# 1.8.1 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

## 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 if a `LZ4F_errorCode_t` function result is an error code */

    const char* LZ4F_getErrorName(LZ4F_errorCode_t code);   /**< return error code string; useful 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;  /* if enabled, frame is terminated with a 32-bits 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 the compressor to help decoder select the correct dictionary; 0 == no dictID provided */
      LZ4F_blockChecksum_t   blockChecksumFlag;    /* if enabled, each block is followed by a checksum of block's compressed data ; 0 == disabled (default)  */
    } LZ4F_frameInfo_t;
      makes it possible to set or read frame parameters.
      It's not required to set all fields, as long as the structure was initially memset() to zero.
      For all fields, 0 sets it to default value

    typedef struct {
      LZ4F_frameInfo_t frameInfo;
      int      compressionLevel;       /* 0 == default (fast mode); values above LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values below 0 trigger "fast acceleration", proportional to value */
      unsigned autoFlush;              /* 1 == always flush, to reduce usage of internal buffers */
      unsigned reserved[4];            /* must be zero for forward compatibility */
    } LZ4F_preferences_t;
      makes it possible to supply detailed compression parameters to the stream interface.
      It's not required to set all fields, as long as the structure was initially memset() to zero.
      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 size of a frame compressed with LZ4F_compressFrame() given srcSize content and preferences.
      Note : this result is only usable with LZ4F_compressFrame(), not with multi-segments compression.

    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 dstCapacity given a srcSize to guarantee operation success in worst case situations.
     prefsPtr is optional : you can provide NULL as argument, preferences will be set to cover worst case scenario.
     Result is always the same for a srcSize and prefsPtr, so it can be trusted to size reusable buffers.
     When srcSize==0, LZ4F_compressBound() provides an upper bound for LZ4F_flush() and LZ4F_compressEnd() operations.

    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.
     An important rule is that 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 : number of bytes written into dstBuffer (it can be zero, which means there was no data stored within cctx)
               or an error code if it fails (which can be tested using LZ4F_isError())

    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 : number of bytes written into dstBuffer (necessarily >= 4 (endMark), or 8 if optional frame checksum is enabled)
               or an error code if it fails (which can be tested using LZ4F_isError())
      A successful call to LZ4F_compressEnd() makes `cctx` available again for another compression task.

## Decompression functions

    typedef struct {
      unsigned stableDst;    /* pledge that at least 64KB+64Bytes of previously decompressed data remain unmodifed where it was decoded. 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();
     The result of LZ4F_freeDecompressionContext() is indicative of the 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_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.
      Extracted information is typically useful for allocation and dictionary.
      This function works in 2 situations :
       - At the beginning of a new frame, in which case
         it will decode information from `srcBuffer`, starting the decoding process.
         Input size must be large enough to successfully decode the entire frame header.
         Frame header size is variable, but is guaranteed to be <= LZ4F_HEADER_SIZE_MAX bytes.
         It's allowed to provide more input data than this minimum.
       - After decoding has been started.
         In which case, no input is read, frame parameters are extracted from dctx.
       - If decoding has barely started, but not yet extracted information from header,
         LZ4F_getFrameInfo() will fail.
      The number of bytes consumed from srcBuffer will be updated within *srcSizePtr (necessarily <= original value).
      Decompression must resume from (srcBuffer + *srcSizePtr).
     @return : an 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 number of bytes consumed from srcBuffer will be written into *srcSizePtr (necessarily <= original value).
      The number 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.