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使用zlib/minizip确定压缩块大小

zlib zip c++

George Marques · 技术社区 · 8 年前

Appx 打包程序(用于Windows应用商店应用)。格式只是包含一些元数据文件的压缩文件。

我需要制作一个XML文件,其中包含格式所需的文件哈希。问题是,每个文件的每64KB未压缩数据都需要一个哈希 compressed size of such 64KB block . 我该怎么做?

我正在使用 Minizip library 也可以使用 zlib 如果需要,可以直接进行。

在我看来,我需要要么避免压缩文件(我想避免),要么跳过Minizip的压缩,并使用zlib中的原始数据来压缩文件(对于zlib的API,我不太熟悉,不知道是否可以使每个64KB块都足够单独)。

TL公司;DR:我如何知道Zip文件中64KB未压缩数据块的压缩大小?

1 回复 | 直到 8 年前

George Marques 8 年前

最后,我“手动”制作了Zip文件,并分别压缩块以计算其哈希值。

#include <zlib.h>
#define BLOCK_SIZE 65536

z_stream strm;
// Using init2 to avold the zlib header
deflateInit2(&strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED, -15, 8, Z_DEFAULT_STRATEGY);

int step = 0.

// len is the length of the whole input file
while (len - step > 0) {
    // Get the size of this block (either 64k or the remaining of the file if less)
    long block_size = (len - step) > BLOCK_SIZE ? BLOCK_SIZE : (len - step);

    // strm_in is the input buffer for the compression
    // skipped the buffer allocation for simplicity
    for (int i = 0; i < block_size; i++) {
        strm_in[i] = input_file_buffer[step + i];
    }

    // Calculate the hash (out of the scope for this question)
    // Store in a particular structure for reference later
    BlockData bd;
    bd.hash = make_block_hash(strm_in, block_size);

    // Update the zlib stream info
    // also skipped the out buffer allocation in this sample
    strm.avail_in = block_size;
    strm.avail_out = out_buffer_size;
    strm.next_in = strm_in;
    strm.next_out = strm_out;

    // Save the total bytes for comparison later
    int total_out_before = strm.total_out; 

    // Compress (assume the out buffer size will be always enough)
    deflate(&strm, Z_FULL_FLUSH); // A Full flush here is needed for the APPX format

    // Save the compressed block in the size
    compressed_file->save_buffer(strm_out, strm.total_out - total_out_before);

    // Save the size of the compressed block
    bd.compressed_size = strm.total_out - total_out_before;

    // Store the block data in a list
    blocks_info->push(bd);

    // Move to the next block
    step += block_size;
}

// End the compressed stream
strm.avail_in = 0;
strm.avail_out = out_buffer_size;
strm.next_in = strm_in;
strm.next_out = strm_out;

int total_out_before = strm.total_out;

// Finish the stream
deflate(&strm, Z_FINISH);

// Save the compression tail to the file
compressed_file->save_buffer(strm_out, strm.total_out - total_out_before);

// Clean up
deflateEnd(&strm);

在经历了所有这些麻烦之后,我找到了一个跨平台 open source tool 打包并签署Windows商店应用程序。也许对其他人和我都有帮助,因为我认为在Windows之外签名是不可能的。