feat(ci): experiment with tcpdump during FVT

It can be useful to inspect protocol captures as part of debugging an
FVT test, particularly if the test is flakey, so experiment with
capturing an uploading a .pcap file.

Signed-off-by: Dominic Evans <dominic.evans@uk.ibm.com>

.github/workflows/fvt.yml

@@ -38,10 +38,27 @@ jobs:
       uses: actions/setup-go@v4
       with:
         go-version: ${{ matrix.go-version }}
-    - name: Test (Functional)
+    - name: Setup Docker Compose
       run: |
         curl -sSL "https://github.com/docker/compose/releases/download/v2.20.3/docker-compose-$(uname -s)-$(uname -m)" -o /tmp/docker-compose
         sudo install -m755 /tmp/docker-compose "$(dirname $(which docker-compose))"
         docker version --format 'Docker Engine version v{{.Server.Version}}'
         docker-compose version
+    - name: Test (Functional)
+      run: |
+        nohup sudo tcpdump -i lo -w "fvt-kafka-${{ matrix.kafka-version }}.pcap" portrange 29091-29095 >/dev/null 2>&1 &
+        echo $! >tcpdump.pid
         make test_functional
+    - name: Stop tcpdump
+      if: always()
+      run: |
+        if [ -f "tcpdump.pid" ]; then sudo kill "$(cat tcpdump.pid)" || true; fi
+        if [ -f "fvt-kafka-${{ matrix.kafka-version }}.pcap" ]; then sudo chmod a+r "fvt-kafka-${{ matrix.kafka-version }}.pcap"; fi
+    - name: Upload pcap file
+      if: always()
+      uses: actions/upload-artifact@v3
+      with:
+        name: fvt-kafka-${{ matrix.kafka-version }}.pcap
+        path: fvt-kafka-${{ matrix.kafka-version }}.pcap
+        retention-days: 5
+        if-no-files-found: ignore