Add fuzz testing to JSON and EMF formatters

.github/workflows/fuzz-nightly.yml

@@ -0,0 +1,36 @@
+name: Nightly Fuzz
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 6 * * *" # Every day at 06:00 UTC
+
+permissions:
+  contents: read
+
+jobs:
+  fuzz-nightly:
+    name: Nightly Fuzz
+    runs-on: ubuntu-latest
+    env:
+      RUST_BACKTRACE: 1
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+      - uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: fuzz-nightly-${{ runner.os }}
+          workspaces: |
+            . -> target
+            fuzz -> fuzz/target
+      - name: Install cargo-fuzz
+        uses: dtolnay/install@cargo-fuzz
+      - name: Run fuzz_json
+        run: cargo +nightly fuzz run fuzz_json -- -max_total_time=300
+      - name: Run fuzz_emf
+        run: cargo +nightly fuzz run fuzz_emf -- -max_total_time=300
+      - name: Upload crash artifacts
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: fuzz-artifacts
+          path: fuzz/artifacts/

.github/workflows/fuzz.yml

@@ -0,0 +1,30 @@
+name: Fuzz
+on:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  # Quick smoke test on PRs, should catch obvious regressions.
+  fuzz-pr:
+    name: Fuzz Smoke Test
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    env:
+      RUST_BACKTRACE: 1
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+      - uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: fuzz-pr-${{ runner.os }}
+          workspaces: |
+            . -> target
+            fuzz -> fuzz/target
+      - name: Install cargo-fuzz
+        uses: dtolnay/install@cargo-fuzz
+      - name: Run fuzz_json
+        run: cargo +nightly fuzz run fuzz_json -- -max_total_time=60
+      - name: Run fuzz_emf
+        run: cargo +nightly fuzz run fuzz_emf -- -max_total_time=60

.gitignore

@@ -1,3 +1,8 @@
 /target
 /metrique/my
 /metrique-service-metrics/my
+
+# Fuzzing
+fuzz/target
+fuzz/artifacts
+fuzz/corpus