[android_webview] Don't block the IO thread when reading from an InputStream.

android_webview/native/input_stream_reader.cc

+// Copyright (c) 2012 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.
+
+#include "android_webview/native/input_stream_reader.h"
+
+#include "android_webview/native/input_stream.h"
+#include "base/message_loop.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/base/net_errors.h"
+#include "net/http/http_byte_range.h"
+

[joth, 2012/11/07 16:55:38]

ISTM this class is now fairly well abstracted from the JNI goop so could live in
aw/browser (if we also define a input_stream abstract base class in there).

[mkosiba (inactive), 2012/11/15 19:18:50]

Done.

+using base::android::AttachCurrentThread;
+using content::BrowserThread;
+
+namespace android_webview {
+
+InputStreamReader::InputStreamReader(
+    android_webview::InputStream* stream)
+    : stream_(stream) {
+  DCHECK(stream);
+}
+
+InputStreamReader::~InputStreamReader() {
+}
+
+void InputStreamReader::Seek(net::HttpByteRange byte_range,
+                             net::CompletionCallback on_seek_completion) {
+  JNIEnv* env = AttachCurrentThread();
+  int content_size = 0;
+  DCHECK(env);
+
+  int error_code = VerifyRequestedRange(env, &byte_range, &content_size);
+  if (error_code != net::OK) {
+    PostCompletionCallback(on_seek_completion, error_code);
+    return;
+  }
+
+  error_code = SkipToRequestedRange(env, byte_range);
+  if (error_code != net::OK) {
+    PostCompletionCallback(on_seek_completion, error_code);
+    return;
+  }
+
+  DCHECK_GE(content_size, 0);
+  PostCompletionCallback(on_seek_completion, content_size);
+}
+
+void InputStreamReader::ReadRawData(
+    net::IOBuffer* dest,
+    int dest_size,
+    net::CompletionCallback on_read_completion) {
+  if (!dest_size) {
+    PostCompletionCallback(on_read_completion, 0);
+    return;
+  }
+
+  JNIEnv* env = AttachCurrentThread();
+  DCHECK(env);
+  DCHECK_GT(dest_size, 0);
+
+  int bytes_read = 0;
+  if (!stream_->Read(env, dest, dest_size, &bytes_read))
+    PostCompletionCallback(on_read_completion, net::ERR_FAILED);
+  else
+    PostCompletionCallback(on_read_completion, bytes_read);
+}
+
+int InputStreamReader::VerifyRequestedRange(
+    JNIEnv* env,
+    net::HttpByteRange* byte_range,
+    int* content_size) {
+  DCHECK(content_size);
+  int32_t size = 0;
+  if (!stream_->BytesAvailable(env, &size)) {
+    return net::ERR_FAILED;
+  }
+
+  if (size <= 0)
+    return net::OK;
+
+  // Check that the requested range was valid.
+  if (!byte_range->ComputeBounds(size)) {
+    return net::ERR_REQUEST_RANGE_NOT_SATISFIABLE;
+  }
+
+  size = byte_range->last_byte_position() -
+         byte_range->first_byte_position() + 1;
+  DCHECK_GE(size, 0);
+  *content_size = size;
+
+  return net::OK;
+}
+
+int InputStreamReader::SkipToRequestedRange(
+    JNIEnv* env,
+    const net::HttpByteRange& byte_range) {
+  // Skip to the start of the requested data. This has to be done in a loop
+  // because the underlying InputStream is not guaranteed to skip the requested
+  // number of bytes.
+  if (byte_range.IsValid() && byte_range.first_byte_position() != 0) {
+    int64_t skipped, bytes_to_skip = byte_range.first_byte_position();
+    do {
+      if (!stream_->Skip(env, bytes_to_skip, &skipped)) {
+        return net::ERR_FAILED;
+      }
+      if (skipped <= 0) {
+        return net::ERR_REQUEST_RANGE_NOT_SATISFIABLE;
+      }
+    } while ((bytes_to_skip -= skipped) > 0);
+  }
+  return net::OK;
+}
+
+void InputStreamReader::PostCompletionCallback(
+    const net::CompletionCallback& callback,
+    int result) {
+  BrowserThread::PostTask(BrowserThread::IO,

[joth, 2012/11/07 16:55:38]

this class is a little bit shady, that you can call into it on "any" arbitrary
(single) thread, but it will always call you back on the IO thread.
I'd rather we make it symmetrical and put all the thread-hopping in one place -
either inside or outside this thread, not sure which I prefer.

[benm (inactive), 2012/11/15 17:39:01]

Agree, it'd be nice if you're always called back on the thread that you call
into it from. So here we'd hop back to the worker thread, and the worker thread
would transfer to the IO thread? Comments in the header would be simpler too.

WDYT?

[mkosiba (inactive), 2012/11/15 19:18:50]

Done.

+                          FROM_HERE,
+                          base::Bind(callback, result));
+}
+
+} // namespace android_webview