cpp libcurl send zip file in http post call without using multipart\form-data

Question

We were using formdata in cpp libcurl to send data to our server using the following code:

curl_formadd(&form, &lastptr, CURLFORM_COPYNAME, "file", CURLFORM_FILE, filePath.c_str(), CURLFORM_END);

curl_easy_setopt(curl_handle, CURLOPT_HTTPPOST, form); 

But now our server has been updated to accept binary in http request body & not multipart\form-data. I have found curl command to attach zipfile without using multipart\form-data as follows

curl --request POST --data-binary "@file" $URL

but I cannot find its equivalent in cpp curl. Our requirement is to upload a zipfile in the http request

Answer 1

You need to set the CURLOPT_READDATA and CURLOPT_READFUNCTION options. Curl will repeatedly call CURLOPT_READFUNCTION with whatever you pass as CURLOPT_READDATA as argument, until it returns 0 or CURL_READFUNC_ABORT .

By default, libcurl assumes your READFUNCTION reads from a filehandle. The documentation shows the following example:

size_t read_callback(void *ptr, size_t size, size_t nmemb, void *userdata)
{
  FILE *readhere = (FILE *)userdata;
  curl_off_t nread;

  /* copy as much data as possible into the 'ptr' buffer, but no more than
     'size' * 'nmemb' bytes! */
  size_t retcode = fread(ptr, size, nmemb, readhere);

  nread = (curl_off_t)retcode;

  fprintf(stderr, "*** We read %" CURL_FORMAT_CURL_OFF_T
          " bytes from file\n", nread);
  return retcode;
}

void setup(char *uploadthis)
{
  FILE *file = fopen("rb", uploadthis);
  CURLcode result;

  /* set callback to use */
  curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback);

  /* pass in suitable argument to callback */
  curl_easy_setopt(curl, CURLOPT_READDATA, uploadthis);

  result = curl_easy_perform(curl);
}

If you wanted to read from an in-memory buffer, your READFUNCTION would need to remember an offset somewhere and memcpy chunks every invocation until it reaches the end of the in-memory buffer.

Answer 2

I have used POST_FIELDS to upload a zip file. Read the zip file in binary mode into a char pointer and passed it to like this:

    char * buffer;
    //read file into buffer
    curl_easy_setopt(curl_handle, CURLOPT_POSTFIELDSIZE_LARGE, (curl_off_t)total);
    curl_easy_setopt(curl_handle, CURLOPT_POSTFIELDS, buffer);

Kindly correct me if I am wrong or suggest me for alternative