Ignore accept header in requests to metrics service (#1345)

Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Bug Fixes
 
+* The metrics HTTP server no longer rejects requests containing `Accept` header that doesn't precisely match the prometheus text format [\#1345](https://github.com/hyperledger/besu/pull/1345)
+
 #### Previously identified known issues
  
 - [Logs queries missing results against chain head](KNOWN_ISSUES.md#Logs-queries-missing-results-against-chain-head)

metrics/core/src/main/java/org/hyperledger/besu/metrics/prometheus/MetricsHttpService.java

@@ -91,11 +91,7 @@ class MetricsHttpService implements MetricsService {
     router.route("/").method(HttpMethod.GET).handler(this::handleEmptyRequest);
 
     // Endpoint for Prometheus metrics monitoring.
-    router
-        .route("/metrics")
-        .method(HttpMethod.GET)
-        .produces(TextFormat.CONTENT_TYPE_004)
-        .handler(this::metricsRequest);
+    router.route("/metrics").method(HttpMethod.GET).handler(this::metricsRequest);
 
     final CompletableFuture<?> resultFuture = new CompletableFuture<>();
     httpServer

metrics/core/src/test/java/org/hyperledger/besu/metrics/prometheus/MetricsHttpServiceTest.java

@@ -21,6 +21,7 @@ import static org.hyperledger.besu.util.NetworkUtility.urlForSocketAddress;
 import java.net.InetSocketAddress;
 import java.util.Properties;
 
+import io.prometheus.client.exporter.common.TextFormat;
 import io.vertx.core.Vertx;
 import okhttp3.OkHttpClient;
 import okhttp3.Request;
@@ -174,6 +175,23 @@ public class MetricsHttpServiceTest {
     }
   }
 
+  @Test
+  // There is only one available representation so content negotiation should not be used
+  public void acceptHeaderIgnored() throws Exception {
+    final Request metricsRequest =
+        new Request.Builder().addHeader("Accept", "text/xml").url(baseUrl + "/metrics").build();
+    try (final Response resp = client.newCall(metricsRequest).execute()) {
+      assertThat(resp.code()).isEqualTo(200);
+      // Check general format of result, it maps to java.util.Properties
+      final Properties props = new Properties();
+      props.load(resp.body().byteStream());
+
+      // We should have JVM metrics already loaded, verify a simple key.
+      assertThat(props).containsKey("jvm_threads_deadlocked");
+      assertThat(resp.header("Content-Type")).contains(TextFormat.CONTENT_TYPE_004);
+    }
+  }
+
   private Request buildGetRequest(final String path) {
     return new Request.Builder().get().url(baseUrl + path).build();
   }