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Subtle change to liblzma Block handling API.

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lzma_block.version has to be initialized even for
lzma_block_header_decode(). This way a future version
of liblzma won't allocate memory in a way that an old
application doesn't know how to free it.

The subtlety of this change is that all current apps
using lzma_block_header_decode() will keep working for
now, because the only possible version value is zero,
and lzma_block_header_decode() unconditionally sets the
version to zero even now. Unless fixed, these apps will
break in the future if a new version of the Block options
is ever needed.
This commit is contained in:
Lasse Collin 2010-02-07 19:48:06 +02:00
parent dd7c3841ff
commit 6503fde658
2 changed files with 20 additions and 22 deletions
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39
src/liblzma/api/lzma/block.h
View file

@ -32,27 +32,14 @@ typedef struct {
* \brief Block format version
*
* To prevent API and ABI breakages if new features are needed in
* Block, a version number is used to indicate which fields in this
* structure are in use. For now, version must always be zero.
* With non-zero version, most Block related functions will return
* LZMA_OPTIONS_ERROR.
*
* The decoding functions will always set this to the lowest value
* that supports all the features indicated by the Block Header field.
* The application must check that the version number set by the
* decoding functions is supported by the application. Otherwise it
* is possible that the application will decode the Block incorrectly.
* the Block field, a version number is used to indicate which
* fields in this structure are in use. For now, version must always
* be zero. With non-zero version, most Block related functions will
* return LZMA_OPTIONS_ERROR.
*
* Read by:
* - lzma_block_header_size()
* - lzma_block_header_encode()
* - lzma_block_compressed_size()
* - lzma_block_unpadded_size()
* - lzma_block_total_size()
* - lzma_block_encoder()
* - lzma_block_decoder()
* - lzma_block_buffer_encode()
* - lzma_block_buffer_decode()
* - All functions that take pointer to lzma_block as argument,
* including lzma_block_header_decode().
*
* Written by:
* - lzma_block_header_decode()
@ -323,13 +310,18 @@ extern LZMA_API(lzma_ret) lzma_block_header_encode(
/**
* \brief Decode Block Header
*
* block->version should be set to the highest value supported by the
* application; currently the only possible version is zero. This function
* will set version to the lowest value that still supports all the features
* required by the Block Header.
*
* The size of the Block Header must have already been decoded with
* lzma_block_header_size_decode() macro and stored to block->header_size.
*
* block->filters must have been allocated, but not necessarily initialized.
* Possible existing filter options are _not_ freed.
*
* \param block Destination for block options with header_size
* properly initialized.
* \param block Destination for Block options.
* \param allocator lzma_allocator for custom allocator functions.
* Set to NULL to use malloc() (and also free()
* if an error occurs).
@ -339,7 +331,10 @@ extern LZMA_API(lzma_ret) lzma_block_header_encode(
* \return - LZMA_OK: Decoding was successful. block->header_size
* bytes were read from the input buffer.
* - LZMA_OPTIONS_ERROR: The Block Header specifies some
* unsupported options such as unsupported filters.
* unsupported options such as unsupported filters. This can
* happen also if block->version was set to a too low value
* compared to what would be required to properly represent
* the information stored in the Block Header.
* - LZMA_DATA_ERROR: Block Header is corrupt, for example,
* the CRC32 doesn't match.
* - LZMA_PROG_ERROR: Invalid arguments, for example

3
src/liblzma/common/stream_decoder.c
View file

@ -182,6 +182,9 @@ stream_decode(lzma_coder *coder, lzma_allocator *allocator,
coder->pos = 0;
// Version 0 is currently the only possible version.
coder->block_options.version = 0;
// Set up a buffer to hold the filter chain. Block Header
// decoder will initialize all members of this array so
// we don't need to do it here.