c++ - cURL 条件终止下载

Question

我正在使用 libcurl 下载二进制文件，但我想读取这些二进制文件的 header ，即前几个字节。如果 header 字节匹配我要继续下载的条件，否则我不想取消下载。

size_t writeData(void *contents, size_t size, 
                                  size_t nmemb, FILE *stream) {

    const unsigned char * cPtr;
    cPtr = (const unsigned char*)contents;
    bool isByte = checkByte(cPtr, nmemb);
    if (isByte){
        // Continue Download, and write to disk.
        size_t written = fwrite(contents, size, nmemb, stream);
        return written;
        }
    else
        // Kill Download.
}

Answer 1

定义您自己的写函数设置选项 CURLOPT_WRITEFUNCTION。在此处查看文档:https://curl.haxx.se/libcurl/c/CURLOPT_WRITEFUNCTION.html .

要中止传输，您只需从写入函数返回值，该值小于传递给写入函数的字节数。文档中的相应行:

If that amount differs from the amount passed to your callback function, it'll signal an error condition to the library. This will cause the transfer to get aborted and the libcurl function used will return CURLE_WRITE_ERROR