Issue 2161: set metrics endpoint content-type (#4208)

* fix: set metrics endpoint content-type when bookie http server is enabled

* fix: checkstyle

* fix: use existing prometheus content type constant

* chore: use minimal dependency / license fixes

* Revert "chore: use minimal dependency / license fixes"

This reverts commit 7daf8be.

* Revert "fix: use existing prometheus content type constant"

This reverts commit c265c49.

bookkeeper-http/http-server/src/main/java/org/apache/bookkeeper/http/service/HttpServiceResponse.java

@@ -28,6 +28,7 @@
  */
 public class HttpServiceResponse {
     private String body;
+    private String contentType;
     private HttpServer.StatusCode code = HttpServer.StatusCode.OK;
 
     public HttpServiceResponse() {}
@@ -41,6 +42,10 @@ public String getBody() {
         return body;
     }
 
+    public String getContentType() {
+        return contentType;
+    }
+
     public int getStatusCode() {
         return code.getValue();
     }
@@ -50,6 +55,11 @@ public HttpServiceResponse setBody(String body) {
         return this;
     }
 
+    public HttpServiceResponse setContentType(String contentType) {
+        this.contentType = contentType;
+        return this;
+    }
+
     public HttpServiceResponse setCode(HttpServer.StatusCode code) {
         this.code = code;
         return this;

bookkeeper-http/vertx-http-server/src/main/java/org/apache/bookkeeper/http/vertx/VertxAbstractHandler.java

@@ -20,6 +20,7 @@
  */
 package org.apache.bookkeeper.http.vertx;
 
+import io.netty.handler.codec.http.HttpHeaderNames;
 import io.vertx.core.Handler;
 import io.vertx.core.http.HttpMethod;
 import io.vertx.core.http.HttpServerRequest;
@@ -56,6 +57,9 @@ void processRequest(HttpEndpointService httpEndpointService, RoutingContext cont
             response = new ErrorHttpService().handle(request);
         }
         httpResponse.setStatusCode(response.getStatusCode());
+        if (response.getContentType() != null) {
+            httpResponse.putHeader(HttpHeaderNames.CONTENT_TYPE, response.getContentType());
+        }
         httpResponse.end(response.getBody());
     }
 

bookkeeper-server/src/main/java/org/apache/bookkeeper/server/http/service/MetricsService.java

@@ -35,6 +35,8 @@
  */
 public class MetricsService implements HttpEndpointService {
 
+    public static final String PROMETHEUS_CONTENT_TYPE_004 = "text/plain; version=0.0.4; charset=utf-8";
+
     private final ServerConfiguration conf;
     private final StatsProvider statsProvider;
 
@@ -65,6 +67,7 @@ public HttpServiceResponse handle(HttpServiceRequest request) throws Exception {
             statsProvider.writeAllMetrics(writer);
             writer.flush();
             response.setCode(StatusCode.OK);
+            response.setContentType(PROMETHEUS_CONTENT_TYPE_004);
             response.setBody(writer.getBuffer().toString());
         } catch (UnsupportedOperationException uoe) {
             response.setCode(StatusCode.INTERNAL_ERROR);

bookkeeper-server/src/test/java/org/apache/bookkeeper/server/http/service/MetricsServiceTest.java

@@ -19,6 +19,7 @@
 package org.apache.bookkeeper.server.http.service;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.CALLS_REAL_METHODS;
 import static org.mockito.Mockito.doAnswer;
@@ -55,6 +56,7 @@ public void testForbiddenMethods() throws Exception {
         HttpServiceRequest request = new HttpServiceRequest().setMethod(Method.PUT);
         HttpServiceResponse response = service.handle(request);
         assertEquals(StatusCode.FORBIDDEN.getValue(), response.getStatusCode());
+        assertNull(response.getContentType());
         assertEquals(
             "PUT is forbidden. Should be GET method",
             response.getBody());
@@ -66,6 +68,7 @@ public void testNullStatsProvider() throws Exception {
         HttpServiceRequest request = new HttpServiceRequest().setMethod(Method.GET);
         HttpServiceResponse response = service.handle(request);
         assertEquals(StatusCode.INTERNAL_ERROR.getValue(), response.getStatusCode());
+        assertNull(response.getContentType());
         assertEquals(
             "Stats provider is not enabled. Please enable it by set statsProviderClass"
                 + " on bookie configuration",
@@ -86,6 +89,7 @@ public void testWriteMetrics() throws Exception {
         HttpServiceResponse response = service.handle(request);
 
         assertEquals(StatusCode.OK.getValue(), response.getStatusCode());
+        assertEquals(MetricsService.PROMETHEUS_CONTENT_TYPE_004, response.getContentType());
         assertEquals(content, response.getBody());
     }
 
@@ -98,6 +102,7 @@ public void testWriteMetricsException() throws Exception {
         HttpServiceResponse response = service.handle(request);
 
         assertEquals(StatusCode.INTERNAL_ERROR.getValue(), response.getStatusCode());
+        assertNull(response.getContentType());
         assertEquals("Exceptions are thrown when exporting metrics : write-metrics-exception",
             response.getBody());
     }
@@ -111,6 +116,7 @@ public void testWriteMetricsUnimplemented() throws Exception {
         HttpServiceResponse response = service.handle(request);
 
         assertEquals(StatusCode.INTERNAL_ERROR.getValue(), response.getStatusCode());
+        assertNull(response.getContentType());
         assertEquals("Currently stats provider doesn't support exporting metrics in http service",
             response.getBody());
     }