zLib inflate 在某些情况下结果为空

发布于 2024-10-15 10:21:28 字数 1492 浏览 8 评论 0原文

我的程序处理 PDF 文件并从中读取一些流。那里还有 FlateEncoded 流。我使用 zlib 的“inflate()”方法来解压缩它们。

这通常与以下代码配合得很好：

static string FlateDecode(string s){

    int factor = 50;
    z_stream stream;
    while(true){
        char * out = new char[s.length()*factor];           

        stream.zalloc = Z_NULL;
        stream.zfree = Z_NULL;
        stream.opaque = Z_NULL;
        stream.avail_in = s.length();
        stream.next_in = (Bytef*)s.c_str();
        stream.avail_out = s.length()*factor;
        stream.next_out = (Bytef*)out;
        inflateInit(&stream);
        inflate(&stream, Z_FINISH);
        inflateEnd(&stream);


        if(stream.total_out >= factor*s.length()){
            delete[] out;
            factor *= 2;
            continue;

        }
        string result;
        for(unsigned long i = 0; i < stream.total_out; i++){
            result += out[i];
        }

        delete[] out;
        return result;
    }
}

但是对于某些流，inflate 的结果为空。这种情况并不常见，但确实会发生。有人知道为什么吗？

流必须正常，因为所有 PDF 阅读器都能正确读取 PDF 文件。

感谢您的帮助！

更新

我已经上传了 PDF 和流，以便您可以自己检查。

PDF ->流从字节 43296 开始

Stream

UPDATE 2

I将无法解压缩的流与可以解压缩的流进行比较。我注意到一件有趣的事情：工作流都以 2 字节 H% 开头。有问题的流以 ö> 开头。现在有人知道这意味着什么吗？

感谢您的帮助！

原文

My program processes PDF files and reads some streams out of them. There are also FlateEncoded streams in there. I use the "inflate()" method of zlib to decompress them.

This usually works really well with the following code:

static string FlateDecode(string s){

    int factor = 50;
    z_stream stream;
    while(true){
        char * out = new char[s.length()*factor];           

        stream.zalloc = Z_NULL;
        stream.zfree = Z_NULL;
        stream.opaque = Z_NULL;
        stream.avail_in = s.length();
        stream.next_in = (Bytef*)s.c_str();
        stream.avail_out = s.length()*factor;
        stream.next_out = (Bytef*)out;
        inflateInit(&stream);
        inflate(&stream, Z_FINISH);
        inflateEnd(&stream);


        if(stream.total_out >= factor*s.length()){
            delete[] out;
            factor *= 2;
            continue;

        }
        string result;
        for(unsigned long i = 0; i < stream.total_out; i++){
            result += out[i];
        }

        delete[] out;
        return result;
    }
}

But inflate has an empty result for some streams. It´s not often, but it happens. Has someone an idea why?

The streams must be ok because all PDF readers read the PDF files correctly.

Thanks for your help!

UPDATE

I've uploaded the PDF and the stream so you can check it by your own.

PDF -> The stream starts at byte 43296

Stream

UPDATE 2

I compared the streams that can´t be decompressed with the streams that can be decompressed. I've noticed an interesting thing: The working streams all begin with the 2 bytes H%. The problematic streams begin with ö>. Does anyone now what this means?

Thanks for any help!

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