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

android_webview/native/input_stream_impl.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_impl.h"
+
+#include "base/android/jni_android.h"
+#include "net/base/io_buffer.h"
+// Disable "Warnings treated as errors" for input_stream_jni as it's a Java
+// system class and we have to generate C++ hooks for all methods in the class
+// even if they're unused.
+#pragma GCC diagnostic ignored "-Wunused-function"
+#include "jni/InputStream_jni.h"
+
+using base::android::ClearException;
+using base::android::JavaRef;
+using JNI_InputStream::Java_InputStream_available;
+using JNI_InputStream::Java_InputStream_skip;
+using JNI_InputStream::Java_InputStream_readI_AB_I_I;
+
+namespace android_webview {
+
+bool RegisterInputStream(JNIEnv* env) {
+  return JNI_InputStream::RegisterNativesImpl(env);
+}
+
+// Maximum number of bytes to be read in a single read.
+const int InputStreamImpl::kBufferSize = 4096;
+
+//static
+const InputStreamImpl* InputStreamImpl::FromInputStream(
+        const InputStream* input_stream) {
+    return reinterpret_cast<const InputStreamImpl*>(input_stream);

[mkosiba (inactive), 2012/11/15 19:18:51]

so according to the standard this is undefined behavior, and the alternative is
to add the jobj() getter to the browser/input_stream.h interface.

[joth, 2012/11/15 20:04:26]

use a static_cast, and it's totally legit (unless I'm missing something).
See also http://go/down_cast (unfortunately we don't have one of those as we
don't have rtti even in debug builds, afaik)

[mkosiba (inactive), 2012/11/16 14:47:01]

duh.. I tried using a static_cast before and gcc complained about not being able
to cast one pointer to the other. I tried it now and it works fine... I guess I
was missing some type definitions or something..

+}
+
+InputStreamImpl::InputStreamImpl() {
+}
+
+InputStreamImpl::InputStreamImpl(const JavaRef<jobject>& stream)
+    : jobject_(stream) {
+  DCHECK(!stream.is_null());
+}
+
+InputStreamImpl::~InputStreamImpl() {
+}
+
+bool InputStreamImpl::BytesAvailable(JNIEnv* env,
+                                     int* bytes_available) const {
+  // TODO: Use unsafe version once BUG 157880 is fixed.
+  int bytes = Java_InputStream_available(env, jobject_.obj());
+  if (ClearException(env))
+    return false;
+  *bytes_available = bytes;
+  return true;
+}
+
+bool InputStreamImpl::Skip(JNIEnv* env,
+                           int64_t n,
+                           int64_t* bytes_skipped) {
+  // TODO: Use unsafe version once BUG 157880 is fixed.
+  int bytes = Java_InputStream_skip(env, jobject_.obj(), n);
+  if (ClearException(env))
+    return false;
+  *bytes_skipped = bytes;
+  return true;
+}
+
+bool InputStreamImpl::Read(JNIEnv* env,
+                           net::IOBuffer* dest,
+                           int length,
+                           int* bytes_read) {
+  if (!buffer_.obj()) {
+    // Allocate transfer buffer.
+    buffer_.Reset(env, env->NewByteArray(kBufferSize));
+    if (ClearException(env))
+      return false;
+  }
+
+  jbyteArray buffer = buffer_.obj();
+  int read_size = std::min(length, kBufferSize);
+  *bytes_read = 0;
+
+  while (length > 0) {
+    int32_t byte_count =
+      Java_InputStream_readI_AB_I_I(
+          env, jobject_.obj(), buffer, 0, read_size);
+
+    if (ClearException(env))
+      return false;
+
+    if (byte_count <= 0)
+      break;
+
+#ifndef NDEBUG
+    int32_t buffer_length = env->GetArrayLength(buffer);
+    DCHECK_GE(read_size, byte_count);
+    DCHECK_GE(buffer_length, byte_count);
+#endif // NDEBUG
+
+    // Copy the data over to the provided C++ side buffer.
+    DCHECK_GE(length, byte_count);
+    env->GetByteArrayRegion(buffer, 0, byte_count,
+        reinterpret_cast<jbyte*>(dest->data() + *bytes_read));
+    if (ClearException(env))
+      return false;
+
+    *bytes_read += byte_count;
+    length -= byte_count;
+  }
+  return true;
+}
+
+} // namespace android_webview