[wpinet] Add mDNS discovery tests and fix mDNS JNI bugs (#8682)

In https://github.com/wpilibsuite/allwpilib/issues/8681 we discovered
that multicast service types need to be valid (end with _tcp or _udp),
or else errors are silently swallowed. Let's make our C++ unit test use
a valid name and also check that it works. I think if we
should/shouldn't do this is up for debate still.

I also discovered two bugs in the JNI code that lead to incorrect
results being returned
- Return array index was always 0
- Use of JLocal for the return value seems to mean that the array will
always be NULL in java

.github/workflows/bazel.yml

@@ -73,7 +73,7 @@ jobs:
 
       - name: Install apt dependencies
         if: matrix.os == 'ubuntu-24.04'
-        run: sudo apt-get update && sudo apt-get install -y libgl1-mesa-dev libx11-dev libxcursor-dev libxi-dev libxinerama-dev libxrandr-dev
+        run: sudo apt-get update && sudo apt-get install -y libgl1-mesa-dev libx11-dev libxcursor-dev libxi-dev libxinerama-dev libxrandr-dev avahi-daemon
 
       - if: matrix.os == 'ubuntu-24.04'
         uses: bazel-contrib/setup-bazel@0.15.0

.github/workflows/cmake.yml

@@ -37,6 +37,12 @@ jobs:
         if: runner.os == 'Linux'
         run: sudo apt-get update && sudo apt-get install -y libopencv-dev libopencv-java ninja-build
 
+      - name: Setup avahi-daemon
+        if: runner.os == 'Linux'
+        run: |
+          sudo service dbus start
+          sudo avahi-daemon -D
+
       - name: Install dependencies (macOS)
         if: runner.os == 'macOS'
         run: brew install opencv ninja

.github/workflows/gradle.yml

@@ -60,7 +60,11 @@ jobs:
         with:
           image: ${{ matrix.container }}
           options: -v ${{ github.workspace }}:/work -w /work -e ARTIFACTORY_PUBLISH_USERNAME -e ARTIFACTORY_PUBLISH_PASSWORD -e GITHUB_REF -e CI
-          run: ./gradlew build --build-cache -PbuildServer -PskipJavaFormat ${{ matrix.build-options }} ${{ env.EXTRA_GRADLE_ARGS }}
+          # Start avahi-daemon and build
+          run: |
+            service dbus start
+            avahi-daemon -D
+            ./gradlew build --build-cache -PbuildServer -PskipJavaFormat ${{ matrix.build-options }} ${{ env.EXTRA_GRADLE_ARGS }}
         env:
           ARTIFACTORY_PUBLISH_USERNAME: ${{ secrets.ARTIFACTORY_USERNAME }}
           ARTIFACTORY_PUBLISH_PASSWORD: ${{ secrets.ARTIFACTORY_PASSWORD }}

.github/workflows/sanitizers.yml

@@ -22,7 +22,7 @@ jobs:
             ctest-flags: "-E 'wpilibc'"
           - name: tsan
             cmake-flags: "-DCMAKE_BUILD_TYPE=Tsan"
-            ctest-env: "TSAN_OPTIONS=second_deadlock_stack=1"
+            ctest-env: "TSAN_OPTIONS=second_deadlock_stack=1:suppressions=$GITHUB_WORKSPACE/tsan_suppressions.txt"
             ctest-flags: "-E 'cscore|cameraserver'"
           - name: ubsan
             cmake-flags: "-DCMAKE_BUILD_TYPE=Ubsan"
@@ -33,7 +33,7 @@ jobs:
     container: wpilib/roborio-cross-ubuntu:2025-24.04
     steps:
       - name: Install Dependencies
-        run: sudo apt-get update && sudo apt-get install -y libopencv-dev libopencv-java clang-18 ninja-build
+        run: sudo apt-get update && sudo apt-get install -y libopencv-dev libopencv-java clang-18 ninja-build avahi-daemon
 
       - name: Install sccache
         uses: mozilla-actions/sccache-action@v0.0.9
@@ -46,6 +46,11 @@ jobs:
           SCCACHE_WEBDAV_USERNAME: ${{ secrets.ARTIFACTORY_USERNAME }}
           SCCACHE_WEBDAV_PASSWORD: ${{ secrets.ARTIFACTORY_PASSWORD }}
 
+      - name: Setup avahi-daemon
+        run: |
+          sudo service dbus start
+          sudo avahi-daemon -D
+
       - name: build
         working-directory: build
         run: cmake --build . --parallel $(nproc)

tsan_suppressions.txt

@@ -0,0 +1 @@
+deadlock:libdbus-1.so.3

wpinet/src/main/native/cpp/jni/WPINetJNI.cpp

@@ -330,9 +330,10 @@ Java_org_wpilib_net_WPINetJNI_getMulticastServiceResolverData
     return serviceDataEmptyArray;
   }
 
-  JLocal<jobjectArray> returnData{
+  jobjectArray returnData =
-      env, env->NewObjectArray(allData.size(), serviceDataCls, nullptr)};
+      env->NewObjectArray(allData.size(), serviceDataCls, nullptr);
 
+  size_t index = 0;
   for (auto&& data : allData) {
     JLocal<jstring> serviceName{env, MakeJString(env, data.serviceName)};
     JLocal<jstring> hostName{env, MakeJString(env, data.hostName)};
@@ -340,7 +341,6 @@ Java_org_wpilib_net_WPINetJNI_getMulticastServiceResolverData
     wpi::util::SmallVector<std::string_view, 8> keysRef;
     wpi::util::SmallVector<std::string_view, 8> valuesRef;
 
-    size_t index = 0;
     for (auto&& txt : data.txt) {
       keysRef.emplace_back(txt.first);
       valuesRef.emplace_back(txt.second);

wpinet/src/test/java/org/wpilib/net/MulticastServiceAnnouncerTest.java

@@ -0,0 +1,53 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package org.wpilib.net;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.net.UnknownHostException;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class MulticastServiceAnnouncerTest {
+  @Test
+  void emptyText() throws InterruptedException, UnknownHostException {
+    final String serviceName = "Foaksdfjasklfj";
+    final String serviceType = "_wpinotxt._tcp";
+    final int port = 12345;
+
+    try (MulticastServiceAnnouncer announcer =
+            new MulticastServiceAnnouncer(serviceName, serviceType, port);
+        MulticastServiceResolver resolver = new MulticastServiceResolver(serviceType)) {
+      assertTrue(announcer.hasImplementation() && resolver.hasImplementation());
+
+      announcer.start();
+      resolver.start();
+
+      List<ServiceData> allData = new ArrayList<>();
+
+      for (int i = 0; i < 10; i++) {
+        ServiceData[] data = resolver.getData();
+        if (data == null) {
+          continue;
+        }
+
+        allData.addAll(List.of(data));
+
+        if (!allData.isEmpty()) {
+          break;
+        }
+
+        Thread.sleep(1000);
+      }
+
+      assertFalse(allData.isEmpty(), "Expected at least one service entry, but got none");
+
+      resolver.stop();
+      announcer.stop();
+    }
+  }
+}

wpinet/src/test/native/cpp/MulticastTest.cpp

@@ -3,11 +3,10 @@
 // the WPILib BSD license file in the root directory of this project.
 
 #include <array>
-#include <chrono>
 #include <string>
 #include <string_view>
 #include <thread>
-#include <utility>
+#include <vector>
 
 #include <gtest/gtest.h>
 
@@ -17,7 +16,7 @@
 
 TEST(MulticastServiceAnnouncerTest, EmptyText) {
   const std::string_view serviceName = "TestServiceNoText";
-  const std::string_view serviceType = "_wpinotxt";
+  const std::string_view serviceType = "_wpinotxt._tcp";
   const int port = std::rand();
   wpi::net::MulticastServiceAnnouncer announcer(serviceName, serviceType, port);
   wpi::net::MulticastServiceResolver resolver(serviceType);
@@ -26,7 +25,20 @@ TEST(MulticastServiceAnnouncerTest, EmptyText) {
     announcer.Start();
     resolver.Start();
 
-    std::this_thread::sleep_for(std::chrono::seconds(1));
+    std::vector<wpi::net::MulticastServiceResolver::ServiceData> allData;
+
+    for (int i = 0; i < 15; i++) {
+      // GetData gives me new data since last time. This smoketest is just
+      // looking for -any- response
+      allData = resolver.GetData();
+      if (!allData.empty()) {
+        break;
+      }
+
+      std::this_thread::sleep_for(std::chrono::seconds(1));
+    }
+
+    ASSERT_GT(allData.size(), 0ul);
 
     resolver.Stop();
     announcer.Stop();