问题描述

使用zlib库解压http数据时遇到的问题

最近在用c++写一个爬虫程序，遇到一个问题，不能解压服务器返回的压缩数据，解压数据的函数是在网上看的，如下：

bool GzipDecompress(Byte *source, uLong source_length, Byte *dest, uLong *dest_length)
{
    int err = 0;
    z_stream d_stream = {0};
    static char dummy_head[2] =
    {
    0x8 + 0x7 * 0x10,
    (((0x8 + 0x7 * 0x10) * 0x100 + 30) / 31 * 31) & 0xFF,
    };
    d_stream.zalloc = (alloc_func)0;
    d_stream.zfree = (free_func)0;
    d_stream.opaque = (voidpf)0;
    d_stream.next_in = source;
    d_stream.avail_in = 0;
    d_stream.next_out = dest;
    if(inflateInit2(&d_stream, 47) != Z_OK)
        return false;
    while (d_stream.total_out < *dest_length && d_stream.total_in < source_length) {
        d_stream.avail_in = d_stream.avail_out = 1;
        if((err = inflate(&d_stream, Z_NO_FLUSH)) == Z_STREAM_END)
            break;
        if(err != Z_OK )
        {
            if(err == Z_DATA_ERROR)
            {
                d_stream.next_in = (Bytef*) dummy_head;
                d_stream.avail_in = sizeof(dummy_head);
                if((err = inflate(&d_stream, Z_NO_FLUSH)) != Z_OK)
                {
                    return false;
                }
            }
            else
                return false;
        }
    }
    if(inflateEnd(&d_stream) != Z_OK)
        return false;
    *dest_length = d_stream.total_out;
    return true;
}

然后我是这样调用的，

bool HttpHandle::Decompress(ofstream &out_stream)
{
    out_stream << "Decompress() is called" << endl;

    char *tmp_buffer = new char[BufferSize];
    memset(tmp_buffer, 0, BufferSize);

    unsigned long data_length = 0;
    if (!GzipDecompress((Byte*)m_content_begin, m_content_length,
        (Byte*)tmp_buffer, &data_length))
        return false;

    m_content_begin = tmp_buffer;
    m_content_length = data_length;

//  out_stream << "content--------n" << tmp_buffer;
//  out_stream << "end------------" << endl;

    return true;
}

GzipDecompress总是可以成功返回，但是，tmp_buffer里面却什么都没有，解压后的数据长度data_length也是0. 然而把收到的压缩数据写入文件，却可以用命令gzip成功解压。
现在找不出是哪个位置出了问题，希望懂得的人能够帮我一下。

解决方案

同问 我是用libpcap抓http包，解压gzip 也是压缩数据长度为0 buff为空