lzma_.block

.xz Block handling

Source:

Author:
Lasse Collin (original liblzma author), Johannes Pfau (D bindings)

License:
public domain

struct lzma_block;

Options for the Block and Block Header encoders and decoders

Different Block handling functions use different parts of this structure. Some read some members, other functions write, and some do both. Only the members listed for reading need to be initialized when the specified functions are called. The members marked for writing will be assigned new values at some point either by calling the given function or by later calls to lzma_code().

uint version_;

Block format version

To prevent API and ABI breakages if new features are needed in 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: - All functions that take pointer to lzma_block as argument, including lzma_block_header_decode().

Written by: - lzma_block_header_decode()

uint header_size;

Size of the Block Header field

This is always a multiple of four.

Read by: - lzma_block_header_encode() - lzma_block_header_decode() - lzma_block_compressed_size() - lzma_block_unpadded_size() - lzma_block_total_size() - lzma_block_decoder() - lzma_block_buffer_decode()

Written by: - lzma_block_header_size() - lzma_block_buffer_encode()

int LZMA_BLOCK_HEADER_SIZE_MIN;

int LZMA_BLOCK_HEADER_SIZE_MAX;

lzma_check check;

Type of integrity Check

The Check ID is not stored into the Block Header, thus its value must be provided also when decoding.

lzma_vli compressed_size;

Size of the Compressed Data in bytes

Encoding:
If this is not LZMA_VLI_UNKNOWN, Block Header encoder will store this value to the Block Header. Block encoder doesn't care about this value, but will set it once the encoding has been finished.

Decoding:
If this is not LZMA_VLI_UNKNOWN, Block decoder will verify that the size of the Compressed Data field matches compressed_size.

Usually you don't know this value when encoding in streamed mode, and thus cannot write this field into the Block Header.

In non-streamed mode you can reserve space for this field before encoding the actual Block. After encoding the data, finish the Block by encoding the Block Header. Steps in detail:

- Set compressed_size to some big enough value. If you don't know better, use LZMA_VLI_MAX, but remember that bigger values take more space in Block Header.

- Call lzma_block_header_size() to see how much space you need to reserve for the Block Header.

- Encode the Block using lzma_block_encoder() and lzma_code(). It sets compressed_size to the correct value.

- Use lzma_block_header_encode() to encode the Block Header. Because space was reserved in the first step, you don't need to call lzma_block_header_size() anymore, because due to reserving, header_size has to be big enough. If it is "too big", lzma_block_header_encode() will add enough Header Padding to make Block Header to match the size specified by header_size.

Read by: - lzma_block_header_size() - lzma_block_header_encode() - lzma_block_compressed_size() - lzma_block_unpadded_size() - lzma_block_total_size() - lzma_block_decoder() - lzma_block_buffer_decode()

Written by: - lzma_block_header_decode() - lzma_block_compressed_size() - lzma_block_encoder() - lzma_block_decoder() - lzma_block_buffer_encode() - lzma_block_buffer_decode()

lzma_vli uncompressed_size;

Uncompressed Size in bytes

This is handled very similarly to compressed_size above.

uncompressed_size is needed by fewer functions than compressed_size. This is because uncompressed_size isn't needed to validate that Block stays within proper limits.

Read by: - lzma_block_header_size() - lzma_block_header_encode() - lzma_block_decoder() - lzma_block_buffer_decode()

Written by: - lzma_block_header_decode() - lzma_block_encoder() - lzma_block_decoder() - lzma_block_buffer_encode() - lzma_block_buffer_decode()

lzma_filter* filters;

Array of filters

There can be 1-4 filters. The end of the array is marked with .id = LZMA_VLI_UNKNOWN.

Read by: - lzma_block_header_size() - lzma_block_header_encode() - lzma_block_encoder() - lzma_block_decoder() - lzma_block_buffer_encode() - lzma_block_buffer_decode()

Written by: - lzma_block_header_decode(): Note that this does NOT free() the old filter options structures. All unused filters[] will have .id == LZMA_VLI_UNKNOWN and .options == NULL. If decoding fails, all filters[] are guaranteed to be LZMA_VLI_UNKNOWN and NULL.

Note:
Because of the array is terminated with .id = LZMA_VLI_UNKNOWN, the actual array must have LZMA_FILTERS_MAX + 1 members or the Block Header decoder will overflow the buffer.

ubyte[LZMA_CHECK_SIZE_MAX] raw_check;

Raw value stored in the Check field

After successful coding, the first lzma_check_size(check) bytes of this array contain the raw value stored in the Check field.

Note that CRC32 and CRC64 are stored in little endian byte order. Take it into account if you display the Check values to the user.

Written by: - lzma_block_encoder() - lzma_block_decoder() - lzma_block_buffer_encode() - lzma_block_buffer_decode()

template lzma_block_header_size_decode(uint b)

Decode the Block Header Size field

To decode Block Header using lzma_block_header_decode(), the size of the Block Header has to be known and stored into lzma_block.header_size. The size can be calculated from the first byte of a Block using this macro. Note that if the first byte is 0x00, it indicates beginning of Index; use this macro only when the byte is not 0x00.

There is no encoding macro, because Block Header encoder is enough for that.

lzma_ret lzma_block_header_size(lzma_block* block);

Calculate Block Header Size

Calculate the minimum size needed for the Block Header field using the settings specified in the lzma_block structure. Note that it is OK to increase the calculated header_size value as long as it is a multiple of four and doesn't exceed LZMA_BLOCK_HEADER_SIZE_MAX. Increasing header_size just means that lzma_block_header_encode() will add Header Padding.

Returns:
- LZMA_OK: Size calculated successfully and stored to block.header_size. - LZMA_OPTIONS_ERROR: Unsupported version, filters or filter options. - LZMA_PROG_ERROR: Invalid values like compressed_size == 0.

Note:
This doesn't check that all the options are valid i.e. this may return LZMA_OK even if lzma_block_header_encode() or lzma_block_encoder() would fail. If you want to validate the filter chain, consider using lzma_memlimit_encoder() which as a side-effect validates the filter chain.

lzma_ret lzma_block_header_encode(const(lzma_block)* block, ubyte* out_);

Encode Block Header

The caller must have calculated the size of the Block Header already with lzma_block_header_size(). If a value larger than the one calculated by lzma_block_header_size() is used, the Block Header will be padded to the specified size.

Parameters:

ubyte* out_	Beginning of the output buffer. This must be at least block.header_size bytes.
const(lzma_block)* block	Block options to be encoded.

Returns:
- LZMA_OK: Encoding was successful. block.header_size bytes were written to output buffer. - LZMA_OPTIONS_ERROR: Invalid or unsupported options. - LZMA_PROG_ERROR: Invalid arguments, for example block.header_size is invalid or block.filters is NULL.

lzma_ret lzma_block_header_decode(lzma_block* block, lzma_allocator* allocator, const(ubyte)* in_);

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 they don't need to be initialized (possible existing filter options are not freed).

Parameters:

lzma_block* block	Destination for Block options.
lzma_allocator* allocator	lzma_allocator for custom allocator functions. Set to NULL to use malloc() (and also free() if an error occurs).
const(ubyte)* in_	Beginning of the input buffer. This must be at least block.header_size bytes.

Returns:
- 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. 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 block.header_size is invalid or block.filters is NULL.

lzma_ret lzma_block_compressed_size(lzma_block* block, lzma_vli unpadded_size);

Validate and set Compressed Size according to Unpadded Size

Block Header stores Compressed Size, but Index has Unpadded Size. If the application has already parsed the Index and is now decoding Blocks, it can calculate Compressed Size from Unpadded Size. This function does exactly that with error checking:

- Compressed Size calculated from Unpadded Size must be positive integer, that is, Unpadded Size must be big enough that after Block Header and Check fields there's still at least one byte for Compressed Size.

- If Compressed Size was present in Block Header, the new value calculated from Unpadded Size is compared against the value from Block Header.

Note:
This function must be called after_ decoding the Block Header field so that it can properly validate Compressed Size if it was present in Block Header.

Returns:
- LZMA_OK: block.compressed_size was set successfully. - LZMA_DATA_ERROR: unpadded_size is too small compared to block.header_size and lzma_check_size(block.check). - LZMA_PROG_ERROR: Some values are invalid. For example, block.header_size must be a multiple of four and between 8 and 1024 inclusive.

lzma_vli lzma_block_unpadded_size(const lzma_block* block);

Calculate Unpadded Size

The Index field stores Unpadded Size and Uncompressed Size. The latter can be taken directly from the lzma_block structure after coding a Block, but Unpadded Size needs to be calculated from Block Header Size, Compressed Size, and size of the Check field. This is where this function is needed.

Returns:
Unpadded Size on success, or zero on error.

lzma_vli lzma_block_total_size(const(lzma_block*) block);

Calculate the total encoded size of a Block

This is equivalent to lzma_block_unpadded_size() except that the returned value includes the size of the Block Padding field.

Returns:
On success, total encoded size of the Block. On error, zero is returned.

lzma_ret lzma_block_encoder(lzma_stream* strm, lzma_block* block);

Initialize .xz Block encoder

Valid actions for lzma_code() are LZMA_RUN, LZMA_SYNC_FLUSH (only if the filter chain supports it), and LZMA_FINISH.

Returns:
- LZMA_OK: All good, continue with lzma_code(). - LZMA_MEM_ERROR - LZMA_OPTIONS_ERROR - LZMA_UNSUPPORTED_CHECK: block.check specifies a Check ID that is not supported by this buid of liblzma. Initializing the encoder failed. - LZMA_PROG_ERROR

lzma_ret lzma_block_decoder(lzma_stream* strm, lzma_block* block);

Initialize .xz Block decoder

Valid actions for lzma_code() are LZMA_RUN and LZMA_FINISH. Using LZMA_FINISH is not required. It is supported only for convenience.

Returns:
- LZMA_OK: All good, continue with lzma_code(). - LZMA_UNSUPPORTED_CHECK: Initialization was successful, but the given Check ID is not supported, thus Check will be ignored. - LZMA_PROG_ERROR - LZMA_MEM_ERROR

size_t lzma_block_buffer_bound(size_t uncompressed_size);

Calculate maximum output size for single-call Block encoding

This is equivalent to lzma_stream_buffer_bound() but for .xz Blocks. See the documentation of lzma_stream_buffer_bound().

lzma_ret lzma_block_buffer_encode(lzma_block* block, lzma_allocator* allocator, const(ubyte)* in_, size_t in_size, ubyte* out_, uint* out_pos, size_t out_size);

Single-call .xz Block encoder

In contrast to the multi-call encoder initialized with lzma_block_encoder(), this function encodes also the Block Header. This is required to make it possible to write appropriate Block Header also in case the data isn't compressible, and different filter chain has to be used to encode the data in uncompressed form using uncompressed chunks of the LZMA2 filter.

When the data isn't compressible, header_size, compressed_size, and uncompressed_size are set just like when the data was compressible, but it is possible that header_size is too small to hold the filter chain specified in block.filters, because that isn't necessarily the filter chain that was actually used to encode the data. lzma_block_unpadded_size() still works normally, because it doesn't read the filters array.

Parameters:

lzma_block* block	Block options: block.version_, block.check, and block.filters must have been initialized.
lzma_allocator* allocator	lzma_allocator for custom allocator functions. Set to NULL to use malloc() and free().
const(ubyte)* in_	Beginning of the input buffer
size_t in_size	Size of the input buffer
ubyte* out_	Beginning of the output buffer
uint* out_pos	The next byte will be written to out[*out_pos]. *out_pos is updated only if encoding succeeds.
size_t out_size	Size of the out buffer; the first byte into which no data is written to is out[out_size]. Returns - LZMA_OK: Encoding was successful. - LZMA_BUF_ERROR: Not enough output buffer space. - LZMA_OPTIONS_ERROR - LZMA_MEM_ERROR - LZMA_DATA_ERROR - LZMA_PROG_ERROR

lzma_ret lzma_block_buffer_decode(lzma_block* block, lzma_allocator* allocator, const(ubyte)* in_, uint* in_pos, size_t in_size, ubyte* out_, uint* out_pos, size_t out_size);

Single-call .xz Block decoder

This is single-call equivalent of lzma_block_decoder(), and requires that the caller has already decoded Block Header and checked its memory usage.

Parameters:

lzma_block* block	Block options just like with lzma_block_decoder().
lzma_allocator* allocator	lzma_allocator for custom allocator functions. Set to NULL to use malloc() and free().
const(ubyte)* in_	Beginning of the input buffer
uint* in_pos	The next byte will be read from in[*in_pos]. *in_pos is updated only if decoding succeeds.
size_t in_size	Size of the input buffer; the first byte that won't be read is in[in_size].
ubyte* out_	Beginning of the output buffer
uint* out_pos	The next byte will be written to out[*out_pos]. *out_pos is updated only if encoding succeeds.
size_t out_size	Size of the out buffer; the first byte into which no data is written to is out[out_size]. Returns - LZMA_OK: Decoding was successful. - LZMA_OPTIONS_ERROR - LZMA_DATA_ERROR - LZMA_MEM_ERROR - LZMA_BUF_ERROR: Output buffer was too small. - LZMA_PROG_ERROR

Main module

lzma_

lzma_.block