Provide native Java 11 HTTP client versions of FormValidation#URLCheck methods

core/src/main/java/hudson/ProxyConfiguration.java

@@ -357,7 +357,7 @@ public static InputStream getInputStream(URL url) throws IOException {
     /**
      * Return a new {@link HttpClient} with Jenkins-specific default settings.
      *
-     * <p>Equivalent to {@code newHttpClientBuilder().build()}.
+     * <p>Equivalent to {@code newHttpClientBuilder().followRedirects(HttpClient.Redirect.NORMAL).build()}.
      *
      * <p>The Jenkins-specific default settings include a proxy server and proxy authentication (as
      * configured by {@link ProxyConfiguration}) and a connection timeout (as configured by {@link
@@ -367,7 +367,7 @@ public static InputStream getInputStream(URL url) throws IOException {
      * @since TODO
      */
     public static HttpClient newHttpClient() {
-        return newHttpClientBuilder().build();
+        return newHttpClientBuilder().followRedirects(HttpClient.Redirect.NORMAL).build();
     }
 
     /**

core/src/main/java/hudson/util/FormValidation.java

@@ -44,14 +44,19 @@
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.lang.reflect.Method;
+import java.net.HttpURLConnection;
+import java.net.URI;
 import java.net.URL;
 import java.net.URLConnection;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Base64;
 import java.util.Collection;
 import java.util.List;
 import java.util.Locale;
+import java.util.stream.Stream;
 import javax.servlet.ServletException;
 import jenkins.model.Jenkins;
 import jenkins.util.SystemProperties;
@@ -461,10 +466,46 @@ public static FormValidation validateBase64(String value, boolean allowWhitespac
      * This allows the check method to call various utility methods in a concise syntax.
      */
     public abstract static class URLCheck {
+        /**
+         * Open the given URI and read text content from it. This method honors the Content-type
+         * header.
+         *
+         * @throws IOException if the URI scheme is not supported, the connection was interrupted,
+         *     or the response was an error
+         * @since TODO
+         */
+        protected Stream<String> open(URI uri) throws IOException {
+            HttpClient httpClient = ProxyConfiguration.newHttpClient();
+            HttpRequest httpRequest;
+            try {
+                httpRequest = ProxyConfiguration.newHttpRequestBuilder(uri).GET().build();
+            } catch (IllegalArgumentException e) {
+                throw new IOException(e);
+            }
+            java.net.http.HttpResponse<Stream<String>> httpResponse;
+            try {
+                httpResponse =
+                        httpClient.send(httpRequest, java.net.http.HttpResponse.BodyHandlers.ofLines());
+            } catch (InterruptedException e) {
+                throw new IOException(e);
+            }
+            if (httpResponse.statusCode() != HttpURLConnection.HTTP_OK) {
+                throw new IOException(
+                        "Server returned HTTP response code "
+                                + httpResponse.statusCode()
+                                + " for URI "
+                                + uri);
+            }
+            return httpResponse.body();
+        }
+
         /**
          * Opens the given URL and reads text content from it.
          * This method honors Content-type header.
+         *
+         * @deprecated use {@link #open(URI)}
          */
+        @Deprecated
         protected BufferedReader open(URL url) throws IOException {
             // use HTTP content type to find out the charset.
             URLConnection con = ProxyConfiguration.open(url);
@@ -475,11 +516,25 @@ protected BufferedReader open(URL url) throws IOException {
                 new InputStreamReader(con.getInputStream(), getCharset(con)));
         }
 
+        /**
+         * Find the string literal from the given stream of lines.
+         *
+         * @return true if found, false otherwise
+         * @since TODO
+         */
+        protected boolean findText(Stream<String> in, String literal) {
+            try (in) {
+                return in.anyMatch(line -> line.contains(literal));
+            }
+        }
+
         /**
          * Finds the string literal from the given reader.
          * @return
          *      true if found, false otherwise.
+         * @deprecated use {@link #findText(Stream, String)}
          */
+        @Deprecated
         protected boolean findText(BufferedReader in, String literal) throws IOException {
             String line;
             while ((line = in.readLine()) != null)
@@ -499,9 +554,9 @@ protected FormValidation handleIOException(String url, IOException e) throws IOE
             // any invalid URL comes here
             if (e.getMessage().equals(url))
                 // Sun JRE (and probably others too) often return just the URL in the error.
-                return error("Unable to connect " + url);
+                return error("Unable to connect " + url, e);
             else
-                return error(e.getMessage());
+                return error(e.getMessage(), e);
         }
 
         /**

core/src/test/java/hudson/util/FormValidationTest.java

@@ -27,11 +27,15 @@
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.not;
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
+import java.io.IOException;
+import java.net.URI;
 import java.util.Arrays;
+import javax.servlet.ServletException;
 import org.junit.Test;
 
 /**
@@ -116,4 +120,24 @@ public void formValidationException() {
         FormValidation fv = FormValidation.error(new Exception("<html"), "Message<html");
         assertThat(fv.renderHtml(), not(containsString("<html")));
     }
+
+    @Test
+    public void testUrlCheck() throws IOException, ServletException {
+        FormValidation.URLCheck urlCheck = new FormValidation.URLCheck() {
+            @Override
+            protected FormValidation check() throws ServletException, IOException {
+                String uri = "https://www.jenkins.io/";
+                try {
+                    if (findText(open(URI.create(uri)), "Jenkins")) {
+                        return FormValidation.ok();
+                    } else {
+                        return FormValidation.error("This is a valid URI but it does not look like Jenkins");
+                    }
+                } catch (IOException e) {
+                    return handleIOException(uri, e);
+                }
+            }
+        };
+        assertThat(urlCheck.check(), is(FormValidation.ok()));
+    }
 }