Snappy压缩库安装和使用之一



近日需要在毕业设计中引入一个压缩库，要求压缩与解压缩速度快，但是压缩率可以不那么苛刻。查找资料发现Google的snappy库比较合适，而且该库开源，由C++写成。所以就拿来使用一下，下面权作记录。下面引出的任何涉及Google公司的源代码，版权归Google公司所有，我权作学习交流。文章安排如下，首先简要介绍Snappy，之后安装之，然后以实际例子介绍如何使用，接着bzip2和gzip做了性能比较，最后提出一些使用上面的疑问。

（一）简要介绍

去官网下载之http://code.google.com/p/snappy/。在ProjectHome处有这么一段英文，我想许多地方都引用和翻译了这段。我也尝试翻译一下。

Snappyisacompression/decompressionlibrary.

Itdoesnotaimformaximumcompression,

orcompatibilitywithanyothercompressionlibrary;

instead,itaimsforveryhighspeedsandreasonablecompression.

Forinstance,comparedtothefastestmodeofzlib,

Snappyisanorderofmagnitudefasterformostinputs,

buttheresultingcompressedfilesareanywherefrom20%to100%bigger.

OnasinglecoreofaCorei7processorin64-bitmode,

Snappycompressesatabout250MB/secormoreand

decompressesatabout500MB/secormore.

SnappyiswidelyusedinsideGoogle,ineverythingfromBigTable

andMapReducetoourinternalRPCsystems.

译文：Snappy是一个压缩/解压缩库。它不是以最大压缩率，或者与其他压缩库兼容为目标；它旨在获得高速的压缩和合理的压缩率。例如，Snappy对大多数的输入比zlib的最快模式要快几个数量级，但是其压缩过后的文件通常会比zlib大20%到100%。在Corei7的单核64位模式下，Snappy压缩速度大概可以达到250MB/s或者更快，解压缩可以达到大约500MB/s或更快。

Snappy在Google内部广泛使用，从BigTable，MapReduce到公司内部的RPC系统。

（二）安装过程

下面描述安装过程：

下载snappy-1.0.5.tar.gz，snappy的安装过程与传统的安装过程一样。解压后的INSTALL文件有详细的安装说明。

gunzipsnappy-1.0.5.tar.gz

tarxfsnappy-1.0.5.tar

cdsnappy-1.0.5

./configure

make

makeinstall

安装完成后，生成的动态库和静态库位于/usr/local/lib处，编程需要用到的头文件位于/usr/local/include处。注意需要将这些库文件cp至/usr/lib处，不然就算在链接的时候加上-L/usr/local/lib，在运行时也会报错。./main:errorwhileloadingsharedlibraries:libsnappy.so.1:

cannotopensharedobjectfile:Nosuchfileordirectory

当然这是我的LD_LIBRARY_PATH环境变量的设置问题。

（三）使用snappy

解压出来的README文件介绍了一简单的使用方式。snappy是各种库标示符所在的命名空间。C++使用需要包含#include<snappy.h>头文件，C语言使用需要包含#include<snapyy-c.h>头文件。Snappy使用较为简单，我指的是跟bzip2的库比起来。所有的函数接口都暴露在上述两个头文件中，头文件中有详细的使用说明，并有简单的示例，而且英文通俗易懂。摘抄如下（Google公司版权所有）：

snappy.h

//Copyright2005andonwardsGoogleInc.
//
//Redistributionanduseinsourceandbinaryforms,withorwithout
//modification,arepermittedprovidedthatthefollowingconditionsare
//met:
//
//*Redistributionsofsourcecodemustretaintheabovecopyright
//notice,thislistofconditionsandthefollowingdisclaimer.
//*Redistributionsinbinaryformmustreproducetheabove
//copyrightnotice,thislistofconditionsandthefollowingdisclaimer
//inthedocumentationand/orothermaterialsprovidedwiththe
//distribution.
//*NeitherthenameofGoogleInc.northenamesofits
//contributorsmaybeusedtoendorseorpromoteproductsderivedfrom
//thissoftwarewithoutspecificpriorwrittenpermission.
//
//THISSOFTWAREISPROVIDEDBYTHECOPYRIGHTHOLDERSANDCONTRIBUTORS
//"ASIS"ANDANYEXPRESSORIMPLIEDWARRANTIES,INCLUDING,BUTNOT
//LIMITEDTO,THEIMPLIEDWARRANTIESOFMERCHANTABILITYANDFITNESSFOR
//APARTICULARPURPOSEAREDISCLAIMED.INNOEVENTSHALLTHECOPYRIGHT
//OWNERORCONTRIBUTORSBELIABLEFORANYDIRECT,INDIRECT,INCIDENTAL,
//SPECIAL,EXEMPLARY,ORCONSEQUENTIALDAMAGES(INCLUDING,BUTNOT
//LIMITEDTO,PROCUREMENTOFSUBSTITUTEGOODSORSERVICES;LOSSOFUSE,
//DATA,ORPROFITS;ORBUSINESSINTERRUPTION)HOWEVERCAUSEDANDONANY
//THEORYOFLIABILITY,WHETHERINCONTRACT,STRICTLIABILITY,ORTORT
//(INCLUDINGNEGLIGENCEOROTHERWISE)ARISINGINANYWAYOUTOFTHEUSE
//OFTHISSOFTWARE,EVENIFADVISEDOFTHEPOSSIBILITYOFSUCHDAMAGE.
//
//Alight-weightcompressionalgorithm.Itisdesignedforspeedof
//compressionanddecompression,ratherthanfortheutmostinspace
//savings.
//
//Forgettingbettercompressionratioswhenyouarecompressingdata
//withlongrepeatedsequencesorcompressingdatathatissimilarto
//otherdata,whilestillcompressingfast,youmightlookatfirst
//usingBMDiffandthencompressingtheoutputofBMDiffwith
//Snappy.

#ifndefUTIL_SNAPPY_SNAPPY_H__
#defineUTIL_SNAPPY_SNAPPY_H__

#include<stddef.h>
#include<string>

#include"snappy-stubs-public.h"

namespacesnappy{
classSource;
classSink;

//------------------------------------------------------------------------
//Genericcompression/decompressionroutines.
//------------------------------------------------------------------------

//Compressthebytesreadfrom"*source"andappendto"*sink".Returnthe
//numberofbyteswritten.
size_tCompress(Source*source,Sink*sink);

boolGetUncompressedLength(Source*source,uint32*result);

//------------------------------------------------------------------------
//Higher-levelstringbasedroutines(shouldbesufficientformostusers)
//------------------------------------------------------------------------

//Sets"*output"tothecompressedversionof"input[0,input_length-1]".
//Originalcontentsof*outputarelost.
//
//REQUIRES:"input[]"isnotanaliasof"*output".
size_tCompress(constchar*input,size_tinput_length,string*output);

//Decompresses"compressed[0,compressed_length-1]"to"*uncompressed".
//Originalcontentsof"*uncompressed"arelost.
//
//REQUIRES:"compressed[]"isnotanaliasof"*uncompressed".
//
//returnsfalseifthemessageiscorruptedandcouldnotbedecompressed
boolUncompress(constchar*compressed,size_tcompressed_length,
string*uncompressed);


//------------------------------------------------------------------------
//Lower-levelcharacterarraybasedroutines.Maybeusefulfor
//efficiencyreasonsincertaincircumstances.
//------------------------------------------------------------------------

//REQUIRES:"compressed"mustpointtoanareaofmemorythatisat
//least"MaxCompressedLength(input_length)"bytesinlength.
//
//Takesthedatastoredin"input[0..input_length]"andstores
//itinthearraypointedtoby"compressed".
//
//"*compressed_length"issettothelengthofthecompressedoutput.
//
//Example:
//char*output=newchar[snappy::MaxCompressedLength(input_length)];
//size_toutput_length;
//RawCompress(input,input_length,output,&output_length);
//...Process(output,output_length)...
//delete[]output;
voidRawCompress(constchar*input,
size_tinput_length,
char*compressed,
size_t*compressed_length);

//Givendatain"compressed[0..compressed_length-1]"generatedby
//callingtheSnappy::Compressroutine,thisroutine
//storestheuncompresseddatato
//uncompressed[0..GetUncompressedLength(compressed)-1]
//returnsfalseifthemessageiscorruptedandcouldnotbedecrypted
boolRawUncompress(constchar*compressed,size_tcompressed_length,
char*uncompressed);

//Givendatafromthebytesource'compressed'generatedbycalling
//theSnappy::Compressroutine,thisroutinestorestheuncompressed
//datato
//uncompressed[0..GetUncompressedLength(compressed,compressed_length)-1]
//returnsfalseifthemessageiscorruptedandcouldnotbedecrypted
boolRawUncompress(Source*compressed,char*uncompressed);

//Returnsthemaximalsizeofthecompressedrepresentationof
//inputdatathatis"source_bytes"bytesinlength;
size_tMaxCompressedLength(size_tsource_bytes);

//REQUIRES:"compressed[]"wasproducedbyRawCompress()orCompress()
//Returnstrueandstoresthelengthoftheuncompresseddatain
//*resultnormally.Returnsfalseonparsingerror.
//ThisoperationtakesO(1)time.
boolGetUncompressedLength(constchar*compressed,size_tcompressed_length,
size_t*result);

//Returnstrueiffthecontentsof"compressed[]"canbeuncompressed
//successfully.Doesnotreturntheuncompresseddata.Takes
//timeproportionaltocompressed_length,butisusuallyatleast
//afactoroffourfasterthanactualdecompression.
boolIsValidCompressedBuffer(constchar*compressed,
size_tcompressed_length);

//***DONOTCHANGETHEVALUEOFkBlockSize***
//
//NewCompressioncodechopsuptheinputintoblocksofatmost
//thefollowingsize.Thisensuresthatback-referencesinthe
//outputnevercrosskBlockSizeblockboundaries.Thiscanbe
//helpfulinimplementingblockeddecompression.Howeverthe
//decompressioncodeshouldnotrelyonthisguaranteesinceolder
//compressioncodemaynotobeyit.
staticconstintkBlockLog=15;
staticconstsize_tkBlockSize=1<<kBlockLog;

staticconstintkMaxHashTableBits=14;
staticconstsize_tkMaxHashTableSize=1<<kMaxHashTableBits;

}//endnamespacesnappy


#endif//UTIL_SNAPPY_SNAPPY_H__

// Copyright 2005 and onwards Google Inc.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// A light-weight compression algorithm.  It is designed for speed of
// compression and decompression, rather than for the utmost in space
// savings.
//
// For getting better compression ratios when you are compressing data
// with long repeated sequences or compressing data that is similar to
// other data, while still compressing fast, you might look at first
// using BMDiff and then compressing the output of BMDiff with
// Snappy.

#ifndef UTIL_SNAPPY_SNAPPY_H__
#define UTIL_SNAPPY_SNAPPY_H__

#include <stddef.h>
#include <string>

#include "snappy-stubs-public.h"

namespace snappy {
  class Source;
  class Sink;

  // ------------------------------------------------------------------------
  // Generic compression/decompression routines.
  // ------------------------------------------------------------------------

  // Compress the bytes read from "*source" and append to "*sink". Return the
  // number of bytes written.
  size_t Compress(Source* source, Sink* sink);

  bool GetUncompressedLength(Source* source, uint32* result);

  // ------------------------------------------------------------------------
  // Higher-level string based routines (should be sufficient for most users)
  // ------------------------------------------------------------------------

  // Sets "*output" to the compressed version of "input[0,input_length-1]".
  // Original contents of *output are lost.
  //
  // REQUIRES: "input[]" is not an alias of "*output".
  size_t Compress(const char* input, size_t input_length, string* output);

  // Decompresses "compressed[0,compressed_length-1]" to "*uncompressed".
  // Original contents of "*uncompressed" are lost.
  //
  // REQUIRES: "compressed[]" is not an alias of "*uncompressed".
  //
  // returns false if the message is corrupted and could not be decompressed
  bool Uncompress(const char* compressed, size_t compressed_length,
                  string* uncompressed);


  // ------------------------------------------------------------------------
  // Lower-level character array based routines.  May be useful for
  // efficiency reasons in certain circumstances.
  // ------------------------------------------------------------------------

  // REQUIRES: "compressed" must point to an area of memory that is at
  // least "MaxCompressedLength(input_length)" bytes in length.
  //
  // Takes the data stored in "input[0..input_length]" and stores
  // it in the array pointed to by "compressed".
  //
  // "*compressed_length" is set to the length of the compressed output.
  //
  // Example:
  //    char* output = new char[snappy::MaxCompressedLength(input_length)];
  //    size_t output_length;
  //    RawCompress(input, input_length, output, &output_length);
  //    ... Process(output, output_length) ...
  //    delete [] output;
  void RawCompress(const char* input,
                   size_t input_length,
                   char* compressed,
                   size_t* compressed_length);

  // Given data in "compressed[0..compressed_length-1]" generated by
  // calling the Snappy::Compress routine, this routine
  // stores the uncompressed data to
  //    uncompressed[0..GetUncompressedLength(compressed)-1]
  // returns false if the message is corrupted and could not be decrypted
  bool RawUncompress(const char* compressed, size_t compressed_length,
                     char* uncompressed);

  // Given data from the byte source 'compressed' generated by calling
  // the Snappy::Compress routine, this routine stores the uncompressed
  // data to
  //    uncompressed[0..GetUncompressedLength(compressed,compressed_length)-1]
  // returns false if the message is corrupted and could not be decrypted
  bool RawUncompress(Source* compressed, char* uncompressed);

  // Returns the maximal size of the compressed representation of
  // input data that is "source_bytes" bytes in length;
  size_t MaxCompressedLength(size_t source_bytes);

  // REQUIRES: "compressed[]" was produced by RawCompress() or Compress()
  // Returns true and stores the length of the uncompressed data in
  // *result normally.  Returns false on parsing error.
  // This operation takes O(1) time.
  bool GetUncompressedLength(const char* compressed, size_t compressed_length,
                             size_t* result);

  // Returns true iff the contents of "compressed[]" can be uncompressed
  // successfully.  Does not return the uncompressed data.  Takes
  // time proportional to compressed_length, but is usually at least
  // a factor of four faster than actual decompression.
  bool IsValidCompressedBuffer(const char* compressed,
                               size_t compressed_length);

  // *** DO NOT CHANGE THE VALUE OF kBlockSize ***
  //
  // New Compression code chops up the input into blocks of at most
  // the following size.  This ensures that back-references in the
  // output never cross kBlockSize block boundaries.  This can be
  // helpful in implementing blocked decompression.  However the
  // decompression code should not rely on this guarantee since older
  // compression code may not obey it.
  static const int kBlockLog = 15;
  static const size_t kBlockSize = 1 << kBlockLog;

  static const int kMaxHashTableBits = 14;
  static const size_t kMaxHashTableSize = 1 << kMaxHashTableBits;

}  // end namespace snappy


#endif  // UTIL_SNAPPY_SNAPPY_H__

snapp-c.h

/*
*Copyright2011MartinGieseking<[e-mail]>.
*
*Redistributionanduseinsourceandbinaryforms,withorwithout
*modification,arepermittedprovidedthatthefollowingconditionsare
*met:
*
**Redistributionsofsourcecodemustretaintheabovecopyright
*notice,thislistofconditionsandthefollowingdisclaimer.
**Redistributionsinbinaryformmustreproducetheabove
*copyrightnotice,thislistofconditionsandthefollowingdisclaimer
*inthedocumentationand/orothermaterialsprovidedwiththe
*distribution.
**NeitherthenameofGoogleInc.northenamesofits
*contributorsmaybeusedtoendorseorpromoteproductsderivedfrom
*thissoftwarewithoutspecificpriorwrittenpermission.
*
*THISSOFTWAREISPROVIDEDBYTHECOPYRIGHTHOLDERSANDCONTRIBUTORS
*"ASIS"ANDANYEXPRESSORIMPLIEDWARRANTIES,INCLUDING,BUTNOT
*LIMITEDTO,THEIMPLIEDWARRANTIESOFMERCHANTABILITYANDFITNESSFOR
*APARTICULARPURPOSEAREDISCLAIMED.INNOEVENTSHALLTHECOPYRIGHT
*OWNERORCONTRIBUTORSBELIABLEFORANYDIRECT,INDIRECT,INCIDENTAL,
*SPECIAL,EXEMPLARY,ORCONSEQUENTIALDAMAGES(INCLUDING,BUTNOT
*LIMITEDTO,PROCUREMENTOFSUBSTITUTEGOODSORSERVICES;LOSSOFUSE,
*DATA,ORPROFITS;ORBUSINESSINTERRUPTION)HOWEVERCAUSEDANDONANY
*THEORYOFLIABILITY,WHETHERINCONTRACT,STRICTLIABILITY,ORTORT
*(INCLUDINGNEGLIGENCEOROTHERWISE)ARISINGINANYWAYOUTOFTHEUSE
*OFTHISSOFTWARE,EVENIFADVISEDOFTHEPOSSIBILITYOFSUCHDAMAGE.
*
*PlainCinterface(awrapperaroundtheC++implementation).
*/

#ifndefUTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_
#defineUTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_

#ifdef__cplusplus
extern"C"{
#endif

#include<stddef.h>

/*
*Returnvalues;seethedocumentationforeachfunctiontoknow
*whateachcanreturn.
*/
typedefenum{
SNAPPY_OK=0,
SNAPPY_INVALID_INPUT=1,
SNAPPY_BUFFER_TOO_SMALL=2,
}snappy_status;

/*
*Takesthedatastoredin"input[0..input_length-1]"andstores
*itinthearraypointedtoby"compressed".
*
*<compressed_length>signalsthespaceavailablein"compressed".
*Ifitisnotatleastequalto"snappy_max_compressed_length(input_length)",
*SNAPPY_BUFFER_TOO_SMALLisreturned.Aftersuccessfulcompression,
*<compressed_length>containsthetruelengthofthecompressedoutput,
*andSNAPPY_OKisreturned.
*
*Example:
*size_toutput_length=snappy_max_compressed_length(input_length);
*char*output=(char*)malloc(output_length);
*if(snappy_compress(input,input_length,output,&output_length)
*==SNAPPY_OK){
*...Process(output,output_length)...
*}
*free(output);
*/
snappy_statussnappy_compress(constchar*input,
size_tinput_length,
char*compressed,
size_t*compressed_length);

/*
*Givendatain"compressed[0..compressed_length-1]"generatedby
*callingthesnappy_compressroutine,thisroutinestores
*theuncompresseddatato
*uncompressed[0..uncompressed_length-1].
*Returnsfailure(avaluenotequaltoSNAPPY_OK)ifthemessage
*iscorruptedandcouldnotbedecrypted.
*
*<uncompressed_length>signalsthespaceavailablein"uncompressed".
*Ifitisnotatleastequaltothevaluereturnedby
*snappy_uncompressed_lengthforthisstream,SNAPPY_BUFFER_TOO_SMALL
*isreturned.Aftersuccessfuldecompression,<uncompressed_length>
*containsthetruelengthofthedecompressedoutput.
*
*Example:
*size_toutput_length;
*if(snappy_uncompressed_length(input,input_length,&output_length)
*!=SNAPPY_OK){
*...fail...
*}
*char*output=(char*)malloc(output_length);
*if(snappy_uncompress(input,input_length,output,&output_length)
*==SNAPPY_OK){
*...Process(output,output_length)...
*}
*free(output);
*/
snappy_statussnappy_uncompress(constchar*compressed,
size_tcompressed_length,
char*uncompressed,
size_t*uncompressed_length);

/*
*Returnsthemaximalsizeofthecompressedrepresentationof
*inputdatathatis"source_length"bytesinlength.
*/
size_tsnappy_max_compressed_length(size_tsource_length);

/*
*REQUIRES:"compressed[]"wasproducedbysnappy_compress()
*ReturnsSNAPPY_OKandstoresthelengthoftheuncompresseddatain
**resultnormally.ReturnsSNAPPY_INVALID_INPUTonparsingerror.
*ThisoperationtakesO(1)time.
*/
snappy_statussnappy_uncompressed_length(constchar*compressed,
size_tcompressed_length,
size_t*result);

/*
*Checkifthecontentsof"compressed[]"canbeuncompressedsuccessfully.
*Doesnotreturntheuncompresseddata;ifso,returnsSNAPPY_OK,
*orifnot,returnsSNAPPY_INVALID_INPUT.
*Takestimeproportionaltocompressed_length,butisusuallyatleasta
*factoroffourfasterthanactualdecompression.
*/
snappy_statussnappy_validate_compressed_buffer(constchar*compressed,
size_tcompressed_length);

#ifdef__cplusplus
}//extern"C"
#endif

#endif/*UTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_*/

/*
 * Copyright 2011 Martin Gieseking <[e-mail]>.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Plain C interface (a wrapper around the C++ implementation).
 */

#ifndef UTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_
#define UTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_

#ifdef __cplusplus
extern "C" {
#endif

#include <stddef.h>

/*
 * Return values; see the documentation for each function to know
 * what each can return.
 */
typedef enum {
  SNAPPY_OK = 0,
  SNAPPY_INVALID_INPUT = 1,
  SNAPPY_BUFFER_TOO_SMALL = 2,
} snappy_status;

/*
 * Takes the data stored in "input[0..input_length-1]" and stores
 * it in the array pointed to by "compressed".
 *
 * <compressed_length> signals the space available in "compressed".
 * If it is not at least equal to "snappy_max_compressed_length(input_length)",
 * SNAPPY_BUFFER_TOO_SMALL is returned. After successful compression,
 * <compressed_length> contains the true length of the compressed output,
 * and SNAPPY_OK is returned.
 *
 * Example:
 *   size_t output_length = snappy_max_compressed_length(input_length);
 *   char* output = (char*)malloc(output_length);
 *   if (snappy_compress(input, input_length, output, &output_length)
 *       == SNAPPY_OK) {
 *     ... Process(output, output_length) ...
 *   }
 *   free(output);
 */
snappy_status snappy_compress(const char* input,
                              size_t input_length,
                              char* compressed,
                              size_t* compressed_length);

/*
 * Given data in "compressed[0..compressed_length-1]" generated by
 * calling the snappy_compress routine, this routine stores
 * the uncompressed data to
 *   uncompressed[0..uncompressed_length-1].
 * Returns failure (a value not equal to SNAPPY_OK) if the message
 * is corrupted and could not be decrypted.
 *
 * <uncompressed_length> signals the space available in "uncompressed".
 * If it is not at least equal to the value returned by
 * snappy_uncompressed_length for this stream, SNAPPY_BUFFER_TOO_SMALL
 * is returned. After successful decompression, <uncompressed_length>
 * contains the true length of the decompressed output.
 *
 * Example:
 *   size_t output_length;
 *   if (snappy_uncompressed_length(input, input_length, &output_length)
 *       != SNAPPY_OK) {
 *     ... fail ...
 *   }
 *   char* output = (char*)malloc(output_length);
 *   if (snappy_uncompress(input, input_length, output, &output_length)
 *       == SNAPPY_OK) {
 *     ... Process(output, output_length) ...
 *   }
 *   free(output);
 */
snappy_status snappy_uncompress(const char* compressed,
                                size_t compressed_length,
                                char* uncompressed,
                                size_t* uncompressed_length);

/*
 * Returns the maximal size of the compressed representation of
 * input data that is "source_length" bytes in length.
 */
size_t snappy_max_compressed_length(size_t source_length);

/*
 * REQUIRES: "compressed[]" was produced by snappy_compress()
 * Returns SNAPPY_OK and stores the length of the uncompressed data in
 * *result normally. Returns SNAPPY_INVALID_INPUT on parsing error.
 * This operation takes O(1) time.
 */
snappy_status snappy_uncompressed_length(const char* compressed,
                                         size_t compressed_length,
                                         size_t* result);

/*
 * Check if the contents of "compressed[]" can be uncompressed successfully.
 * Does not return the uncompressed data; if so, returns SNAPPY_OK,
 * or if not, returns SNAPPY_INVALID_INPUT.
 * Takes time proportional to compressed_length, but is usually at least a
 * factor of four faster than actual decompression.
 */
snappy_status snappy_validate_compressed_buffer(const char* compressed,
                                                size_t compressed_length);

#ifdef __cplusplus
}  // extern "C"
#endif

#endif  /* UTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_ */