libpng错误：PNG无符号整数超出范围 [英] libpng error: PNG unsigned integer out of range

问题描述

当尝试从内存中读取PNG时，我遇到了这个有趣的错误：

  libpng错误:: PNG无符号整数的范围
  

此错误是由

  png_read_info（png_ptr，info_ptr）; 
  

其中使用以下处理程序：

  static void ReadDataFromBuffer（png_structp png_ptr，png_bytep outBytes，
 png_size_t byteCountToRead）{
 PNGDataPtr dataptr =（PNGDataPtr）png_get_io_ptr（png_ptr）; 
 png_uint_32 i; 
 cout<< byteCountToRead<< endl; 
 cout<<& outBytes<< endl; 
 cout<< dataptr-> len<<< endl; 
 cout<< dataptr-> p<< endl; 
 
 if（byteCountToRead> dataptr-> len）{
 png_error（png_ptr，EOF）; 
 return; 
} 
 
 for（i = 0; i  
 outBytes [i] = dataptr-> p [i] 
} 
 dataptr-> p + = byteCountToRead; 
 dataptr-> len- = byteCountToRead; 
 png_uint_32 a = png_get_uint_32（outBytes）; 
 cout<< a<<<<< PNG_UINT_31_MAX<< endl; 
 
} 
  

通过一些密集的搜索我发现错误被调用
中的以下代码pgnrutil.c：

  png_uint_32 / * PRIVATE * / 
 png_get_uint_31（png_structp png_ptr ，png_bytep buf）
 {
 png_uint_32 i = png_get_uint_32（buf）; 
 if（i> PNG_UINT_31_MAX）
 png_error（png_ptr，PNG unsigned integer out of range.\\\
）; 
 return（i）; 
} 
  

$ b $ p因此我检查了png_get_uint_32（outBytes）的值， PNG_UINT_31_MAX，230374511。

如何解决此问题？

编辑：

有关PNGDataPtr的一些说明：

  typedef struct {
 png_bytep p; 
 png_uint_32 len; 
} PNGData，* PNGDataPtr; 
  

调用

时

  png_set_read_fn（png_ptr，（png_voidp）& pngdata，ReadDataFromBuffer）; 
  

pngdata表示一个PNGData对象，它有一个指向我的databuffer的指针，和len包含整个PNG的大小，在40到80KB之间

编辑：这里是一个链接到一个png我使用fwrite保存接收的databuffer ： https://www.dropbox.com/s/m5enp9jljglhs5c/test.png

解决方案

以前我写的：
你可能有你的endian条件混合...

编辑：

当您跳过前8个字节时，您正在阅读PNG签名。您的报告有一个拼写错误：该数字实际上是2303741511（您从您的问题中省略了1），它是字节字符串\211 PNG

对于此问题，您的代码是使用

  png_set_sig_bytes（png_ptr，0）
  
 
 
 
通知libpng您的数据指针指向8字节签名的开头，读者需要跳过它们。
 
When trying to read a PNG from memory I came across this funky error:
libpng error:: PNG unsigned integer out of range
This error is caused by 
png_read_info(png_ptr,info_ptr);
Which uses following handler:
static void ReadDataFromBuffer(png_structp png_ptr, png_bytep outBytes,
    png_size_t byteCountToRead){
        PNGDataPtr dataptr=(PNGDataPtr)png_get_io_ptr(png_ptr);
        png_uint_32 i;
        cout<<byteCountToRead<<endl;
        cout<<&outBytes<<endl;
        cout<<dataptr->len<<endl;
        cout<<dataptr->p<<endl;

        if(byteCountToRead>dataptr->len){
            png_error(png_ptr,"EOF");
            return;
        }

        for(i=0;i<byteCountToRead;i++){

            outBytes[i]=dataptr->p[i];
        }
        dataptr->p+=byteCountToRead;
        dataptr->len-=byteCountToRead;
        png_uint_32 a = png_get_uint_32(outBytes);
        cout<<a<<" "<<PNG_UINT_31_MAX<<endl;

}
Through some intensive searching I found that the error gets called by the following code in
pgnrutil.c:
png_uint_32 /* PRIVATE */
png_get_uint_31(png_structp png_ptr, png_bytep buf)
{
    png_uint_32 i = png_get_uint_32(buf);
    if (i > PNG_UINT_31_MAX)
    png_error(png_ptr, "PNG unsigned integer out of range.\n");
    return (i);
}
So I checked the value of png_get_uint_32(outBytes) and it was indeed higher than PNG_UINT_31_MAX, 230374511 to be exact.

How do I fix this?

Edit: 

Some clarification on the PNGDataPtr:
typedef struct{
    png_bytep p;
    png_uint_32 len;
} PNGData,*PNGDataPtr;
When calling
png_set_read_fn(png_ptr,(png_voidp) &pngdata, ReadDataFromBuffer);
pngdata represents a PNGData object, which has a pointer to my databuffer which contains the entire PNG in memory, and len contains the size of the entire PNG, which is between 40 and 80KB

Edit: Here's a link to a png I get when I use fwrite to save the received databuffer: https://www.dropbox.com/s/m5enp9jljglhs5c/test.png
解决方案
Previously I wrote:
You've probably got your endian condition mixed up...

EDIT:

You are reading the PNG signature when you should have skipped past the first 8 bytes.  Your report has a typo: the number is actually 2303741511 (you omitted a "1" from your question) which is the byte string "\211 P N G"

A workaround for this problem in your code is to use
png_set_sig_bytes(png_ptr,0)
to inform libpng that your data pointer is pointing to the beginning of the 8-byte signature and the reader needs to skip them.

                        
这篇关于libpng错误：PNG无符号整数超出范围的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！