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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 UrlListener_h__
#define UrlListener_h__
#include <functional> // For std::function.
#include "nsIUrlListener.h"
class nsIURI;
/**
* UrlListener is a small nsIUrlListener implementation which allows
* callable objects (including lambdas) to be plugged in instead of deriving
* your own nsIUrlListener.
*
* The aim is to encourage more readable code by allowing the start/stop
* notifications of a long-running operation to be handled near to where the
* operation was initiated.
*
* A contrived example:
*
* void Kick() {
* UrlListener* listener = new UrlListener;
* listener->mStopFn = [](nsIURI* url, nsresult status) -> nsresult {
* // Note that we may get here waaaaaaay after Kick() has returned...
* printf("LongRunningOperation is finished.\n");
* return NS_OK;
* };
* thingService.startLongRunningOperation(listener);
* //...continue doing other stuff while operation is ongoing...
* }
*
* Traditionally, c-c code has tended to use multiple inheritance to add
* listener callbacks to the class of the object initiating the operation.
* This has a couple of undesirable side effects:
*
* 1) It separates out the onStopRunningUrl handling into some other
* part of the code, which makes the order of things much harder to follow.
* 2) Often the same onStopRunningUrl handler will be used for many different
* kinds of operations (see nsImapMailFolder::OnStopRunningUrl(), for
* example).
* 3) It exposes implementation details as part of the public interface
* e.g see all the listener types nsMsgDBFolder derives from to implement
* it's internals. That's all just confusing noise that shouldn't be seen
* from outside the class.
*
* Just as PromiseTestUtils.jsm brings the Javascript side up from callback
* hell to async lovelyness, this can be used to raise the C++ side from
* callback-somewhere-else-maybe-in-this-class-but-who-can-really-tell hell
* up to normal callback hell :-)
*
*/
class UrlListener : public nsIUrlListener {
public:
NS_DECL_ISUPPORTS
NS_DECL_NSIURLLISTENER
UrlListener() {}
/**
* mStartFn and mStopFn are the OnStartRunning() and OnStopRunningUrl()
* handlers. It's fine for them to be null (often you'll only need mStopFn).
*/
std::function<nsresult(nsIURI*)> mStartFn;
std::function<nsresult(nsIURI*, nsresult)> mStopFn;
protected:
virtual ~UrlListener() {}
};
#endif // UrlListener_h__
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