Determine webdriver variant spoken by remote end.

We do this with a pretty simple handshake, that looks for
fields specific to each dialect of the wire protocol.

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

@@ -66,6 +66,7 @@ java_library(name = 'remote-lib',
     'CommandCodec.java',
     'CommandInfo.java',
     'CoordinatesUtils.java',
+    'Dialect.java',
     'DriverCommand.java',
     'ErrorCodes.java',
     'ErrorHandler.java',
@@ -75,6 +76,7 @@ java_library(name = 'remote-lib',
     'JsonException.java',
     'JsonToBeanConverter.java',
     'LocalFileDetector.java',
+    'ProtocolHandshake.java',
     'RemoteActionChainExecutor.java',
     'RemoteExecuteMethod.java',
     'RemoteKeyboard.java',

java/client/src/org/openqa/selenium/remote/Dialect.java

@@ -0,0 +1,23 @@
+// 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;
+
+public enum Dialect {
+  OSS,
+  W3C;
+}

java/client/src/org/openqa/selenium/remote/ProtocolHandshake.java

@@ -0,0 +1,199 @@
+// 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;
+
+import static com.google.common.base.Charsets.UTF_8;
+import static com.google.common.net.HttpHeaders.CONTENT_LENGTH;
+import static com.google.common.net.HttpHeaders.CONTENT_TYPE;
+import static com.google.common.net.MediaType.JSON_UTF_8;
+
+import com.google.common.base.Preconditions;
+
+import org.openqa.selenium.Capabilities;
+import org.openqa.selenium.SessionNotCreatedException;
+import org.openqa.selenium.remote.http.HttpClient;
+import org.openqa.selenium.remote.http.HttpMethod;
+import org.openqa.selenium.remote.http.HttpRequest;
+import org.openqa.selenium.remote.http.HttpResponse;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.logging.Logger;
+
+public class ProtocolHandshake {
+
+  private final static Logger LOG = Logger.getLogger(ProtocolHandshake.class.getName());
+
+  public Result createSession(HttpClient client, Command command)
+    throws IOException {
+    Capabilities desired = (Capabilities) command.getParameters().get("desiredCapabilities");
+    Capabilities required = (Capabilities) command.getParameters().get("requiredCapabilities");
+
+    // Assume the remote end obeys the robustness principle.
+    Map<String, Object> parameters = new HashMap<>();
+    amendW3CParameters(parameters, desired, required);
+    amendOssParamters(parameters, desired, required);
+    LOG.info("Attempting bi-dialect session, assuming Postel's Law holds true on the remote end");
+    Optional<Result> result = createSession(client, parameters);
+
+    // Assume a fragile w3c implementation
+    if (!result.isPresent()) {
+      parameters = new HashMap<>();
+      amendW3CParameters(parameters, desired, required);
+      LOG.info("Falling back to straight W3C remote end connection");
+      result = createSession(client, parameters);
+    }
+
+    // Assume a fragile OSS webdriver implementation
+    if (!result.isPresent()) {
+      parameters = new HashMap<>();
+      amendOssParamters(parameters, desired, required);
+      LOG.info("Falling back to original OSS JSON Wire Protocol.");
+      result = createSession(client, parameters);
+    }
+
+    if (result.isPresent()) {
+      return result.get();
+    }
+
+    throw new SessionNotCreatedException(
+      String.format(
+        "Unable to create new remote session. " +
+        "desired capabilities = %s, required capabilities = %s",
+        desired,
+        required));
+  }
+
+  private Optional<Result> createSession(HttpClient client, Map<String, Object> parameters)
+    throws IOException {
+    // Create the http request and send it
+    HttpRequest request = new HttpRequest(HttpMethod.POST, "/session");
+    String content = new BeanToJsonConverter().convert(parameters);
+    byte[] data = content.getBytes(UTF_8);
+
+    request.setHeader(CONTENT_LENGTH, String.valueOf(data.length));
+    request.setHeader(CONTENT_TYPE, JSON_UTF_8.toString());
+    request.setContent(data);
+    HttpResponse response = client.execute(request, true);
+
+    Map<?, ?> jsonBlob = null;
+    try {
+      String resultString = response.getContentString();
+      jsonBlob = new JsonToBeanConverter().convert(Map.class, resultString);
+    } catch (JsonException e) {
+      // Fine. Handle that below
+    }
+
+    if (jsonBlob == null) {
+      jsonBlob = new HashMap<>();
+    }
+
+    // If the result looks positive, return the result.
+    Object sessionId = jsonBlob.get("sessionId");
+    Object value = jsonBlob.get("value");
+    Object w3cError = jsonBlob.get("error");
+    Object ossStatus = jsonBlob.get("status");
+    Map<String, ?> capabilities = null;
+    if (value != null && value instanceof Map) {
+      capabilities = (Map<String, ?>) value;
+    } else if (value != null && value instanceof Capabilities) {
+      capabilities = ((Capabilities) capabilities).asMap();
+    }
+
+    if (response.getStatus() == HttpURLConnection.HTTP_OK) {
+      if (sessionId != null && capabilities != null) {
+        Dialect dialect = ossStatus == null ? Dialect.W3C : Dialect.OSS;
+        return Optional.of(
+          new Result(dialect, String.valueOf(sessionId), capabilities));
+      }
+    }
+
+    // If the result was an error that we believe has to do with the remote end failing to start the
+    // session, create an exception and throw it.
+    Response tempResponse = null;
+    if ("session not created".equals(w3cError)) {
+      tempResponse = new Response(null);
+      tempResponse.setStatus(ErrorCodes.SESSION_NOT_CREATED);
+      tempResponse.setValue(jsonBlob);
+    } else if (
+      ossStatus instanceof Number &&
+      ((Number) ossStatus).intValue() == ErrorCodes.SESSION_NOT_CREATED) {
+      tempResponse = new Response(null);
+      tempResponse.setStatus(ErrorCodes.SESSION_NOT_CREATED);
+      tempResponse.setValue(jsonBlob);
+    }
+
+    if (tempResponse != null) {
+      new ErrorHandler(true).throwIfResponseFailed(tempResponse, 0);
+    }
+
+    // Otherwise, just return empty.
+    return Optional.empty();
+  }
+
+  private void amendW3CParameters(
+    Map<String, Object> params,
+    Capabilities desired,
+    Capabilities required) {
+    HashMap<String, Object> caps = new HashMap<>();
+    caps.put("desiredCapabilities", desired);
+    caps.put("requiredCapabilities", required);
+
+    params.put("capabilities", caps);
+  }
+
+  private void amendOssParamters(
+    Map<String, Object> params,
+    Capabilities desired,
+    Capabilities required) {
+    params.put("desiredCapabilities", desired);
+    params.put("requiredCapabilities", required);
+  }
+
+
+  public class Result {
+    private final Dialect dialect;
+    private final Map<String, ?> capabilities;
+    private final SessionId sessionId;
+
+    private Result(Dialect dialect, String sessionId, Map<String, ?> capabilities) {
+      this.dialect = dialect;
+      this.sessionId = new SessionId(Preconditions.checkNotNull(sessionId));
+      this.capabilities = capabilities;
+    }
+
+    public Dialect getDialect() {
+      return dialect;
+    }
+
+    public Response createResponse() {
+      Response response = new Response(sessionId);
+      response.setValue(capabilities);
+      response.setStatus(ErrorCodes.SUCCESS);
+      return response;
+    }
+
+    @Override
+    public String toString() {
+      return String.format("%s: %s", dialect, capabilities);
+    }
+  }
+}