ci: mirror release artifacts to Cloudflare R2 (#1114)

Mirrors every release artifact into Cloudflare R2 alongside the existing AWS S3
upload, so both buckets carry the same objects during a parallel period. S3 is
untouched and stays authoritative for now; once R2 is confirmed complete it can
be dropped by deleting the `blobs:` block and pointing this at R2 alone.

### Why `publishers:` and not a second `blobs:` entry

goreleaser's blob pipe authenticates from the global `AWS_*` environment and has
no per-entry credential fields, so two different credential sets (AWS S3 and
Cloudflare R2) cannot coexist in `blobs:`. Custom publishers do support
per-entry `env:`, which is the supported way to isolate the two.

### Why `curl --aws-sigv4` and not `aws`/`rclone`

The CI image `docker.gitea.com/runner-images:ubuntu-latest` ships none of `aws`,
`rclone`, `s3cmd` or `mc`, but does ship curl 8.5 with `--aws-sigv4`. This keeps
the change zero-install. Credentials are fed to curl through a config file on
stdin rather than argv, so they never appear in the process list.

### Behaviour

- Object layout is identical to S3 (`gitea-runner/<version>/<artifact>`), so
  migrating consumers later means changing only the host, not the path.
- Nightly gets R2 too, matching the existing nightly-to-S3 behaviour.
- Missing R2 configuration fails the build. Because custom publishers run as the
  very last step of the publish pipeline, a preflight `--check-config` step runs
  right after checkout so the failure happens before anything is built or
  published rather than after the release already exists.
- Verified against a local MinIO instance (site region `auto`, matching R2):
  successful upload byte-compared after download, plus the missing-variable,
  wrong-credentials, missing-file and bad-argument paths.

### Required repository secrets

These must be configured before the next release run, otherwise the new
preflight step will fail the workflow:

- `R2_ENDPOINT` (full base URL, e.g. `https://<account>.r2.cloudflarestorage.com`)
- `R2_BUCKET`
- `R2_ACCESS_KEY_ID`
- `R2_SECRET_ACCESS_KEY`

### Known, deliberate wart

The publisher runs 109 times for 73 distinct object keys: goreleaser's release
pipe already registers `release.extra_files` as `UploadableFile` artifacts, and
`internal/exec` appends the publisher's own `extra_files` on top with no
de-duplication. It cannot be globbed away because `gobwas/glob` has no
substring-exclusion matcher, so `./**.sha256` cannot be narrowed to exclude
`*.xz.sha256`. It is harmless since PUT is idempotent, and the redundant
`./**.xz` glob is kept on purpose so the publisher declares its own complete
file set instead of implicitly depending on the `release:` block's globs. This
is documented in a comment above the block.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1114
Reviewed-by: Zettat123 <39446+zettat123@noreply.gitea.com>

scripts/upload-r2.sh

@@ -0,0 +1,112 @@
+#!/bin/sh
+# Copyright 2026 The Gitea Authors. All rights reserved.
+# SPDX-License-Identifier: MIT
+#
+# upload-r2.sh uploads a single local file to a single object key in a
+# Cloudflare R2 bucket, using curl's built-in AWS SigV4 signer (R2 is
+# S3-API compatible).
+#
+# This is the R2 half of the release process's parallel S3+R2 upload
+# period: goreleaser's `blobs:` pipe still uploads every release
+# artifact to AWS S3, and this script is invoked once per artifact
+# (via a goreleaser `publishers:` entry) to mirror the same artifact
+# into R2. Once the migration away from S3 is complete, the `blobs:`
+# block and the AWS_* secrets can be dropped without touching this
+# script.
+#
+# Usage:
+#   upload-r2.sh <local-file> <remote-key>
+#   upload-r2.sh --check-config
+#
+# The second form only validates that the required environment
+# variables below are set (it does not touch the network or the
+# filesystem beyond that), and is meant to be run as an early
+# preflight step in CI: goreleaser custom publishers run as the very
+# last step of the publish pipeline, so without a preflight check a
+# missing R2_* secret would only be discovered after the Gitea release
+# has already been created and every artifact already uploaded to S3.
+#
+# Required environment variables:
+#   R2_ENDPOINT          Base URL of the R2 endpoint, e.g.
+#                        https://<account>.r2.cloudflarestorage.com
+#   R2_BUCKET            Destination bucket name.
+#   R2_ACCESS_KEY_ID     R2 access key id.
+#   R2_SECRET_ACCESS_KEY R2 secret access key.
+
+set -eu
+
+# check_env validates that all required R2_* environment variables are
+# set and non-empty, printing a single "missing required environment
+# variable(s): ..." message and exiting non-zero otherwise. Used by
+# both the normal upload mode and --check-config, so the validation
+# logic only exists in one place.
+check_env() {
+  missing=""
+
+  if [ -z "${R2_ENDPOINT:-}" ]; then
+    missing="$missing R2_ENDPOINT"
+  fi
+  if [ -z "${R2_BUCKET:-}" ]; then
+    missing="$missing R2_BUCKET"
+  fi
+  if [ -z "${R2_ACCESS_KEY_ID:-}" ]; then
+    missing="$missing R2_ACCESS_KEY_ID"
+  fi
+  if [ -z "${R2_SECRET_ACCESS_KEY:-}" ]; then
+    missing="$missing R2_SECRET_ACCESS_KEY"
+  fi
+
+  if [ -n "$missing" ]; then
+    echo "upload-r2.sh: missing required environment variable(s):$missing" >&2
+    exit 1
+  fi
+}
+
+if [ "$#" -eq 1 ] && [ "$1" = "--check-config" ]; then
+  check_env
+  echo "upload-r2.sh: R2 configuration OK"
+  exit 0
+fi
+
+if [ "$#" -ne 2 ]; then
+  echo "usage: upload-r2.sh <local-file> <remote-key>" >&2
+  echo "       upload-r2.sh --check-config" >&2
+  exit 1
+fi
+
+local_file="$1"
+remote_key="$2"
+
+if [ ! -f "$local_file" ]; then
+  echo "upload-r2.sh: local file not found: $local_file" >&2
+  exit 1
+fi
+
+check_env
+
+# Strip a single trailing slash from the endpoint, if present, so that
+# building the path-style URL below never produces a double slash.
+endpoint="${R2_ENDPOINT%/}"
+url="$endpoint/$R2_BUCKET/$remote_key"
+
+# Credentials are passed to curl through a config file read from
+# stdin rather than as a command-line argument, so they never show up
+# in `ps` output.
+#
+# --fail-with-body (instead of plain --fail) still exits non-zero on
+# HTTP errors, but also prints R2's XML error body, which is where the
+# actual error code lives (SignatureDoesNotMatch, NoSuchBucket,
+# AccessDenied, ...); with plain --fail that body is discarded and the
+# failure is silent. --retry 3 (without --retry-all-errors) still
+# retries the transient cases (5xx, 408, 429, connection failures);
+# --retry-all-errors would additionally retry permanent 4xx responses
+# three times with backoff, which only delays an inevitable failure.
+printf 'user = "%s:%s"\n' "$R2_ACCESS_KEY_ID" "$R2_SECRET_ACCESS_KEY" | curl \
+  --config - \
+  --fail-with-body \
+  --silent \
+  --show-error \
+  --retry 3 \
+  --aws-sigv4 "aws:amz:auto:s3" \
+  --upload-file "$local_file" \
+  "$url"