feat: Android support

.github/workflows/check.yml

@@ -408,3 +408,89 @@ jobs:
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
       - run: cargo update -w --locked
+
+  check-android:
+    runs-on: ubuntu-latest
+    env:
+      # https://searchfox.org/mozilla-central/search?q=NDK_VERSION =&path=python/mozboot/mozboot/android.py
+      NDK_VERSION: 27.2.12479018 # r27c
+      # https://searchfox.org/mozilla-central/search?q=\bapi_level=&path=taskcluster/scripts/misc/build-llvm-common.sh&regexp=true
+      API_LEVEL: 21
+
+    strategy:
+      matrix:
+        include:
+          - target: x86_64-linux-android
+            emulator-arch: x86_64
+            # Note that x86_64 image is only available for API 21+. See
+            # https://github.com/ReactiveCircus/android-emulator-runner?tab=readme-ov-file#configurations.
+          - target: i686-linux-android
+            emulator-arch: x86
+          # FIXME: https://github.com/ReactiveCircus/android-emulator-runner/issues/404
+          # - target: armv7-linux-androideabi
+          #   emulator-arch: arm64-v8
+
+    steps:
+    - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      with:
+        persist-credentials: false
+
+    - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      with:
+        repository: mozilla/neqo
+        sparse-checkout: |
+          .github/actions/rust
+        path: neqo
+        persist-credentials: false
+
+    - uses: actions/setup-java@3a4f6e1af504cf6a31855fa899c6aa5355ba6c12 # v4.7.0
+      with:
+        distribution: zulu
+        java-version: 23
+
+    - uses: android-actions/setup-android@9fc6c4e9069bf8d3d10b2204b1fb8f6ef7065407 # v3.2.2
+    - run: sdkmanager --install "ndk;${{ env.NDK_VERSION }}"
+
+    - uses: ./neqo/.github/actions/rust
+      with:
+        version: stable
+        targets: ${{ matrix.target }}
+        tools: cargo-ndk
+        token: ${{ secrets.GITHUB_TOKEN }}
+
+    - run: cargo ndk -t ${{ matrix.target }} test --no-run
+
+    - env:
+        TARGET: ${{ matrix.target }}
+      run: |
+        echo 'KERNEL=="kvm", GROUP="kvm", MODE="0666", OPTIONS+="static_node=kvm"' | sudo tee /etc/udev/rules.d/99-kvm4all.rules
+        sudo udevadm control --reload-rules
+        sudo udevadm trigger --name-match=kvm
+        cat <<'EOF' > /tmp/rust-android-run-tests-on-emulator.sh
+        #!/bin/bash
+        set -e
+        adb shell ip addr show
+        export GITHUB_ACTIONS=1
+        adb wait-for-device
+        while [ -z "$(adb shell getprop sys.boot_completed | tr -d '\r')" ]; do sleep 1; done
+        any_failures=0
+        for test in $(find target/$TARGET/debug/deps/ -type f -executable ! -name "*.so" -name "*-*"); do
+          adb push "$test" /data/local/tmp/
+          adb shell chmod +x /data/local/tmp/$(basename "$test")
+          # See https://unix.stackexchange.com/a/451140/409256
+          adb shell "API_LEVEL=$API_LEVEL /data/local/tmp/$(basename "$test") || echo _FAIL_" 2>&1 | tee output
+          grep _FAIL_ output && any_failures=1
+        done
+        exit $any_failures
+        EOF
+        chmod a+x /tmp/rust-android-run-tests-on-emulator.sh
+
+    - uses: reactivecircus/android-emulator-runner@62dbb605bba737720e10b196cb4220d374026a6d # v2.33.0
+      with:
+        api-level: ${{ env.API_LEVEL }}
+        arch: ${{ matrix.emulator-arch == 'arm64-v8' && 'arm64-v8a' || matrix.emulator-arch }}
+        ndk: ${{ env.NDK_VERSION }}
+        emulator-boot-timeout: 120
+        script: /tmp/rust-android-run-tests-on-emulator.sh
+      env:
+        TARGET: ${{ matrix.target }}

Cargo.toml

@@ -7,7 +7,7 @@ homepage = "https://github.com/mozilla/mtu/"
 repository = "https://github.com/mozilla/mtu/"
 authors = ["The Mozilla Necko Team <necko@mozilla.com>"]
 readme = "README.md"
-version = "0.2.6"
+version = "0.2.7"
 edition = "2021"
 license = "MIT OR Apache-2.0"
 # Don't increase beyond what Firefox is currently using:
@@ -77,7 +77,7 @@ infinite_loop = "warn"
 large_include_file = "warn"
 let_underscore_must_use = "warn"
 let_underscore_untyped = "warn"
-literal_string_with_formatting_args = "allow" # FIXME: Re-enable "warn" when MRSV is > 1.87. See https://github.com/rust-lang/rust-clippy/pull/13953#issuecomment-2676336899
+literal_string_with_formatting_args = "allow" # FIXME: Re-enable "warn" when MSRV is > 1.87. See https://github.com/rust-lang/rust-clippy/pull/13953#issuecomment-2676336899
 lossy_float_literal = "warn"
 mem_forget = "warn"
 mixed_read_write_in_expression = "warn"

README.md

@@ -15,6 +15,7 @@ This crate exports a single function `interface_and_mtu` that returns the name a
 of the outgoing network interface towards a remote destination identified by an `IpAddr`.
 
 ## Example
+
 ```rust
 let destination = IpAddr::V4(Ipv4Addr::LOCALHOST);
 let (name, mtu): (String, usize) = mtu::interface_and_mtu(destination).unwrap();
@@ -24,6 +25,7 @@ println!("MTU towards {destination} is {mtu} on {name}");
 ## Supported Platforms
 
 * Linux
+* Android
 * macOS
 * Windows
 * FreeBSD

build.rs

@@ -11,7 +11,7 @@ use std::env;
 const BINDINGS: &str = "bindings.rs";
 
 #[cfg(feature = "gecko")]
-fn clang_args() -> Vec<String> {
+fn clang_args(_target_os: &str) -> Vec<String> {
     use mozbuild::{config::BINDGEN_SYSTEM_FLAGS, TOPOBJDIR};
 
     let mut flags: Vec<String> = BINDGEN_SYSTEM_FLAGS.iter().map(|s| s.to_string()).collect();
@@ -30,8 +30,15 @@ fn clang_args() -> Vec<String> {
 }
 
 #[cfg(not(feature = "gecko"))]
-const fn clang_args() -> Vec<String> {
-    Vec::new()
+fn clang_args(target_os: &str) -> Vec<String> {
+    match target_os {
+        "android" => {
+            let sysroot =
+                env::var("CARGO_NDK_SYSROOT_PATH").expect("CARGO_NDK_SYSROOT_PATH was not set");
+            vec![format!("--sysroot={sysroot}")]
+        }
+        _ => Vec::new(),
+    }
 }
 
 fn bindgen() {
@@ -65,7 +72,7 @@ fn bindgen() {
     };
 
     let bindings = bindings
-        .clang_args(clang_args())
+        .clang_args(clang_args(&target_os))
         // Tell cargo to invalidate the built crate whenever any of the
         // included header files changed.
         .parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))

src/lib.rs

@@ -14,6 +14,7 @@
 //! of the outgoing network interface towards a remote destination identified by an `IpAddr`.
 //!
 //! # Example
+//!
 //! ```
 //! # use std::net::{IpAddr, Ipv4Addr};
 //! let destination = IpAddr::V4(Ipv4Addr::LOCALHOST);
@@ -24,6 +25,7 @@
 //! # Supported Platforms
 //!
 //! * Linux
+//! * Android
 //! * macOS
 //! * Windows
 //! * FreeBSD
@@ -144,25 +146,36 @@ mod test {
         }
     }
 
-    #[cfg(any(target_os = "macos", target_os = "freebsd",))]
-    const LOOPBACK: &[NameMtu] = &[NameMtu(Some("lo0"), 16_384), NameMtu(Some("lo0"), 16_384)];
-    #[cfg(any(target_os = "linux", target_os = "android"))]
-    const LOOPBACK: &[NameMtu] = &[NameMtu(Some("lo"), 65_536), NameMtu(Some("lo"), 65_536)];
-    #[cfg(target_os = "windows")]
-    const LOOPBACK: &[NameMtu] = &[
-        NameMtu(Some("loopback_0"), 4_294_967_295),
-        NameMtu(Some("loopback_0"), 4_294_967_295),
-    ];
-    #[cfg(target_os = "openbsd")]
-    const LOOPBACK: &[NameMtu] = &[NameMtu(Some("lo0"), 32_768), NameMtu(Some("lo0"), 32_768)];
-    #[cfg(target_os = "netbsd")]
-    const LOOPBACK: &[NameMtu] = &[NameMtu(Some("lo0"), 33_624), NameMtu(Some("lo0"), 33_624)];
-    #[cfg(target_os = "solaris")]
-    // Note: Different loopback MTUs for IPv4 and IPv6?!
-    const LOOPBACK: &[NameMtu] = &[NameMtu(Some("lo0"), 8_232), NameMtu(Some("lo0"), 8_252)];
+    const LOOPBACK: [NameMtu; 2] = // [IPv4, IPv6]
+        if cfg!(any(target_os = "macos", target_os = "freebsd")) {
+            [NameMtu(Some("lo0"), 16_384), NameMtu(Some("lo0"), 16_384)]
+        } else if cfg!(any(target_os = "linux", target_os = "android")) {
+            [NameMtu(Some("lo"), 65_536), NameMtu(Some("lo"), 65_536)]
+        } else if cfg!(target_os = "windows") {
+            [
+                NameMtu(Some("loopback_0"), 4_294_967_295),
+                NameMtu(Some("loopback_0"), 4_294_967_295),
+            ]
+        } else if cfg!(target_os = "openbsd") {
+            [NameMtu(Some("lo0"), 32_768), NameMtu(Some("lo0"), 32_768)]
+        } else if cfg!(target_os = "netbsd") {
+            [NameMtu(Some("lo0"), 33_624), NameMtu(Some("lo0"), 33_624)]
+        } else if cfg!(target_os = "solaris") {
+            // Note: Different loopback MTUs for IPv4 and IPv6?!
+            [NameMtu(Some("lo0"), 8_232), NameMtu(Some("lo0"), 8_252)]
+        } else {
+            unreachable!();
+        };
 
     // Non-loopback interface names are unpredictable, so we only check the MTU.
-    const INET: NameMtu = NameMtu(None, 1_500);
+    const INET: NameMtu = NameMtu(
+        None,
+        if cfg!(target_os = "android") {
+            1_440 // At least inside the Android emulator we use in CI.
+        } else {
+            1_500
+        },
+    );
 
     #[test]
     fn loopback_v4() {