[UrlConnectionHttpClient] Wrap erroneous NPE from HttpURLConnection as IOException

.changes/next-release/bugfix-AWSSDKforJavav2-a3c92c2.json

@@ -0,0 +1,6 @@
+{
+    "category": "AWS SDK for Java v2", 
+    "contributor": "Bennett-Lynch", 
+    "type": "bugfix", 
+    "description": "[UrlConnectionHttpClient] Wrap erroneous NPE from HttpURLConnection as IOException"
+}

http-clients/url-connection-client/src/main/java/software/amazon/awssdk/http/urlconnection/UrlConnectionHttpClient.java

@@ -207,7 +207,7 @@ public HttpExecuteResponse call() throws IOException {
             request.contentStreamProvider().ifPresent(provider ->
                     invokeSafely(() -> IoUtils.copy(provider.newStream(), connection.getOutputStream())));
 
-            int responseCode = connection.getResponseCode();
+            int responseCode = getResponseCodeSafely(connection);
             boolean isErrorResponse = HttpStatusFamily.of(responseCode).isOneOf(CLIENT_ERROR, SERVER_ERROR);
             InputStream content = !isErrorResponse ? connection.getInputStream() : connection.getErrorStream();
             AbortableInputStream responseBody = content != null ?
@@ -224,6 +224,24 @@ public HttpExecuteResponse call() throws IOException {
                                       .build();
         }
 
+        /**
+         * {@link sun.net.www.protocol.http.HttpURLConnection#getInputStream0()} has been observed to intermittently throw
+         * {@link NullPointerException}s for reasons that still require further investigation, but are assumed to be due to a
+         * bug in the JDK. Propagating such NPEs is confusing for users and are not subject to being retried on by the default 
+         * retry policy configuration, so instead we bias towards propagating these as {@link IOException}s.
+         * <p>
+         * TODO: Determine precise root cause of intermittent NPEs, submit JDK bug report if applicable, and consider applying
+         * this behavior only on unpatched JVM runtime versions.
+         */
+        private static int getResponseCodeSafely(HttpURLConnection connection) throws IOException {
+            Validate.paramNotNull(connection, "connection");
+            try {
+                return connection.getResponseCode();
+            } catch (NullPointerException e) {
+                throw new IOException("Unexpected NullPointerException when trying to read response from HttpURLConnection", e);
+            }
+        }
+
         private Map<String, List<String>> extractHeaders(HttpURLConnection response) {
             return response.getHeaderFields().entrySet().stream()
                            .filter(e -> e.getKey() != null)

http-clients/url-connection-client/src/test/java/software/amazon/awssdk/http/urlconnection/UrlConnectionHttpClientWithCustomCreateWireMockTest.java

@@ -14,17 +14,30 @@
  */
 package software.amazon.awssdk.http.urlconnection;
 
+import static org.assertj.core.api.AssertionsForClassTypes.assertThatThrownBy;
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.spy;
 import static software.amazon.awssdk.utils.FunctionalUtils.invokeSafely;
+import static software.amazon.awssdk.utils.FunctionalUtils.safeFunction;
 
+import java.io.IOException;
 import java.net.HttpURLConnection;
+import java.util.function.Function;
 import org.junit.Ignore;
+import org.junit.Test;
 import software.amazon.awssdk.http.SdkHttpClient;
 import software.amazon.awssdk.http.SdkHttpClientTestSuite;
 
 public final class UrlConnectionHttpClientWithCustomCreateWireMockTest extends SdkHttpClientTestSuite {
+
+    private Function<HttpURLConnection, HttpURLConnection> connectionInterceptor = Function.identity();
+
     @Override
     protected SdkHttpClient createSdkHttpClient(SdkHttpClientOptions options) {
-        return UrlConnectionHttpClient.create((uri) -> invokeSafely(() -> (HttpURLConnection) uri.toURL().openConnection()));
+        return UrlConnectionHttpClient.create(uri -> invokeSafely(() -> {
+            HttpURLConnection connection = (HttpURLConnection) uri.toURL().openConnection();
+            return connectionInterceptor.apply(connection);
+        }));
     }
 
     @Ignore // Not supported when using custom factory
@@ -41,4 +54,18 @@ public void testTrustAllWorks() {
     @Override
     public void testCustomTlsTrustManagerAndTrustAllFails() {
     }
+
+    @Test
+    public void testGetResponseCodeNpeIsWrappedAsIo() throws Exception {
+        connectionInterceptor = safeFunction(connection -> {
+            connection = spy(connection);
+            doThrow(new NullPointerException()).when(connection).getResponseCode();
+            return connection;
+        });
+
+        assertThatThrownBy(() -> testForResponseCode(HttpURLConnection.HTTP_OK))
+            .isInstanceOf(IOException.class)
+            .hasMessage("Unexpected NullPointerException when trying to read response from HttpURLConnection")
+            .hasCauseInstanceOf(NullPointerException.class);
+    }
 }

test/http-client-tests/src/main/java/software/amazon/awssdk/http/SdkHttpClientTestSuite.java

@@ -152,7 +152,7 @@ public void testCustomTlsTrustManagerAndTrustAllFails() throws Exception {
         assertThatThrownBy(() -> createSdkHttpClient(httpClientOptions)).isInstanceOf(IllegalArgumentException.class);
     }
 
-    private void testForResponseCode(int returnCode) throws Exception {
+    protected void testForResponseCode(int returnCode) throws Exception {
         testForResponseCode(returnCode, SdkHttpMethod.POST);
     }