e2e setup: Linux's apt packages from the Actions cache

.github/actions/e2e-setup/action.yml

@@ -30,19 +30,29 @@ runs:
     # Windows e2e jobs. The key is the ISO week, so a newer ffmpeg arrives within a week:
     # the jobs that miss install it through Chocolatey as before, and the first to finish
     # saves it (the others are refused the same key, a warning). Linux keeps apt: Firefox
-    # decodes through the system's libavcodec, not a program in a folder.
+    # decodes through the system's libavcodec, not a program in a folder. But the packages
+    # apt fetches are kept the same way, a week per runner image, so the mirror only has
+    # to send its package lists and what changed that week: on 2026-10-22 it sent less
+    # than a package a second, and three runs failed with three 300 s attempts each.
     - name: This week's ffmpeg cache key
-      if: runner.os == 'Windows'
       id: ffmpeg-key
       shell: bash
-      run: echo "key=e2e-ffmpeg-windows-$(date -u +%G-W%V)" >> "$GITHUB_OUTPUT"
+      run: |
+        if [ "$RUNNER_OS" = Windows ]; then
+          echo "key=e2e-ffmpeg-windows-$(date -u +%G-W%V)" >> "$GITHUB_OUTPUT"
+          echo "path=~/ffmpeg-e2e" >> "$GITHUB_OUTPUT"
+        else
+          echo "key=e2e-apt-${ImageOS:-linux}-$(date -u +%G-W%V)" >> "$GITHUB_OUTPUT"
+          # The packages only: apt's lock file and partial/ are root's, which the save
+          # (not root) could not read.
+          echo "path=~/apt-e2e/*.deb" >> "$GITHUB_OUTPUT"
+        fi
 
     - name: Restore ffmpeg from the cache
-      if: runner.os == 'Windows'
       id: ffmpeg-cache
       uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
       with:
-        path: ~/ffmpeg-e2e
+        path: ${{ steps.ffmpeg-key.outputs.path }}
         key: ${{ steps.ffmpeg-key.outputs.key }}
 
     # Linux: Firefox decodes H.264/AAC through the system ffmpeg; without it every stream
@@ -74,17 +84,25 @@ runs:
             # it is a failed attempt like any other.
             printf 'Acquire::http::Timeout "30";\nAcquire::https::Timeout "30";\nAcquire::Retries "3";\n' |
               sudo tee /etc/apt/apt.conf.d/99-faststream-e2e-timeouts > /dev/null
+            # apt takes the packages from, and downloads them to, the folder the cache keeps.
+            archives="$HOME/apt-e2e"
+            mkdir -p "$archives/partial"
           fi
           for attempt in 1 2 3; do
             if [ "$RUNNER_OS" = Windows ]; then
               choco install ffmpeg -y --no-progress && break
             else
               sudo timeout -k 10 120 apt-get update &&
-                sudo timeout -k 10 300 apt-get install -y --no-install-recommends ffmpeg pulseaudio pulseaudio-utils && break
+                sudo timeout -k 10 300 apt-get install -y --no-install-recommends ffmpeg pulseaudio pulseaudio-utils \
+                  -o Dir::Cache::Archives="$archives" && break
             fi
             echo "::warning::Installing ffmpeg failed (attempt $attempt of 3); trying again in 30 s."
             sleep 30
           done
+          # A miss saves this week's packages for the jobs after it.
+          if [ "$RUNNER_OS" != Windows ] && [ "$CACHE_HIT" != true ] && compgen -G "$archives/*.deb" > /dev/null; then
+            echo "save=true" >> "$GITHUB_OUTPUT"
+          fi
           if [ "$RUNNER_OS" = Windows ]; then
             # The programs themselves for the cache, not Chocolatey's shims to them, from where
             # Chocolatey is (ChocolateyInstall, on the runner C:\ProgramData\chocolatey).
@@ -107,12 +125,12 @@ runs:
         ffmpeg -hide_banner -version | sed -n 1p
 
     - name: Save ffmpeg to the cache
-      if: runner.os == 'Windows' && steps.ffmpeg.outputs.save == 'true'
+      if: steps.ffmpeg.outputs.save == 'true'
       # Jobs that missed the same week race to save it; a refused save fails no job.
       continue-on-error: true
       uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
       with:
-        path: ~/ffmpeg-e2e
+        path: ${{ steps.ffmpeg-key.outputs.path }}
         key: ${{ steps.ffmpeg-key.outputs.key }}
 
     # sample.mp4, which every e2e fixture is made from, comes from test-videos.co.uk, which

tests/workflows/e2e-setup.test.sh

@@ -79,6 +79,10 @@ echo "apt-get $*" >> "$FIX/calls"
 [ -e "$FIX/apt-fails" ] && exit 100
 if [ "$1" = install ]; then
   cp "$STUBS/pulseaudio" "$STUBS/pactl" "$FIX/bin/"
+  # With -o Dir::Cache::Archives=<folder>, a downloaded package is left there, as apt does.
+  for arg in "$@"; do
+    case "$arg" in Dir::Cache::Archives=*) : > "${arg#*=}/ffmpeg_7.0_amd64.deb" ;; esac
+  done
 fi
 EOF
 cat > "$here/stubs/sleep" <<'EOF'
@@ -247,7 +251,11 @@ check '... the update too' contains "$FIX/calls" 'sudo timeout -k 10 120 apt-get
 check 'logs the version' contains "$FIX/out" 'ffmpeg version'
 check 'no Chocolatey' lacks "$FIX/calls" 'choco'
 check 'adds nothing to PATH' test ! -s "$FIX/path"
-check 'saves nothing' test ! -s "$FIX/output"
+# A mirror that sent less than a package a second failed three runs (2026-10-22).
+check 'keeps the packages in the folder the cache saves' contains "$FIX/calls" \
+  "pulseaudio-utils -o Dir::Cache::Archives=$FIX/home/apt-e2e"
+check '... with the partial/ folder apt needs' test -d "$FIX/home/apt-e2e/partial"
+check 'a miss asks the save step to save them' contains "$FIX/output" 'save=true'
 # A mirror that stopped sending held the step for 19 minutes (2026-10-06).
 check 'sets apt to give up on a stalled download' contains "$FIX/calls" 'sudo tee /etc/apt/apt.conf.d/99-faststream-e2e-timeouts'
 check '... after 30 s without data' contains "$FIX/tee-99-faststream-e2e-timeouts" 'Acquire::http::Timeout "30";'
@@ -263,6 +271,15 @@ check 'then updated again' test "$(grep -c '^apt-get update$' "$FIX/calls")" -eq
 check 'installed once' test "$(grep -c '^apt-get install' "$FIX/calls")" -eq 1
 check 'logs the version' contains "$FIX/out" 'ffmpeg version'
 
+ffmpeg_scenario 'Linux, a cache hit: apt installs from the restored packages, nothing saved' Linux true
+check 'succeeds' test "$status" -eq 0
+check 'installs from the cached folder' contains "$FIX/calls" "-o Dir::Cache::Archives=$FIX/home/apt-e2e"
+check 'saves nothing' test ! -s "$FIX/output"
+
+ffmpeg_scenario 'Linux, apt that keeps failing: nothing saved' Linux '' apt-fails
+check 'tried three times' test "$(grep -c '^apt-get update' "$FIX/calls")" -eq 3
+check 'saves nothing' test ! -s "$FIX/output"
+
 ffmpeg_scenario 'Windows, a cache hit: the cached programs, no Chocolatey' Windows true cache-has
 check 'succeeds' test "$status" -eq 0
 check 'says so' contains "$FIX/out" "ffmpeg from the cache ($FIX/home/ffmpeg-e2e)."