CURLOPT_UPLOAD(3)

💅 CURLOPT_UPLOAD(3) — data upload 💅

okay so bestie, we're in the libcurl Library Functions Manual, and today's main character is CURLOPT_UPLOAD — the option that makes your program, like, send stuff up. No cap. 🦋

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✨ NAME ✨

CURLOPT_UPLOAD — data upload

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🌸 SYNOPSIS 🌸

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_UPLOAD, long upload);

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🎀 DESCRIPTION 🎀

So the long parameter upload — you set it to 1 and that literally tells the library "get ready, we're doing an upload," and then it prepares for and performs an upload. That's it, that's the vibe. ✨

Now, CURLOPT_READDATA(3) and CURLOPT_INFILESIZE(3) or CURLOPT_INFILESIZE_LARGE(3) are also super interesting for uploads — like, they're the supporting cast, and you're gonna want them. iykyk.

If the protocol is HTTP, uploading means using the PUT request, unless you tell libcurl otherwise. (Your call, bestie, but that's the default energy.)

Using PUT with HTTP 1.1 implies the use of a "Expect: 100-continue" header. Not everyone's fave, so heads up: you can disable this header with CURLOPT_HTTPHEADER(3) as usual. 🫶

If you use PUT to an HTTP 1.1 server, you can upload data without knowing the size before starting the transfer — iconic, honestly. The library enables this by adding a header "Transfer-Encoding: chunked". With HTTP 1.0, or if you prefer not to use chunked transfer, you must specify the size of the data with CURLOPT_INFILESIZE(3) or CURLOPT_INFILESIZE_LARGE(3). No skipping that part, fr fr. 😭

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🌈 DEFAULT 🌈

0

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🧚 PROTOCOLS 🧚

This functionality affects all supported protocols. all of them. periodt. 👑

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⭐ EXAMPLE ⭐

static size_t read_cb(char *ptr, size_t size, size_t nmemb, void *userdata)
{
  FILE *src = userdata;
  /* copy as much data as possible into the 'ptr' buffer, but no more than
     'size' * 'nmemb' bytes */
  size_t retcode = fread(ptr, size, nmemb, src);

  return retcode;
}

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    FILE *src = fopen("local-file", "r");
    curl_off_t fsize = 1234; /* set this to the size of the input file */

    /* we want to use our own read function */
    curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_cb);

    /* enable uploading */
    curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

    /* specify target */
    curl_easy_setopt(curl, CURLOPT_URL, "ftp://example.com/dir/to/newfile");

    /* now specify which pointer to pass to our callback */
    curl_easy_setopt(curl, CURLOPT_READDATA, src);

    /* Set the size of the file to upload */
    curl_easy_setopt(curl, CURLOPT_INFILESIZE_LARGE, (curl_off_t)fsize);

    /* Now run off and do what you have been told */
    curl_easy_perform(curl);
  }
}

like, just copy it, it works. 💖

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🦋 AVAILABILITY 🦋

Added in curl 7.1 — she's been around a minute, lowkey a legend.

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💜 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 — go check libcurl-errors(3), bestie. 🔥

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👑 SEE ALSO 👑

• CURLOPT_INFILESIZE_LARGE(3)
• CURLOPT_PUT(3)
• CURLOPT_READFUNCTION(3)

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and that's the whole page, diva. ✨ this lil masterpiece came to you from libcurl, dated 2026-10-12 — go upload something iconic, CURLOPT_UPLOAD(3) out. 💅🎀