动态使用zlib deflateBound（） [英] Using zlib deflateBound() dynamically

问题描述

我一直在研究如何动态地使用deflateBound（），却找不到我真正想要的东西。

I have been looking at how to use deflateBound() dynamically and have not found exactly what I am looking for.

我看过zlip的手册，示例包含在库中，并在以下位置找到它们：
ARM Cortex M3的压缩库/ 4
确定已压缩C中Z-lib的/ uncompressed缓冲区大小
zlib，deflate：要分配多少内存？

I looked at the manual for zlip, examples included in library and found these here: Compression Libraries for ARM Cortex M3/4 Determine compressed/uncompressed buffer size for Z-lib in C zlib, deflate: How much memory to allocate?

我缺少的是在调用deflateBound（）之后如何分配。
例如看来这会引起问题

What I am missing is how to allocate after calling deflateBound(). E.g. this looks like it will cause problems

   z_stream defstream;
   uint8_t *outBuf=NULL;
   uint32_t outLen=0;

   defstream.zalloc = Z_NULL;
   defstream.zfree = Z_NULL;
   defstream.opaque = Z_NULL;
   defstream.avail_in = (uInt)inLen;
   defstream.next_in = (Bytef *)inBuf:
   defstream.avail_out = (uInt)0;
   defstream.next_out = (Bytef *)outBuf;

   deflateInit(&defstream, Z_DEFAULT_COMPRESSION);
   uint32_t  estimateLen = deflateBound(&defstream, inLen);
   outBuf = malloc(estimateLen);
   defstream.avail_out = (uInt)estimateLen;
   deflate(&defstream, Z_FINISH);
   deflateEnd(&defstream);

我看到有人提到realloc，这是否意味着建议从初始（可能太小）缓冲区开始？

I see realloc being mentioned, does this mean starting with an initial (probably too small) buffer is recommended?

   z_stream defstream;
   uint8_t *outBuf=NULL;
   uint32_t outLen=100;
   outBuf = malloc(outLen);

   defstream.zalloc = Z_NULL;
   defstream.zfree = Z_NULL;
   defstream.opaque = Z_NULL;
   defstream.avail_in = (uInt)inLen;
   defstream.next_in = (Bytef *)inBuf:
   defstream.avail_out = (uInt)outLen;
   defstream.next_out = (Bytef *)outBuf;

   deflateInit(&defstream, Z_DEFAULT_COMPRESSION);
   uint32_t  estimateLen = deflateBound(&defstream, inLen);
   outBuf = realloc(outBufestimateLen);
   defstream.avail_out = (uInt)estimateLen;
   deflate(&defstream, Z_FINISH);
   deflateEnd(&defstream);

作为嵌入式系统，我试图使事情变得简单。

Being an embedded system, I am trying to keep things simple.

更新02/08/2019
以下代码有效（注意Mark的修复）：

Update 02/08/2019 the following code works (note Mark's fix):

static uint8_t *compressBuffer(char *inBuf, uint32_t *outLen)
{
   uint32_t inLen = strlen(inBuf)+1;  //  +1 so the null terminator will get encoded
   uint8_t *outBuf = NULL;
   int result;
   uint32_t tmpLen=0;

   // initialize zlib
   z_stream defstream;
   defstream.zalloc    = Z_NULL;
   defstream.zfree     = Z_NULL;
   defstream.opaque    = Z_NULL;
   defstream.avail_in  = inLen;
   defstream.next_in   = (Bytef *)inBuf;
   defstream.avail_out = 0;
   defstream.next_out  = (Bytef *)outBuf;
   if ((result = deflateInit(&defstream, Z_DEFAULT_COMPRESSION)) == Z_OK)
   {
      // calculate actual output length and update structure
      uint32_t  estimateLen = deflateBound(&defstream, inLen);
      outBuf = malloc(estimateLen+10);
      if (outBuf != NULL)
      {
         // update zlib configuration
         defstream.avail_out = (uInt)estimateLen;
         defstream.next_out = (Bytef *)outBuf;

         // do the compression
         deflate(&defstream, Z_FINISH);
         tmpLen = (uint8_t*)defstream.next_out - outBuf;
      }
   }

   // do the followimg regardless of outcome to leave in a good place
   deflateEnd(&defstream);

   // return whatever we have
   *outLen = tmpLen;
   return outBuf;
}

推荐答案

在两个示例中，您都不是在 deflateBound（）之后设置 next_out 。您需要 defstream.next_out =（Bytef *）outBuf; 在 malloc（）之后。

In both examples you are not setting next_out after the deflateBound(). You need defstream.next_out = (Bytef *)outBuf; after the malloc().

您不需要执行 realloc（）。

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