8306040: HttpResponseInputStream.available() returns 1 on empty stream

Backport-of: acaab6fd74f507bb6b18167505d88e505bdf24bd

src/java.net.http/share/classes/jdk/internal/net/http/ResponseSubscribers.java

@@ -538,8 +538,8 @@ public int available() throws IOException {
             if (available != 0) return available;
             Iterator<?> iterator = currentListItr;
             if (iterator != null && iterator.hasNext()) return 1;
-            if (buffers.isEmpty()) return 0;
-            return 1;
+            if (!buffers.isEmpty() && buffers.peek() != LAST_LIST ) return 1;
+            return available;
         }
 
         @Override

test/jdk/java/net/httpclient/HttpInputStreamAvailableTest.java

@@ -0,0 +1,161 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8306040
+ * @summary HttpResponseInputStream.available() returns 1 on empty stream
+ * @library /test/lib /test/jdk/java/net/httpclient/lib
+ * @run junit/othervm HttpInputStreamAvailableTest
+ *
+ */
+import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpHandler;
+import com.sun.net.httpserver.HttpServer;
+import jdk.test.lib.net.URIBuilder;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInstance;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+public class HttpInputStreamAvailableTest {
+
+    private HttpServer server;
+    private int port;
+    static final String TEST_MESSAGE = "This is test message";
+    static final int ZERO = 0;
+
+    @BeforeAll
+    void setup() throws Exception {
+        InetAddress loopback = InetAddress.getLoopbackAddress();
+        InetSocketAddress addr = new InetSocketAddress(loopback, 0);
+        server = HttpServer.create(addr, 0);
+        port = server.getAddress().getPort();
+        FirstHandler fHandler = new FirstHandler();
+        server.createContext("/NonZeroResponse/", fHandler);
+        SecondHandler sHandler = new SecondHandler();
+        server.createContext("/ZeroResponse/", sHandler);
+        server.start();
+    }
+
+    @AfterAll
+    void teardown() throws Exception {
+        server.stop(0);
+    }
+
+    @Test
+    public void test() throws Exception {
+        HttpClient client = HttpClient
+                .newBuilder()
+                .proxy(HttpClient.Builder.NO_PROXY)
+                .build();
+
+        URI uri = URIBuilder.newBuilder()
+                .scheme("http")
+                .loopback()
+                .port(port)
+                .path("/NonZeroResponse/")
+                .build();
+
+        HttpRequest request = HttpRequest
+                .newBuilder(uri)
+                .GET()
+                .build();
+
+        // Send a httpRequest and assert the bytes available
+        HttpResponse<InputStream> response = client.send(request,
+                HttpResponse.BodyHandlers.ofInputStream());
+        try ( InputStream in = response.body()) {
+            in.readNBytes(2);
+            // this is not guaranteed, but a failure here would be surprising
+            assertEquals(TEST_MESSAGE.length() - 2, in.available());
+            //read the remaining data
+            in.readAllBytes();
+            //available should return 0
+            assertEquals(ZERO, in.available());
+        }
+    }
+
+    @Test
+    public void test1() throws Exception {
+        HttpClient client = HttpClient
+                .newBuilder()
+                .proxy(HttpClient.Builder.NO_PROXY)
+                .build();
+
+        URI uri = URIBuilder.newBuilder()
+                .scheme("http")
+                .loopback()
+                .port(port)
+                .path("/ZeroResponse/")
+                .build();
+
+        HttpRequest request = HttpRequest
+                .newBuilder(uri)
+                .GET()
+                .build();
+
+        // Send a httpRequest and assert the bytes available
+        HttpResponse<InputStream> response = client.send(request,
+                HttpResponse.BodyHandlers.ofInputStream());
+        try ( InputStream in = response.body()) {
+            assertEquals(ZERO, in.available());
+            in.readAllBytes();
+            assertEquals(ZERO, in.available());
+        }
+    }
+
+    static class FirstHandler implements HttpHandler {
+
+        @Override
+        public void handle(HttpExchange exchange) throws IOException {
+            try ( OutputStream os = exchange.getResponseBody()) {
+                byte[] workingResponse = TEST_MESSAGE.getBytes();
+                exchange.sendResponseHeaders(200, workingResponse.length);
+                os.write(workingResponse);
+                os.flush();
+            }
+        }
+    }
+
+    static class SecondHandler implements HttpHandler {
+
+        @Override
+        public void handle(HttpExchange exchange) throws IOException {
+            exchange.sendResponseHeaders(204, -1);
+        }
+    }
+}