libbnetapi: BUrlRequest now outputs to BDataIO

Previously, BUrlRequest returns data received via a callback that can't
return any value. This approach have several issues:

- It's not possible to signify failures to the request.
- Users have to implement custom listeners just to handle the common
  case of outputting to a buffer/file/etc.
- The received data has to be serialized into BMessage when
  BUrlProtocolDispatchingListener is employed. This can cause a
  noticible slowdown in real-world scenarios as evident by #10748.

With this change, BUrlRequest will output directly into a BDataIO, which
exposes a richer API for request handlers to work with (for example a
BitTorrent client can request a BPositionIO for non-linear data
delivery), as well as simplifying common cases for users.

The adaptation only requires one additional API:
BHttpRequest::SetStopOnError(). This API simply instructs the HTTP
request handler to cancel the request if an HTTP error is occurred.

Change-Id: I4160884d77bff0e7678e0a623e2587987704443a
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3084
Reviewed-by: Adrien Destugues <[email protected]>

docs/user/netservices/UrlProtocolListener.dox

@@ -113,16 +113,18 @@
 */
 
 /*!
-	\fn virtual void BUrlProtocolListener::DataReceived(BUrlRequest* caller,
-		const char* data, off_t position, size_t size)
-	\brief Called each time a block of data is received.
+	\fn virtual void BUrlProtocolListener::BytesWritten(BUrlRequest* caller,
+		size_t size)
+	\brief Called each time a block of data is written.
+
+	This callback is called whenever a block of data is written to the
+	BDataIO associated with the request. If no BDataIO is associated, the
+	callback will not be invoked.
 
 	\b Frequency: Zero or more
 
 	\param caller The BUrlRequest that invoked this callback.
-	\param data Pointer to the data block in memory.
-	\param position Offset of the data in the stream.
-	\param size Size of the data block.
+	\param size Size of the written data block.
 */
 
 /*!
@@ -130,15 +132,17 @@
 		off_t bytesReceived, off_t bytesTotal)
 	\brief Called each time a block of data is downloaded.
 
-	This callback will usually be called after DataReceived().
+	This callback might still be invoked even when no BDataIO is associated
+	with the request, as data can still be downloaded and discarded so that the
+	request can be completed and the socket can be reused.
 
-	\b Frequency: Once or more
+	\b Frequency: Zero or more
 
 	\param caller The BUrlRequest that invoked this callback.
 	\param bytesReceived Number of data bytes received. This is the number of
 		bytes received prior to any processing and can be smaller than the
-		size of the data block sent to DataReceived() as the transport might
-		be compressed.
+		size of the data block written to the output BDataIO as the transport
+		might be compressed.
 	\param bytesTotal Total number of data bytes expected. \c 0 will be passed
 		if the total number of data bytes is not available.
 */

docs/user/netservices/UrlProtocolRoster.dox

@@ -27,10 +27,12 @@
 
 /*!
 	\fn static BUrlRequest* BUrlProtocolRoster::MakeRequest(const BUrl& url,
-		BUrlProtocolListener* listener = NULL, BUrlContext* context = NULL)
+		BDataIO* output, BUrlProtocolListener* listener = NULL,
+		BUrlContext* context = NULL)
 	\brief Create a BUrlRequest that can handle the given BUrl
 
 	\param url The URL to create a request for
+	\param output The BDataIO to output to
 	\param listener The BUrlProtocolListener to be registered with the created
 		BUrlRequest, can be \c NULL
 	\param context The BUrlContext to be registered with the created