CURLOPT_BUFFERSIZE(3)

💖 CURLOPT_BUFFERSIZE(3) 💖

okay so real talk, this is the libcurl manual, Library Functions Manual, and we're talking about receive buffer size today bestie. it's giving "small detail, big vibes" and i'm obsessed actually.

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🌸 NAME 🌸

CURLOPT_BUFFERSIZE — receive buffer size. that's it. that's the whole name. iconic brevity honestly.

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✨ SYNOPSIS ✨

#include <curl/curl.h>

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

so you're passing a long called size into curl_easy_setopt on your CURL *handle, and it hands you back a CURLcode. slay.

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🦋 DESCRIPTION 🦋

so bestie, you pass a long that says your preferred size, in bytes, for the receive buffer in libcurl. the big main character reason you'd do this? your write callback gets called more often and with smaller chunks. lowkey that's the whole point. and secondly, for some protocols there's a genuine benefit to having a larger buffer for performance. so it swings both ways, iykyk.

⚠️ okay but here's the thing — this is treated as a request, not an order. you are not guaranteed to actually get the size you asked for. it's giving "suggestion box" energy, not "manager voice". 💅

the buffer size is by default CURL_MAX_WRITE_SIZE (16kB). the maximum buffer size you're allowed to set is CURL_MAX_READ_SIZE (10MB). the minimum you're allowed to set is 1024.

🚨 DO NOT set this option on a handle that's currently used for an active transfer, because that may lead to unintended consequences. like, don't do it mid-transfer bestie, that's chaos behavior and i will not be held responsible 😭

the maximum size was 512kB until 7.88.0 — so if you're on something ancient, that's your ceiling, keep that in mind.

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. and the buffer remains allocated as long as there are active transfers. one buffer to rule them all fr fr 👑

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🎀 DEFAULT 🎀

CURL_MAX_WRITE_SIZE (16kB). that's the default, that's the baseline, that's the starting point. 💜

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🌈 PROTOCOLS 🌈

this functionality affects all supported protocols. all of them. every single one. no cap. ⭐

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🍓 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);
  }
}

see how it's just vibing there with 120000L? asked for a bigger receive buffer, got a bigger receive buffer (probably, remember the request-not-an-order thing). ate. 🔥

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🧚 AVAILABILITY 🧚

added in curl 7.10. vintage but still thriving, we love a legacy icon. ✨

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💅 RETURN VALUE 💅

curl_easy_setopt(3) returns a CURLcode indicating success or error — that's the whole deal.

CURLE_OK (0) means everything was OK 💖. non-zero means an error occurred, and you should go see libcurl-errors(3) for the deets. read the error, bestie, it's literally trying to tell you something 🙈

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👑 SEE ALSO 👑

• CURLOPT_MAXFILESIZE(3)
• CURLOPT_MAX_RECV_SPEED_LARGE(3)
• CURLOPT_UPLOAD_BUFFERSIZE(3)
• CURLOPT_WRITEFUNCTION(3)

go read them, they're all part of the same little friend group 🫶

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okay that's the page!! brought to you by libcurl, dated 2026-10-12, and the manpage header says CURLOPT_BUFFERSIZE(3) in case you forgot where you were. stay buffered, stay gorgeous, mwah 💖✨🎀🦋