CURLOPT_BUFFERSIZE(3) Library Functions Manual CURLOPT_BUFFERSIZE(3)
NAME
CURLOPT_BUFFERSIZE - receive buffer size
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_BUFFERSIZE, long size);
DESCRIPTION
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 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 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.
DEFAULT
CURL_MAX_WRITE_SIZE (16kB)
PROTOCOLS
This functionality affects all supported protocols
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
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);
result = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
AVAILABILITY
Added in curl 7.10
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_MAXFILESIZE(3), CURLOPT_MAX_RECV_SPEED_LARGE(3),
CURLOPT_UPLOAD_BUFFERSIZE(3), CURLOPT_WRITEFUNCTION(3)
libcurl 2026-03-23 CURLOPT_BUFFERSIZE(3)
curl 8.19.0 - Generated Thu Mar 26 18:28:37 CDT 2026