Add a JSON response instead of default error page

Use custom error handler instead of default that leaks server info.

- Use in API context
- Use in default/web context
- Add tests

services/git-bridge/src/main/java/uk/ac/ic/wlgitbridge/server/GitBridgeServer.java

@@ -123,6 +123,9 @@ public class GitBridgeServer {
         handlers.addHandler(new DefaultHandler());
 
         api.setHandler(handlers);
+
+        ProductionErrorHandler errorHandler = new ProductionErrorHandler();
+        api.setErrorHandler(errorHandler);
         return api;
     }
 
@@ -149,6 +152,8 @@ public class GitBridgeServer {
                 ),
                 "/*"
         );
+        ProductionErrorHandler errorHandler = new ProductionErrorHandler();
+        servletContextHandler.setErrorHandler(errorHandler);
         return servletContextHandler;
     }
 

services/git-bridge/src/main/java/uk/ac/ic/wlgitbridge/server/ProductionErrorHandler.java

@@ -0,0 +1,21 @@
+package uk.ac.ic.wlgitbridge.server;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.eclipse.jetty.server.handler.ErrorHandler;
+import java.io.IOException;
+
+public class ProductionErrorHandler extends ErrorHandler {
+    @Override
+    public void handle(
+    		String target, 
+    		org.eclipse.jetty.server.Request baseRequest, 
+    		HttpServletRequest request, 
+    		HttpServletResponse response
+    	) throws IOException {
+	        response.getWriter()
+	            .append("{\"message\":\"HTTP error ")
+	            .append(String.valueOf(response.getStatus()))
+	            .append("\"}");
+    	}
+}