Allow a specific HttpServer to be specified, so HttpsServer could be used (prometheus#470) (prometheus#471)

Signed-off-by: Simon Cooper <thecoop@runbox.com>

Author: thecoop

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

@@ -142,13 +142,15 @@ static ThreadFactory defaultThreadFactory(boolean daemon) {
     protected final HttpServer server;
     protected final ExecutorService executorService;
 
-
     /**
-     * Start a HTTP server serving Prometheus metrics from the given registry.
+     * Start a HTTP server serving Prometheus metrics from the given registry using the given {@link HttpServer}.
+     * The {@code httpServer} is expected to already be bound to an address
      */
-    public HTTPServer(InetSocketAddress addr, CollectorRegistry registry, boolean daemon) throws IOException {
-        server = HttpServer.create();
-        server.bind(addr, 3);
+    public HTTPServer(HttpServer httpServer, CollectorRegistry registry, boolean daemon) throws IOException {
+        if (httpServer.getAddress() == null)
+            throw new IllegalArgumentException("HttpServer hasn't been bound to an address");
+
+        server = httpServer;
         HttpHandler mHandler = new HTTPMetricHandler(registry);
         server.createContext("/", mHandler);
         server.createContext("/metrics", mHandler);
@@ -157,6 +159,13 @@ public HTTPServer(InetSocketAddress addr, CollectorRegistry registry, boolean da
         start(daemon);
     }
 
+    /**
+     * Start a HTTP server serving Prometheus metrics from the given registry.
+     */
+    public HTTPServer(InetSocketAddress addr, CollectorRegistry registry, boolean daemon) throws IOException {
+        this(HttpServer.create(addr, 3), registry, daemon);
+    }
+
     /**
      * Start a HTTP server serving Prometheus metrics from the given registry using non-daemon threads.
      */

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

@@ -1,5 +1,6 @@
 package io.prometheus.client.exporter;
 
+import com.sun.net.httpserver.HttpServer;
 import io.prometheus.client.Gauge;
 import io.prometheus.client.CollectorRegistry;
 import java.io.IOException;
@@ -14,6 +15,7 @@
 import org.junit.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
 
 public class TestHTTPServer {
 
@@ -54,6 +56,17 @@ String requestWithCompression(String suffix) throws IOException {
     return s.hasNext() ? s.next() : "";
   }
 
+  @Test
+  public void testUnbound() throws IOException {
+    CollectorRegistry registry = new CollectorRegistry();
+    try {
+      HTTPServer s = new HTTPServer(HttpServer.create(), registry, true);
+      s.stop();
+      fail("Should refuse to use an unbound HttpServer");
+    }
+    catch (IllegalArgumentException expected) {}
+  }
+
   @Test
   public void testSimpleRequest() throws IOException {
     String response = request("");