# 1.9.2 Manual

## Contents

1. Introduction
2. Compiler specifics
3. Error management
4. Frame compression types
5. Simple compression function
6. Advanced compression functions
7. Resource Management
8. Compression
9. Decompression functions
10. Streaming decompression functions
11. Bulk processing dictionary API

## Introduction

      lz4frame.h implements LZ4 frame specification (doc/lz4_Frame_format.md).
      lz4frame.h provides frame compression functions that take care
      of encoding standard metadata alongside LZ4-compressed blocks.

## Compiler specifics

## Error management

    unsigned    LZ4F_isError(LZ4F_errorCode_t code);   /**< tells when a function result is an error code */

    const char* LZ4F_getErrorName(LZ4F_errorCode_t code);   /**< return error code string; for debugging */

## Frame compression types

    typedef enum {
        LZ4F_default=0,
        LZ4F_max64KB=4,
        LZ4F_max256KB=5,
        LZ4F_max1MB=6,
        LZ4F_max4MB=7
        LZ4F_OBSOLETE_ENUM(max64KB)
        LZ4F_OBSOLETE_ENUM(max256KB)
        LZ4F_OBSOLETE_ENUM(max1MB)
        LZ4F_OBSOLETE_ENUM(max4MB)
    } LZ4F_blockSizeID_t;

    typedef enum {
        LZ4F_blockLinked=0,
        LZ4F_blockIndependent
        LZ4F_OBSOLETE_ENUM(blockLinked)
        LZ4F_OBSOLETE_ENUM(blockIndependent)
    } LZ4F_blockMode_t;

    typedef enum {
        LZ4F_noContentChecksum=0,
        LZ4F_contentChecksumEnabled
        LZ4F_OBSOLETE_ENUM(noContentChecksum)
        LZ4F_OBSOLETE_ENUM(contentChecksumEnabled)
    } LZ4F_contentChecksum_t;

    typedef enum {
        LZ4F_noBlockChecksum=0,
        LZ4F_blockChecksumEnabled
    } LZ4F_blockChecksum_t;

    typedef enum {
        LZ4F_frame=0,
        LZ4F_skippableFrame
        LZ4F_OBSOLETE_ENUM(skippableFrame)
    } LZ4F_frameType_t;

    typedef struct {
      LZ4F_blockSizeID_t     blockSizeID;         /* max64KB, max256KB, max1MB, max4MB; 0 == default */
      LZ4F_blockMode_t       blockMode;           /* LZ4F_blockLinked, LZ4F_blockIndependent; 0 == default */
      LZ4F_contentChecksum_t contentChecksumFlag; /* 1: frame terminated with 32-bit checksum of decompressed data; 0: disabled (default) */
      LZ4F_frameType_t       frameType;           /* read-only field : LZ4F_frame or LZ4F_skippableFrame */
      unsigned long long     contentSize;         /* Size of uncompressed content ; 0 == unknown */
      unsigned               dictID;              /* Dictionary ID, sent by compressor to help decoder select correct dictionary; 0 == no dictID provided */
      LZ4F_blockChecksum_t   blockChecksumFlag;   /* 1: each block followed by a checksum of block's compressed data; 0: disabled (default) */
    } LZ4F_frameInfo_t;
      makes it possible to set or read frame parameters.
      Structure must be first init to 0, using memset() or LZ4F_INIT_FRAMEINFO,
      setting all parameters to default.
      It's then possible to update selectively some parameters

    typedef struct {
      LZ4F_frameInfo_t frameInfo;
      int      compressionLevel;    /* 0: default (fast mode); values > LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values < 0 trigger "fast acceleration" */
      unsigned autoFlush;           /* 1: always flush; reduces usage of internal buffers */
      unsigned favorDecSpeed;       /* 1: parser favors decompression speed vs compression ratio. Only works for high compression modes (>= LZ4HC_CLEVEL_OPT_MIN) */  /* v1.8.2+ */
      unsigned reserved[3];         /* must be zero for forward compatibility */
    } LZ4F_preferences_t;
      makes it possible to supply advanced compression instructions to streaming interface.
      Structure must be first init to 0, using memset() or LZ4F_INIT_PREFERENCES,
      setting all parameters to default.
      All reserved fields must be set to zero.

## Simple compression function

    size_t LZ4F_compressFrameBound(size_t srcSize, const LZ4F_preferences_t* preferencesPtr);
      Returns the maximum possible compressed size with LZ4F_compressFrame() given srcSize and preferences.
     `preferencesPtr` is optional. It can be replaced by NULL, in which case, the function will assume default preferences.
      Note : this result is only usable with LZ4F_compressFrame().
             It may also be used with LZ4F_compressUpdate() _if no flush() operation_ is performed.

    size_t LZ4F_compressFrame(void* dstBuffer, size_t dstCapacity,
                                    const void* srcBuffer, size_t srcSize,
                                    const LZ4F_preferences_t* preferencesPtr);
      Compress an entire srcBuffer into a valid LZ4 frame.
      dstCapacity MUST be >= LZ4F_compressFrameBound(srcSize, preferencesPtr).
      The LZ4F_preferences_t structure is optional : you can provide NULL as argument. All preferences will be set to default.
     @return : number of bytes written into dstBuffer.
               or an error code if it fails (can be tested using LZ4F_isError())

## Advanced compression functions

    typedef struct {
      unsigned stableSrc;    /* 1 == src content will remain present on future calls to LZ4F_compress(); skip copying src content within tmp buffer */
      unsigned reserved[3];
    } LZ4F_compressOptions_t;

## Resource Management

    LZ4F_errorCode_t LZ4F_createCompressionContext(LZ4F_cctx** cctxPtr, unsigned version);
    LZ4F_errorCode_t LZ4F_freeCompressionContext(LZ4F_cctx* cctx);
     The first thing to do is to create a compressionContext object, which will be used in all compression operations.
     This is achieved using LZ4F_createCompressionContext(), which takes as argument a version.
     The version provided MUST be LZ4F_VERSION. It is intended to track potential version mismatch, notably when using DLL.
     The function will provide a pointer to a fully allocated LZ4F_cctx object.
     If @return != zero, there was an error during context creation.
     Object can release its memory using LZ4F_freeCompressionContext();

## Compression

    size_t LZ4F_compressBegin(LZ4F_cctx* cctx,
                                          void* dstBuffer, size_t dstCapacity,
                                          const LZ4F_preferences_t* prefsPtr);
      will write the frame header into dstBuffer.
      dstCapacity must be >= LZ4F_HEADER_SIZE_MAX bytes.
     `prefsPtr` is optional : you can provide NULL as argument, all preferences will then be set to default.
     @return : number of bytes written into dstBuffer for the header
               or an error code (which can be tested using LZ4F_isError())

    size_t LZ4F_compressBound(size_t srcSize, const LZ4F_preferences_t* prefsPtr);
      Provides minimum dstCapacity required to guarantee success of
      LZ4F_compressUpdate(), given a srcSize and preferences, for a worst case scenario.
      When srcSize==0, LZ4F_compressBound() provides an upper bound for LZ4F_flush() and LZ4F_compressEnd() instead.
      Note that the result is only valid for a single invocation of LZ4F_compressUpdate().
      When invoking LZ4F_compressUpdate() multiple times,
      if the output buffer is gradually filled up instead of emptied and re-used from its start,
      one must check if there is enough remaining capacity before each invocation, using LZ4F_compressBound().
     @return is always the same for a srcSize and prefsPtr.
      prefsPtr is optional : when NULL is provided, preferences will be set to cover worst case scenario.
      tech details :
     @return includes the possibility that internal buffer might already be filled by up to (blockSize-1) bytes.
      It also includes frame footer (ending + checksum), since it might be generated by LZ4F_compressEnd().
     @return doesn't include frame header, as it was already generated by LZ4F_compressBegin().

    size_t LZ4F_compressUpdate(LZ4F_cctx* cctx,
                                           void* dstBuffer, size_t dstCapacity,
                                     const void* srcBuffer, size_t srcSize,
                                     const LZ4F_compressOptions_t* cOptPtr);
      LZ4F_compressUpdate() can be called repetitively to compress as much data as necessary.
      Important rule: dstCapacity MUST be large enough to ensure operation success even in worst case situations.
      This value is provided by LZ4F_compressBound().
      If this condition is not respected, LZ4F_compress() will fail (result is an errorCode).
      LZ4F_compressUpdate() doesn't guarantee error recovery.
      When an error occurs, compression context must be freed or resized.
     `cOptPtr` is optional : NULL can be provided, in which case all options are set to default.
     @return : number of bytes written into `dstBuffer` (it can be zero, meaning input data was just buffered).
               or an error code if it fails (which can be tested using LZ4F_isError())

    size_t LZ4F_flush(LZ4F_cctx* cctx,
                                  void* dstBuffer, size_t dstCapacity,
                            const LZ4F_compressOptions_t* cOptPtr);
      When data must be generated and sent immediately, without waiting for a block to be completely filled,
      it's possible to call LZ4_flush(). It will immediately compress any data buffered within cctx.
     `dstCapacity` must be large enough to ensure the operation will be successful.
     `cOptPtr` is optional : it's possible to provide NULL, all options will be set to default.
     @return : nb of bytes written into dstBuffer (can be zero, when there is no data stored within cctx)
               or an error code if it fails (which can be tested using LZ4F_isError())
      Note : LZ4F_flush() is guaranteed to be successful when dstCapacity >= LZ4F_compressBound(0, prefsPtr).

    size_t LZ4F_compressEnd(LZ4F_cctx* cctx,
                                        void* dstBuffer, size_t dstCapacity,
                                  const LZ4F_compressOptions_t* cOptPtr);
      To properly finish an LZ4 frame, invoke LZ4F_compressEnd().
      It will flush whatever data remained within `cctx` (like LZ4_flush())
      and properly finalize the frame, with an endMark and a checksum.
     `cOptPtr` is optional : NULL can be provided, in which case all options will be set to default.
     @return : nb of bytes written into dstBuffer, necessarily >= 4 (endMark),
               or an error code if it fails (which can be tested using LZ4F_isError())
      Note : LZ4F_compressEnd() is guaranteed to be successful when dstCapacity >= LZ4F_compressBound(0, prefsPtr).
      A successful call to LZ4F_compressEnd() makes `cctx` available again for another compression task.

## Decompression functions

    typedef struct {
      unsigned stableDst;    /* pledges that last 64KB decompressed data will remain available unmodified. This optimization skips storage operations in tmp buffers. */
      unsigned reserved[3];  /* must be set to zero for forward compatibility */
    } LZ4F_decompressOptions_t;

    LZ4F_errorCode_t LZ4F_createDecompressionContext(LZ4F_dctx** dctxPtr, unsigned version);
    LZ4F_errorCode_t LZ4F_freeDecompressionContext(LZ4F_dctx* dctx);
      Create an LZ4F_dctx object, to track all decompression operations.
      The version provided MUST be LZ4F_VERSION.
      The function provides a pointer to an allocated and initialized LZ4F_dctx object.
      The result is an errorCode, which can be tested using LZ4F_isError().
      dctx memory can be released using LZ4F_freeDecompressionContext();
      Result of LZ4F_freeDecompressionContext() indicates current state of decompressionContext when being released.
      That is, it should be == 0 if decompression has been completed fully and correctly.

## Streaming decompression functions

    size_t LZ4F_headerSize(const void* src, size_t srcSize);
      Provide the header size of a frame starting at `src`.
     `srcSize` must be >= LZ4F_MIN_SIZE_TO_KNOW_HEADER_LENGTH,
      which is enough to decode the header length.
     @return : size of frame header
               or an error code, which can be tested using LZ4F_isError()
      note : Frame header size is variable, but is guaranteed to be
             >= LZ4F_HEADER_SIZE_MIN bytes, and <= LZ4F_HEADER_SIZE_MAX bytes.

    size_t LZ4F_getFrameInfo(LZ4F_dctx* dctx,
                                         LZ4F_frameInfo_t* frameInfoPtr,
                                         const void* srcBuffer, size_t* srcSizePtr);
      This function extracts frame parameters (max blockSize, dictID, etc.).
      Its usage is optional: user can call LZ4F_decompress() directly.

      Extracted information will fill an existing LZ4F_frameInfo_t structure.
      This can be useful for allocation and dictionary identification purposes.

      LZ4F_getFrameInfo() can work in the following situations :

      1) At the beginning of a new frame, before any invocation of LZ4F_decompress().
         It will decode header from `srcBuffer`,
         consuming the header and starting the decoding process.

         Input size must be large enough to contain the full frame header.
         Frame header size can be known beforehand by LZ4F_headerSize().
         Frame header size is variable, but is guaranteed to be >= LZ4F_HEADER_SIZE_MIN bytes,
         and not more than <= LZ4F_HEADER_SIZE_MAX bytes.
         Hence, blindly providing LZ4F_HEADER_SIZE_MAX bytes or more will always work.
         It's allowed to provide more input data than the header size,
         LZ4F_getFrameInfo() will only consume the header.

         If input size is not large enough,
         aka if it's smaller than header size,
         function will fail and return an error code.

      2) After decoding has been started,
         it's possible to invoke LZ4F_getFrameInfo() anytime
         to extract already decoded frame parameters stored within dctx.

         Note that, if decoding has barely started,
         and not yet read enough information to decode the header,
         LZ4F_getFrameInfo() will fail.

      The number of bytes consumed from srcBuffer will be updated in *srcSizePtr (necessarily <= original value).
      LZ4F_getFrameInfo() only consumes bytes when decoding has not yet started,
      and when decoding the header has been successful.
      Decompression must then resume from (srcBuffer + *srcSizePtr).

     @return : a hint about how many srcSize bytes LZ4F_decompress() expects for next call,
               or an error code which can be tested using LZ4F_isError().
      note 1 : in case of error, dctx is not modified. Decoding operation can resume from beginning safely.
      note 2 : frame parameters are *copied into* an already allocated LZ4F_frameInfo_t structure.

    size_t LZ4F_decompress(LZ4F_dctx* dctx,
                                       void* dstBuffer, size_t* dstSizePtr,
                                       const void* srcBuffer, size_t* srcSizePtr,
                                       const LZ4F_decompressOptions_t* dOptPtr);
      Call this function repetitively to regenerate compressed data from `srcBuffer`.
      The function will read up to *srcSizePtr bytes from srcBuffer,
      and decompress data into dstBuffer, of capacity *dstSizePtr.

      The nb of bytes consumed from srcBuffer will be written into *srcSizePtr (necessarily <= original value).
      The nb of bytes decompressed into dstBuffer will be written into *dstSizePtr (necessarily <= original value).

      The function does not necessarily read all input bytes, so always check value in *srcSizePtr.
      Unconsumed source data must be presented again in subsequent invocations.

     `dstBuffer` can freely change between each consecutive function invocation.
     `dstBuffer` content will be overwritten.

     @return : an hint of how many `srcSize` bytes LZ4F_decompress() expects for next call.
      Schematically, it's the size of the current (or remaining) compressed block + header of next block.
      Respecting the hint provides some small speed benefit, because it skips intermediate buffers.
      This is just a hint though, it's always possible to provide any srcSize.

      When a frame is fully decoded, @return will be 0 (no more data expected).
      When provided with more bytes than necessary to decode a frame,
      LZ4F_decompress() will stop reading exactly at end of current frame, and @return 0.

      If decompression failed, @return is an error code, which can be tested using LZ4F_isError().
      After a decompression error, the `dctx` context is not resumable.
      Use LZ4F_resetDecompressionContext() to return to clean state.

      After a frame is fully decoded, dctx can be used again to decompress another frame.

    void LZ4F_resetDecompressionContext(LZ4F_dctx* dctx);   /* always successful */
      In case of an error, the context is left in "undefined" state.
      In which case, it's necessary to reset it, before re-using it.
      This method can also be used to abruptly stop any unfinished decompression,
      and start a new one using same context resources.

    typedef enum { LZ4F_LIST_ERRORS(LZ4F_GENERATE_ENUM)
                  _LZ4F_dummy_error_enum_for_c89_never_used } LZ4F_errorCodes;

## Bulk processing dictionary API

    LZ4FLIB_STATIC_API LZ4F_CDict* LZ4F_createCDict(const void* dictBuffer, size_t dictSize);
    LZ4FLIB_STATIC_API void        LZ4F_freeCDict(LZ4F_CDict* CDict);
      When compressing multiple messages / blocks using the same dictionary, it's recommended to load it just once.
      LZ4_createCDict() will create a digested dictionary, ready to start future compression operations without startup delay.
      LZ4_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only.
     `dictBuffer` can be released after LZ4_CDict creation, since its content is copied within CDict

    LZ4FLIB_STATIC_API size_t LZ4F_compressFrame_usingCDict(
        LZ4F_cctx* cctx,
        void* dst, size_t dstCapacity,
        const void* src, size_t srcSize,
        const LZ4F_CDict* cdict,
        const LZ4F_preferences_t* preferencesPtr);
      Compress an entire srcBuffer into a valid LZ4 frame using a digested Dictionary.
      cctx must point to a context created by LZ4F_createCompressionContext().
      If cdict==NULL, compress without a dictionary.
      dstBuffer MUST be >= LZ4F_compressFrameBound(srcSize, preferencesPtr).
      If this condition is not respected, function will fail (@return an errorCode).
      The LZ4F_preferences_t structure is optional : you may provide NULL as argument,
      but it's not recommended, as it's the only way to provide dictID in the frame header.
     @return : number of bytes written into dstBuffer.
               or an error code if it fails (can be tested using LZ4F_isError())

    LZ4FLIB_STATIC_API size_t LZ4F_compressBegin_usingCDict(
        LZ4F_cctx* cctx,
        void* dstBuffer, size_t dstCapacity,
        const LZ4F_CDict* cdict,
        const LZ4F_preferences_t* prefsPtr);
      Inits streaming dictionary compression, and writes the frame header into dstBuffer.
      dstCapacity must be >= LZ4F_HEADER_SIZE_MAX bytes.
     `prefsPtr` is optional : you may provide NULL as argument,
      however, it's the only way to provide dictID in the frame header.
     @return : number of bytes written into dstBuffer for the header,
               or an error code (which can be tested using LZ4F_isError())

    LZ4FLIB_STATIC_API size_t LZ4F_decompress_usingDict(
        LZ4F_dctx* dctxPtr,
        void* dstBuffer, size_t* dstSizePtr,
        const void* srcBuffer, size_t* srcSizePtr,
        const void* dict, size_t dictSize,
        const LZ4F_decompressOptions_t* decompressOptionsPtr);
      Same as LZ4F_decompress(), using a predefined dictionary.
      Dictionary is used "in place", without any preprocessing.
      It must remain accessible throughout the entire frame decoding.