} indicates that
the current member has been fully read (with the function
@samp{LZ_compress_read}). @xref{member_size}, for a description of
@var{member_size}.
@end deftypefun


@anchor{sync_flush}
@deftypefun int LZ_compress_sync_flush ( struct LZ_Encoder * const @var{encoder} )
Use this function to make available to @samp{LZ_compress_read} all the data
already written with the function @samp{LZ_compress_write}. First call
@samp{LZ_compress_sync_flush}. Then call @samp{LZ_compress_read} until it
returns 0.

This function writes at least one LZMA marker @samp{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 @samp{application/lzip}. The LZMA marker
@samp{2} ("End Of Stream" marker) is the only marker allowed in lzip files.
@xref{Data format}.

Repeated use of @samp{LZ_compress_sync_flush} may degrade compression
ratio, so use it only when needed. If the interval between calls to
@samp{LZ_compress_sync_flush} is large (comparable to dictionary size),
creating a multimember data stream with @samp{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 @var{member_size},
@samp{LZ_compress_restart_member} needs to be called when
@samp{LZ_compress_member_finished} returns 1, followed by a new call to
@samp{LZ_compress_sync_flush}.
@end deftypefun


@deftypefun int LZ_compress_read ( struct LZ_Encoder * const @var{encoder}, uint8_t * const @var{buffer}, const int @var{size} )
Reads up to @var{size} bytes from the stream pointed to by @var{encoder},
storing the results in @var{buffer}. If @w{LZ_API_VERSION >= 1012},
@var{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
@var{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
@samp{LZ_compress_write}. Note that reading less than @var{size} bytes is
not an error.
@end deftypefun


@deftypefun int LZ_compress_write ( struct LZ_Encoder * const @var{encoder}, uint8_t * const @var{buffer}, const int @var{size} )
Writes up to @var{size} bytes from @var{buffer} to the stream pointed to by
@var{encoder}. Returns the number of bytes actually written. This might be
less than @var{size}. Note that writing less than @var{size} bytes is not an
error.
@end deftypefun


@deftypefun int LZ_compress_write_size ( struct LZ_Encoder * const @var{encoder} )
Returns the maximum number of bytes that can be immediately written through
@samp{LZ_compress_write}. For efficiency reasons, once the input buffer is
full and @samp{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 @samp{LZ_compress_write} will
accept a @var{size} up to the returned number of bytes.
@end deftypefun


@deftypefun {enum LZ_Errno} LZ_compress_errno ( struct LZ_Encoder * const @var{encoder} )
Returns the current error code for @var{encoder}. @xref{Error codes}.
It is safe to call @samp{LZ_compress_errno} with a null argument, in which
case it returns @samp{LZ_bad_argument}.
@end deftypefun


@deftypefun int LZ_compress_finished ( struct LZ_Encoder * const @var{encoder} )
Returns 1 if all the data have been read and @samp{LZ_compress_close}
can be safely called. Otherwise it returns 0. @samp{LZ_compress_finished}
implies @samp{LZ_compress_member_finished}.
@end deftypefun


@deftypefun int LZ_compress_member_finished ( struct LZ_Encoder * const @var{encoder} )
Returns 1 if the current member, in a multimember data stream, has been
fully read and @samp{LZ_compress_restart_member} can be safely called.
Otherwise it returns 0.
@end deftypefun


@deftypefun {unsigned long long} LZ_compress_data_position ( struct LZ_Encoder * const @var{encoder} )
Returns the number of input bytes already compressed in the current member.
@end deftypefun


@deftypefun {unsigned long long} LZ_compress_member_position ( struct LZ_Encoder * const @var{encoder} )
Returns the number of compressed bytes already produced, but perhaps not
yet read, in the current member.
@end deftypefun


@deftypefun {unsigned long long} LZ_compress_total_in_size ( struct LZ_Encoder * const @var{encoder} )
Returns the total number of input bytes already compressed.
@end deftypefun


@deftypefun {unsigned long long} LZ_compress_total_out_size ( struct LZ_Encoder * const @var{encoder} )
Returns the total number of compressed bytes already produced, but
perhaps not yet read.
@end deftypefun


@node Decompression functions
@chapter Decompression functions
@cindex 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 @samp{LZ_decompress_open} whose return value must be verified by
calling @samp{LZ_decompress_errno} before using it.


@deftypefun {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 @var{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
@samp{LZ_decompress_errno} before using it. If
@samp{LZ_decompress_errno} does not return @samp{LZ_ok}, the returned
pointer must not be used and should be freed with
@samp{LZ_decompress_close} to avoid memory leaks.
@end deftypefun


@deftypefun int LZ_decompress_close ( struct LZ_Decoder * const @var{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 @samp{LZ_decompress_close}, @var{decoder} can no
longer be used as an argument to any LZ_decompress function.
It is safe to call @samp{LZ_decompress_close} with a null argument.
@end deftypefun


@deftypefun int LZ_decompress_finish ( struct LZ_Decoder * const @var{decoder} )
Use this function to tell @samp{lzlib} that all the data for this stream
have already been written (with the function @samp{LZ_decompress_write}).
It is safe to call @samp{LZ_decompress_finish} as many times as needed.
It is not required to call @samp{LZ_decompress_finish} if the input stream
only contains whole members, but not calling it prevents lzlib from
detecting a truncated member.
@end deftypefun


@deftypefun int LZ_decompress_reset ( struct LZ_Decoder * const @var{decoder} )
Resets the internal state of @var{decoder} as it was just after opening
it with the function @samp{LZ_decompress_open}. Data stored in the
internal buffers is discarded. Position counters are set to 0.
@end deftypefun


@deftypefun int LZ_decompress_sync_to_member ( struct LZ_Decoder * const @var{decoder} )
Resets the error state of @var{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 @samp{LZ_decompress_sync_to_member}, data
written with @samp{LZ_decompress_write} will be consumed and
@samp{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.
@end deftypefun


@deftypefun int LZ_decompress_read ( struct LZ_Decoder * const @var{decoder}, uint8_t * const @var{buffer}, const int @var{size} )
Reads up to @var{size} bytes from the stream pointed to by @var{decoder},
storing the results in @var{buffer}. If @w{LZ_API_VERSION >= 1012},
@var{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
@var{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
@samp{LZ_decompress_write}. Note that reading less than @var{size} bytes is
not an error.

@samp{LZ_decompress_read} returns at least once per member so that
@samp{LZ_decompress_member_finished} can be called (and trailer data
retrieved) for each member, even for empty members. Therefore,
@samp{LZ_decompress_read} returning 0 does not mean that the end of the
stream has been reached. The increase in the value returned by
@samp{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,
@samp{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
@uref{http://www.nongnu.org/lzip/manual/tarlz_manual.html,,tarlz} to
recover as much data as possible from each damaged member.
@ifnothtml
@xref{Top,tarlz manual,,tarlz}.
@end ifnothtml
@end deftypefun


@deftypefun int LZ_decompress_write ( struct LZ_Decoder * const @var{decoder}, uint8_t * const @var{buffer}, const int @var{size} )
Writes up to @var{size} bytes from @var{buffer} to the stream pointed to by
@var{decoder}. Returns the number of bytes actually written. This might be
less than @var{size}. Note that writing less than @var{size} bytes is not an
error.
@end deftypefun


@deftypefun int LZ_decompress_write_size ( struct LZ_Decoder * const @var{decoder} )
Returns the maximum number of bytes that can be immediately written through
@samp{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 @samp{LZ_decompress_write} will
accept a @var{size} up to the returned number of bytes.
@end deftypefun


@deftypefun {enum LZ_Errno} LZ_decompress_errno ( struct LZ_Decoder * const @var{decoder} )
Returns the current error code for @var{decoder}. @xref{Error codes}.
It is safe to call @samp{LZ_decompress_errno} with a null argument, in which
case it returns @samp{LZ_bad_argument}.
@end deftypefun


@deftypefun int LZ_decompress_finished ( struct LZ_Decoder * const @var{decoder} )
Returns 1 if all the data have been read and @samp{LZ_decompress_close}
can be safely called. Otherwise it returns 0. @samp{LZ_decompress_finished}
does not imply @samp{LZ_decompress_member_finished}.
@end deftypefun


@deftypefun int LZ_decompress_member_finished ( struct LZ_Decoder * const @var{decoder} )
Returns 1 if the previous call to @samp{LZ_decompress_read} finished reading
the current member, indicating that final values for the member are available
through @samp{LZ_decompress_data_crc}, @samp{LZ_decompress_data_position},
and @samp{LZ_decompress_member_position}. Otherwise it returns 0.
@end deftypefun


@deftypefun int LZ_decompress_member_version ( struct LZ_Decoder * const @var{decoder} )
Returns the version of the current member, read from the member header.
@end deftypefun


@deftypefun int LZ_decompress_dictionary_size ( struct LZ_Decoder * const @var{decoder} )
Returns the dictionary size of the current member, read from the member header.
@end deftypefun


@deftypefun {unsigned} LZ_decompress_data_crc ( struct LZ_Decoder * const @var{decoder} )
Returns the 32 bit Cyclic Redundancy Check of the data decompressed from
the current member. The value returned is valid only when
@samp{LZ_decompress_member_finished} returns 1.
@end deftypefun


@deftypefun {unsigned long long} LZ_decompress_data_position ( struct LZ_Decoder * const @var{decoder} )
Returns the number of decompressed bytes already produced, but perhaps
not yet read, in the current member.
@end deftypefun


@deftypefun {unsigned long long} LZ_decompress_member_position ( struct LZ_Decoder * const @var{decoder} )
Returns the number of input bytes already decompressed in the current member.
@end deftypefun


@deftypefun {unsigned long long} LZ_decompress_total_in_size ( struct LZ_Decoder * const @var{decoder} )
Returns the total number of input bytes already decompressed.
@end deftypefun


@deftypefun {unsigned long long} LZ_decompress_total_out_size ( struct LZ_Decoder * const @var{decoder} )
Returns the total number of decompressed bytes already produced, but
perhaps not yet read.
@end deftypefun


@node Error codes
@chapter Error codes
@cindex 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
@samp{LZ_(de)compress_errno}.

Library functions don't change the value returned by
@samp{LZ_(de)compress_errno} when they succeed; thus, the value returned
by @samp{LZ_(de)compress_errno} after a successful call is not
necessarily LZ_ok, and you should not use @samp{LZ_(de)compress_errno}
to determine whether a call failed. If the call failed, then you can
examine @samp{LZ_(de)compress_errno}.

The error codes are defined in the header file @samp{lzlib.h}.

@deftypevr Constant {enum LZ_Errno} LZ_ok
The value of this constant is 0 and is used to indicate that there is no error.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_bad_argument
At least one of the arguments passed to the library function was invalid.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_mem_error
No memory available. The system cannot allocate more virtual memory
because its capacity is full.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_sequence_error
A library function was called in the wrong order. For example
@samp{LZ_compress_restart_member} was called before
@samp{LZ_compress_member_finished} indicates that the current member is
finished.
@end deftypevr

@deftypevr 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.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_unexpected_eof
The end of the data stream was reached in the middle of a member.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_data_error
The data stream is corrupt. If @samp{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.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_library_error
A bug was detected in the library. Please, report it. @xref{Problems}.
@end deftypevr


@node Error messages
@chapter Error messages
@cindex error messages

@deftypefun {const char *} LZ_strerror ( const enum LZ_Errno @var{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 @var{lz_errno} normally comes from a call to
@samp{LZ_(de)compress_errno}.
@end deftypefun


@node Invoking minilzip
@chapter Invoking minilzip
@cindex invoking
@cindex options

Minilzip is a test program for the compression library lzlib, fully
compatible with lzip 1.4 or newer.

@uref{http://www.nongnu.org/lzip/lzip.html,,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 @w{(lzip -0)} or compress most files more than bzip2
@w{(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.

@noindent
The format for running minilzip is:

@example
minilzip [@var{options}] [@var{files}]
@end example

@noindent
If no file names are specified, minilzip compresses (or decompresses) from
standard input to standard output. A hyphen @samp{-} used as a @var{file}
argument means standard input. It can be mixed with other @var{files} and is
read just once, the first time it appears in the command line.

minilzip supports the following
@uref{http://www.nongnu.org/arg-parser/manual/arg_parser_manual.html#Argument-syntax,,options}:
@ifnothtml
@xref{Argument syntax,,,arg_parser}.
@end ifnothtml

@table @code
@item -h
@itemx --help
Print an informative help message describing the options and exit.

@item -V
@itemx --version
Print the version number of minilzip on the standard output and exit.
This version number should be included in all bug reports.

@item -a
@itemx --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.

@item -b @var{bytes}
@itemx --member-size=@var{bytes}
When compressing, set the member size limit to @var{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
@w{100 kB} to @w{2 PiB}. Defaults to @w{2 PiB}.

@item -c
@itemx --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 @samp{-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. @samp{-c} overrides @samp{-o}
and @samp{-S}. @samp{-c} has no effect when testing or listing.

@item -d
@itemx --decompress
Decompress the files specified. If a file does not exist, can't be opened,
or the destination file already exists and @samp{--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.

@item -f
@itemx --force
Force overwrite of output files.

@item -F
@itemx --recompress
When compressing, force re-compression of files whose name already has
the @samp{.lz} or @samp{.tlz} suffix.

@item -k
@itemx --keep
Keep (don't delete) input files during compression or decompression.

@item -m @var{bytes}
@itemx --match-length=@var{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.

@item -o @var{file}
@itemx --output=@var{file}
If @samp{-c} has not been also specified, write the (de)compressed output to
@var{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 @samp{-c}) is needed when
reading from a named pipe (fifo) or from a device. @w{@samp{-o -}} is
equivalent to @samp{-c}. @samp{-o} has no effect when testing or listing.

When compressing and splitting the output in volumes, @var{file} is used as
a prefix, and several files named @samp{@var{file}00001.lz},
@samp{@var{file}00002.lz}, etc, are created. In this case, only one input
file is allowed.

@item -q
@itemx --quiet
Quiet operation. Suppress all messages.

@item -s @var{bytes}
@itemx --dictionary-size=@var{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 @w{4 KiB} to
@w{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 (@pxref{coded-dict-size}). If the size specified
does not match one of the valid sizes, it will be rounded upwards by
adding up to @w{(@var{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.

@item -S @var{bytes}
@itemx --volume-size=@var{bytes}
When compressing, and @samp{-c} has not been also specified, split the
compressed output into several volume files with names
@samp{original_name00001.lz}, @samp{original_name00002.lz}, etc, and set the
volume size limit to @var{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 @w{100 kB} to @w{4 EiB}.

@item -t
@itemx --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 @samp{-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.

@item -v
@itemx --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).

@item -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 @samp{-6}, equivalent to @w{@samp{-s8MiB -m36}}. Note that
@samp{-9} can be much slower than @samp{-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 @samp{--dictionary-size} and
@samp{--match-length} directly to achieve optimal performance.

If several compression levels or @samp{-s} or @samp{-m} options are
given, the last setting is used. For example @w{@samp{-9 -s64MiB}} is
equivalent to @w{@samp{-s64MiB -m273}}

@multitable {Level} {Dictionary size (-s)} {Match length limit (-m)}
@item Level @tab Dictionary size (-s) @tab Match length limit (-m)
@item -0 @tab 64 KiB @tab  16 bytes
@item -1 @tab  1 MiB @tab   5 bytes
@item -2 @tab  1.5 MiB @tab   6 bytes
@item -3 @tab  2 MiB @tab   8 bytes
@item -4 @tab  3 MiB @tab  12 bytes
@item -5 @tab  4 MiB @tab  20 bytes
@item -6 @tab  8 MiB @tab  36 bytes
@item -7 @tab 16 MiB @tab  68 bytes
@item -8 @tab 24 MiB @tab 132 bytes
@item -9 @tab 32 MiB @tab 273 bytes
@end multitable

@item --fast
@itemx --best
Aliases for GNU gzip compatibility.

@item --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.

@item --check-lib
Compare the @uref{#Library-version,,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. @w{@samp{minilzip -v --check-lib}} shows the
version of lzlib being used and the value of LZ_API_VERSION (if defined).
@ifnothtml
@xref{Library version}.
@end ifnothtml

@end table

Numbers given as arguments to options may be followed by a multiplier
and an optional @samp{B} for "byte".

Table of SI and binary prefixes (unit multipliers):

@multitable {Prefix} {kilobyte  (10^3 = 1000)} {|} {Prefix} {kibibyte (2^10 = 1024)}
@item Prefix @tab Value               @tab | @tab Prefix @tab Value
@item k @tab kilobyte  (10^3 = 1000)  @tab | @tab Ki @tab kibibyte (2^10 = 1024)
@item M @tab megabyte  (10^6)         @tab | @tab Mi @tab mebibyte (2^20)
@item G @tab gigabyte  (10^9)         @tab | @tab Gi @tab gibibyte (2^30)
@item T @tab terabyte  (10^12)        @tab | @tab Ti @tab tebibyte (2^40)
@item P @tab petabyte  (10^15)        @tab | @tab Pi @tab pebibyte (2^50)
@item E @tab exabyte   (10^18)        @tab | @tab Ei @tab exbibyte (2^60)
@item Z @tab zettabyte (10^21)        @tab | @tab Zi @tab zebibyte (2^70)
@item Y @tab yottabyte (10^24)        @tab | @tab Yi @tab yobibyte (2^80)
@end multitable

@sp 1
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.


@node Data format
@chapter Data format
@cindex 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

@sp 1
In the diagram below, a box like this:

@verbatim
+---+
|   | <-- the vertical bars might be missing
+---+
@end verbatim

represents one byte; a box like this:

@verbatim
+==============+
|              |
+==============+
@end verbatim

represents a variable number of bytes.

@sp 1
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 @w{16 EiB - 1 byte} of uncompressed data.
The size of a multimember data stream is unlimited.

Each member has the following structure:

@verbatim
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | LZMA stream | CRC32 |   Data size   |  Member size  |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@end verbatim

All multibyte values are stored in little endian order.

@table @samp
@item ID string (the "magic" bytes)
A four byte string, identifying the lzip format, with the value "LZIP"
(0x4C, 0x5A, 0x49, 0x50).

@item VN (version number, 1 byte)
Just in case something needs to be modified in the future. 1 for now.

@anchor{coded-dict-size}
@item 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.

@item LZMA stream
The LZMA stream, finished by an "End Of Stream" marker. Uses default values
for encoder properties.
@ifnothtml
@xref{Stream format,,,lzip},
@end ifnothtml
@ifhtml
See
@uref{http://www.nongnu.org/lzip/manual/lzip_manual.html#Stream-format,,Stream format}
@end ifhtml
for a complete description.@*
Lzip only uses the LZMA marker @samp{2} ("End Of Stream" marker). Lzlib
also uses the LZMA marker @samp{3} ("Sync Flush" marker). @xref{sync_flush}.

@item CRC32 (4 bytes)
Cyclic Redundancy Check (CRC) of the original uncompressed data.

@item Data size (8 bytes)
Size of the original uncompressed data.

@item 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 @w{2 PiB} to prevent the data size field
from overflowing.

@end table


@node Examples
@chapter A small tutorial with examples
@cindex examples

This chapter provides real code examples for the most common uses of the
library. See these examples in context in the files @samp{bbexample.c} and
@samp{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
@end menu


@node Buffer compression
@section Buffer compression
@cindex buffer compression

Buffer-to-buffer single-member compression
@w{(@var{member_size} > total output)}.

@verbatim
/* 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;
  }
@end verbatim


@node Buffer decompression
@section Buffer decompression
@cindex buffer decompression

Buffer-to-buffer decompression.

@verbatim
/* 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;
  }
@end verbatim


@node File compression
@section File compression
@cindex file compression

File-to-file compression using LZ_compress_write_size.

@verbatim
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;
  }
@end verbatim


@node File decompression
@section File decompression
@cindex file decompression

File-to-file decompression using LZ_decompress_write_size.

@verbatim
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;
  }
@end verbatim


@node File compression mm
@section File-to-file multimember compression
@cindex multimember compression

Example 1: Multimember compression with members of fixed size
@w{(@var{member_size} < total output)}.

@verbatim
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;
  }
@end verbatim

@sp 1
@noindent
Example 2: Multimember compression (user-restarted members).
(Call LZ_compress_open with @var{member_size} > largest member).

@verbatim
/* 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;
  }
@end verbatim


@node Skipping data errors
@section Skipping data errors
@cindex skipping data errors

@verbatim
/* 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;
  }
@end verbatim


@node Problems
@chapter Reporting bugs
@cindex bugs
@cindex getting help

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
@email{lzip-bug@@nongnu.org}. Include the version number, which you can
find by running @w{@samp{minilzip --version}} and
@w{@samp{minilzip -v --check-lib}}.


@node Concept index
@unnumbered Concept index

@printindex cp

@bye