xref: /haiku/docs/user/book.dox (revision 1111dda699f8093bfdc9b232a919110a1c1b49a7)

/*!
	\mainpage Welcome to the Haiku Book

	Below you will find documentation on the Application Programming
	Interface (API) of the Haiku operating system. This API describes
	the internals of the operating system allowing developers to write
	native C++ applications and device drivers. See the
	<a href="https://api.haiku-os.org">online version</a> for the most
	updated version of this document. If you would like to help contribute
	contact the <a href="https://www.freelists.org/list/haiku-doc">documentation
	mailing list</a>. For guidelines on how to help document the API see
	the \link apidoc Documenting the API\endlink page. A list of
	contributors can be found \ref credits page. Documenting the API is
	an ongoing process so contributions are greatly appreciated.

	The Haiku API is based on the BeOS R5 API but changes and additions have
	been included where appropriate. Important compatibility differences are
	detailed on the \ref compatibility page. New classes and methods
	and incompatible API changes to the BeOS R5 API are noted in the
	appropriate sections.

	A complete reference to the BeOS R5 API is available on the web in
	<a href="https://haiku-os.org/legacy-docs/bebook/">The Be Book</a>.
	The Be Book is used with permission from
	<a href="https://www.access-company.com/">Access Co.</a>, the current
	owners of Be's intellectual property.

	\section book_kits Kits and Servers

	The API is split into several kits and servers each detailing a different
	aspect of the operating system.
		- The \ref app is the starting point for developing applications
			and includes classes for messaging and for interacting with
			the rest of the system.
		- The \ref game provides classes for producing game sounds and
			working with full screen apps.
		- The \ref interface is used to create responsive and attractive
			graphical user interfaces building on the messaging facilities
			provided by the Application Kit.
			- A \link interface_intro general introduction \endlink to the
				Interface Kit.
			- The \link layout_intro Layout API \endlink is a new addition
				to the Interface Kit in Haiku which provides resources to
				layout your application flexibly and easily.
		- The \ref locale includes classes to localize your application to
			different languages, timezones, number formatting conventions and
			much more.
		- The \ref mail includes classes to work with e-mail files, folders,
			protocols, and filters, as part of Haiku's unique mail handling system.
		- The \ref media provides a unified and consistent interface for media
			streams and applications to intercommunicate.
		- The \ref midi2 describes an interface to generating, processing,
			and playing music in MIDI format. For reference documentation on the
			\ref midi1 is also included.
		- The \ref network handles everything network related, from interface
			IP address settings to HTTP connections.
		- The \ref storage is a collection of classes that deal with storing and
			retrieving information from disk.
		- The \ref support contains support classes to use in your application
			including resources for thread safety, IO, and serialization.
		- The \ref translation provides a framework for converting data streams
			between media formats.

	\section book_special_topics Special Topics

	- \ref libroot
	- \ref drivers
	- \ref keyboard
	- \ref json
	- \ref netservices
*/

///// Define main kits /////

/*!
	\defgroup app Application Kit
	\brief The Application Kit is the starting point for writing native Haiku
		GUI applications.

	The application kit is exactly what its name suggests &mdash; it is the
	basis of Haiku applications. You should first read through this document
	and the references here before moving on to the other parts of the API.

	The Application Kit classes can be divided into two groups: the messaging
	classes and the system interaction classes. The larger of the two groups is
	the messaging classes. Since the Haiku API relies on pervasive
	multithreading messaging is an essential topic for any application. Have a
	look at the \link app_messaging Introduction to Messaging \endlink for more
	information.

	The following messaging classes which allow you to easily and securely
	communicate between threads.
		- BHandler
		- BInvoker
		- BLooper
		- BMessage
		- BMessageFilter
		- BMessageQueue
		- BMessageRunner
		- BMessenger

	The second group is the system interaction classes. These classes
	provide hooks for your application to interact with the rest of the system.
	The most important class in this group is BApplication. Below is a list of
	all system interaction classes:
		- BApplication
		- BClipboard
		- BCursor
		- BLaunchRoster
		- BNotification
		- BPropertyInfo
		- BRoster

	A third special category is the \link app_keystore Password and Key storage
	API:\endlink
		- BKey
		- BKeyStore


	\defgroup game Game Kit
	\brief The Game Kit provides classes for producing game sounds and
		working with full screen apps.


	\defgroup interface Interface Kit
	\brief API for displaying a graphical user interface.

	\defgroup locale Locale Kit
	\brief Collection of classes for localizing applications.

	\defgroup mail Mail Kit
	\brief API for working with e-mail messages and protocols.

	\defgroup media Media Kit
	\brief Collection of classes that deal with audio and video.

	\defgroup midi1 The old MIDI Kit (libmidi.so)
	\brief The old MIDI kit.


	\defgroup midi2 MIDI 2 Kit
	\brief The Midi Kit is the API that implements support for generating,
		processing, and playing music in MIDI format.

	<A HREF="https://www.midi.org/">MIDI</A>, which  stands for 'Musical
	Instrument Digital Interface', is a well-established  standard for
	representing and communicating musical data. This document serves as
	an overview. If you would like to see all the components, please look
	at \link midi2 the list with classes \endlink.

	\section book_midi2twokits A Tale of Two MIDI Kits

	BeOS comes with two different, but compatible Midi Kits. This
	documentation focuses on the "new" Midi Kit, or midi2 as we like to
	call it, that was  introduced with BeOS R5. The old kit, which we'll
	refer to as midi1, is more complete than the new kit, but less powerful.

	Both kits let you create so-called MIDI endpoints, but the endpoints
	from midi1 cannot be shared between different applications. The midi2
	kit solves that  problem, but unlike midi1 it does not include a General
	MIDI softsynth, nor does it have a facility for reading and playing
	Standard MIDI Files. Don't worry: both kits are compatible and you can
	mix-and-match them in your applications.

	The main differences between the two kits:
		- Instead of one BMidi object that both produces and consumes events,
			we have BMidiProducer and BMidiConsumer.
		- Applications are capable of sharing MIDI producers and consumers
			with other applications via the centralized Midi Roster.
		- Physical MIDI ports are now sharable without apps "stealing" events
			from each other.
		- Applications can now send/receive raw MIDI byte streams (useful if
			an application has its own MIDI parser/engine).
		- Channels are numbered 0&ndash;15, not 1&ndash;16
		- Timing is now specified in microseconds rather than milliseconds.

	\section book_midi2concepts Midi Kit Concepts

	A brief overview of the elements that comprise the Midi Kit:
		- \b Endpoints. This is what the Midi Kit is all about: sending MIDI
			messages between endpoints. An endpoint is like a MIDI In or MIDI
			Out socket on your equipment; it either receives information or it
			sends information. Endpoints that send MIDI events are called
			\b producers; the endpoints that receive those events are called
			\b consumers. An endpoint that is created by your own application
			is called \b local; endpoints from other applications are
			\b remote. You can access remote endpoints using \b proxies.
		- \b Filters. A filter is an object that has a consumer and a producer
			endpoint. It reads incoming events from its consumer, performs some
			operation, and tells its producer to send out the results. In its
			current form, the Midi  Kit doesn't provide any special facilities
			for writing filters.
		- \b Midi \b Roster. The roster is the list of all published producers
			and consumers. By publishing an endpoint, you allow other
			applications to talk to it. You are not required to publish your
			endpoints, in which case only your own application can use them.
		- \b Midi \b Server. The Midi Server does the behind-the-scenes work.
			It manages the roster, it connects endpoints, it makes sure that
			endpoints can communicate, and so on. The Midi Server is started
			automatically when BeOS boots, and you never have to deal with it
			directly. Just remember that it runs the show.
		- \b libmidi. The BMidi* classes live inside two shared libraries:
			libmidi.so and libmidi2.so. If you write an application that uses
			old Midi Kit, you must link it to libmidi.so. Applications that use
			the new Midi Kit must link to libmidi2.so. If you want to
			mix-and-match both kits, you should also link to both libraries.

	Here is a pretty picture:

	\image html midi2concepts.png

	\section book_midi2mediakit Midi Kit != Media Kit

	Be chose not to integrate the Midi Kit into the Media Kit as another media
	type, mainly because MIDI doesn't require any of the format negotiation that
	other media types need. Although the two kits look similar -- both have a
	"roster" for finding or registering "consumers" and "producers" -- there are
	some very important differences.

	The first and most important point to note is that BMidiConsumer and
	BMidiProducer in the Midi Kit are \b NOT directly analogous to
	BBufferConsumer and  BBufferProducer in the Media Kit! In the Media Kit,
	consumers and producers are the data consuming and producing properties
	of a media node. A filter in the Media Kit, therefore, inherits from both
	BBufferConsumer and BBufferProducer, and implements their virtual member
	functions to do its work.

	In the Midi Kit, consumers and producers act as endpoints of MIDI data
	connections, much as media_source and media_destination do in the Media Kit.
	Thus, a MIDI filter does not derive from BMidiConsumer and BMidiProducer;
	instead, it contains BMidiConsumer and BMidiProducer objects for each of its
	distinct endpoints that connect to other MIDI objects. The Midi Kit does not
	allow the use of multiple virtual inheritance, so you can't create an object
	that's both a BMidiConsumer and a BMidiProducer.

	This also contrasts with the old Midi Kit's conception of a BMidi object,
	which stood for an object that both received and sent MIDI data. In the new
	Midi Kit, the endpoints of MIDI connections are all that matters. What lies
	between the endpoints, i.e. how a MIDI filter is actually structured, is
	entirely at your discretion.

	Also, rather than use token structs like media_node to make connections
	via the MediaRoster, the new kit makes the connections directly via the
	BMidiProducer object.

	\section book_midi2remotelocal Remote vs. Local Objects

	The Midi Kit makes a distinction between remote and local MIDI objects.
	You can  only create local MIDI endpoints, which derive from either
	BMidiLocalConsumer or BMidiLocalProducer. Remote endpoints are endpoints
	that live in other applications, and you access them through BMidiRoster.

	BMidiRoster only gives you access to BMidiEndpoints, BMidiConsumers, and
	BMidiProducers. When you want to talk to remote MIDI objects, you do so
	through the proxy objects that BMidiRoster provides. Unlike
	BMidiLocalConsumer and BMidiLocalProducer, these classes do not provide a
	lot of functions. That is intentional. In order to hide the details of
	communication with MIDI endpoints in other applications, the Midi Kit must
	hide the details of how a particular endpoint is implemented.

	So what can you do with remote objects? Only what BMidiConsumer,
	BMidiProducer, and BMidiEndpoint will let you do. You can connect
	objects, get the properties of these objects -- and that's about it.

	\section book_midi2lifespan Creating and Destroying Objects

	The constructors and destructors of most midi2 classes are private,
	which means that you cannot directly create them using the C++
	<CODE>new</CODE> operator, on the  stack, or as globals. Nor can you
	<CODE>delete</CODE> them. Instead, these objects are obtained through
	BMidiRoster. The only two exceptions to this rule are BMidiLocalConsumer
	and BMidiLocalProducer. These two objects may be directly created and
	subclassed by developers.

	\section book_midi2refcount Reference Counting

	Each MIDI endpoint has a reference count associated with it, so that
	the Midi Roster can do proper bookkeeping. When you construct a
	BMidiLocalProducer or  BMidiLocalConsumer endpoint, it starts with a
	reference count of 1. In addition, BMidiRoster increments the reference
	count of any object it hands to you as a result of
	\link BMidiRoster::NextEndpoint() NextEndpoint() \endlink or
	\link BMidiRoster::FindEndpoint() FindEndpoint() \endlink.
	Once the count hits  0, the endpoint will be deleted.

	This means that, to delete an endpoint, you don't call the
	<CODE>delete</CODE>  operator directly; instead, you call
	\link BMidiEndpoint::Release() Release() \endlink.
	To balance this call, there's also an
	\link BMidiEndpoint::Acquire() Acquire() \endlink, in case you have two
	disparate parts of your application working with the endpoint, and you
	don't want to have to keep track of who needs to Release() the endpoint.

	When you're done with any endpoint object, you must Release() it.
	This is true  for both local and remote objects. Repeat after me:
	Release() when you're done.

	\section book_midi2events MIDI Events

	To make some actual music, you need to
	\link BMidiProducer::Connect() Connect() \endlink your consumers to
	your producers. Then you tell the producer to "spray" MIDI events to all
	the connected consumers. The consumers are notified of these incoming
	events through a set of hook functions.

	The Midi Kit already provides a set of commonly used spray functions,
	such as  \link BMidiLocalProducer::SprayNoteOn() SprayNoteOn() \endlink,
	\link BMidiLocalProducer::SprayControlChange() SprayControlChange()
	\endlink, and so on. These correspond one-to-one with the message types
	from the MIDI spec. You don't need to be a MIDI expert to use the kit, but
	of course some knowledge of the protocol helps. If you are really hardcore,
	you can also use the
	\link BMidiLocalProducer::SprayData() SprayData() \endlink to send raw MIDI
	events to the consumers.

	At the consumer side, a dedicated thread invokes a hook function for every
	incoming MIDI event. For every spray function, there is a corresponding hook
	function, e.g. \link BMidiLocalConsumer::NoteOn() NoteOn() \endlink and
	\link  BMidiLocalConsumer::ControlChange() ControlChange() \endlink.
	The hardcore MIDI fanatics among you will be pleased to know that you can
	also tap into the \link BMidiLocalConsumer::Data() Data() \endlink hook and
	get your hands dirty with the raw MIDI data.

	\section book_midi2time Time

	The spray and hook functions accept a bigtime_t parameter named "time". This
	indicates when the MIDI event should be performed. The time is given in
	microseconds since the computer booted. To get the current tick measurement,
	you call the system_time() function from the Kernel Kit.

	If you override a hook function in one of your consumer objects, it should
	look  at the time argument, wait until the designated time, and then perform
	its action. The preferred method is to use the Kernel Kit's
	<CODE>snooze_until()</CODE> function, which sends the consumer thread to
	sleep  until the requested time has come. (Or, if the time has already
	passed, returns immediately.)

	Like this:

	\code
void MyConsumer::NoteOn(
    uchar channel, uchar note, uchar velocity, bigtime_t time)
{
    snooze_until(time, B_SYSTEM_TIMEBASE);
    ...do your thing...
}
	\endcode

	If you want your producers to run in real time, i.e. they produce MIDI data
	that needs to be performed immediately, you should pass time 0 to the spray
	functions (which also happens to be the default value). Since time 0 has
	already passed, <CODE>snooze_until()</CODE> returns immediately, and the
	consumer will process the events as soon as they are received.

	To schedule MIDI events for a performance time that lies somewhere in the
	future, the producer must take into account the consumer's latency.
	Producers  should attempt to get notes to the consumer by or before
	<I>(scheduled_performance_time - latency)</I>. The time argument is still
	the scheduled performance time, so if your consumer has latency, it should
	snooze like this before it starts to perform the events:

	\code
snooze_until(time - Latency(), B_SYSTEM_TIMEBASE);
	\endcode

	Note that a typical producer sends out its events as soon as it can;
	unlike a consumer, it does not have to snooze.

	\section book_midi2ports Other Timing Issues

	Each consumer object uses a Kernel Kit port to receive MIDI events from
	connected producers. The queue for this port is only 1 message deep.
	This means that if the consumer thread is asleep in a
	<CODE>snooze_until()</CODE>, it will not read its port. Consequently,
	any producer that tries to write a new event to this port will block until
	the consumer thread is ready to receive a new message. This is intentional,
	because it prevents producers from generating and queueing up thousands of
	events.

	This mechanism, while simple, puts on the producer the responsibility
	for sorting the events in time. Suppose your producer sends three Note
	On events, the first on t + 0, the second on t + 4, and the third on t + 2.
	This last event won't be received until after t + 4, so it will be two ticks
	too late. If this sort of thing can happen with your producer, you should
	somehow sort the events before you spray them. Of course, if you have two or
	more producers connected to the same consumer, it is nearly impossible to
	sort this all out (pardon the pun). So it is not wise to send the same kinds
	of events from more than one producer to one consumer at the same time.

	The article Introduction to MIDI, Part 2 in <A
	HREF="https://open-beos.sourceforge.net/nsl.php?mode=display&id=36">OpenBeOS
	Newsletter 36</A> describes this problem in more detail, and provides a
	solution. Go read it now!

	\section book_midi2filters Writing a Filter

	A typical filter contains a consumer and a producer endpoint. It receives
	events from the consumer, processes them, and sends them out again using the
	producer. The consumer endpoint is a subclass of BMidiLocalConsumer, whereas
	the producer is simply a BMidiLocalProducer, not a subclass. This is a
	common  configuration, because consumers work by overriding the event hooks
	to do work  when MIDI data arrives. Producers work by sending an event when
	you call their  member functions. You should hardly ever need to derive from
	BMidiLocalProducer (unless you need to know when the producer gets connected
	or disconnected, perhaps), but you'll always have to override one or more of
	BMidiLocalConsumer's member functions to do something useful with incoming
	data.

	Filters should ignore the time argument from the spray and hook functions,
	and  simply pass it on unchanged. Objects that only filter data should
	process the  event as quickly as possible and be done with it. Do not
	<CODE>snooze_until()</CODE> in the consumer endpoint of a filter!

	\section book_midi2apidiffs API Differences

	As far as the end user is concerned, the Haiku Midi Kit is mostly the same
	as the BeOS R5 kits, although there are a few small differences in the API
	(mostly bug fixes):
		- BMidiEndpoint::IsPersistent() always returns false.
		- The B_MIDI_CHANGE_LATENCY notification is now properly sent. The Be
			kit  incorrectly set be:op to B_MIDI_CHANGED_NAME, even though the
			rest of the  message was properly structured.
		- If creating a local endpoint fails, you can still Release() the object
		  without crashing into the debugger.

	\section book_midi2seealso See also

	More about the Midi Kit:
		- \ref Midi2Defs.h
		- Be Newsletter Volume 3, Issue 47 - Motor Mix sample code
		- Be Newsletter Volume 4, Issue 3 - Overview of the new kit
		- <A HREF="https://haiku-os.org/documents/dev/introduction_to_midi_part_1">Newsletter
		  33</A>, Introduction to MIDI, Part 1
		- <A HREF="https://haiku-os.org/documents/dev/introduction_to_midi_part_2">Newsletter
		  36</A>, Introduction to MIDI, Part 2
		- Sample code and other goodies at the
		  <A HREF="https://haiku-os.org/about/teams/midi_kit">Haiku Midi Kit team page</A>

	Information about MIDI in general:
		- <A HREF="https://www.midi.org">MIDI Manufacturers Association</A>
		- <A HREF="https://www.borg.com/~jglatt/tutr/miditutr.htm">MIDI Tutorials</A>
		- <A HREF="https://www.borg.com/~jglatt/tech/midispec.htm">MIDI Specification</A>
		- <A HREF="https://www.borg.com/~jglatt/tech/midifile.htm">Standard MIDI File Format</A>
		- <A HREF="https://www.io.com/~jimm/midi_ref.html">Jim Menard's MIDI Reference</A>


	\defgroup network Network Kit
	\brief Classes that deal with all network connections and communications.

	The Haiku Network Kit consists of:
	- A modular, add-ons based network stack
	- Two shared libraries, libnetwork.so and libnetapi.so
	- A stack driver, acting as interface between the network stack and
	  libnetwork.so
	- Basic network apps
	- A modular GUI preflet

	The libnet.so shared library is the way that BeOS R5 provided POSIX/BSD
	API sockets to apps. Being binary compatible with BeOS R5 has made this
	library implementation tedious. To counter this, the libnetapi.so shared
	library was developed. It contains thin C++ classes wrapping the C
	sockets POSIX/BSD API into these BNet* classes we're used under BeOS.

	The stack driver is the interface between libnet.so and the real stack
	behind it, hosted by the network stack kernel modules. Its purposes
	include:
	-# Providing sockets to file descriptors translation support
	-# Providing support for select() on sockets
	-# Loading the network stack on first access, and then keeping it for
	   further accesses

	The following diagram illustrates the network stack design on Haiku:

	\image html obos_net_stack_design_1.gif

	The Network Kit includes a handful of useful networking related apps
	including ping, ifconfig, route, traceroute, and arp.

	See the User Guide for more information about the
	<a href="https://haiku-os.org/docs/userguide/en/preferences/network.html">Network preferences app</a>
	included as part of the Network Kit.


	\defgroup storage Storage Kit
	\brief Collection of classes that deal with storing and retrieving
		information from disk.


	\defgroup support Support Kit
	\brief Collection of utility classes that are used throughout the API.

	The Support Kit provides a handy set of classes that you can use in your
	applications. These classes provide:
		- \b Thread \b Safety. Haiku can execute multiple threads of an
			application in parallel, letting certain parts of an application
			continue when one part is stalled, as well as letting an application
			process multiple pieces of data at the same time on multicore or
			multiprocessor systems. However, there are times when multiple
			threads desire to work on the same piece of data at the same time,
			potentially causing a conflict where variables or pointers are
			changed by one thread causing another to execute incorrectly. To
			prevent this, Haiku implements a \"locking\" mechanism, allowing one
			thread to \"lock out\" other threads from executing code that might
			modify the same data.
		- \b Archiving \b and \b IO. These classes allow a programmer to
			convert objects into a form that can more easily be transferred to
			other applications or stored to disk, as well as performing basic
			input and output operations.
		- \b Memory \b Allocation. This class allows a programmer to hand off
			some of the duties of memory accounting and management.
		- \b Common \b Datatypes. To avoid unnecessary duplication of code
			and to make life easier for programmers, Haiku includes classes that
			handle management of ordered lists and strings.

	There are also a number of utility functions to time actions, play system
	alert sounds, compare strings, and atomically manipulate integers. Have a
	look at the overview, or go straight to the complete
	\link support list of components \endlink of this kit.

	\section book_overview Overview
		- Thread Safety:
			- BLocker provides a semaphore-like locking mechanism allowing for
				recursive locks.
			- BAutolock provides a simple method of automatically removing a
				lock when a function ends.
			- \ref TLS.h "Thread Local Storage" allows a global variable\'s
				content to be sensitive to thread context.
		- Archiving and IO:
			- BArchivable provides an interface for \"archiving\" objects so
				that they may be sent to other applications where an identical
				copy will be recreated.
			- BArchiver simplifies archiving of BArchivable hierarchies.
			- BUnarchiver simplifies unarchiving hierarchies that have been
				archived using BArchiver.
			- BFlattenable provides an interface for \"flattening\" objects so
				that they may be easily stored to disk.
		- BDataIO provides an interface for generalized read/write streams.
			- BPositionIO extends BDataIO to allow seeking within the data.
			- BBufferIO creates a buffer and attaches it to a BPositionIO
				stream, allowing for reduced load on the underlying stream.
			- BMemoryIO allows operation on an already-existing buffer.
			- BMallocIO creates and allows operation on a buffer.
		- Memory Allocation:
			- BBlockCache allows an application to allocate a \"pool\" of
				memory blocks that the application can fetch and dispose of as
				it pleases, letting the application make only a few large memory
				allocations, instead of many small expensive allocations.
		- Common Datatypes:
			- BList allows simple ordered lists and provides common access,
				modification, and comparison functions.
			- BString allows strings and provides common access, modification,
				and comparison functions.
		- BStopWatch allows an application to measure the time an action takes.
		- \ref support_globals "Global functions"
		- \ref TypeConstants.h "Common types and constants"
		- Error codes for all kits


	\defgroup translation Translation Kit
	\brief Provides a framework for converting data streams between media
		formats.


	\defgroup libtranslation (libtranslation.so)

	\defgroup libbe (libbe.so)


	\defgroup libroot (libroot.so)
	\brief Implements the C and POSIX standard libraries.
*/

///// Subgroups /////

/*!
	\defgroup support_globals Global functions
	\ingroup support

	\defgroup layout Layout API
	\brief Provides classes for automatically laying out UIs.
	\ingroup interface
*/


///// Special Topics /////

/*!
	\defgroup drivers Device Drivers

	\defgroup json Json Handling
	\brief Provides for parsing and writing of data in Json encoding.
*/


#if __cplusplus >= 201703L
/*!
	\defgroup netservices Experimental Network Services Support
	\brief Experimental API to do higher level network requests

	This API currently is marked as experimental. It is part of the
	<code>BPrivate::Network</code> namespace, the header files are found at
	<code>headers\\private\\netservices2</code>, and you have to link your
	application to <code>libnetservices2.a</code>. The new API is only
	available for modern platforms (x86 and x86_64), and not for the legacy
	platform (x86_gcc2). The compiler needs to support C++17 or higher.

	<h3>Asynchronous handling of the result.</h3>

	In GUI applications, networking operations are often triggered by a user action. For example,
	downloading a file will be initiated by the user clicking a button. When you initiate that
	action in the window's thread, and you block the message loop until the request is finished,
	the user will be left with a non-responsive UI. That is why one would usually run a network
	request asynchronously. And instead of checking the status every few CPU cycles, you'd want
	to be proactively informed when something important happens, like the progress of the download
	or a signal when the request is finished.

	The Network Services kit support using the Haiku API's Looper and Handler system to keep you up
	to date about relevant events that happen to the requests.

	The following messages are available for all requests (HTTP and other). The messages below are
	in the order that they will arrive (when applicable).

	<table>
		<tr>
			<th>Message Constant</th>
			<th>Description</th>
			<th>Applies to</th>
			<th> Additional Data</th>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::HostNameResolved "UrlEvent::HostNameResolved"</td>
			<td>
				The hostname has been resolved. This message is even sent when you set an
				IP-address in the URL object
			</td>
			<td>All protocols that use network connections.</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
				\ref BPrivate::Network::UrlEventData::HostName "UrlEventData::HostName"
					\ref BString
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::ConnectionOpened "UrlEvent::ConnectionOpened"</td>
			<td>
				The connection to the remote server is opened. After this event, data will be
				written.
			</td>
			<td>All protocols that use network connections.</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::UploadProgress "UrlEvent::UploadProgress"</td>
			<td>
				If there is a request body to be sent, this informs you of the progress. When the
				total size of the request body is known, this will be part of the message.
			</td>
			<td>
				All protocols that use network connections and support writing data to the server
				(like HTTP(S)).
			</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
				\ref BPrivate::Network::UrlEventData::NumBytes "UrlEventData::NumBytes"
					\c int64 <br/>
				\ref BPrivate::Network::UrlEventData::TotalBytes "UrlEventData::TotalBytes"
					\c int64 (optional)
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::ResponseStarted "UrlEvent::ResponseStarted"</td>
			<td>The server has started transmitting the response.</td>
			<td>All Protocols</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::HttpRedirect "UrlEvent::HttpRedirect"</td>
			<td>
				The network services kit is handling a HTTP redirect. The request will be repeated
				for a new URL.
			</td>
			<td>HTTP/HTTPS</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
				\ref BPrivate::Network::UrlEventData::HttpRedirectUrl
					"UrlEventData::HttpRedirectUrl" \ref BString
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::HttpStatus "UrlEvent::HttpStatus"</td>
			<td>
				The response status is available. This means it can also be accessed through
				\ref BPrivate::Network::BHttpResult::Status() "BHttpResult::Status()" without
				blocking the system.
			</td>
			<td>HTTP/HTTPS</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
				\ref BPrivate::Network::UrlEventData::HttpStatusCode "UrlEventData::HttpStatusCode"
					\c int16
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::HttpFields "UrlEvent::HttpFields"</td>
			<td>
				The HTTP header block has been fully received, and the HTTP fields can be accessed
				using \ref BPrivate::Network::BHttpResult::Fields() "BHttpResult::Fields()" without
				blocking the system.
			</td>
			<td>HTTP/HTTPS</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::DownloadProgress "UrlEvent::DownloadProgress"</td>
			<td>
				If there is a response body to be received, this informs you of the progress. If
				the total size of the body is known, this will be included in the message as well.
			</td>
			<td>All protocols that use network connections.</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
				\ref BPrivate::Network::UrlEventData::NumBytes "UrlEventData::NumBytes"
					\c int64 <br/>
				\ref BPrivate::Network::UrlEventData::TotalBytes "UrlEventData::TotalBytes"
					\c int64 (optional)
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::BytesWritten "UrlEvent::BytesWritten"</td>
			<td>
				An interim update on how many bytes have been written to the target. This message
				is only sent when you supplied a custom target to store the body of the request in.
				Note that the number of bytes written to the target may differ from the network
				transfer size, due to compression in the protocol.
			</td>
			<td>All protocols.</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
				\ref BPrivate::Network::UrlEventData::NumBytes "UrlEventData::NumBytes"
					\c int64
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::RequestCompleted "UrlEvent::RequestCompleted"</td>
			<td>
				The request is completed and all the data is written to the target, or there was
				an error.
			</td>
			<td>All protocols.</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
				\ref BPrivate::Network::UrlEventData::Success "UrlEventData::Success" \c bool
			</td>
		</tr>
		<tr>
			<td>\ref BPrivate::Network::UrlEvent::DebugMessage "UrlEvent::DebugMessage"</td>
			<td>
				Additional debug information on the request. This is enabled or disabled per
				request. See the details in the protocol description.
			</td>
			<td>All protocols.</td>
			<td>
				\ref BPrivate::Network::UrlEventData::Id "UrlEventData::Id" \c int32 <br/>
				\ref BPrivate::Network::UrlEventData::DebugType "UrlEventData::DebugType"
					\c uint32 <br/>
				\ref BPrivate::Network::UrlEventData::DebugMessage "UrlEventData::DebugMessage"
					\ref BString
			</td>
		</tr>
	</table>
*/
#endif


///// Namespace Documentation /////


//! \brief Internal or experimental API
namespace BPrivate {

#if __cplusplus >= 201703L
	/*!
		\brief Experimental Network Services API

		See \ref netservices for more information.
	*/
	namespace Network {

	}
#endif

}