Add validateEndpoint method to WavefrontClient.Builder (#169)

pom.xml

@@ -148,6 +148,12 @@
             <version>5.3.1</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.sun.net.httpserver</groupId>
+            <artifactId>http</artifactId>
+            <version>20070405</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.easymock</groupId>
             <artifactId>easymock</artifactId>

src/main/java/com/wavefront/sdk/common/clients/WavefrontClient.java

@@ -22,8 +22,11 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.lang.management.ManagementFactory;
+import java.net.HttpURLConnection;
 import java.net.InetAddress;
+import java.net.MalformedURLException;
 import java.net.URI;
+import java.net.URL;
 import java.net.UnknownHostException;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
@@ -237,6 +240,33 @@ public Builder sdkMetricsTags(Map<String, String> tags) {
       return this;
     }
 
+  /**
+   * For a given server endpoint, validate according to RFC 2396 and attempt
+   * to make a connection
+   *
+   * @return {@code this}
+   * @throws IllegalStateException
+   */
+    public Builder validateEndpoint() throws IllegalStateException {
+      URL url = null;
+
+      try {
+        url = new URL(this.server);
+      } catch (MalformedURLException e) {
+        throw new IllegalArgumentException(this.server + " is not a valid url", e);
+      }
+
+      try {
+        HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
+        urlConn.connect();
+        urlConn.disconnect();
+      } catch (IOException e) {
+        throw new IllegalArgumentException("Unable to connect to " + this.server, e);
+      }
+
+      return this;
+    }
+
     /**
      * Creates a new client that flushes directly to a Proxy or Wavefront service.
      *

src/test/java/com/wavefront/sdk/common/clients/WavefrontClientTest.java

@@ -5,6 +5,9 @@
 import com.wavefront.sdk.common.metrics.WavefrontSdkDeltaCounter;
 import org.junit.jupiter.api.Test;
 
+import com.sun.net.httpserver.HttpServer;
+import java.io.IOException;
+import java.net.InetSocketAddress;
 import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
@@ -17,6 +20,8 @@
 import static org.easymock.EasyMock.replay;
 import static org.easymock.EasyMock.verify;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
 
 /**
@@ -64,6 +69,43 @@ private String createString(int size) {
     return new String(new char[size]).replace("\0", "a");
   }
 
+  @Test
+  public void testUrlFormatForBuilder() {
+    HttpServer server = runFakeServer("127.0.0.1", 28788);
+
+    assertTrue(validateBuilderEndpoint("http://127.0.0.1:28788"));
+
+    assertFalse(validateBuilderEndpoint("http://127.0.0.1"));
+    assertFalse(validateBuilderEndpoint("http://127.0.0.1:28789"));
+    assertFalse(validateBuilderEndpoint("127.0.0.1:28788"));
+    assertFalse(validateBuilderEndpoint("not a valid endpoint"));
+    assertFalse(validateBuilderEndpoint(null));
+
+    server.stop(0);
+  }
+
+  private HttpServer runFakeServer(String address, int port) {
+    HttpServer httpserver = null;
+
+    try {
+      httpserver = HttpServer.create(new InetSocketAddress(address, port), 0);
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+
+    return httpserver;
+  }
+
+  private boolean validateBuilderEndpoint(String uri) {
+    try {
+      WavefrontClient.Builder wfClientBuilder = new WavefrontClient.Builder(uri, "token");
+      wfClientBuilder.validateEndpoint();
+      return true;
+    } catch (IllegalArgumentException e) {
+      return false;
+    }
+  }
+
   @Test
   public void testUrlFormatForService() {
     validateURI(URI.create("http://127.0.0.1:2878"), "http://127.0.0.1:2878/report?f=wavefront");