support SimulateScenario through FFI to improve testing

.changeset/support_simulatescenario_through_ffi_to_improve_testing.md

@@ -0,0 +1,6 @@
+---
+livekit: patch
+livekit-ffi: patch
+---
+
+support SimulateScenario through FFI to improve testing - #1069 (@davidzhao)

.github/workflows/builds.yml

@@ -23,6 +23,13 @@ on:
 
 env:
   CARGO_TERM_COLOR: always
+  # sccache caches rustc invocations across runs (key: source hash + flags).
+  # RUSTC_WRAPPER is intentionally NOT set at workflow scope — see the probe
+  # step below for why (transient GHA cache backend errors should not fail
+  # the whole build). We do NOT wrap CC/CXX in this workflow because the
+  # matrix includes cross-compile targets (iOS, Android, Windows-arm64)
+  # where wrapping is fragile.
+  SCCACHE_GHA_ENABLED: "true"
 
 jobs:
   build:
@@ -101,7 +108,41 @@ jobs:
         run: |
           rustup target add ${{ matrix.target }}
 
-      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+      - name: Setup sccache
+        uses: mozilla-actions/sccache-action@054db53350805f83040bf3e6e9b8cf5a139aa7c9 # v0.0.7
+
+      - name: Enable sccache wrapping (probe first)
+        shell: bash
+        run: |
+          # Probe the GHA cache backend by starting the sccache server. If it
+          # fails (transient HTTP 400 from actions.githubusercontent.com has
+          # been seen in practice), skip exporting RUSTC_WRAPPER so the build
+          # falls back to vanilla rustc instead of erroring out.
+          if sccache --start-server >/dev/null 2>&1; then
+            echo "RUSTC_WRAPPER=sccache" >> "$GITHUB_ENV"
+            echo "::notice::sccache enabled (RUSTC_WRAPPER=sccache)"
+          else
+            echo "::warning::sccache backend unreachable; building without compile cache this run"
+          fi
+
+      - name: Cache cargo registry
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        with:
+          path: |
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-registry-
+
+      - name: Cache cargo target
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        with:
+          path: target/
+          key: ${{ runner.os }}-cargo-target-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-target-${{ matrix.target }}-
 
       - name: Build (Cargo)
         if: ${{ !contains(matrix.target, 'android') }}

.github/workflows/ffi-builds.yml

@@ -153,7 +153,24 @@ jobs:
         run: |
           rustup target add ${{ matrix.target }}
 
-      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+      - name: Cache cargo registry
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        with:
+          path: |
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-registry-
+
+      - name: Cache cargo target
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        with:
+          path: target/
+          key: ${{ runner.os }}-cargo-target-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-target-${{ matrix.target }}-
 
       - name: Install Protoc
         uses: arduino/setup-protoc@a8b67ba40b37d35169e222f3bb352603327985b6 # v2.1.0

.github/workflows/node-builds.yml

@@ -78,7 +78,24 @@ jobs:
           toolchain: stable
           targets: ${{ matrix.target }}
 
-      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+      - name: Cache cargo registry
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        with:
+          path: |
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-registry-
+
+      - name: Cache cargo target
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        with:
+          path: target/
+          key: ${{ runner.os }}-cargo-target-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-target-${{ matrix.target }}-
 
       - name: Install Protoc
         uses: arduino/setup-protoc@c65c819552d16ad3c9b72d9dfd5ba5237b9c906b # v3.0.0

.github/workflows/tests.yml

@@ -23,6 +23,13 @@ on:
 env:
   CARGO_TERM_COLOR: always
   RUST_LOG: debug
+  # sccache stores its cache in GitHub Actions' cache backend; both rustc and
+  # C/C++ invocations route through it. RUSTC_WRAPPER is intentionally NOT set
+  # at workflow scope — the "Enable sccache" step only exports it after the
+  # backend probe succeeds, so transient outages of the GHA cache service
+  # (which return HTTP 400 and abort sccache server startup) make CI continue
+  # without sccache instead of failing the whole build.
+  SCCACHE_GHA_ENABLED: "true"
 
 jobs:
   build:
@@ -58,8 +65,38 @@ jobs:
           version: "25.2"
           repo-token: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Cache Cargo registry
-        uses: actions/cache@6f8efc29b200d32929f49075959781ed54ec270c # v3.5.0
+      # sccache wraps both rustc and the C/C++ compilers used by `cxx_build`
+      # in `webrtc-sys`. The Mozilla action installs the binary; the probe
+      # step below only enables wrapping if the GHA cache backend is reachable
+      # (it occasionally returns transient HTTP 400s that crash sccache
+      # startup — we want builds to continue, not fail, in that case).
+      - name: Setup sccache
+        uses: mozilla-actions/sccache-action@054db53350805f83040bf3e6e9b8cf5a139aa7c9 # v0.0.7
+
+      - name: Enable sccache wrapping (probe first)
+        shell: bash
+        run: |
+          # `sccache --start-server` actually exercises the configured backend
+          # (here: GHA cache). If it fails — e.g. azure-side outage — log a
+          # warning and skip exporting RUSTC_WRAPPER / CC / CXX so the build
+          # falls back to vanilla rustc. Slower, but green.
+          if sccache --start-server >/dev/null 2>&1; then
+            echo "RUSTC_WRAPPER=sccache" >> "$GITHUB_ENV"
+            # All three matrix targets in tests.yml are host targets (no
+            # cross-compile), so wrapping CC/CXX is safe. Skip on Windows:
+            # MSVC `cl` setup needs more care.
+            if [ "${{ runner.os }}" != "Windows" ]; then
+              echo "CC=sccache cc"  >> "$GITHUB_ENV"
+              echo "CXX=sccache c++" >> "$GITHUB_ENV"
+            fi
+            echo "::notice::sccache enabled (RUSTC_WRAPPER=sccache)"
+          else
+            echo "::warning::sccache backend unreachable; building without compile cache this run"
+          fi
+
+      # Cache cargo's downloaded crate sources + per-target build outputs.
+      - name: Cache cargo registry
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
         with:
           path: |
             ~/.cargo/registry/index/
@@ -69,14 +106,13 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-cargo-registry-
 
-      - name: Cache Cargo build
-        uses: actions/cache@6f8efc29b200d32929f49075959781ed54ec270c # v3.5.0
+      - name: Cache cargo target
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
         with:
           path: target/
-          key: ${{ runner.os }}-cargo-build-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}
+          key: ${{ runner.os }}-cargo-target-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}
           restore-keys: |
-            ${{ runner.os }}-cargo-build-${{ matrix.target }}-
-            ${{ runner.os }}-cargo-build-
+            ${{ runner.os }}-cargo-target-${{ matrix.target }}-
 
       - name: Install linux dependencies
         if: ${{ matrix.os == 'ubuntu-latest' }}
@@ -118,14 +154,18 @@ jobs:
           LIVEKIT_CONFIG: "enable_data_tracks: true"
         run: livekit-server --dev &
 
+      # Tests run in dev profile to keep CI compile time reasonable. The e2e
+      # path is timing-sensitive (ICE handshake, reconnect windows) but the
+      # timeouts in those tests are real-clock seconds and have plenty of
+      # headroom — dev's slower runtime doesn't push past them in practice.
       - name: Test (no E2E)
         if: ${{ !matrix.e2e-testing }}
         env:
           RUST_LOG: info
-        run: cargo +nightly test --release --verbose --target ${{ matrix.target }} -- --nocapture
+        run: cargo +nightly test --verbose --target ${{ matrix.target }} -- --nocapture
 
       - name: Test (with E2E)
         if: ${{ matrix.e2e-testing }}
         env:
           RUST_LOG: info
-        run: cargo +nightly test --release --verbose --target ${{ matrix.target }} --features __lk-e2e-test -- --nocapture --test-threads=1
+        run: cargo +nightly test --verbose --target ${{ matrix.target }} --features __lk-e2e-test -- --nocapture --test-threads=1