Rework how we obtain command handlers

Ideally, each time we request a handler it is
created anew. The `CommandHandlerFactory` makes
this a simpler task.

java/server/src/org/openqa/selenium/grid/router/Router.java

@@ -23,6 +23,7 @@
 import org.openqa.selenium.grid.sessionmap.SessionMap;
 import org.openqa.selenium.grid.web.CommandHandler;
 import org.openqa.selenium.grid.web.CompoundHandler;
+import org.openqa.selenium.grid.web.Routes;
 import org.openqa.selenium.injector.Injector;
 import org.openqa.selenium.remote.http.HttpRequest;
 import org.openqa.selenium.remote.http.HttpResponse;
@@ -35,7 +36,8 @@
  */
 public class Router implements Predicate<HttpRequest>, CommandHandler {
 
-  private final CompoundHandler handler;
+  private final Injector injector;
+  private final Routes handlerFactory;
 
   public Router(SessionMap sessions, Distributor distributor) {
     HandleSession activeSession = new HandleSession(sessions);

java/server/src/org/openqa/selenium/grid/web/CombinedRoute.java

@@ -0,0 +1,57 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.grid.web;
+
+import com.google.common.collect.ImmutableList;
+
+import org.openqa.selenium.injector.Injector;
+import org.openqa.selenium.injector.UnableToInstaniateInstanceException;
+import org.openqa.selenium.remote.http.HttpRequest;
+
+import java.util.List;
+import java.util.Optional;
+
+public class CombinedRoute extends Route<CombinedRoute> {
+
+  private final List<Routes> factories;
+
+  CombinedRoute(List<Routes> factories) {
+    this.factories = ImmutableList.copyOf(factories);
+  }
+
+  @Override
+  protected void validate() {
+    // No-op
+  }
+
+  @Override
+  protected CommandHandler newHandler(Injector injector, HttpRequest request) {
+    for (Routes factory : factories) {
+      try {
+        Optional<CommandHandler> handler = factory.match(injector, request);
+        if (handler.isPresent()) {
+          return handler.get();
+        }
+      } catch (IllegalArgumentException | UnableToInstaniateInstanceException e) {
+        // ignore and carry on
+      }
+    }
+    return getFallback(injector);
+  }
+
+}

java/server/src/org/openqa/selenium/grid/web/PredicatedRoute.java

@@ -0,0 +1,63 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.grid.web;
+
+import org.openqa.selenium.injector.Injector;
+import org.openqa.selenium.remote.http.HttpRequest;
+
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+public class PredicatedRoute extends Route<PredicatedRoute> {
+
+  private Function<Injector, CommandHandler> handlerFunc;
+  private final Predicate<HttpRequest> predicate;
+
+  PredicatedRoute(Predicate<HttpRequest> predicate) {
+    this.predicate = Objects.requireNonNull(predicate);
+  }
+
+  public PredicatedRoute using(Class<? extends CommandHandler> handlerClass) {
+    Objects.requireNonNull(handlerClass);
+    handlerFunc = (inj) -> inj.newInstance(handlerClass);
+    return this;
+  }
+
+  public PredicatedRoute using(CommandHandler handlerInstance) {
+    Objects.requireNonNull(handlerInstance);
+    handlerFunc = (inj) -> handlerInstance;
+    return this;
+  }
+
+  @Override
+  protected void validate() {
+    if (handlerFunc == null) {
+      throw new IllegalStateException("Handler for route is required");
+    }
+  }
+
+  @Override
+  protected CommandHandler newHandler(Injector injector, HttpRequest request) {
+    if (!predicate.test(request)) {
+      return getFallback(injector);
+    }
+
+    return handlerFunc.apply(injector);
+  }
+}

java/server/src/org/openqa/selenium/grid/web/Route.java

@@ -0,0 +1,106 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.grid.web;
+
+import org.openqa.selenium.injector.Injector;
+import org.openqa.selenium.remote.http.HttpRequest;
+
+import java.lang.reflect.Constructor;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Objects;
+import java.util.function.BiFunction;
+
+public abstract class Route<T extends Route> {
+
+  private final List<Class<? extends CommandHandler>> decorators = new ArrayList<>();
+  private Class<? extends CommandHandler> fallback;
+
+  protected Route() {
+    // no-op
+  }
+
+  protected abstract void validate();
+
+  protected abstract CommandHandler newHandler(Injector injector, HttpRequest request);
+
+  /**
+   * The given {@code decorator} must take a {@link CommandHandler} in its longest constructor.
+   */
+  public T decorateWith(Class<? extends CommandHandler> decorator) {
+    Objects.requireNonNull(decorator);
+
+    // Find the longest constructor, which is what the injector uses
+    Constructor<?> constructor = Arrays.stream(decorator.getDeclaredConstructors())
+        .max(Comparator.comparing(Constructor::getParameterCount))
+        .orElse(null);
+
+    if (constructor == null) {
+      throw new IllegalArgumentException("Unable to find a constructor for " + decorator);
+    }
+
+    Boolean hasHandlerArg = Arrays.stream(constructor.getParameterTypes())
+        .map(CommandHandler.class::isAssignableFrom)
+        .reduce(Boolean::logicalOr)
+        .orElse(false);
+
+    if (!hasHandlerArg) {
+      throw new IllegalArgumentException(
+          "Decorator must take a CommandHandler as a constructor arg in its longest " +
+          "constructor. " + decorator);
+    }
+
+    decorators.add(decorator);
+
+    //noinspection unchecked
+    return (T) this;
+  }
+
+  public T fallbackTo(Class<? extends CommandHandler> fallback) {
+    this.fallback = Objects.requireNonNull(fallback);
+    //noinspection unchecked
+    return (T) this;
+  }
+
+  public Routes build() {
+    validate();
+
+    BiFunction<Injector, HttpRequest, CommandHandler> func = (inj, req) -> {
+      CommandHandler handler = newHandler(inj, req);
+      if (handler == null) {
+        return getFallback(inj);
+      }
+
+      Injector injector = inj;
+      for (Class<? extends CommandHandler> decorator : decorators) {
+        injector = Injector.builder().parent(injector).register(handler).build();
+        handler = injector.newInstance(decorator);
+      }
+
+      return handler;
+    };
+
+    return new Routes(func);
+  }
+
+  protected CommandHandler getFallback(Injector injector) {
+    return fallback == null ? null : injector.newInstance(fallback);
+  }
+}

java/server/src/org/openqa/selenium/grid/web/Routes.java

@@ -0,0 +1,80 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.grid.web;
+
+import static org.openqa.selenium.remote.http.HttpMethod.DELETE;
+import static org.openqa.selenium.remote.http.HttpMethod.GET;
+import static org.openqa.selenium.remote.http.HttpMethod.POST;
+
+import com.google.common.collect.ImmutableList;
+
+import org.openqa.selenium.injector.Injector;
+import org.openqa.selenium.remote.http.HttpRequest;
+
+import java.util.Arrays;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.function.BiFunction;
+import java.util.function.Predicate;
+import java.util.stream.Stream;
+
+public class Routes {
+
+  private final BiFunction<Injector, HttpRequest, CommandHandler> handlerFunc;
+
+  Routes(BiFunction<Injector, HttpRequest, CommandHandler> handlerFunc) {
+    this.handlerFunc = Objects.requireNonNull(handlerFunc);
+  }
+
+  public static PredicatedRoute matching(Predicate<HttpRequest> predicate) {
+    return new PredicatedRoute(predicate);
+  }
+
+  public static SpecificRoute delete(String template) {
+    return new SpecificRoute(DELETE, template);
+  }
+
+  public static SpecificRoute get(String template) {
+    return new SpecificRoute(GET, template);
+  }
+
+  public static SpecificRoute post(String template) {
+    return new SpecificRoute(POST, template);
+  }
+
+  public static CombinedRoute combine(Route atLeastOne, Route... optionalOthers) {
+    return combine(
+        atLeastOne.build(),
+        Arrays.stream(optionalOthers).map(Route::build).toArray(Routes[]::new));
+  }
+
+  public static CombinedRoute combine(
+      Routes atLeastOne,
+      Routes... optionalOthers) {
+    ImmutableList<Routes> queue =
+        Stream.concat(Stream.of(atLeastOne), Arrays.stream(optionalOthers))
+            .collect(ImmutableList.toImmutableList());
+
+    return new CombinedRoute(queue.reverse());
+  }
+
+  public  Optional<CommandHandler> match(Injector injector, HttpRequest request) {
+    return Optional.of(handlerFunc.apply(injector, request));
+  }
+
+}