libcurl download file size exceed buffer size

Question

I have a question regarding this code at https://curl.haxx.se/libcurl/c/ftpget.html

In the call back function

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, "wb");
    if(!out->stream)
      return -1; /* failure, can't open file to write */ 
  }
  return fwrite(buffer, size, nmemb, out->stream);
}

What if the file size exceed the buffer size? I think the function will not be called iteratively since it overwrites the file everytime. Is there a work-around of it? Thanks!

Answer 1

From curl documentation :

The callback function will be passed as much data as possible in all invokes, but you must not make any assumptions. It may be one byte, it may be thousands. The maximum amount of body data that will be passed to the write callback is defined in the curl.h header file: CURL_MAX_WRITE_SIZE (the usual default is 16K) . If CURLOPT_HEADER is enabled, which makes header data get passed to the write callback, you can get up to CURL_MAX_HTTP_HEADER bytes of header data passed into it. This usually means 100K.