enet/docs/tutorial.dox

/**
@page Tutorial Tutorial

@ref Initialization

@ref CreateServer

@ref CreateClient

@ref ManageHost

@ref SendingPacket

@ref Disconnecting

@ref Connecting

@section Initialization Initialization

You should include the file <enet/enet.h> when using ENet. Do not
include <enet.h> without the directory prefix, as this may cause
file name conflicts on some systems.

Before using ENet, you must call enet_initialize() to initialize the
library. Upon program exit, you should call enet_deinitialize() so
that the library may clean up any used resources.

@code
#include <enet/enet.h>

int 
main (int argc, char ** argv) 
{
    if (enet_initialize () != 0)
    {
        fprintf (stderr, "An error occurred while initializing ENet.\n");
        return EXIT_FAILURE;
    }
    atexit (enet_deinitialize);
    ...
    ...
    ...
}
@endcode
        
@section CreateServer Creating an ENet server

Servers in ENet are constructed with enet_host_create(). You must
specify an address on which to receive data and new connections, as
well as the maximum allowable numbers of connected peers. You may
optionally specify the incoming and outgoing bandwidth of the server
in bytes per second so that ENet may try to statically manage
bandwidth resources among connected peers in addition to its dynamic
throttling algorithm; specifying 0 for these two options will cause
ENet to rely entirely upon its dynamic throttling algorithm to manage
bandwidth.

When done with a host, the host may be destroyed with
enet_host_destroy().  All connected peers to the host will be reset,
and the resources used by the host will be freed.

@code
    ENetAddress address;
    ENetHost * server;

    /* Bind the server to the default localhost.     */
    /* A specific host address can be specified by   */
    /* enet_address_set_host (& address, "x.x.x.x"); */

    address.host = ENET_HOST_ANY;
    /* Bind the server to port 1234. */
    address.port = 1234;

    server = enet_host_create (& address /* the address to bind the server host to */, 
                                 32      /* allow up to 32 clients and/or outgoing connections */,
                                  2      /* allow up to 2 channels to be used, 0 and 1 */,
                                  0      /* assume any amount of incoming bandwidth */,
                                  0      /* assume any amount of outgoing bandwidth */);
    if (server == NULL)
    {
        fprintf (stderr, 
                 "An error occurred while trying to create an ENet server host.\n");
        exit (EXIT_FAILURE);
    }
    ...
    ...
    ...
    enet_host_destroy(server);
@endcode

@section CreateClient Creating an ENet client

Clients in ENet are similarly constructed with enet_host_create() when
no address is specified to bind the host to. Bandwidth may be
specified for the client host as in the above example. The peer count
controls the maximum number of connections to other server hosts that
may be simultaneously open.

@code
    ENetHost * client;

    client = enet_host_create (NULL /* create a client host */,
                1 /* only allow 1 outgoing connection */,
                2 /* allow up 2 channels to be used, 0 and 1 */,
                0 /* assume any amount of incoming bandwidth */,
                0 /* assume any amount of outgoing bandwidth */);

    if (client == NULL)
    {
        fprintf (stderr, 
                 "An error occurred while trying to create an ENet client host.\n");
        exit (EXIT_FAILURE);
    }
    ...
    ...
    ...
    enet_host_destroy(client);
@endcode

@section ManageHost Managing an ENet host

ENet uses a polled event model to notify the programmer of significant
events. ENet hosts are polled for events with enet_host_service(),
where an optional timeout value in milliseconds may be specified to
control how long ENet will poll; if a timeout of 0 is specified,
enet_host_service() will return immediately if there are no events to
dispatch. enet_host_service() will return 1 if an event was dispatched
within the specified timeout.

Beware that most processing of the network with the ENet stack is done 
inside enet_host_service(). Both hosts that make up the sides of a connection 
must regularly call this function to ensure packets are actually sent and
received. A common symptom of not actively calling enet_host_service()
on both ends is that one side receives events while the other does not.
The best way to schedule this activity to ensure adequate service is, for
example, to call enet_host_service() with a 0 timeout (meaning non-blocking)
at the beginning of every frame in a game loop.

Currently there are only four types of significant events in ENet:

An event of type ENET_EVENT_TYPE_NONE is returned if no event occurred
within the specified time limit. enet_host_service() will return 0
with this event.

An event of type ENET_EVENT_TYPE_CONNECT is returned when either a new client
host has connected to the server host or when an attempt to establish a 
connection with a foreign host has succeeded. Only the "peer" field of the 
event structure is valid for this event and contains the newly connected peer.

An event of type ENET_EVENT_TYPE_RECEIVE is returned when a packet is received
from a connected peer. The "peer" field contains the peer the packet was 
received from, "channelID" is the channel on which the packet was sent, and 
"packet" is the packet that was sent. The packet contained in the "packet" 
field must be destroyed with enet_packet_destroy() when you are done 
inspecting its contents.

An event of type ENET_EVENT_TYPE_DISCONNECT is returned when a connected peer
has either explicitly disconnected or timed out. Only the "peer" field of the
event structure is valid for this event and contains the peer that 
disconnected. Only the "data" field of the peer is still valid on a 
disconnect event and must be explicitly reset.

@code
    ENetEvent event;
    
    /* Wait up to 1000 milliseconds for an event. */
    while (enet_host_service (client, & event, 1000) > 0)
    {
        switch (event.type)
        {
        case ENET_EVENT_TYPE_CONNECT:
            printf ("A new client connected from %x:%u.\n", 
                    event.peer -> address.host,
                    event.peer -> address.port);

            /* Store any relevant client information here. */
            event.peer -> data = "Client information";

            break;

        case ENET_EVENT_TYPE_RECEIVE:
            printf ("A packet of length %u containing %s was received from %s on channel %u.\n",
                    event.packet -> dataLength,
                    event.packet -> data,
                    event.peer -> data,
                    event.channelID);

            /* Clean up the packet now that we're done using it. */
            enet_packet_destroy (event.packet);
            
            break;
           
        case ENET_EVENT_TYPE_DISCONNECT:
            printf ("%s disconnected.\n", event.peer -> data);

            /* Reset the peer's client information. */

            event.peer -> data = NULL;
        }
    }
    ...
    ...
    ...
@endcode

@section SendingPacket Sending a packet to an ENet peer

Packets in ENet are created with enet_packet_create(), where the size
of the packet must be specified. Optionally, initial data may be
specified to copy into the packet.

Certain flags may also be supplied to enet_packet_create() to control
various packet features:

ENET_PACKET_FLAG_RELIABLE specifies that the packet must use reliable
delivery.  A reliable packet is guaranteed to be delivered, and a
number of retry attempts will be made until an acknowledgement is
received from the foreign host the packet is sent to. If a certain
number of retry attempts is reached without any acknowledgement, ENet
will assume the peer has disconnected and forcefully reset the
connection. If this flag is not specified, the packet is assumed an
unreliable packet, and no retry attempts will be made nor
acknowledgements generated.

A packet may be resized (extended or truncated) with
enet_packet_resize().

A packet is sent to a foreign host with
enet_peer_send(). enet_peer_send() accepts a channel id over which to
send the packet to a given peer. Once the packet is handed over to
ENet with enet_peer_send(), ENet will handle its deallocation and
enet_packet_destroy() should not be used upon it.

One may also use enet_host_broadcast() to send a packet to all
connected peers on a given host over a specified channel id, as with
enet_peer_send().

Queued packets will be sent on a call to enet_host_service().
Alternatively, enet_host_flush() will send out queued packets without
dispatching any events.

@code
    /* Create a reliable packet of size 7 containing "packet\0" */
    ENetPacket * packet = enet_packet_create ("packet", 
                                              strlen ("packet") + 1, 
                                              ENET_PACKET_FLAG_RELIABLE);

    /* Extend the packet so and append the string "foo", so it now */
    /* contains "packetfoo\0"                                      */
    enet_packet_resize (packet, strlen ("packetfoo") + 1);
    strcpy (& packet -> data [strlen ("packet")], "foo");
    
    /* Send the packet to the peer over channel id 0. */
    /* One could also broadcast the packet by         */
    /* enet_host_broadcast (host, 0, packet);         */
    enet_peer_send (peer, 0, packet);
    ...
    ...
    ...
    /* One could just use enet_host_service() instead. */
    enet_host_flush (host);
@endcode

@section Disconnecting Disconnecting an ENet peer

Peers may be gently disconnected with enet_peer_disconnect(). A
disconnect request will be sent to the foreign host, and ENet will
wait for an acknowledgement from the foreign host before finally
disconnecting. An event of type ENET_EVENT_TYPE_DISCONNECT will be
generated once the disconnection succeeds. Normally timeouts apply to
the disconnect acknowledgement, and so if no acknowledgement is
received after a length of time the peer will be forcefully
disconnected.

enet_peer_reset() will forcefully disconnect a peer. The foreign host
will get no notification of a disconnect and will time out on the
foreign host. No event is generated.

@code
    ENetEvent event;
    
    enet_peer_disconnect (peer, 0);

    /* Allow up to 3 seconds for the disconnect to succeed
     * and drop any packets received packets.
     */
    while (enet_host_service (client, & event, 3000) > 0)
    {
        switch (event.type)
        {
        case ENET_EVENT_TYPE_RECEIVE:
            enet_packet_destroy (event.packet);
            break;

        case ENET_EVENT_TYPE_DISCONNECT:
            puts ("Disconnection succeeded.");
            return;
        ...
        ...
        ...
        }
    }
    
    /* We've arrived here, so the disconnect attempt didn't */
    /* succeed yet.  Force the connection down.             */
    enet_peer_reset (peer);
    ...
    ...
    ...
@endcode

@section Connecting Connecting to an ENet host

A connection to a foreign host is initiated with enet_host_connect().
It accepts the address of a foreign host to connect to, and the number
of channels that should be allocated for communication. If N channels
are allocated for use, their channel ids will be numbered 0 through
N-1.  A peer representing the connection attempt is returned, or NULL
if there were no available peers over which to initiate the
connection. When the connection attempt succeeds, an event of type
ENET_EVENT_TYPE_CONNECT will be generated. If the connection attempt
times out or otherwise fails, an event of type
ENET_EVENT_TYPE_DISCONNECT will be generated.

@code
    ENetAddress address;
    ENetEvent event;
    ENetPeer *peer;

    /* Connect to some.server.net:1234. */
    enet_address_set_host (& address, "some.server.net");
    address.port = 1234;

    /* Initiate the connection, allocating the two channels 0 and 1. */
    peer = enet_host_connect (client, & address, 2, 0);    
    
    if (peer == NULL)
    {
       fprintf (stderr, 
                "No available peers for initiating an ENet connection.\n");
       exit (EXIT_FAILURE);
    }
    
    /* Wait up to 5 seconds for the connection attempt to succeed. */
    if (enet_host_service (client, & event, 5000) > 0 &&
        event.type == ENET_EVENT_TYPE_CONNECT)
    {
        puts ("Connection to some.server.net:1234 succeeded.");
        ...
        ...
        ...
    }
    else
    {
        /* Either the 5 seconds are up or a disconnect event was */
        /* received. Reset the peer in the event the 5 seconds   */
        /* had run out without any significant event.            */
        enet_peer_reset (peer);

        puts ("Connection to some.server.net:1234 failed.");
    }
    ...
    ...
    ...
@endcode
*/