Added health check api to the client. (#534)

* Added health check api to the client.
prometheus/jmx_exporter#465

Signed-off-by: Brajesh Kumar <[email protected]>

Author: bristy

simpleclient_httpserver/src/main/java/io/prometheus/client/exporter/HTTPServer.java

@@ -42,9 +42,13 @@ protected ByteArrayOutputStream initialValue()
         }
     }
 
+    /**
+     * Handles Metrics collections from the given registry.
+     */
     static class HTTPMetricHandler implements HttpHandler {
         private CollectorRegistry registry;
         private final LocalByteArray response = new LocalByteArray();
+        private final static String HEALTHY_RESPONSE = "Exporter is Healthy.";
 
         HTTPMetricHandler(CollectorRegistry registry) {
           this.registry = registry;
@@ -54,16 +58,21 @@ static class HTTPMetricHandler implements HttpHandler {
         public void handle(HttpExchange t) throws IOException {
             String query = t.getRequestURI().getRawQuery();
 
+            String contextPath = t.getHttpContext().getPath();
             ByteArrayOutputStream response = this.response.get();
             response.reset();
             OutputStreamWriter osw = new OutputStreamWriter(response);
-            TextFormat.write004(osw,
-                    registry.filteredMetricFamilySamples(parseQuery(query)));
+            if ("/-/healthy".equals(contextPath)) {
+                osw.write(HEALTHY_RESPONSE);
+            } else {
+                TextFormat.write004(osw,
+                        registry.filteredMetricFamilySamples(parseQuery(query)));
+            }
+
             osw.flush();
             osw.close();
             response.flush();
             response.close();
-
             t.getResponseHeaders().set("Content-Type",
                     TextFormat.CONTENT_TYPE_004);
             if (shouldUseCompression(t)) {
@@ -154,6 +163,7 @@ public HTTPServer(HttpServer httpServer, CollectorRegistry registry, boolean dae
         HttpHandler mHandler = new HTTPMetricHandler(registry);
         server.createContext("/", mHandler);
         server.createContext("/metrics", mHandler);
+        server.createContext("/-/healthy", mHandler);
         executorService = Executors.newFixedThreadPool(5, NamedDaemonThreadFactory.defaultThreadFactory(daemon));
         server.setExecutor(executorService);
         start(daemon);

simpleclient_httpserver/src/test/java/io/prometheus/client/exporter/TestHTTPServer.java

@@ -35,17 +35,26 @@ public void cleanup() {
     s.stop();
   }
 
-  String request(String suffix) throws IOException {
-    String url = "http://localhost:" + s.server.getAddress().getPort() + "/metrics" + suffix;
+
+  String request(String context, String suffix) throws IOException {
+    String url = "http://localhost:" + s.server.getAddress().getPort() + context + suffix;
     URLConnection connection = new URL(url).openConnection();
     connection.setDoOutput(true);
     connection.connect();
     Scanner s = new Scanner(connection.getInputStream(), "UTF-8").useDelimiter("\\A");
     return s.hasNext() ? s.next() : "";
   }
 
+  String request(String suffix) throws IOException {
+    return request("/metrics", suffix);
+  }
+
   String requestWithCompression(String suffix) throws IOException {
-    String url = "http://localhost:" + s.server.getAddress().getPort() + "/metrics" + suffix;
+    return requestWithCompression("/metrics", suffix);
+  }
+
+  String requestWithCompression(String context, String suffix) throws IOException {
+    String url = "http://localhost:" + s.server.getAddress().getPort() + context + suffix;
     URLConnection connection = new URL(url).openConnection();
     connection.setDoOutput(true);
     connection.setDoInput(true);
@@ -63,8 +72,8 @@ public void testUnbound() throws IOException {
       HTTPServer s = new HTTPServer(HttpServer.create(), registry, true);
       s.stop();
       fail("Should refuse to use an unbound HttpServer");
+    } catch (IllegalArgumentException expected) {
     }
-    catch (IllegalArgumentException expected) {}
   }
 
   @Test
@@ -114,4 +123,16 @@ public void testGzipCompression() throws IOException {
     assertThat(response).contains("b 0.0");
     assertThat(response).contains("c 0.0");
   }
+
+  @Test
+  public void testHealth() throws IOException {
+    String response = request("/-/healthy", "");
+    assertThat(response).contains("Exporter is Healthy");
+  }
+
+  @Test
+  public void testHealthGzipCompression() throws IOException {
+    String response = requestWithCompression("/-/healthy", "");
+    assertThat(response).contains("Exporter is Healthy");
+  }
 }