Stop being stubborn and admit that it's okay to use inheritance.

java/client/src/org/openqa/selenium/remote/BUCK

@@ -101,6 +101,8 @@ java_library(name = 'remote-lib',
     'http/HttpMethod.java',
     'http/HttpRequest.java',
     'http/HttpResponse.java',
+    'http/AbstractHttpCommandCodec.java',
+    'http/AbstractHttpResponseCodec.java',
     'http/JsonHttpCommandCodec.java',
     'http/JsonHttpResponseCodec.java',
     'http/W3CHttpCommandCodec.java',

java/client/src/org/openqa/selenium/remote/http/AbstractHttpResponseCodec.java

@@ -0,0 +1,125 @@
+// 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.remote.http;
+
+import static com.google.common.base.Charsets.UTF_8;
+import static com.google.common.base.Strings.nullToEmpty;
+import static com.google.common.net.HttpHeaders.CACHE_CONTROL;
+import static com.google.common.net.HttpHeaders.CONTENT_LENGTH;
+import static com.google.common.net.HttpHeaders.CONTENT_TYPE;
+import static com.google.common.net.HttpHeaders.EXPIRES;
+import static com.google.common.net.MediaType.JSON_UTF_8;
+import static java.net.HttpURLConnection.HTTP_INTERNAL_ERROR;
+import static java.net.HttpURLConnection.HTTP_OK;
+
+import org.openqa.selenium.remote.BeanToJsonConverter;
+import org.openqa.selenium.remote.ErrorCodes;
+import org.openqa.selenium.remote.JsonException;
+import org.openqa.selenium.remote.JsonToBeanConverter;
+import org.openqa.selenium.remote.Response;
+import org.openqa.selenium.remote.ResponseCodec;
+
+/**
+ * A response codec that adheres to the W3C WebDriver wire protocol.
+ *
+ * @see <a href="https://w3.org/tr/webdriver">W3C WebDriver spec</a>
+ */
+public abstract class AbstractHttpResponseCodec implements ResponseCodec<HttpResponse> {
+  private final ErrorCodes errorCodes = new ErrorCodes();
+  private final BeanToJsonConverter beanToJsonConverter = new BeanToJsonConverter();
+  private final JsonToBeanConverter jsonToBeanConverter = new JsonToBeanConverter();
+
+  /**
+   * Encodes the given response as a HTTP response message. This method is guaranteed not to throw.
+   *
+   * @param response The response to encode.
+   * @return The encoded response.
+   */
+  @Override
+  public HttpResponse encode(Response response) {
+    int status = response.getStatus() == ErrorCodes.SUCCESS
+                 ? HTTP_OK
+                 : HTTP_INTERNAL_ERROR;
+
+    byte[] data = beanToJsonConverter.convert(response).getBytes(UTF_8);
+
+    HttpResponse httpResponse = new HttpResponse();
+    httpResponse.setStatus(status);
+    httpResponse.setHeader(CACHE_CONTROL, "no-cache");
+    httpResponse.setHeader(EXPIRES, "Thu, 01 Jan 1970 00:00:00 GMT");
+    httpResponse.setHeader(CONTENT_LENGTH, String.valueOf(data.length));
+    httpResponse.setHeader(CONTENT_TYPE, JSON_UTF_8.toString());
+    httpResponse.setContent(data);
+
+    return httpResponse;
+  }
+
+  @Override
+  public Response decode(HttpResponse encodedResponse) {
+    String contentType = nullToEmpty(encodedResponse.getHeader(CONTENT_TYPE));
+    String content = encodedResponse.getContentString().trim();
+    try {
+      return jsonToBeanConverter.convert(Response.class, content);
+    } catch (JsonException e) {
+      if (contentType.startsWith("application/json")) {
+        throw new IllegalArgumentException(
+            "Cannot decode response content: " + content, e);
+      }
+    } catch (ClassCastException e) {
+      if (contentType.startsWith("application/json")) {
+        if (content.isEmpty()) {
+          // The remote server has died, but has already set some headers.
+          // Normally this occurs when the final window of the firefox driver
+          // is closed on OS X. Return null, as the return value _should_ be
+          // being ignored. This is not an elegant solution.
+          return new Response();
+        }
+        throw new IllegalArgumentException(
+            "Cannot decode response content: " + content, e);
+      }
+    }
+
+    Response response = new Response();
+    int statusCode = encodedResponse.getStatus();
+    if (statusCode < 200 || statusCode > 299) {
+      // 4xx represents an unknown command or a bad request.
+      if (statusCode > 399 && statusCode < 500) {
+        response.setStatus(ErrorCodes.UNKNOWN_COMMAND);
+      } else {
+        response.setStatus(ErrorCodes.UNHANDLED_ERROR);
+      }
+    }
+
+    if (encodedResponse.getContent().length > 0) {
+      response.setValue(content);
+    }
+
+    if (response.getValue() instanceof String) {
+      // We normalise to \n because Java will translate this to \r\n
+      // if this is suitable on our platform, and if we have \r\n, java will
+      // turn this into \r\r\n, which would be Bad!
+      response.setValue(((String) response.getValue()).replace("\r\n", "\n"));
+    }
+    if (response.getStatus() != null) {
+      response.setState(errorCodes.toState(response.getStatus()));
+    } else if (statusCode == 200) {
+      response.setState(errorCodes.toState(ErrorCodes.SUCCESS));
+    }
+    return response;
+  }
+}