Favour the OSS dialect when hand-shaking

The W3C dialect is experimental and still under active development
and so should not be the preferred dialect to use.

To avoid being too demanding with memory usage, and to avoid
expensive operations such as laying profiles out on disk being run
more times than is strictly necessary, we now build the payloads
using StringBuilder.

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

@@ -44,29 +44,40 @@ public class ProtocolHandshake {
 
   public Result createSession(HttpClient client, Command command)
     throws IOException {
+    // Avoid serialising the capabilities too many times. Things like profiles are expensive.
+
     Capabilities desired = (Capabilities) command.getParameters().get("desiredCapabilities");
+    desired = desired == null ? new DesiredCapabilities() : desired;
     Capabilities required = (Capabilities) command.getParameters().get("requiredCapabilities");
+    required = required == null ? new DesiredCapabilities() : required;
+
+    String des = new BeanToJsonConverter().convert(desired);
+    String req = new BeanToJsonConverter().convert(required);
 
     // Assume the remote end obeys the robustness principle.
-    Map<String, Object> parameters = new HashMap<>();
-    amendW3CParameters(parameters, desired, required);
-    amendOssParamters(parameters, desired, required);
+    StringBuilder parameters = new StringBuilder("{");
+    amendW3CParameters(parameters, des, req);
+    parameters.append(",");
+    amendOssParamters(parameters, des, req);
+    parameters.append("}");
     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
+    // Assume a fragile OSS webdriver implementation
     if (!result.isPresent()) {
-      parameters = new HashMap<>();
-      amendW3CParameters(parameters, desired, required);
-      LOG.info("Falling back to straight W3C remote end connection");
+      parameters = new StringBuilder("{");
+      amendOssParamters(parameters, des, req);
+      parameters.append("}");
+      LOG.info("Falling back to original OSS JSON Wire Protocol.");
       result = createSession(client, parameters);
     }
 
-    // Assume a fragile OSS webdriver implementation
+    // Assume a fragile w3c implementation
     if (!result.isPresent()) {
-      parameters = new HashMap<>();
-      amendOssParamters(parameters, desired, required);
-      LOG.info("Falling back to original OSS JSON Wire Protocol.");
+      parameters = new StringBuilder("{");
+      amendW3CParameters(parameters, des, req);
+      parameters.append("}");
+      LOG.info("Falling back to straight W3C remote end connection");
       result = createSession(client, parameters);
     }
 
@@ -84,11 +95,11 @@ public Result createSession(HttpClient client, Command command)
         required));
   }
 
-  private Optional<Result> createSession(HttpClient client, Map<String, Object> parameters)
+  private Optional<Result> createSession(HttpClient client, StringBuilder params)
     throws IOException {
     // Create the http request and send it
     HttpRequest request = new HttpRequest(HttpMethod.POST, "/session");
-    String content = new BeanToJsonConverter().convert(parameters);
+    String content = params.toString();
     byte[] data = content.getBytes(UTF_8);
 
     request.setHeader(CONTENT_LENGTH, String.valueOf(data.length));
@@ -155,22 +166,23 @@ private Optional<Result> createSession(HttpClient client, Map<String, Object> pa
   }
 
   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);
+    StringBuilder params,
+    String desired,
+    String required) {
+    params.append("\"capabilities\": {");
+    params.append("\"desiredCapabilities\": ").append(desired);
+    params.append(",");
+    params.append("\"requiredCapabilities\": ").append(required);
+    params.append("}");
   }
 
   private void amendOssParamters(
-    Map<String, Object> params,
-    Capabilities desired,
-    Capabilities required) {
-    params.put("desiredCapabilities", desired);
-    params.put("requiredCapabilities", required);
+    StringBuilder params,
+    String desired,
+    String required) {
+    params.append("\"desiredCapabilities\": ").append(desired);
+    params.append(",");
+    params.append("\"requiredCapabilities\": ").append(required);
   }