xds: use fallback PN if you get exception while retrieving SslContextProvider (#7137)

xds/src/main/java/io/grpc/xds/internal/sds/SdsProtocolNegotiators.java

@@ -305,7 +305,11 @@ public final class SdsProtocolNegotiators {
           return;
         } else {
           ctx.pipeline()
-              .replace(this, null, new ServerSdsHandler(grpcHandler, downstreamTlsContext));
+              .replace(
+                  this,
+                  null,
+                  new ServerSdsHandler(
+                      grpcHandler, downstreamTlsContext, fallbackProtocolNegotiator));
           ProtocolNegotiationEvent pne = InternalProtocolNegotiationEvent.getDefault();
           ctx.fireUserEventTriggered(pne);
           return;
@@ -321,10 +325,12 @@ public final class SdsProtocolNegotiators {
           extends InternalProtocolNegotiators.ProtocolNegotiationHandler {
     private final GrpcHttp2ConnectionHandler grpcHandler;
     private final DownstreamTlsContext downstreamTlsContext;
+    @Nullable private final ProtocolNegotiator fallbackProtocolNegotiator;
 
     ServerSdsHandler(
             GrpcHttp2ConnectionHandler grpcHandler,
-            DownstreamTlsContext downstreamTlsContext) {
+            DownstreamTlsContext downstreamTlsContext,
+            ProtocolNegotiator fallbackProtocolNegotiator) {
       super(
           // superclass (InternalProtocolNegotiators.ProtocolNegotiationHandler) expects 'next'
           // handler but we don't have a next handler _yet_. So we "disable" superclass's behavior
@@ -338,6 +344,7 @@ public final class SdsProtocolNegotiators {
       checkNotNull(grpcHandler, "grpcHandler");
       this.grpcHandler = grpcHandler;
       this.downstreamTlsContext = downstreamTlsContext;
+      this.fallbackProtocolNegotiator = fallbackProtocolNegotiator;
     }
 
     @Override
@@ -345,10 +352,23 @@ public final class SdsProtocolNegotiators {
       final BufferReadsHandler bufferReads = new BufferReadsHandler();
       ctx.pipeline().addBefore(ctx.name(), null, bufferReads);
 
-      final SslContextProvider sslContextProvider =
+      SslContextProvider sslContextProviderTemp = null;
-              TlsContextManagerImpl.getInstance()
+      try {
-                      .findOrCreateServerSslContextProvider(downstreamTlsContext);
+        sslContextProviderTemp =
-
+            TlsContextManagerImpl.getInstance()
+                .findOrCreateServerSslContextProvider(downstreamTlsContext);
+      } catch (Exception e) {
+        if (fallbackProtocolNegotiator == null) {
+          ctx.fireExceptionCaught(new CertStoreException("No certificate source found!", e));
+          return;
+        }
+        logger.log(Level.INFO, "Using fallback for {0}", ctx.channel().localAddress());
+        // Delegate rest of handshake to fallback handler
+        ctx.pipeline().replace(this, null, fallbackProtocolNegotiator.newHandler(grpcHandler));
+        ctx.pipeline().remove(bufferReads);
+        return;
+      }
+      final SslContextProvider sslContextProvider = sslContextProviderTemp;
       sslContextProvider.addCallback(
           new SslContextProvider.Callback() {
 

xds/src/test/java/io/grpc/xds/XdsSdsClientServerTest.java

@@ -89,6 +89,18 @@ public class XdsSdsClientServerTest {
     assertThat(unaryRpc("buddy", blockingStub)).isEqualTo("Hello buddy");
   }
 
+  @Test
+  public void plaintextClientServer_withDefaultTlsContext() throws IOException, URISyntaxException {
+    DownstreamTlsContext defaultTlsContext =
+        EnvoyServerProtoData.DownstreamTlsContext.fromEnvoyProtoDownstreamTlsContext(
+            io.envoyproxy.envoy.api.v2.auth.DownstreamTlsContext.getDefaultInstance());
+    buildServerWithTlsContext(/* downstreamTlsContext= */ defaultTlsContext);
+
+    SimpleServiceGrpc.SimpleServiceBlockingStub blockingStub =
+            getBlockingStub(/* upstreamTlsContext= */ null, /* overrideAuthority= */ null);
+    assertThat(unaryRpc("buddy", blockingStub)).isEqualTo("Hello buddy");
+  }
+
   @Test
   public void nullFallbackProtocolNegotiator_expectException()
       throws IOException, URISyntaxException {

xds/src/test/java/io/grpc/xds/internal/sds/SdsProtocolNegotiatorsTest.java

@@ -245,6 +245,46 @@ public class SdsProtocolNegotiatorsTest {
         .contains("ProtocolNegotiators.ServerTlsHandler");
   }
 
+  @Test
+  public void serverSdsHandler_defaultDownstreamTlsContext_expectFallbackProtocolNegotiator()
+      throws IOException {
+    ChannelHandler mockChannelHandler = mock(ChannelHandler.class);
+    ProtocolNegotiator mockProtocolNegotiator = mock(ProtocolNegotiator.class);
+    when(mockProtocolNegotiator.newHandler(grpcHandler)).thenReturn(mockChannelHandler);
+    // we need InetSocketAddress instead of EmbeddedSocketAddress as localAddress for this test
+    channel =
+        new EmbeddedChannel() {
+          @Override
+          public SocketAddress localAddress() {
+            return new InetSocketAddress("172.168.1.1", 80);
+          }
+        };
+    pipeline = channel.pipeline();
+    DownstreamTlsContext downstreamTlsContext =
+        DownstreamTlsContext.fromEnvoyProtoDownstreamTlsContext(
+            io.envoyproxy.envoy.api.v2.auth.DownstreamTlsContext.getDefaultInstance());
+
+    XdsClientWrapperForServerSds xdsClientWrapperForServerSds =
+        XdsClientWrapperForServerSdsTest.createXdsClientWrapperForServerSds(
+            80, downstreamTlsContext);
+    SdsProtocolNegotiators.HandlerPickerHandler handlerPickerHandler =
+        new SdsProtocolNegotiators.HandlerPickerHandler(
+            grpcHandler, xdsClientWrapperForServerSds, mockProtocolNegotiator);
+    pipeline.addLast(handlerPickerHandler);
+    channelHandlerCtx = pipeline.context(handlerPickerHandler);
+    assertThat(channelHandlerCtx).isNotNull(); // should find HandlerPickerHandler
+
+    // kick off protocol negotiation: should replace HandlerPickerHandler with ServerSdsHandler
+    pipeline.fireUserEventTriggered(InternalProtocolNegotiationEvent.getDefault());
+    channelHandlerCtx = pipeline.context(handlerPickerHandler);
+    assertThat(channelHandlerCtx).isNull();
+    channel.runPendingTasks(); // need this for tasks to execute on eventLoop
+    Iterator<Map.Entry<String, ChannelHandler>> iterator = pipeline.iterator();
+    assertThat(iterator.next().getValue()).isSameInstanceAs(mockChannelHandler);
+    // no more handlers in the pipeline
+    assertThat(iterator.hasNext()).isFalse();
+  }
+
   @Test
   public void serverSdsHandler_nullTlsContext_expectFallbackProtocolNegotiator() {
     ChannelHandler mockChannelHandler = mock(ChannelHandler.class);