Initial rework of the existing DriverServlet

This introduces the scaffolding for later work, but
does not introduce any new functionality.

java/server/src/org/openqa/selenium/remote/server/ActiveSession.java

@@ -0,0 +1,22 @@
+package org.openqa.selenium.remote.server;
+
+import org.openqa.selenium.remote.SessionId;
+
+import java.util.Map;
+
+interface ActiveSession extends CommandHandler {
+
+  /**
+   * Used to provide logging information and thread names.
+   */
+  String getDescription();
+
+  SessionId getId();
+
+  /**
+   * Desribe the current webdriver session's capabilities.
+   */
+  Map<String, Object> getCapabilities();
+
+  void stop();
+}

java/server/src/org/openqa/selenium/remote/server/AllHandlers.java

@@ -0,0 +1,86 @@
+package org.openqa.selenium.remote.server;
+
+import static com.google.common.net.MediaType.JAVASCRIPT_UTF_8;
+import static java.net.HttpURLConnection.HTTP_NOT_FOUND;
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.openqa.selenium.remote.ErrorCodes.UNKNOWN_COMMAND;
+
+import com.google.common.base.Splitter;
+import com.google.common.base.Strings;
+import com.google.common.cache.Cache;
+import com.google.common.collect.ImmutableMap;
+import com.google.gson.GsonBuilder;
+
+import org.openqa.selenium.remote.SessionId;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.List;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+
+class AllHandlers {
+
+  private final Cache<SessionId, ActiveSession> allSessions;
+  private final DriverSessions legacySessions;
+
+  public AllHandlers(Cache<SessionId, ActiveSession> allSessions, DriverSessions legacySessions) {
+    this.allSessions = allSessions;
+    this.legacySessions = legacySessions;
+  }
+
+  public CommandHandler match(HttpServletRequest req) {
+    String path = Strings.isNullOrEmpty(req.getPathInfo()) ? "/" : req.getPathInfo();
+
+    // All commands that take a session id expect that as the path fragment immediately after "/session".
+    SessionId id = null;
+    List<String> fragments = Splitter.on('/').limit(4).splitToList(path);
+    if (fragments.size() > 2) {
+      if ("session".equals(fragments.get(1))) {
+        id = new SessionId(fragments.get(2));
+      }
+    }
+
+    if (id != null) {
+      ActiveSession session = allSessions.getIfPresent(id);
+      if (session != null) {
+        return session;
+      }
+    }
+
+    if ("POST".equalsIgnoreCase(req.getMethod()) && "/session".equals(path)) {
+      return new BeginSession(allSessions, legacySessions);
+    }
+
+    return new NoHandler();
+  }
+
+  private static class NoHandler implements CommandHandler {
+
+    @Override
+    public void execute(HttpServletRequest req, HttpServletResponse resp) throws IOException {
+      resp.reset();
+
+      byte[] payload = new GsonBuilder().serializeNulls().create().toJson(ImmutableMap.of(
+          "sessionId", null,
+          "status", UNKNOWN_COMMAND,
+          "value", ImmutableMap.of(
+              "error", "unknown command",
+              "message", String.format(
+                  "Unable to find command matching %s to %s",
+                  req.getMethod(),
+                  req.getPathInfo()),
+              "stacktrace", ""))).getBytes(UTF_8);
+
+      resp.setStatus(HTTP_NOT_FOUND);
+      resp.setContentType(JAVASCRIPT_UTF_8.toString());
+      resp.setContentLengthLong(payload.length);
+
+      try (OutputStream out = resp.getOutputStream()) {
+        out.write(payload);
+      }
+    }
+  }
+}

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

@@ -60,6 +60,29 @@ java_library(name = 'server',
   ],
 )
 
+java_library(
+  name = 'webdriver-servlet',
+  srcs = [
+    'ActiveSession.java',
+    'BeginSession.java',
+    'AllHandlers.java',
+    'CommandHandler.java',
+    'ExceptionHandler.java',
+    'InMemorySession.java',
+    'WebDriverServlet.java',
+  ],
+  provided_deps = [
+    '//third_party/java/servlet:servlet-api',
+  ],
+  deps = [
+    ':server',
+    ':sessions',
+    '//java/client/src/org/openqa/selenium/remote:remote',
+    '//third_party/java/gson:gson',
+    '//third_party/java/guava:guava',
+  ]
+)
+
 export_file(name = 'client',
   src = '//javascript/remote:client',
   out = 'client.js',
@@ -82,6 +105,7 @@ java_library(name = 'standalone-server-lib',
   deps = [
     ':server',
     ':sessions',
+    ':webdriver-servlet',
     '//java/client/src/org/openqa/selenium/chrome:chrome',
     '//java/client/src/org/openqa/selenium/edge:edge',
     '//java/client/src/org/openqa/selenium/firefox:firefox',