fix: Return proper response in case of missing route

app/src/main/java/io/appium/uiautomator2/common/exceptions/UnknownCommandException.java

@@ -20,7 +20,8 @@
 
 public class UnknownCommandException extends UiAutomator2Exception {
     public UnknownCommandException() {
-        super("The requested resource could not be found, or a request was received using an HTTP method that is not supported by the mapped resource");
+        super("The requested resource could not be found, or a request was received " +
+                "using an HTTP method that is not supported by the mapped resource");
     }
 
     public UnknownCommandException(String message) {

app/src/main/java/io/appium/uiautomator2/http/AppiumResponse.java

@@ -38,7 +38,7 @@ public class AppiumResponse {
     private final String sessionId;
     private final HttpResponseStatus httpStatus;
 
-    public AppiumResponse(String sessionId, @Nullable Object value) {
+    public AppiumResponse(@Nullable String sessionId, @Nullable Object value) {
         this.sessionId = sessionId;
         this.value = value;
         if (value instanceof Throwable) {

app/src/main/java/io/appium/uiautomator2/http/HttpServer.java

@@ -1,3 +1,19 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ * 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 io.appium.uiautomator2.http;
 
 import java.util.ArrayList;

app/src/main/java/io/appium/uiautomator2/http/IHttpRequest.java

@@ -1,3 +1,19 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ * 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 io.appium.uiautomator2.http;
 
 import java.util.Map;

app/src/main/java/io/appium/uiautomator2/http/IHttpResponse.java

@@ -1,3 +1,19 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ * 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 io.appium.uiautomator2.http;
 
 import java.nio.charset.Charset;

app/src/main/java/io/appium/uiautomator2/http/IHttpServlet.java

@@ -1,3 +1,19 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ * 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 io.appium.uiautomator2.http;
 
 public interface IHttpServlet {

app/src/main/java/io/appium/uiautomator2/http/KeepAliveStateHandler.java

@@ -1,3 +1,19 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ * 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 io.appium.uiautomator2.http;
 
 import io.appium.uiautomator2.utils.Logger;

app/src/main/java/io/appium/uiautomator2/http/ServerHandler.java

@@ -1,9 +1,27 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ * 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 io.appium.uiautomator2.http;
 
 import java.util.List;
 
+import io.appium.uiautomator2.common.exceptions.UnknownCommandException;
 import io.appium.uiautomator2.http.impl.NettyHttpRequest;
 import io.appium.uiautomator2.http.impl.NettyHttpResponse;
+import io.appium.uiautomator2.server.AppiumServlet;
 import io.appium.uiautomator2.utils.Logger;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
@@ -53,7 +71,9 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
             }
         }
         if (!httpResponse.isClosed()) {
-            httpResponse.setStatus(404);
+            Object sessionId = httpRequest.data().get(AppiumServlet.SESSION_ID_KEY);
+            new AppiumResponse(sessionId == null ? null : (String) sessionId, new UnknownCommandException())
+                    .renderTo(httpResponse);
             httpResponse.end();
         }
 

app/src/main/java/io/appium/uiautomator2/http/ServerInitializer.java

@@ -1,3 +1,19 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ * 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 io.appium.uiautomator2.http;
 
 import java.util.List;

app/src/main/java/io/appium/uiautomator2/server/AppiumServlet.java

@@ -83,7 +83,6 @@
 import io.appium.uiautomator2.http.IHttpRequest;
 import io.appium.uiautomator2.http.IHttpResponse;
 import io.appium.uiautomator2.http.IHttpServlet;
-import io.netty.handler.codec.http.HttpResponseStatus;
 
 public class AppiumServlet implements IHttpServlet {
 
@@ -244,15 +243,12 @@ public void handleHttpRequest(IHttpRequest request, IHttpResponse response) {
         } else if ("DELETE".equals(request.method())) {
             handler = findMatcher(request, deleteHandler);
         }
-        handleRequest(request, response, handler);
+        if (handler != null) {
+            handleRequest(request, response, handler);
+        }
     }
 
-    private void handleRequest(IHttpRequest request, IHttpResponse response,
-                               @Nullable BaseRequestHandler handler) {
-        if (handler == null) {
-            response.setStatus(HttpResponseStatus.NOT_FOUND.code()).end();
-            return;
-        }
+    private void handleRequest(IHttpRequest request, IHttpResponse response, BaseRequestHandler handler) {
         addHandlerAttributesToRequest(request, handler.getMappedUri());
         AppiumResponse result = handler.handle(request);
         handleResponse(response, result);