Adding upstream version 1.8.upstream/1.8

Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>

1 files changed, 119 insertions, 46 deletions

diff --git a/doc/clzip.texi b/doc/clzip.texi
index e2ca889..331d4eb 100644
--- a/doc/clzip.texi
+++ b/doc/clzip.texi
@@ -6,8 +6,8 @@
 @finalout
 @c %**end of header
 
-@set UPDATED 7 July 2015
-@set VERSION 1.7
+@set UPDATED 13 May 2016
+@set VERSION 1.8
 
 @dircategory Data Compression
 @direntry
@@ -39,13 +39,14 @@ This manual is for Clzip (version @value{VERSION}, @value{UPDATED}).
 * Invoking clzip::         Command line interface
 * File format::            Detailed format of the compressed file
 * Algorithm::              How clzip compresses the data
+* Trailing data::          Extra data appended to the file
 * Examples::               A small tutorial with examples
 * Problems::               Reporting bugs
 * Concept index::          Index of concepts
 @end menu
 
 @sp 1
-Copyright @copyright{} 2010-2015 Antonio Diaz Diaz.
+Copyright @copyright{} 2010-2016 Antonio Diaz Diaz.
 
 This manual is free documentation: you have unlimited permission
 to copy, distribute and modify it.
@@ -78,7 +79,7 @@ program 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
-@ref{Data safety,,,lziprecover}.
+@xref{Data safety,,,lziprecover}.
 @end ifnothtml
 
 @item
@@ -101,14 +102,14 @@ corrupt byte near the beginning is a thing of the past.
 
 The member trailer stores the 32-bit CRC of the original data, the size
 of the original data and the size of the member. These values, together
-with the value remaining in the range decoder and the end-of-stream
-marker, provide a 4 factor integrity checking which guarantees that the
-decompressed version of the data is identical to the original. This
-guards against corruption of the compressed data, and against undetected
-bugs in clzip (hopefully very unlikely). The chances of data corruption
-going undetected are microscopic. Be aware, though, that the check
-occurs upon decompression, so it can only tell you that something is
-wrong. It can't help you recover the original uncompressed data.
+with the end-of-stream marker, provide a 3 factor integrity checking
+which guarantees that the decompressed version of the data is identical
+to the original. This guards against corruption of the compressed data,
+and against undetected bugs in clzip (hopefully very unlikely). The
+chances of data corruption going undetected are microscopic. Be aware,
+though, that the check occurs upon decompression, so it can only tell
+you that something is wrong. It can't help you recover the original
+uncompressed data.
 
 Clzip uses the same well-defined exit status values used by lzip and
 bzip2, which makes it safer than compressors returning ambiguous warning
@@ -157,14 +158,14 @@ or more compressed files. The result is the concatenation of the
 corresponding uncompressed files. Integrity testing of concatenated
 compressed files is also supported.
 
-Clzip can produce multi-member files and safely recover, with
+Clzip can produce multimember files and safely recover, with
 lziprecover, the undamaged members in case of file damage. Clzip can
 also split the compressed output in volumes of a given size, even when
 reading from standard input. This allows the direct creation of
 multivolume compressed tar archives.
 
 Clzip is able to compress and decompress streams of unlimited size by
-automatically creating multi-member output. The members so created are
+automatically creating multimember output. The members so created are
 large, about 2 PiB each.
 
 
@@ -181,6 +182,11 @@ The format for running clzip is:
 clzip [@var{options}] [@var{files}]
 @end example
 
+@noindent
+@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.
+
 Clzip supports the following options:
 
 @table @code
@@ -192,6 +198,13 @@ Print an informative help message describing the options and exit.
 @itemx --version
 Print the version number of clzip on the standard output and exit.
 
+@anchor{--trailing-error}
+@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. @xref{concat-example}.
+
 @item -b @var{bytes}
 @itemx --member-size=@var{bytes}
 Set the member size limit to @var{bytes}. A small member size may
@@ -200,13 +213,18 @@ range from 100 kB to 2 PiB. Defaults to 2 PiB.
 
 @item -c
 @itemx --stdout
-Compress or decompress to standard output. Needed when reading from a
-named pipe (fifo) or from a device. Use it to recover as much of the
-uncompressed data as possible when decompressing a corrupt file.
+Compress or decompress to standard output; keep input files unchanged.
+If compressing several files, each file is compressed independently.
+This option is needed when reading from a named pipe (fifo) or from a
+device. Use it also to recover as much of the uncompressed data as
+possible when decompressing a corrupt file.
 
 @item -d
 @itemx --decompress
-Decompress.
+Decompress the specified file(s). If a file does not exist or can't be
+opened, clzip continues decompressing the rest of the files. If a file
+fails to decompress, clzip exits immediately without decompressing the
+rest of the files.
 
 @item -f
 @itemx --force
@@ -242,11 +260,13 @@ Quiet operation. Suppress all messages.
 
 @item -s @var{bytes}
 @itemx --dictionary-size=@var{bytes}
-Set the dictionary size limit in bytes. Valid values range from 4 KiB to
-512 MiB. Clzip will use the smallest possible dictionary size for each
-file without exceeding this limit. Note that dictionary sizes are
-quantized. If the specified size does not match one of the valid sizes,
-it will be rounded upwards by adding up to (@var{bytes} / 16) to it.
+Set the dictionary size limit in bytes. Clzip will use the smallest
+possible dictionary size for each file without exceeding 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. Note that
+dictionary sizes are quantized. If the specified size 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
@@ -257,7 +277,7 @@ is affected at compression time by the choice of dictionary size limit.
 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}. Each volume is a complete, maybe
-multi-member, lzip file. A small volume size may degrade compression
+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.
 
@@ -265,7 +285,8 @@ EiB.
 @itemx --test
 Check integrity of the specified file(s), 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 file.
+Use it together with @samp{-v} to see information about the file(s). If
+a file fails the test, clzip continues checking the rest of the files.
 
 @item -v
 @itemx --verbose
@@ -274,18 +295,19 @@ When compressing, show the compression ratio for each file processed. A
 second @samp{-v} shows the progress of compression.@*
 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).
+trailer contents (CRC, data size, member size), and up to 6 bytes of
+trailing data (if any).
 
 @item -0 .. -9
 Set the compression parameters (dictionary size and match length limit)
-as shown in the table below. Note that @samp{-9} can be much slower than
-@samp{-0}. These options have no effect when decompressing.
+as shown in the table below. The default compression level is @samp{-6}.
+Note that @samp{-9} can be much slower than @samp{-0}. These options
+have no effect when decompressing.
 
 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 @samp{--match-length} and
-@samp{--dictionary-size} options directly to achieve optimal
-performance.
+etc, you may need to use the @samp{--dictionary-size} and
+@samp{--match-length} options directly to achieve optimal performance.
 
 @multitable {Level} {Dictionary size} {Match length limit}
 @item Level @tab Dictionary size @tab Match length limit
@@ -364,14 +386,14 @@ additional information before, between, or after them.
 Each member has the following structure:
 @verbatim
 +--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| ID string | VN | DS | Lzma stream | CRC32 |   Data size   |  Member size  |
+| 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
+@item ID string (the "magic" bytes)
 A four byte string, identifying the lzip format, with the value "LZIP"
 (0x4C, 0x5A, 0x49, 0x50).
 
@@ -388,8 +410,8 @@ 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
+@item LZMA stream
+The LZMA stream, finished by an end of stream marker. Uses default
 values for encoder properties.
 @ifnothtml
 @xref{Stream format,,,lzip},
@@ -409,7 +431,7 @@ Size of the uncompressed original 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 safe recovery of undamaged members from multi-member files.
+facilitates safe recovery of undamaged members from multimember files.
 
 @end table
 
@@ -480,6 +502,44 @@ range encoding), Igor Pavlov (for putting all the above together in
 LZMA), and Julian Seward (for bzip2's CLI).
 
 
+@node Trailing data
+@chapter Extra data appended to the file
+@cindex trailing data
+
+Sometimes extra data is found appended to a lzip file after the last
+member. Such trailing data may be:
+
+@itemize @bullet
+@item
+Padding added to make the file size a multiple of some block size, for
+example when writing to a tape.
+
+@item
+Garbage added by some not totally successful copy operation.
+
+@item
+Useful data added by the user; a cryptographically secure hash, a
+description of file contents, etc.
+
+@item
+Malicious data added to the file in order to make its total size and
+hash value (for a chosen hash) coincide with those of another file.
+
+@item
+In very rare cases, trailing data could be the corrupt header of another
+member. In multimember or concatenated files the probability of
+corruption happening in the magic bytes is 5 times smaller than the
+probability of getting a false positive caused by the corruption of the
+integrity information itself. Therefore it can be considered to be below
+the noise level.
+@end itemize
+
+Trailing data can be safely ignored in most cases. In some cases, like
+that of user-added data, it is expected to be ignored. In those cases
+where a file containing trailing data must be rejected, the option
+@samp{--trailing-error} can be used. @xref{--trailing-error}.
+
+
 @node Examples
 @chapter A small tutorial with examples
 @cindex examples
@@ -487,7 +547,7 @@ LZMA), and Julian Seward (for bzip2's CLI).
 WARNING! Even if clzip is bug-free, other causes may result in a corrupt
 compressed file (bugs in the system libraries, memory errors, etc).
 Therefore, if the data you are going to compress are important, give the
-@samp{--keep} option to clzip and do not remove the original file until
+@samp{--keep} option to clzip and don't remove the original file until
 you verify the compressed file with a command like
 @w{@samp{clzip -cd file.lz | cmp file -}}.
 
@@ -502,7 +562,7 @@ clzip -v file
 
 @sp 1
 @noindent
-Example 2: Like example 1 but the created @samp{file.lz} is multi-member
+Example 2: Like example 1 but the created @samp{file.lz} is multimember
 with a member size of 1 MiB. The compression ratio is not shown.
 
 @example
@@ -530,16 +590,29 @@ clzip -tv file.lz
 
 @sp 1
 @noindent
-Example 5: Compress a whole floppy in /dev/fd0 and send the output to
+Example 5: Compress a whole device in /dev/sdc and send the output to
 @samp{file.lz}.
 
 @example
-clzip -c /dev/fd0 > file.lz
+clzip -c /dev/sdc > file.lz
+@end example
+
+@sp 1
+@anchor{concat-example}
+@noindent
+Example 6: The right way of concatenating compressed files.
+@xref{Trailing data}.
+
+@example
+Don't do this
+  cat file1.lz file2.lz file3.lz | clzip -d
+Do this instead
+  clzip -cd file1.lz file2.lz file3.lz
 @end example
 
 @sp 1
 @noindent
-Example 6: Decompress @samp{file.lz} partially until 10 KiB of
+Example 7: Decompress @samp{file.lz} partially until 10 KiB of
 decompressed data are produced.
 
 @example
@@ -548,7 +621,7 @@ clzip -cd file.lz | dd bs=1024 count=10
 
 @sp 1
 @noindent
-Example 7: Decompress @samp{file.lz} partially from decompressed byte
+Example 8: Decompress @samp{file.lz} partially from decompressed byte
 10000 to decompressed byte 15000 (5000 bytes are produced).
 
 @example
@@ -557,7 +630,7 @@ clzip -cd file.lz | dd bs=1000 skip=10 count=5
 
 @sp 1
 @noindent
-Example 8: Create a multivolume compressed tar archive with a volume
+Example 9: Create a multivolume compressed tar archive with a volume
 size of 1440 KiB.
 
 @example
@@ -566,7 +639,7 @@ tar -c some_directory | clzip -S 1440KiB -o volume_name
 
 @sp 1
 @noindent
-Example 9: Extract a multivolume compressed tar archive.
+Example 10: Extract a multivolume compressed tar archive.
 
 @example
 clzip -cd volume_name*.lz | tar -xf -
@@ -574,8 +647,8 @@ clzip -cd volume_name*.lz | tar -xf -
 
 @sp 1
 @noindent
-Example 10: Create a multivolume compressed backup of a large database
-file with a volume size of 650 MB, where each volume is a multi-member
+Example 11: Create a multivolume compressed backup of a large database
+file with a volume size of 650 MB, where each volume is a multimember
 file with a member size of 32 MiB.
 
 @example