Bug 1024774 - Part 2: Implement a google::protobuf::ZeroCopyOutputStream wrapper

around nsIOutputStream; r=jimb

toolkit/devtools/server/ZeroCopyNSIOutputStream.cpp

@@ -0,0 +1,99 @@
+/* -*-  Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/devtools/ZeroCopyNSIOutputStream.h"
+
+#include "mozilla/DebugOnly.h"
+
+namespace mozilla {
+namespace devtools {
+
+ZeroCopyNSIOutputStream::ZeroCopyNSIOutputStream(nsCOMPtr<nsIOutputStream> &out)
+  : out(out)
+  , result_(NS_OK)
+  , amountUsed(0)
+  , writtenCount(0)
+{
+  DebugOnly<bool> nonBlocking = false;
+  MOZ_ASSERT(out->IsNonBlocking(&nonBlocking) == NS_OK);
+  MOZ_ASSERT(!nonBlocking);
+}
+
+ZeroCopyNSIOutputStream::~ZeroCopyNSIOutputStream()
+{
+  if (!failed())
+    NS_WARN_IF(NS_FAILED(writeBuffer()));
+}
+
+nsresult
+ZeroCopyNSIOutputStream::writeBuffer()
+{
+  if (failed())
+    return result_;
+
+  if (amountUsed == 0)
+    return NS_OK;
+
+  int32_t amountWritten = 0;
+  while (amountWritten < amountUsed) {
+    uint32_t justWritten = 0;
+
+    result_ = out->Write(buffer + amountWritten,
+                         amountUsed - amountWritten,
+                         &justWritten);
+    if (NS_WARN_IF(NS_FAILED(result_)))
+      return result_;
+
+    amountWritten += justWritten;
+  }
+
+  writtenCount += amountUsed;
+  amountUsed = 0;
+  return NS_OK;
+}
+
+// ZeroCopyOutputStream Interface
+
+bool
+ZeroCopyNSIOutputStream::Next(void **data, int *size)
+{
+  MOZ_ASSERT(data != nullptr);
+  MOZ_ASSERT(size != nullptr);
+
+  if (failed())
+    return false;
+
+  if (amountUsed == BUFFER_SIZE) {
+    if (NS_FAILED(writeBuffer()))
+      return false;
+  }
+
+  *data = buffer + amountUsed;
+  *size = BUFFER_SIZE - amountUsed;
+  amountUsed = BUFFER_SIZE;
+  return true;
+}
+
+void
+ZeroCopyNSIOutputStream::BackUp(int count)
+{
+  MOZ_ASSERT(count > 0,
+             "Must back up a positive number of bytes.");
+  MOZ_ASSERT(amountUsed == BUFFER_SIZE,
+             "Can only call BackUp directly after calling Next.");
+  MOZ_ASSERT(count <= amountUsed,
+             "Can't back up further than we've given out.");
+
+  amountUsed -= count;
+}
+
+::google::protobuf::int64
+ZeroCopyNSIOutputStream::ByteCount() const
+{
+  return writtenCount + amountUsed;
+}
+
+} // namespace devtools
+} // namespace mozilla

toolkit/devtools/server/ZeroCopyNSIOutputStream.h

@@ -0,0 +1,70 @@
+/* -*-  Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_devtools_ZeroCopyNSIOutputStream__
+#define mozilla_devtools_ZeroCopyNSIOutputStream__
+
+#include <google/protobuf/io/zero_copy_stream.h>
+#include <google/protobuf/stubs/common.h>
+
+#include "nsCOMPtr.h"
+#include "nsIOutputStream.h"
+
+namespace mozilla {
+namespace devtools {
+
+// A `google::protobuf::io::ZeroCopyOutputStream` implementation that uses an
+// `nsIOutputStream` under the covers.
+//
+// This class will automatically write and flush its data to the
+// `nsIOutputStream` in its destructor, but if you care whether that call
+// succeeds or fails, then you should call the `flush` method yourself. Errors
+// will be logged, however.
+class MOZ_STACK_CLASS ZeroCopyNSIOutputStream
+  : public ::google::protobuf::io::ZeroCopyOutputStream
+{
+  static const int BUFFER_SIZE = 8192;
+
+  // The nsIOutputStream we are streaming to.
+  nsCOMPtr<nsIOutputStream> &out;
+
+  // The buffer we write data to before passing it to the output stream.
+  char buffer[BUFFER_SIZE];
+
+  // The status of writing to the underlying output stream.
+  nsresult result_;
+
+  // The number of bytes in the buffer that have been used thus far.
+  int amountUsed;
+
+  // Excluding the amount of the buffer currently used (which hasn't been
+  // written and flushed yet), this is the number of bytes written to the output
+  // stream.
+  int64_t writtenCount;
+
+  // Write the internal buffer to the output stream and flush it.
+  nsresult writeBuffer();
+
+public:
+  explicit ZeroCopyNSIOutputStream(nsCOMPtr<nsIOutputStream> &out);
+
+  nsresult flush() { return writeBuffer(); }
+
+  // Return true if writing to the underlying output stream ever failed.
+  bool failed() const { return NS_FAILED(result_); }
+
+  nsresult result() const { return result_; }
+
+  // ZeroCopyOutputStream Interface
+  virtual ~ZeroCopyNSIOutputStream() override;
+  virtual bool Next(void **data, int *size) override;
+  virtual void BackUp(int count) override;
+  virtual ::google::protobuf::int64 ByteCount() const override;
+};
+
+} // namespace devtools
+} // namespace mozilla
+
+#endif // mozilla_devtools_ZeroCopyNSIOutputStream__

toolkit/devtools/server/moz.build

@@ -14,8 +14,13 @@ XPIDL_SOURCES += [
 
 XPIDL_MODULE = 'jsinspector'
 
+EXPORTS.mozilla.devtools += [
+    'ZeroCopyNSIOutputStream.h',
+]
+
 SOURCES += [
     'nsJSInspector.cpp',
+    'ZeroCopyNSIOutputStream.cpp',
 ]
 
 FINAL_LIBRARY = 'xul'