lzma_.filter

Common filter related types and functions

Source:

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

License:
public domain

int LZMA_FILTERS_MAX;

Maximum number of filters in a chain

A filter chain can have 1-4 filters, of which three are allowed to change the size of the data. Usually only one or two filters are needed.

struct lzma_filter;

Filter options

This structure is used to pass Filter ID and a pointer filter's options to liblzma. A few functions work with a single lzma_filter structure, while most functions expect a filter chain.

A filter chain is indicated with an array of lzma_filter structures. The array is terminated with .id = LZMA_VLI_UNKNOWN. Thus, the filter array must have LZMA_FILTERS_MAX + 1 elements (that is, five) to be able to hold any arbitrary filter chain. This is important when using lzma_block_header_decode() from block.h, because too small array would make liblzma write past the end of the filters array.

lzma_vli id;

Filter ID

Use constants whose name begin with `LZMA_FILTER_' to specify different filters. In an array of lzma_filter structures, use LZMA_VLI_UNKNOWN to indicate end of filters.

Note:
This is not an enum, because on some systems enums cannot be 64-bit.

void* options;

Pointer to filter-specific options structure

If the filter doesn't need options, set this to NULL. If id is set to LZMA_VLI_UNKNOWN, options is ignored, and thus doesn't need be initialized.

lzma_bool lzma_filter_encoder_is_supported(lzma_vli id);

Test if the given Filter ID is supported for encoding

Return true if the give Filter ID is supported for encoding by this liblzma build. Otherwise false is returned.

There is no way to list which filters are available in this particular liblzma version and build. It would be useless, because the application couldn't know what kind of options the filter would need.

lzma_bool lzma_filter_decoder_is_supported(lzma_vli id);

Test if the given Filter ID is supported for decoding

Return true if the give Filter ID is supported for decoding by this liblzma build. Otherwise false is returned.

lzma_ret lzma_filters_copy(const lzma_filter* src, lzma_filter* dest, lzma_allocator* allocator);

Copy the filters array

Copy the Filter IDs and filter-specific options from src to dest. Up to LZMA_FILTERS_MAX filters are copied, plus the terminating .id == LZMA_VLI_UNKNOWN. Thus, dest should have at least LZMA_FILTERS_MAX + 1 elements space unless the caller knows that src is smaller than that.

Unless the filter-specific options is NULL, the Filter ID has to be supported by liblzma, because liblzma needs to know the size of every filter-specific options structure. The filter-specific options are not validated. If options is NULL, any unsupported Filter IDs are copied without returning an error.

Old filter-specific options in dest are not freed, so dest doesn't need to be initialized by the caller in any way.

If an error occurs, memory possibly already allocated by this function is always freed.

Returns:
- LZMA_OK - LZMA_MEM_ERROR - LZMA_OPTIONS_ERROR: Unsupported Filter ID and its options is not NULL. - LZMA_PROG_ERROR: src or dest is NULL.

ulong lzma_raw_encoder_memusage(const lzma_filter* filters);

Calculate approximate memory requirements for raw encoder

This function can be used to calculate the memory requirements for Block and Stream encoders too because Block and Stream encoders don't need significantly more memory than raw encoder.

Parameters:

lzma_filter* filters

Array of filters terminated with .id == LZMA_VLI_UNKNOWN.

Returns:
Number of bytes of memory required for the given filter chain when encoding.

ulong lzma_raw_decoder_memusage(const lzma_filter* filters);

Calculate approximate memory requirements for raw decoder

This function can be used to calculate the memory requirements for Block and Stream decoders too because Block and Stream decoders don't need significantly more memory than raw decoder.

Parameters:

lzma_filter* filters

Array of filters terminated with .id == LZMA_VLI_UNKNOWN.

Returns:
Number of bytes of memory required for the given filter chain when decoding.

lzma_ret lzma_raw_encoder(lzma_stream* strm, const lzma_filter* filters);

Initialize raw encoder

This function may be useful when implementing custom file formats.

Parameters:

Returns:
- LZMA_OK - LZMA_MEM_ERROR - LZMA_OPTIONS_ERROR - LZMA_PROG_ERROR

lzma_ret lzma_raw_decoder(lzma_stream* strm, const lzma_filter* filters);

Initialize raw decoder

The initialization of raw decoder goes similarly to raw encoder.

The `action' with lzma_code() can be LZMA_RUN or LZMA_FINISH. Using LZMA_FINISH is not required, it is supported just for convenience.

Returns:
- LZMA_OK - LZMA_MEM_ERROR - LZMA_OPTIONS_ERROR - LZMA_PROG_ERROR

lzma_ret lzma_filters_update(lzma_stream* strm, const lzma_filter* filters);

Update the filter chain in the encoder

This function is for advanced users only. This function has two slightly different purposes:

- After LZMA_FULL_FLUSH when using Stream encoder: Set a new filter chain, which will be used starting from the next Block.

- After LZMA_SYNC_FLUSH using Raw, Block, or Stream encoder: Change the filter-specific options in the middle of encoding. The actual filters in the chain (Filter IDs) cannot be changed. In the future, it might become possible to change the filter options without using LZMA_SYNC_FLUSH.

While rarely useful, this function may be called also when no data has been compressed yet. In that case, this function will behave as if LZMA_FULL_FLUSH (Stream encoder) or LZMA_SYNC_FLUSH (Raw or Block encoder) had been used right before calling this function.

Returns:
- LZMA_OK - LZMA_MEM_ERROR - LZMA_MEMLIMIT_ERROR - LZMA_OPTIONS_ERROR - LZMA_PROG_ERROR

lzma_ret lzma_raw_buffer_encode(const lzma_filter* filters, lzma_allocator* allocator, const(ubyte)* in_, size_t in_size, ubyte* out_, uint* out_pos, size_t out_size);

Single-call raw encoder

Parameters:

lzma_filter* filters	Array of lzma_filter structures. The end of the array must be marked with .id = LZMA_VLI_UNKNOWN.
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

Note:
There is no function to calculate how big output buffer would surely be big enough. (lzma_stream_buffer_bound() works only for lzma_stream_buffer_encode(); raw encoder won't necessarily meet that bound.)

lzma_ret lzma_raw_buffer_decode(const lzma_filter* filters, lzma_allocator* allocator, const(ubyte)* in_, uint* in_pos, size_t in_size, ubyte* out_, uint* out_pos, size_t out_size);

Single-call raw decoder

Parameters:

lzma_filter* filters	Array of lzma_filter structures. The end of the array must be marked with .id = LZMA_VLI_UNKNOWN.
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].

lzma_ret lzma_properties_size(uint* size, const lzma_filter* filter);

Get the size of the Filter Properties field

This function may be useful when implementing custom file formats using the raw encoder and decoder.

Parameters:

uint* size	Pointer to uint to hold the size of the properties
lzma_filter* filter	Filter ID and options (the size of the properties may vary depending on the options)

Returns:
- LZMA_OK - LZMA_OPTIONS_ERROR - LZMA_PROG_ERROR

Note:
This function validates the Filter ID, but does not necessarily validate the options. Thus, it is possible that this returns LZMA_OK while the following call to lzma_properties_encode() returns LZMA_OPTIONS_ERROR.

lzma_ret lzma_properties_encode(const lzma_filter* filter, ubyte* props);

Encode the Filter Properties field

Parameters:

lzma_filter* filter	Filter ID and options
ubyte* props	Buffer to hold the encoded options. The size of buffer must have been already determined with lzma_properties_size().

Returns:
- LZMA_OK - LZMA_OPTIONS_ERROR - LZMA_PROG_ERROR

Note:
Even this function won't validate more options than actually necessary. Thus, it is possible that encoding the properties succeeds but using the same options to initialize the encoder will fail.

Note:
If lzma_properties_size() indicated that the size of the Filter Properties field is zero, calling lzma_properties_encode() is not required, but it won't do any harm either.

lzma_ret lzma_properties_decode(lzma_filter* filter, lzma_allocator* allocator, const ubyte* props, size_t props_size);

Decode the Filter Properties field

Parameters:

lzma_filter* filter	filter->id must have been set to the correct Filter ID. filter->options doesn't need to be initialized (it's not freed by this function). The decoded options will be stored to filter->options. filter->options is set to NULL if there are no properties or if an error occurs.
lzma_allocator* allocator	Custom memory allocator used to allocate the options. Set to NULL to use the default malloc(), and in case of an error, also free().
ubyte* props	Input buffer containing the properties.
size_t props_size	Size of the properties. This must be the exact size; giving too much or too little input will return LZMA_OPTIONS_ERROR.

Returns:
- LZMA_OK - LZMA_OPTIONS_ERROR - LZMA_MEM_ERROR

lzma_ret lzma_filter_flags_size(uint* size, const lzma_filter* filter);

Calculate encoded size of a Filter Flags field

Knowing the size of Filter Flags is useful to know when allocating memory to hold the encoded Filter Flags.

Parameters:

uint* size	Pointer to integer to hold the calculated size
lzma_filter* filter	Filter ID and associated options whose encoded size is to be calculated

Returns:
- LZMA_OK: *size set successfully. Note that this doesn't guarantee that filter->options is valid, thus lzma_filter_flags_encode() may still fail. - LZMA_OPTIONS_ERROR: Unknown Filter ID or unsupported options. - LZMA_PROG_ERROR: Invalid options

Note:
If you need to calculate size of List of Filter Flags, you need to loop over every lzma_filter entry.

lzma_ret lzma_filter_flags_encode(const lzma_filter* filter, ubyte* out_, uint* out_pos, size_t out_size);

Encode Filter Flags into given buffer

In contrast to some functions, this doesn't allocate the needed buffer. This is due to how this function is used internally by liblzma.

Parameters:

lzma_filter* filter	Filter ID and options to be encoded
ubyte* out_	Beginning of the output buffer
uint* out_pos	out[*out_pos] is the next write position. This = is updated by the encoder.
size_t out_size	out[out_size] is the first byte to not write.

Returns:
- LZMA_OK: Encoding was successful. - LZMA_OPTIONS_ERROR: Invalid or unsupported options. - LZMA_PROG_ERROR: Invalid options or not enough output buffer space (you should have checked it with lzma_filter_flags_size()).

lzma_ret lzma_filter_flags_decode(lzma_filter* filter, lzma_allocator* allocator, const ubyte* in_, uint* in_pos, size_t in_size);

Decode Filter Flags from given buffer

The decoded result is stored into *filter. The old value of filter->options is not free()d.

Returns:
- LZMA_OK - LZMA_OPTIONS_ERROR - LZMA_MEM_ERROR - LZMA_PROG_ERROR

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