8216478: Cleanup HttpResponseImpl back reference to HttpConnection

Retain a reference to Exchange and HttpConnection only when necessary, i.e. for WebSocket initial connection.

Reviewed-by: chegar

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2019, 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
@@ -44,16 +44,13 @@ import jdk.internal.net.http.websocket.RawChannel;
 class HttpResponseImpl<T> implements HttpResponse<T>, RawChannel.Provider {
 
     final int responseCode;
-    final Exchange<T> exchange;
     final HttpRequest initialRequest;
     final Optional<HttpResponse<T>> previousResponse;
     final HttpHeaders headers;
     final Optional<SSLSession> sslSession;
     final URI uri;
     final HttpClient.Version version;
-    RawChannel rawchan;
-    final HttpConnection connection;
-    final Stream<T> stream;
+    final RawChannelProvider rawChannelProvider;
     final T body;
 
     public HttpResponseImpl(HttpRequest initialRequest,
@@ -62,7 +59,6 @@ class HttpResponseImpl<T> implements HttpResponse<T>, RawChannel.Provider {
                             T body,
                             Exchange<T> exch) {
         this.responseCode = response.statusCode();
-        this.exchange = exch;
         this.initialRequest = initialRequest;
         this.previousResponse = Optional.ofNullable(previousResponse);
         this.headers = response.headers();
@@ -70,23 +66,10 @@ class HttpResponseImpl<T> implements HttpResponse<T>, RawChannel.Provider {
         this.sslSession = Optional.ofNullable(response.getSSLSession());
         this.uri = response.request().uri();
         this.version = response.version();
-        this.connection = connection(exch);
-        this.stream = null;
+        this.rawChannelProvider = RawChannelProvider.create(response, exch);
         this.body = body;
     }
 
-    private HttpConnection connection(Exchange<?> exch) {
-        if (exch == null || exch.exchImpl == null) {
-            assert responseCode == 407;
-            return null; // case of Proxy 407
-        }
-        return exch.exchImpl.connection();
-    }
-
-    private ExchangeImpl<?> exchangeImpl() {
-        return exchange != null ? exchange.exchImpl : stream;
-    }
-
     @Override
     public int statusCode() {
         return responseCode;
@@ -141,6 +124,52 @@ class HttpResponseImpl<T> implements HttpResponse<T>, RawChannel.Provider {
      */
     @Override
     public synchronized RawChannel rawChannel() throws IOException {
+        if (rawChannelProvider == null) {
+            throw new UnsupportedOperationException(
+                    "RawChannel is only supported for WebSocket creation");
+        }
+        return rawChannelProvider.rawChannel();
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder sb = new StringBuilder();
+        String method = request().method();
+        URI uri = request().uri();
+        String uristring = uri == null ? "" : uri.toString();
+        sb.append('(')
+          .append(method)
+          .append(" ")
+          .append(uristring)
+          .append(") ")
+          .append(statusCode());
+        return sb.toString();
+    }
+
+    /**
+     * An auxiliary class used for RawChannel creation when creating a WebSocket.
+     * This avoids keeping around references to connection/exchange in the
+     * regular HttpResponse case. Only those responses corresponding to an
+     * initial WebSocket request have a RawChannelProvider.
+     */
+    private static final class RawChannelProvider implements RawChannel.Provider {
+        private final HttpConnection connection;
+        private final Exchange<?> exchange;
+        private RawChannel rawchan;
+        RawChannelProvider(HttpConnection conn, Exchange<?> exch) {
+            connection = conn;
+            exchange = exch;
+        }
+
+        static RawChannelProvider create(Response resp, Exchange<?> exch) {
+            if (resp.request().isWebSocket()) {
+                return new RawChannelProvider(connection(resp, exch), exch);
+            }
+            return null;
+        }
+
+        @Override
+        public synchronized RawChannel rawChannel() {
             if (rawchan == null) {
                 ExchangeImpl<?> exchImpl = exchangeImpl();
                 if (!(exchImpl instanceof Http1Exchange)) {
@@ -160,18 +189,17 @@ class HttpResponseImpl<T> implements HttpResponse<T>, RawChannel.Provider {
             return rawchan;
         }
 
-    @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        String method = request().method();
-        URI uri = request().uri();
-        String uristring = uri == null ? "" : uri.toString();
-        sb.append('(')
-          .append(method)
-          .append(" ")
-          .append(uristring)
-          .append(") ")
-          .append(statusCode());
-        return sb.toString();
+        private static HttpConnection connection(Response resp, Exchange<?> exch) {
+            if (exch == null || exch.exchImpl == null) {
+                assert resp.statusCode == 407;
+                return null; // case of Proxy 407
+            }
+            return exch.exchImpl.connection();
+        }
+
+        private ExchangeImpl<?> exchangeImpl() {
+            return exchange != null ? exchange.exchImpl : null;
+        }
+
     }
 }