Add HttpUrlConnection backed implementation of CronetEngine.

components/cronet/android/api/src/org/chromium/net/InputStreamChannel.java

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.net;
+
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.ByteBuffer;
+import java.nio.channels.ReadableByteChannel;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * Adapts an {@link InputStream} into a {@link ReadableByteChannel}, exactly like
+ * {@link java.nio.channels.Channels#newChannel(InputStream)} does, but more efficiently, since it
+ * does not allocate a temporary buffer if it doesn't have to, and it freely takes advantage of
+ * {@link FileInputStream}'s trivial conversion to {@link java.nio.channels.FileChannel}.
+ */
+final class InputStreamChannel implements ReadableByteChannel {
+    private static final int MAX_TMP_BUFFER_SIZE = 16384;
+    private static final int MIN_TMP_BUFFER_SIZE = 4096;
+    private final InputStream mInputStream;
+    private final AtomicBoolean mIsOpen = new AtomicBoolean(true);
+
+    private InputStreamChannel(InputStream inputStream) {
+        this.mInputStream = inputStream;
+    }
+
+    static ReadableByteChannel wrap(InputStream inputStream) {
+        if (inputStream instanceof FileInputStream) {
+            return ((FileInputStream) inputStream).getChannel();
+        }
+        return new InputStreamChannel(inputStream);
+    }
+
+    @Override
+    public int read(ByteBuffer dst) throws IOException {
+        final int read;
+        if (dst.hasArray()) {
+            read = mInputStream.read(
+                    dst.array(), dst.arrayOffset() + dst.position(), dst.remaining());
+            if (read > 0) {
+                dst.position(dst.position() + read);
+            }
+        } else {
+            // Since we're allocating a buffer for every read, we want to choose a good size - on
+            // Android, the only case where a ByteBuffer won't have a backing byte[] is if it was
+            // created wrapping a void * in native code, or if it represents a memory-mapped file.
+            // Especially in the latter case, we want to avoid allocating a buffer that could be
+            // very large.
+            final int possibleToRead = Math.min(
+                    Math.max(mInputStream.available(), MIN_TMP_BUFFER_SIZE), dst.remaining());
+            final int reasonableToRead = Math.min(MAX_TMP_BUFFER_SIZE, possibleToRead);
+            byte[] tmpBuf = new byte[Math.min(reasonableToRead, MAX_TMP_BUFFER_SIZE)];

[pauljensen, 2015/12/14 20:02:05]

this last min() seems useless.  x = min(a, b); y = min(x, a) should be
equivalent to min(a, b)

[Charles, 2015/12/15 22:32:36]

Done.

+            read = mInputStream.read(tmpBuf);
+            if (read > 0) {
+                dst.put(tmpBuf, 0, read);
+            }
+        }
+        return read;
+    }
+
+    @Override
+    public boolean isOpen() {
+        return mIsOpen.get();
+    }
+
+    @Override
+    public void close() throws IOException {
+        if (mIsOpen.compareAndSet(true, false)) {
+            mInputStream.close();
+        }
+    }
+}