fuzz.yml

# Nightly fuzzing of the internet-facing parsers.
#
# `go test ./...` only ever runs the SEED corpora of these targets - nothing in
# the repo actually fuzzes. This does, one target per job (Go permits only one
# -fuzz target per invocation), and caches the generated corpus so coverage
# compounds night over night instead of restarting from the seeds each time.
#
# None of these packages import the root package, so - unlike every job in
# ci.yml - this workflow needs no frontend/dist.
name: fuzz

on:
  schedule:
    - cron: "0 3 * * *"
  workflow_dispatch:
    inputs:
      fuzztime:
        description: "Duration per target (e.g. 5m, 30m)"
        required: false
        default: "5m"

permissions:
  contents: read

jobs:
  fuzz:
    runs-on: ubuntu-latest
    timeout-minutes: 30
    strategy:
      fail-fast: false
      matrix:
        include:
          - { pkg: ./internal/control, target: FuzzReadMsg }
          - { pkg: ./internal/link, target: FuzzParsePairingCode }
          - { pkg: ./internal/mc, target: FuzzReadVarInt }
          - { pkg: ./internal/mc, target: FuzzParseHandshake }
          - { pkg: ./internal/mc, target: FuzzReadPacket }
          - { pkg: ./internal/mc, target: FuzzParseLoginStart }
          - { pkg: ./internal/mc, target: FuzzSnifferChunked }
          - { pkg: ./internal/mc, target: FuzzServeOffline }
          - { pkg: ./internal/relay, target: FuzzTapChunked }
    steps:
      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          persist-credentials: false
      - uses: actions/setup-go@924ae3a1cded613372ab5595356fb5720e22ba16 # v6.5.0
        with:
          go-version-file: go.mod
          cache-dependency-path: go.sum
          # We manage the corpus cache below; setup-go's cache covers GOCACHE too
          # and the two would fight over the same directory.
          cache: false

      # Go writes generated corpus entries under $GOCACHE/fuzz. Restoring them
      # is what turns 8 nightly 5-minute runs into a corpus that grows, rather
      # than 8 cold starts.
      - name: resolve GOCACHE
        id: gocache
        run: echo "dir=$(go env GOCACHE)" >> "$GITHUB_OUTPUT"
      - uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
        with:
          path: ${{ steps.gocache.outputs.dir }}/fuzz
          key: fuzz-corpus-${{ matrix.target }}-${{ github.run_id }}
          restore-keys: |
            fuzz-corpus-${{ matrix.target }}-

      # FUZZTIME comes from workflow_dispatch, i.e. from a human typing into a
      # form: it goes through env, never interpolated into the shell command, or
      # it would be a template-injection vector.
      - name: fuzz ${{ matrix.target }}
        env:
          TARGET: ${{ matrix.target }}
          PKG: ${{ matrix.pkg }}
          FUZZTIME: ${{ inputs.fuzztime || '5m' }}
        run: go test -run '^$' -fuzz "^${TARGET}$" -fuzztime "$FUZZTIME" "$PKG"

      # A crasher is written to <pkg>/testdata/fuzz/<Target>/. It is a real bug
      # and a permanent regression seed: commit it with the fix.
      - if: failure()
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: crasher-${{ matrix.target }}
          path: ${{ matrix.pkg }}/testdata/fuzz/**
          if-no-files-found: ignore