CURLOPT_BUFFERSIZE(3) Library Functions Manual CURLOPT_BUFFERSIZE(3)

CURLOPT_BUFFERSIZE - receive buffer size

#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_BUFFERSIZE, long size);

Pass a long specifying your preferred size (in bytes) for the receive buffer in libcurl. The main point of this would be that the write callback gets called more often and with smaller chunks. Secondly, for some protocols, there is a benefit of having a larger buffer for performance.

This is just treated as a request, not an order. You cannot be guaranteed to actually get the given size.

This buffer size is by default CURL_MAX_WRITE_SIZE (16kB). The maximum buffer size allowed to be set is CURL_MAX_READ_SIZE (10MB). The minimum buffer size allowed to be set is 1024.

DO NOT set this option on a handle that is currently used for an active transfer as that may lead to unintended consequences.

The maximum size was 512kB until 7.88.0.

Starting in libcurl 8.7.0, there is just a single transfer buffer allocated per multi handle. This buffer is used by all easy handles added to a multi handle no matter how many parallel transfers there are. The buffer remains allocated as long as there are active transfers.

CURL_MAX_WRITE_SIZE (16kB)

All

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "sftp://example.com/foo.bin");
    /* ask libcurl to allocate a larger receive buffer */
    curl_easy_setopt(curl, CURLOPT_BUFFERSIZE, 120000L);
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

Added in 7.10. Growing the buffer was added in 7.53.0.

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

CURLOPT_MAXFILESIZE(3), CURLOPT_MAX_RECV_SPEED_LARGE(3), CURLOPT_UPLOAD_BUFFERSIZE(3), CURLOPT_WRITEFUNCTION(3)

2024-05-22 libcurl