servlet: configurable methodNameResolver (#12333)

Introduces configuring a method name resolver in `ServletServerBuilder` for customizing the servlet context root path for request paths.

servlet/src/jettyTest/java/io/grpc/servlet/JettyTransportTest.java

@@ -69,6 +69,7 @@ public class JettyTransportTest extends AbstractTransportTest {
                 listener.transportCreated(new ServletServerBuilder.ServerTransportImpl(scheduler));
         ServletAdapter adapter =
                 new ServletAdapter(serverTransportListener, streamTracerFactories,
+                        ServletAdapter.DEFAULT_METHOD_NAME_RESOLVER,
                         Integer.MAX_VALUE);
         GrpcServlet grpcServlet = new GrpcServlet(adapter);
 

servlet/src/main/java/io/grpc/servlet/ServletAdapter.java

@@ -45,6 +45,7 @@ import java.util.Arrays;
 import java.util.Enumeration;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
 import java.util.logging.Logger;
 import javax.servlet.AsyncContext;
 import javax.servlet.AsyncEvent;
@@ -72,18 +73,23 @@ import javax.servlet.http.HttpServletResponse;
 public final class ServletAdapter {
 
   static final Logger logger = Logger.getLogger(ServletAdapter.class.getName());
+  static final Function<HttpServletRequest, String> DEFAULT_METHOD_NAME_RESOLVER =
+          req -> req.getRequestURI().substring(1); // remove the leading "/"
 
   private final ServerTransportListener transportListener;
   private final List<? extends ServerStreamTracer.Factory> streamTracerFactories;
+  private final Function<HttpServletRequest, String> methodNameResolver;
   private final int maxInboundMessageSize;
   private final Attributes attributes;
 
   ServletAdapter(
       ServerTransportListener transportListener,
       List<? extends ServerStreamTracer.Factory> streamTracerFactories,
+      Function<HttpServletRequest, String> methodNameResolver,
       int maxInboundMessageSize) {
     this.transportListener = transportListener;
     this.streamTracerFactories = streamTracerFactories;
+    this.methodNameResolver = methodNameResolver;
     this.maxInboundMessageSize = maxInboundMessageSize;
     attributes = transportListener.transportReady(Attributes.EMPTY);
   }
@@ -119,7 +125,7 @@ public final class ServletAdapter {
 
     AsyncContext asyncCtx = req.startAsync(req, resp);
 
-    String method = req.getRequestURI().substring(1); // remove the leading "/"
+    String method = methodNameResolver.apply(req);
     Metadata headers = getHeaders(req);
 
     if (logger.isLoggable(FINEST)) {

servlet/src/main/java/io/grpc/servlet/ServletServerBuilder.java

@@ -49,8 +49,10 @@ import java.net.SocketAddress;
 import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.function.Function;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
+import javax.servlet.http.HttpServletRequest;
 
 /**
  * Builder to build a gRPC server that can run as a servlet. This is for advanced custom settings.
@@ -64,6 +66,8 @@ import javax.annotation.concurrent.NotThreadSafe;
 @NotThreadSafe
 public final class ServletServerBuilder extends ForwardingServerBuilder<ServletServerBuilder> {
   List<? extends ServerStreamTracer.Factory> streamTracerFactories;
+  private Function<HttpServletRequest, String> methodNameResolver =
+      ServletAdapter.DEFAULT_METHOD_NAME_RESOLVER;
   int maxInboundMessageSize = DEFAULT_MAX_MESSAGE_SIZE;
 
   private final ServerImplBuilder serverImplBuilder;
@@ -98,7 +102,8 @@ public final class ServletServerBuilder extends ForwardingServerBuilder<ServletS
    * Creates a {@link ServletAdapter}.
    */
   public ServletAdapter buildServletAdapter() {
-    return new ServletAdapter(buildAndStart(), streamTracerFactories, maxInboundMessageSize);
+    return new ServletAdapter(buildAndStart(), streamTracerFactories, methodNameResolver,
+        maxInboundMessageSize);
   }
 
   /**
@@ -176,6 +181,18 @@ public final class ServletServerBuilder extends ForwardingServerBuilder<ServletS
     throw new UnsupportedOperationException("TLS should be configured by the servlet container");
   }
 
+  /**
+   * Specifies how to determine gRPC method name from servlet request.
+   *
+   * <p>The default strategy is using {@link HttpServletRequest#getRequestURI()} without the leading
+   * slash.</p>
+   */
+  public ServletServerBuilder methodNameResolver(
+      Function<HttpServletRequest, String> methodResolver) {
+    this.methodNameResolver = checkNotNull(methodResolver);
+    return this;
+  }
+
   @Override
   public ServletServerBuilder maxInboundMessageSize(int bytes) {
     checkArgument(bytes >= 0, "bytes must be >= 0");

servlet/src/tomcatTest/java/io/grpc/servlet/TomcatTransportTest.java

@@ -81,7 +81,9 @@ public class TomcatTransportTest extends AbstractTransportTest {
         ServerTransportListener serverTransportListener =
             listener.transportCreated(new ServerTransportImpl(scheduler));
         ServletAdapter adapter =
-            new ServletAdapter(serverTransportListener, streamTracerFactories, Integer.MAX_VALUE);
+            new ServletAdapter(serverTransportListener, streamTracerFactories,
+                ServletAdapter.DEFAULT_METHOD_NAME_RESOLVER,
+                Integer.MAX_VALUE);
         GrpcServlet grpcServlet = new GrpcServlet(adapter);
 
         tomcatServer = new Tomcat();

servlet/src/undertowTest/java/io/grpc/servlet/UndertowTransportTest.java

@@ -100,7 +100,9 @@ public class UndertowTransportTest extends AbstractTransportTest {
         ServerTransportListener serverTransportListener =
             listener.transportCreated(new ServerTransportImpl(scheduler));
         ServletAdapter adapter =
-            new ServletAdapter(serverTransportListener, streamTracerFactories, Integer.MAX_VALUE);
+            new ServletAdapter(serverTransportListener, streamTracerFactories,
+                ServletAdapter.DEFAULT_METHOD_NAME_RESOLVER,
+                Integer.MAX_VALUE);
         GrpcServlet grpcServlet = new GrpcServlet(adapter);
         InstanceFactory<? extends Servlet> instanceFactory =
             () -> new ImmediateInstanceHandle<>(grpcServlet);