Issue #4243 invalid json error response from ErrorHandler (#4249)

* Issue #4243  invalid json error response from ErrorHandler

Signed-off-by: olivier lamy <oliver.lamy@gmail.com>

jetty-server/pom.xml

@@ -74,5 +74,11 @@
       <classifier>tests</classifier>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.eclipse.jetty</groupId>
+      <artifactId>jetty-util-ajax</artifactId>
+      <version>${project.version}</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 </project>

jetty-server/src/main/java/org/eclipse/jetty/server/handler/ErrorHandler.java

@@ -26,7 +26,12 @@ import java.nio.BufferOverflowException;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.Iterator;
 import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
 import javax.servlet.RequestDispatcher;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
@@ -449,23 +454,31 @@ public class ErrorHandler extends AbstractHandler
 
     private void writeErrorJson(HttpServletRequest request, PrintWriter writer, int code, String message)
     {
-        writer
-            .append("{\n")
-            .append("  url: \"").append(request.getRequestURI()).append("\",\n")
-            .append("  status: \"").append(Integer.toString(code)).append("\",\n")
-            .append("  message: ").append(QuotedStringTokenizer.quote(message)).append(",\n");
-        Object servlet = request.getAttribute(Dispatcher.ERROR_SERVLET_NAME);
-        if (servlet != null)
-            writer.append("servlet: \"").append(servlet.toString()).append("\",\n");
         Throwable cause = (Throwable)request.getAttribute(Dispatcher.ERROR_EXCEPTION);
+        Object servlet = request.getAttribute(Dispatcher.ERROR_SERVLET_NAME);
+        Map<String,String> json = new HashMap<>();
+
+        json.put("url", request.getRequestURI());
+        json.put("status", Integer.toString(code));
+        json.put("message", message);
+        if (servlet != null)
+        {
+            json.put("servlet", servlet.toString());
+        }
         int c = 0;
         while (cause != null)
         {
-            writer.append("  cause").append(Integer.toString(c++)).append(": ")
-                .append(QuotedStringTokenizer.quote(cause.toString())).append(",\n");
+            json.put("cause" + c++, cause.toString());
             cause = cause.getCause();
         }
-        writer.append("}");
+
+        writer.append(json.entrySet().stream()
+                .map(e -> QuotedStringTokenizer.quote(e.getKey()) +
+                        ":" +
+                        QuotedStringTokenizer.quote((e.getValue())))
+                .collect(Collectors.joining(",\n", "{\n", "\n}")));
+
+
     }
 
     protected void writeErrorPageStacks(HttpServletRequest request, Writer writer)

jetty-server/src/test/java/org/eclipse/jetty/server/ErrorHandlerTest.java

@@ -19,6 +19,8 @@
 package org.eclipse.jetty.server;
 
 import java.io.IOException;
+import java.util.Map;
+
 import javax.servlet.DispatcherType;
 import javax.servlet.RequestDispatcher;
 import javax.servlet.ServletException;
@@ -30,6 +32,7 @@ import org.eclipse.jetty.http.HttpField;
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.http.HttpTester;
 import org.eclipse.jetty.server.handler.AbstractHandler;
+import org.eclipse.jetty.util.ajax.JSON;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
@@ -303,4 +306,25 @@ public class ErrorHandlerTest
 
         assertThat("Response status code", response.getStatus(), is(444));
     }
+
+    @Test
+    public void testJsonResponse() throws Exception
+    {
+        String rawResponse = connector.getResponse(
+                "GET /badmessage/444 HTTP/1.1\r\n" +
+                        "Host: Localhost\r\n" +
+                        "Accept: text/json\r\n" +
+                        "\r\n");
+        HttpTester.Response response = HttpTester.parseResponse(rawResponse);
+
+        assertThat("Response status code", response.getStatus(), is(444));
+
+        System.out.println("response:" + response.getContent());
+
+        Map<Object,Object> jo = (Map) JSON.parse(response.getContent());
+
+        assertThat("url field null", jo.get("url"), is(notNullValue()));
+        assertThat("status field null", jo.get("status"), is(notNullValue()));
+        assertThat("message field null", jo.get("message"), is(notNullValue()));
+    }
 }