server: Adding a guard that prevents starting "IE instead of Opera" (…

…or some other unwanted browser that obviously does not match the desired capabilities). Previously if a new session request is forwarded to a node it results in a driver instance creation in any case. For example, let's suppose a user starts a node with -browser browserName=opera option, and there is no operadriver in the classpath. Then the user requests a new remote driver with browserName=opera. The hub forwards the request to the node, and the node attempts to find the "best matching" driver provider. As far as opera is not available, it can start any other browser. Because "best matching" does not imply matching. The new guard prevents this unwanted behavior.

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

@@ -23,6 +23,7 @@
 
 import org.openqa.selenium.Capabilities;
 import org.openqa.selenium.WebDriver;
+import org.openqa.selenium.WebDriverException;
 
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
@@ -54,7 +55,14 @@ DriverProvider getProviderMatching(Capabilities desired) {
   }
 
   public WebDriver newInstance(Capabilities capabilities) {
-    return getProviderMatching(capabilities).newInstance(capabilities);
+    DriverProvider provider = getProviderMatching(capabilities);
+    if (provider.canCreateDriverInstanceFor(capabilities)) {
+      return getProviderMatching(capabilities).newInstance(capabilities);
+    } else {
+      throw new WebDriverException(String.format(
+        "The best matching driver provider %s can't create a new driver instance for %s",
+        provider, capabilities));
+    }
   }
 
   public boolean hasMappingFor(Capabilities capabilities) {

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

@@ -25,6 +25,10 @@
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
+/**
+ * This driver provider uses reflection to find and call a driver constructor that accepts
+ * a parameter of Capabilities type.
+ */
 public class DefaultDriverProvider implements DriverProvider {
 
   private static final Logger LOG = Logger.getLogger(DefaultDriverProvider.class.getName());
@@ -48,11 +52,25 @@ public Capabilities getProvidedCapabilities() {
     return capabilities;
   }
 
+  /**
+   * Checks that driver class can be loaded.
+   */
   @Override
   public boolean canCreateDriverInstances() {
     return getDriverClass() != null;
   }
 
+  /**
+   * Checks that the browser name set in the provided capabilities matches the browser name
+   * set in the desired capabilities.
+   * @param capabilities The desired capabilities
+   * @return true if the browser name is the same, false otherwise
+   */
+  @Override
+  public boolean canCreateDriverInstanceFor(Capabilities capabilities) {
+    return this.capabilities.getBrowserName().equals(capabilities.getBrowserName());
+  }
+
   private Class<? extends WebDriver> getDriverClass() {
     if (driverClass != null) {
       return driverClass;

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

@@ -44,12 +44,19 @@ public interface DriverProvider {
   Capabilities getProvidedCapabilities();
 
   /**
-   * Checks if the provider can create driver instances.
+   * Checks if the provider can create driver instances "in general".
    *
    * @return true if the provider can create driver instances.
    */
   boolean canCreateDriverInstances();
 
+  /**
+   * Checks if the provider can create driver instance with the desired capabilities.
+   *
+   * @return true if the provider can create driver instance with the desired capabilities.
+   */
+  boolean canCreateDriverInstanceFor(Capabilities capabilities);
+
   /**
    * Creates a new driver instance. The specified capabilities are to be passed to the driver
    * constructor.