nsBaseContentStream.h

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/* -*- 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 nsBaseContentStream_h__

#define nsBaseContentStream_h__

#include "nsIAsyncInputStream.h"

#include "nsIEventTarget.h"

#include "nsCOMPtr.h"

//-----------------------------------------------------------------------------

// nsBaseContentStream is designed to be subclassed with the intention of being

// used to satisfy the nsBaseChannel::OpenContentStream method.

//

// The subclass typically overrides the default Available, ReadSegments and

// CloseWithStatus methods.  By default, Read is implemented in terms of

// ReadSegments, and Close is implemented in terms of CloseWithStatus.  If

// CloseWithStatus is overriden, then the subclass will usually want to call

// the base class' CloseWithStatus method before returning.

//

// If the stream is non-blocking, then readSegments may return the exception

// NS_BASE_STREAM_WOULD_BLOCK if there is no data available and the stream is

// not at the "end-of-file" or already closed.  This error code must not be

// returned from the Available implementation.  When the caller receives this

// error code, he may choose to call the stream's AsyncWait method, in which

// case the base stream will have a non-null PendingCallback.  When the stream

// has data or encounters an error, it should be sure to dispatch a pending

// callback if one exists (see DispatchCallback).  The implementation of the

// base stream's CloseWithStatus (and Close) method will ensure that any

// pending callback is dispatched.  It is the responsibility of the subclass

// to ensure that the pending callback is dispatched when it wants to have its

// ReadSegments method called again.

class nsBaseContentStream : public nsIAsyncInputStream {

 public:

  NS_DECL_THREADSAFE_ISUPPORTS

  NS_DECL_NSIINPUTSTREAM

  NS_DECL_NSIASYNCINPUTSTREAM

  explicit nsBaseContentStream(bool nonBlocking)

      : mStatus(NS_OK), mNonBlocking(nonBlocking) {}

  nsresult Status() { return mStatus; }

  bool IsNonBlocking() { return mNonBlocking; }

  bool IsClosed() { return NS_FAILED(mStatus); }

  // Called to test if the stream has a pending callback.

  bool HasPendingCallback() { return mCallback != nullptr; }

  // The current dispatch target (may be null) for the pending callback if any.

  nsIEventTarget* CallbackTarget() { return mCallbackTarget; }

  // Called to dispatch a pending callback.  If there is no pending callback,

  // then this function does nothing.  Pass true to this function to cause the

  // callback to occur asynchronously; otherwise, the callback will happen

  // before this function returns.

  void DispatchCallback(bool async = true);

  // Helper function to make code more self-documenting.

  void DispatchCallbackSync() { DispatchCallback(false); }

 protected:

  virtual ~nsBaseContentStream() = default;

 private:

  // Called from the base stream's AsyncWait method when a pending callback

  // is installed on the stream.

  virtual void OnCallbackPending() {}

 private:

  nsCOMPtr<nsIInputStreamCallback> mCallback;

  nsCOMPtr<nsIEventTarget> mCallbackTarget;

  nsresult mStatus;

  bool mNonBlocking;

};

#endif  // nsBaseContentStream_h__