c - libcurl c，超时和成功传输

Question

我必须在 c 中使用 FTP 协议(protocol)和 libcurl 传输文件。它工作正常，但我遇到了一些问题。

1) 如果开始传输，但在某个时刻我断开了网络连接，我的程序仍然在 libcurl 函数中，速度变为 0，我无法做任何其他事情。我尝试设置超时(CURLOPT_TIMEOUT)，但它只是传输时间的超时。

2) 我遇到的第二个问题与第一个问题相关，我如何知道传输是否成功完成？

我的转移码是:

struct FtpFile {

  const char *filename;
  FILE *stream;
};
   long int size;

static size_t my_fwrite(void *buffer, size_t size, size_t nmemb, void *stream)
{
  struct FtpFile *out=(struct FtpFile *)stream;
  if(out && !out->stream) {
    /* open file for writing */
    out->stream=fopen(out->filename, "ab"); 
    if(!out->stream)
      return -1; /* failure, can't open file to write */
  }
  return fwrite(buffer, size, nmemb, out->stream);
}

int sz;

int main(void)
{
  CURL *curl;
  CURLcode res;
  char prova;

   struct stat statbuf;
   FILE *stream;

   /* apro il file per leggere la dimensione*/
   if ((stream = fopen("Pdf.pdf", "rb")) 
       == NULL)
   {
      fprintf(stderr, "Nessun file da aprire, il download partirà da zero.\n");
   }
   else
   {
   /* Ricevo informazioni sul file */
   fstat(fileno(stream), &statbuf);
   fclose(stream);
   size = statbuf.st_size;
   printf("Dimensione del file in byte: %ld\n", size);
   }

  struct FtpFile ftpfile={
    "Pdf.pdf", /* name to store the file as if succesful */
    NULL
  };

  curl_global_init(CURL_GLOBAL_DEFAULT);

  curl = curl_easy_init();
  if(curl) {

    curl_easy_setopt(curl, CURLOPT_URL, "ftp://....");
    /* Define our callback to get called when there's data to be written */
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, my_fwrite);
    /* Set a pointer to our struct to pass to the callback */
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &ftpfile);

    /* Switch on full protocol/debug output */
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L); 

    /*Pass a long as parameter. It contains the offset in number of bytes that you want the transfer to start from.   
    Set this option to 0 to make the transfer start from the beginning (effectively disabling resume). For FTP, set  
    this option to -1 to make the transfer start from the end of the target file (useful to continue an interrupted 
    upload).

    When doing uploads with FTP, the resume position is where in the local/source file libcurl should try to resume 
    the upload from and it will then append the source file to the remote target file. */

    if(stream == NULL)
    {
        curl_easy_setopt(curl, CURLOPT_RESUME_FROM, 0);
    }
    else
    {
        curl_easy_setopt(curl, CURLOPT_RESUME_FROM, size);
    }

    /*Used to show file progress*/
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);

    res = curl_easy_perform(curl);

    /* always cleanup */
    curl_easy_cleanup(curl);

    if(CURLE_OK != res) {
      /* we failed */
      fprintf(stderr, "curl told us %d\n", res);
    }
  }

  if(ftpfile.stream)
    fclose(ftpfile.stream); /* close the local file */

  curl_global_cleanup();

  return 0;
}

Answer 1

我最近回答了一个 similar question对此。

1) 这是设计使然。如果您想使连接超时，请尝试使用这些:

curl_easy_setopt(curl, CURLOPT_LOW_SPEED_LIMIT, dl_lowspeed_bytes);    
curl_easy_setopt(curl, CURLOPT_LOW_SPEED_TIME, dl_lowspeed_time);

如果您的下载速率低于您想要的阈值，您可以检查连接并采取您认为合适的任何操作。

注意:在 7.25.0 中添加:CURLOPT_TCP_KEEPALIVE, CURLOPT_TCP_KEEPIDLE
所以这些可能是另一个适合您的选择。

2) 像这样:

curl_easy_getinfo(curl, CURLINFO_CONTENT_LENGTH_DOWNLOAD, &dl_bytes_remaining);
curl_easy_getinfo(curl, CURLINFO_SIZE_DOWNLOAD, &dl_bytes_received);
if (dl_bytes_remaining == dl_bytes_received)
    printf("our work here is done ;)\n");