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jak-project/third-party/curl/docs/libcurl/curl_mime_encoder.md
T
Alexander J. Semenuk 5d5e35fb9b fix: Windows toolchain compatibility (curl 8.21 re-vendor, endless reconfigure loop) (#4355)
## Problem

Windows builds break with a current local toolchain (Scoop LLVM 22.1.8,
CMake 4.4.0, VS 2026), in two independent ways:

1. The build stops at curl's deliberate guard: `#error "no non-blocking
method was found/used/set"` in `third-party/curl/lib/nonblock.c`.
2. From the second configure onward, `cmake --build` re-runs CMake in an
endless loop (observed 42 consecutive reconfigure cycles in a single
build). Likely the same mechanism behind the "endlessly building" VS
2026 note in `docs/setup/dev/vs.md`.

## Root cause

1. `third-party/curl/CMake/CurlTests.c` passes `int *` to
`ioctlsocket()`, whose third parameter is `u_long *`. Clang 22 promotes
`-Wincompatible-pointer-types` to a hard error in C, so the
`HAVE_IOCTLSOCKET_FIONBIO` try_compile silently fails and
`curl_config.h` never defines it. Upstream CI does not see this because
the windows-2022 runner image ships an older LLVM. GCC 14 promotes the
same warning to a hard error, which is very likely the `CurlTests.c.obj`
failure reported from MSYS2 in open-goal/jak-project#3551. Upstream curl
hit the identical problem with GCC 14 and fixed the probe in curl 8.8.0
(curl/curl#13578).
2. The root CMakeLists copies the build tree's `compile_commands.json`
into `<src>/build/` for clangd using `configure_file()`, which registers
its input as a configure dependency. CMake rewrites
`compile_commands.json` late in every generation, after
`CTestTestfile.cmake` and `cmake_install.cmake` (outputs of the same
Ninja regen rule), so once the dependency is registered the rule is
deterministically dirty and every `ninja` invocation re-runs CMake. A
pristine first configure is safe (the file does not exist yet, so the
`if(EXISTS ...)` guard skips the copy), which is why the loop looks
machine- or IDE-specific.

## Fix

1. Per review, re-vendor `third-party/curl` at the `curl-8_21_0` tag
(previously `curl-8_3_0`), which carries the upstream probe fix plus two
years of upstream development; `vendor.yaml` updated to match.
Adjustments the version jump forced:
- curl 8.15 removed the native macOS Secure Transport backend
(`CURL_USE_SECTRANSP`), so macOS now builds curl against OpenSSL like
Linux. The two macOS workflows install Homebrew `openssl@3` and export
`OPENSSL_ROOT_DIR` (keg-only), and the macOS setup docs gained the same
two lines.
- `CURL_BROTLI` / `CURL_ZSTD` switched to AUTO-detection in curl 8.10;
pinned OFF to keep the previous no-compression behavior and avoid
silently linking whatever the CI images happen to have.
- curl's new top-level `BUILD_EXAMPLES` cache option (default ON) leaked
into discord-rpc's identically named option and broke configure at a
nonexistent `examples/send-presence` directory; pinned OFF ahead of the
third-party subdirectories.

The diff is dominated by the mechanical tag-tree swap under
`third-party/curl` (linguist-vendored, collapsed in review). The
hand-written changes are `CMakeLists.txt`, the two macOS workflows,
`docs/setup/system/macos.md`, and `vendor.yaml`.
2. Swap `configure_file()` for `file(COPY ...)`: the same clangd copy
with no configure dependency registered. (`file(COPY_FILE ...
ONLY_IF_DIFFERENT)` would be cleaner still but requires CMake 3.21,
above the declared `cmake_minimum_required(VERSION 3.10)`.)

## Test plan

- [x] Fresh `cmake --preset Release-windows-clang` (LLVM 22, no cache
seeding) completes and logs `Enabled SSL backends: Schannel`; the
FIONBIO probe passes without the previous `#error`
- [x] Full Windows Release build from scratch in the branch worktree
(all 1422 targets)
- [x] goalc-test suite: 1509 passed, 0 failed
- [x] Second consecutive configure with `compile_commands.json` present:
the regen rule in `build.ninja` has no `compile_commands.json` input;
`<src>/build/compile_commands.json` is still refreshed for clangd
- [x] Repeated `ninja` invocations after a full build no longer re-run
CMake
- [x] macOS Intel and ARM CI green (first exercise of the OpenSSL
backend switch)

---

I work off a self-hosted forge, so this GitHub account is quiet; the
configure logs and ninja dirty-node traces from the investigation are
available if anyone wants the raw data.

(AI-assisted)
2026-07-27 19:19:18 -04:00

2.9 KiB
Vendored
Generated

c, SPDX-License-Identifier, Title, Section, Source, See-also, Protocol, Added-in
c SPDX-License-Identifier Title Section Source See-also Protocol Added-in
Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. curl curl_mime_encoder 3 libcurl
curl_mime_addpart (3)
curl_mime_headers (3)
curl_mime_subparts (3)
HTTP
IMAP
SMTP
7.56.0

NAME

curl_mime_encoder - set a mime part's encoder and content transfer encoding

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_mime_encoder(curl_mimepart *part, const char *encoding);

DESCRIPTION

curl_mime_encoder() requests a mime part's content to be encoded before being transmitted.

part is the part's handle to assign an encoder. encoding is a pointer to a null-terminated encoding scheme. It may be set to NULL to disable an encoder previously attached to the part. The encoding scheme storage may safely be reused after this function returns.

Setting a part's encoder multiple times is valid: only the value set by the last call is retained.

Upon multipart rendering, the part's content is encoded according to the pertaining scheme and a corresponding "Content-Transfer-Encoding" header is added to the part.

Supported encoding schemes are:

"binary": the data is left unchanged, the header is added.

"8bit": header added, no data change.

"7bit": the data is unchanged, but is each byte is checked to be a 7-bit value; if not, a read error occurs.

"base64": Data is converted to base64 encoding, then split in CRLF-terminated lines of at most 76 characters.

"quoted-printable": data is encoded in quoted printable lines of at most 76 characters. Since the resulting size of the final data cannot be determined prior to reading the original data, it is left as unknown, causing chunked transfer in HTTP. For the same reason, this encoder may not be used with IMAP. This encoder targets text data that is mostly ASCII and should not be used with other types of data.

If the original data is already encoded in such a scheme, a custom Content-Transfer-Encoding header should be added with curl_mime_headers(3) instead of setting a part encoder.

Encoding should not be applied to multiparts, thus the use of this function on a part with content set with curl_mime_subparts(3) is strongly discouraged.

%PROTOCOLS%

EXAMPLE

int main(void)
{
  curl_mime *mime;
  curl_mimepart *part;

  CURL *curl = curl_easy_init();
  if(curl) {
    /* create a mime handle */
    mime = curl_mime_init(curl);

    /* add a part */
    part = curl_mime_addpart(mime);

    /* send a file */
    curl_mime_filedata(part, "image.png");

    /* encode file data in base64 for transfer */
    curl_mime_encoder(part, "base64");
  }
}

%AVAILABILITY%

RETURN VALUE

This function returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3). If CURLOPT_ERRORBUFFER(3) was set with curl_easy_setopt(3) there can be an error message stored in the error buffer when non-zero is returned.