Contents

• Functions
• Using callbacks
• Example client connection
• Example server implementation

This is the namespace for high-level network-related operations. Allows plugins to make TCP connections to the outside world using a callback-based API.

All functions in this namespace are static, they should be called on the cNetwork class itself:

local Server = cNetwork:Listen(1024, ListenCallbacks);

There are four different callback variants used: LinkCallbacks, LookupCallbacks, ListenCallbacks and UDPCallbacks. Each is used in the situation appropriate by its name - LinkCallbacks are used for handling the traffic on a single network link (plus additionally creation of such link when connecting as a client), LookupCallbacks are used when doing DNS and reverse-DNS lookups, ListenCallbacks are used for handling incoming connections as a server and UDPCallbacks are used for incoming UDP datagrams.

LinkCallbacks have the following structure:

local LinkCallbacks =
{
	OnConnected = function (a_TCPLink)
		-- The specified link has succeeded in connecting to the remote server.
		-- Only called if the link is being connected as a client (using cNetwork:Connect() )
		-- Not used for incoming server links
		-- All returned values are ignored
	end,
	
	OnError = function (a_TCPLink, a_ErrorCode, a_ErrorMsg)
		-- The specified error has occured on the link
		-- No other callback will be called for this link from now on
		-- For a client link being connected, this reports a connection error (destination unreachable etc.)
		-- It is an Undefined Behavior to send data to a_TCPLink in or after this callback
		-- All returned values are ignored
	end,
	
	OnReceivedData = function (a_TCPLink, a_Data)
		-- Data has been received on the link
		-- Will get called whenever there's new data on the link
		-- a_Data contains the raw received data, as a string
		-- All returned values are ignored
	end,
	
	OnRemoteClosed = function (a_TCPLink)
		-- The remote peer has closed the link
		-- The link is already closed, any data sent to it now will be lost
		-- No other callback will be called for this link from now on
		-- All returned values are ignored
	end,
}

LookupCallbacks have the following structure:

local LookupCallbacks =
{
	OnError = function (a_Query, a_ErrorCode, a_ErrorMsg)
		-- The specified error has occured while doing the lookup
		-- a_Query is the hostname or IP being looked up
		-- No other callback will be called for this lookup from now on
		-- All returned values are ignored
	end,

	OnFinished = function (a_Query)
		-- There are no more DNS records for this query
		-- a_Query is the hostname or IP being looked up
		-- No other callback will be called for this lookup from now on
		-- All returned values are ignored
	end,

	OnNameResolved = function (a_Hostname, a_IP)
		-- A DNS record has been found, the specified hostname resolves to the IP
		-- Called for both Hostname -> IP and IP -> Hostname lookups
		-- May be called multiple times if a hostname resolves to multiple IPs
		-- All returned values are ignored
	end,
}

ListenCallbacks have the following structure:

local ListenCallbacks =
{
	OnAccepted = function (a_TCPLink)
		-- A new connection has been accepted and a Link for it created
		-- It is safe to send data to the link now
		-- All returned values are ignored
	end,
	
	OnError = function (a_ErrorCode, a_ErrorMsg)
		-- The specified error has occured while trying to listen
		-- No other callback will be called for this server handle from now on
		-- This callback is called before the cNetwork:Listen() call returns
		-- All returned values are ignored
	end,

	OnIncomingConnection = function (a_RemoteIP, a_RemotePort, a_LocalPort)
		-- A new connection is being accepted, from the specified remote peer
		-- This function needs to return either nil to drop the connection,
		-- or valid LinkCallbacks to use for the new connection's TCPLink object
		return SomeLinkCallbacks
	end,
}

UDPCallbacks have the following structure:

local UDPCallbacks =
{
	OnError = function (a_ErrorCode, a_ErrorMsg)
		-- The specified error has occured when trying to listen for incoming UDP datagrams
		-- No other callback will be called for this endpoint from now on
		-- This callback is called before the cNetwork:CreateUDPEndpoint() call returns
		-- All returned values are ignored
	end,

	OnReceivedData = function (a_UDPEndpoint, a_Data, a_RemotePeer, a_RemotePort)
		-- A datagram has been received on the endpoint from the specified remote peer
		-- a_Data contains the raw received data, as a string
		-- All returned values are ignored
	end,
}

First, the callbacks are defined in a table. The OnConnected() callback takes care of sending the http request once the socket is connected. The OnReceivedData() callback sends all data to the console. The OnError() callback logs any errors. Then, the connection is initiated using the cNetwork::Connect() API function.

-- Define the callbacks to use for the client connection:
local ConnectCallbacks =
{
	OnConnected = function (a_Link)
		-- Connection succeeded, send the http request:
		a_Link:Send("GET / HTTP/1.0\r\nHost: www.google.com\r\n\r\n")
	end,
	
	OnError = function (a_Link, a_ErrorCode, a_ErrorMsg)
		-- Log the error to console:
		LOG("An error has occurred while talking to google.com: " .. a_ErrorCode .. " (" .. a_ErrorMsg .. ")")
	end,
	
	OnReceivedData = function (a_Link, a_Data)
		-- Log the received data to console:
		LOG("Incoming http data:\r\n" .. a_Data)
	end,
	
	OnRemoteClosed = function (a_Link)
		-- Log the event into the console:
		LOG("Connection to www.google.com closed")
	end,
}

-- Connect:
if not(cNetwork:Connect("www.google.com", 80, ConnectCallbacks)) then
	-- Highly unlikely, but better check for errors
	LOG("Cannot queue connection to www.google.com")
end
-- Note that the connection is being made on the background,
-- there's no guarantee that it's already connected at this point in code

First, the callbacks for the listening server are defined. The most important of those is the OnIncomingConnection() callback that must return the LinkCallbacks that will be used for the new connection. In our simple scenario each connection uses the same callbacks, so a predefined callbacks table is returned; it is, however, possible to define different callbacks for each connection. This allows the callbacks to be "personalised", for example by the remote IP or the time of connection. The OnAccepted() and OnError() callbacks only log that they occurred, there's no processing needed for them.

Finally, the cNetwork:Listen() API function is used to create the listening server. The status of the server is checked and if it is successfully listening, it is stored in a global variable, so that Lua doesn't garbage-collect it until we actually want the server closed.

-- Define the callbacks used for the incoming connections:
local EchoLinkCallbacks =
{
	OnConnected = function (a_Link)
		-- This will not be called for a server connection, ever
		assert(false, "Unexpected Connect callback call")
	end,
	
	OnError = function (a_Link, a_ErrorCode, a_ErrorMsg)
		-- Log the error to console:
		local RemoteName = "'" .. a_Link:GetRemoteIP() .. ":" .. a_Link:GetRemotePort() .. "'"
		LOG("An error has occurred while talking to " .. RemoteName .. ": " .. a_ErrorCode .. " (" .. a_ErrorMsg .. ")")
	end,
	
	OnReceivedData = function (a_Link, a_Data)
		-- Send the received data back to the remote peer
		a_Link:Send(Data)
	end,
	
	OnRemoteClosed = function (a_Link)
		-- Log the event into the console:
		local RemoteName = "'" .. a_Link:GetRemoteIP() .. ":" .. a_Link:GetRemotePort() .. "'"
		LOG("Connection to '" .. RemoteName .. "' closed")
	end,
}

-- Define the callbacks used by the server:
local ListenCallbacks =
{
	OnAccepted = function (a_Link)
		-- No processing needed, just log that this happened:
		LOG("OnAccepted callback called")
	end,
	
	OnError = function (a_ErrorCode, a_ErrorMsg)
		-- An error has occured while listening for incoming connections, log it:
		LOG("Cannot listen, error " .. a_ErrorCode .. " (" .. a_ErrorMsg .. ")"
	end,

	OnIncomingConnection = function (a_RemoteIP, a_RemotePort, a_LocalPort)
		-- A new connection is being accepted, give it the EchoCallbacks
		return EchoLinkCallbacks
	end,
}

-- Start the server:
local Server = cNetwork:Listen(9876, ListenCallbacks)
if not(Server:IsListening()) then
	-- The error has been already printed in the OnError() callbacks
	-- Just bail out
	return;
end

-- Store the server globally, so that it stays open:
g_Server = Server

...

-- Elsewhere in the code, when terminating:
-- Close the server and let it be garbage-collected:
g_Server:Close()
g_Server = nil