Daniel Stenberg e694c8284a

docs/libcurl/opts: clarify the return values

Expand a little.

- mention the type name of the return code
- avoid stating which exact return codes that might be returned, as that
  varies over time, builds and conditions
- avoid stating some always return OK
- refer to the manpage documenting all the return codes

Closes #15900

2025-01-02 17:13:33 +01:00

1.9 KiB

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SPDX-License-Identifier

Title

Section

Source

See-also

Protocol

Added-in

curl

CURLOPT_UPLOAD_BUFFERSIZE

libcurl

CURLOPT_BUFFERSIZE (3)

CURLOPT_READFUNCTION (3)

CURLOPT_TCP_NODELAY (3)

All

7.62.0

NAME

CURLOPT_UPLOAD_BUFFERSIZE - upload buffer size

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_UPLOAD_BUFFERSIZE, long size);

DESCRIPTION

Pass a long specifying your preferred size (in bytes) for the upload buffer in libcurl. It makes libcurl uses a larger buffer that gets passed to the next layer in the stack to get sent off. In some setups and for some protocols, there is a huge performance benefit of having a larger upload buffer.

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

The upload buffer size is by default 64 kilobytes. The maximum buffer size allowed to be set is 2 megabytes. The minimum buffer size allowed to be set is 16 kilobytes.

The upload buffer is allocated on-demand - so if the handle is not used for upload, this buffer is not allocated at all.

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

DEFAULT

65536 bytes

%PROTOCOLS%

EXAMPLE

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 upload buffer */
    curl_easy_setopt(curl, CURLOPT_UPLOAD_BUFFERSIZE, 120000L);

    res = curl_easy_perform(curl);

    curl_easy_cleanup(curl);
  }
}

%AVAILABILITY%

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).

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