LAN Remote Shell

local tArgs = { ... } -- Capture arguments inputted at the top level shell.
--[[
        LAN Cable Remote Shell          PaymentOption
                                        Black Wolf Server
                                        27 November 2012

        This program allows for the connection of one
        computer to another and redirecting terminal
        output to the receving machine. Both the receiving
        machine and transmitting machine will be able
        to provide input to the transmitting machine
        through this program.

        Remember, this program will NOT check if the connection is secure
        or the receiver/transmitter is still running this program. It is
        the responisibility of the user to be aware of this information.
        Results of the aforementioned situation are unknown, so be careful.
]]--

--[[
local shellThread = coroutine.create(function() shell.run("rom/programs/shell") end)
coroutine.resume(shellThread)
while true do
        local event = {os.pullEvent()} -- Get an event from the system.
        coroutine.resume(shellThread, unpack(event)) -- Resume the shell using the event that was given.
end
]]--

local connection = {} -- This will be the connection table for the connection that
                      -- is made to this particular computer.
local session = {}    -- This will be the shell session that has been started
                      -- over the starting shell that will capture and
                      -- resend events to the receiving computer.
local lanCable = nil  -- This will be the wrapped lan cable.
local lanCableSide = nil -- This will be the side on which the lan cable exists.
local receiving = false -- Whether or not this particular computer is receiving
                        -- the terminal output or is transmitting it.



-- Parses the arguments passed from the top level shell. The proper useage
-- of the program is printed if the arguments are in some way incorrect.
-- Params : nil
-- Returns: true or false - Depending on whehter or not the arguments were correct.
function processArguments()
        if #tArgs == 2 then
                if tArgs[1] == "transmit" or tArgs[1] == "receive" then
                        if tArgs[1] == "receive" then
                                receiving = true
                        end

                        if tonumber(tArgs[2]) then
                                connection.id = tonumber(tArgs[2])
                                return true
                        end
                end
        end

        print("Useage: " .. fs.getName(shell.getRunningProgram()) .. " <transmit/receive> <connectionID>")
        return false
end

-- Attempts to locate a lan cable on any side of this particular computer.
-- This function will wrap the lan cable if one is found and return it, along
-- with the side the cable was found on.
-- Params : nil
-- Returns: lanCable, lanCableSide - The wrapped lan cable and the side its on.
function locateAndWrapLanCable()
        local sides = rs.getSides()
        for sideIndex, side in ipairs(sides) do
                if peripheral.getType(side) == "cable" then
                        return peripheral.wrap(side), side
                end
        end

        -- No lan cable found.
        return nil, nil
end

-- Sends an event over the lan cable to the transmitting computer.
-- Params : id, event - The id of the transmitter and the event to be sent in
--                      table format.
-- Returns: nil
function sendEventToTransmitter(id, event)
        lanCable.send(id, textutils.serialize(event))
end

-- Waits for a lan message forever, or until the given amount of time has
-- elapsed.
-- Params : time - The amount of time to be waited for, if any.
-- Returns: id, message or nil, nil - The id of the sender of the message, and
--                                    the message sent if any was found.
function receiveOverLan(time)
        -- Set up a listening timeout timer in the case that we
        -- have been provided with a timeout.
        if time then
                local listenTimeout = os.startTimer(time)
        end

        while true do
                local event, id, message = os.pullEvent()

                if event == "cable_message" then
                        return id, message
                elseif event == "timer" and id == listenTimeout then
                        return nil, nil
                end
        end
end

-- Creates a new local shell session in a thread.
-- Params : nil
-- Returns: shellThread
function newShellThread()
        local shellThread = coroutine.create(function() shell.run("rom/programs/shell") end)
        return shellThread
end

-- Wraps all of the native terminal functions into new functionst that will
-- transmit themselves over lan to the receiving computer in a serialized table.
-- Params : nil
-- Returns: wrappedTerminal - The new native terminal functions that redirect output.
function wrapNativeTerminalFunctions()
        local oldTerminal = {}
        local wrappedTerminal = {}

        local function wrapFunction(functionName)
                return function( ... )
                        lanCable.send(connection.id, textutils.serialize({functionName = functionName, params = { ... }}))
                        return oldTerminal[functionName]( ... )
                end
        end

        for functionName, functionObject in pairs(term.native) do
                oldTerminal[functionName] = functionObject
        end

        for functionName, functionObject in pairs(term.native) do
                wrappedTerminal[functionName] = wrapFunction(functionName)
        end

        return wrappedTerminal
end

-- Transmits information from this particular computer to the receiving computer
-- over lan in a serialized table. Also, this program handles the output on the
-- terminal after the computer has wrapped the native terminal output to be
-- sent over lan.
-- Params : nil
-- Returns: nil
function transmitTerminalOutput()
        -- Wrap all of the native terminal functions into a new table that
        -- will transmit their information to the receiving machine. Then
        -- redirect terminal output through aforementioned table.
        local redirectedTerminal = wrapNativeTerminalFunctions()
        term.redirect(redirectedTerminal)

        -- Create a new shell instance and resume it, all the while handling
        -- messages passed from the receiving computer.
        local shellThread = newShellThread()
        coroutine.resume(shellThread)

        while true do
                -- Wait for an event and handle it accordingly. Use a table to
                -- capture all parameters returned by any event.
                local event = {os.pullEvent()}

                -- If the event was a cable message, then go ahead and check
                -- to see if it was from the receiving machine. In the case
                -- that it is, then handle it like an event.
                if event[1] == "cable_message" and event[2] == connection.id then
                        event = textutils.unserialize(event[3])
                        -- The message should have been an event table. Swap
                        -- the sent event for the current one and update the
                        -- screen.
                end

                -- Update the current shell thread with the event that was
                -- captured this iteration.
                coroutine.resume(shellThread, unpack(event))
        end
end

-- Receives terminal output from the transmitting machine and draws it to the
-- screen. This function also handles local events and redirects them to the
-- transmitting machine. However, rednet events are not redirected, nor are
-- lan cable events to prevent confusion on the transmitter's side.
-- Params : nil
-- Returns: nil
function receiveTerminalOutput()
        -- Runs any function from the transmitting machine from within the
        -- native terminal functions.
        local function runTerminalFunction(functionTable)
                if term.native[functionTable.functionName] then
                        return term.native[functionTable.functionName](unpack(functionTable.params))
                end
        end

        -- Create a new shell instance and resume it, all the while handling
        -- messages passed from the transmitting computer. Also, send
        -- user interaction events that are passsed.
        local shellThread = newShellThread()
        coroutine.resume(shellThread)

        while true do
                -- Wait for an event and handle it accordingly. Use a table to
                -- capture all parameters returned by any event.
                local event = {os.pullEvent()}

                -- Discard rednet events.
                if event[1] == "rednet_message" then
                        event = {}
                else
                        -- If the event was a cable message from the transmitting computer,
                        -- then go ahead and attempt to process it as a function call.
                        if event[1] == "cable_message" and event[2] == connection.id then
                                -- Get the function table from the message by
                                -- unserializing the message, then execute it.
                                local functionTable = textutils.unserialize(event[3])
                                runTerminalFunction(functionTable)
                        -- Any other event can be serialized and sent to the
                        -- transmitting machine.
                        else
                                lanCable.send(connection.id, textutils.serialize(event))
                        end
                end

                -- Update the current shell thread with the event that was
                -- captured this iteration.
                -- coroutine.resume(shellThread, unpack(event))
        end
end

-- Proccess the given arguments to make sure the program has the necessary information
-- to execute properly.
if not processArguments() then
        return
end
-- Attempt to locate and wrap any land cable that can be found.
lanCable, lanCableSide = locateAndWrapLanCable()
if not lanCable or not lanCableSide then
        print("No lan cable found.")
        return
end

-- If we are not to be the receiving computer, then begin transmitting terminal
-- output to the receiving computer and listen for events from the receiving computer.
if not receiving then
        transmitTerminalOutput()
else
        receiveTerminalOutput()
end