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diff --git a/.github/workflows/clang_format.yml b/.github/workflows/clang_format.yml
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+# Copyright (C) 2025 Sebastian Pipping <sebastian@pipping.org>
+# Licensed under the MIT license
+
+name: Enforce clang-format clean code
+
+on:
+  pull_request:
+  push:
+  schedule:
+    - cron: '0 2 * * 5'  # Every Friday at 2am
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  clang_format:
+    runs-on: ubuntu-24.04
+    steps:
+    - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
+
+    - name: Install Clang 21
+      run: |-
+        set -x
+        source /etc/os-release
+        wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
+        sudo add-apt-repository "deb https://apt.llvm.org/${UBUNTU_CODENAME}/ llvm-toolchain-${UBUNTU_CODENAME}-21 main"
+        sudo apt-get update  # due to new repository
+        sudo apt-get install --yes --no-install-recommends -V \
+            clang-format-21
+        echo /usr/lib/llvm-21/bin >>"${GITHUB_PATH}"
+
+    - name: Enforce clang-format clean code
+      run: |
+        set -x -o pipefail
+        clang-format --version
+        git ls-files \*.cpp \*.c \*.h \*.h.in | xargs clang-format -i
+        sed 's,#\( \+\)cmakedefine,#cmakedefine,' -i.bak src/UriConfig.h.in  # this helps Meson
+        git -c color.ui=always diff --exit-code  # i.e. fail CI for non-empty diff