NetBootServer

-- Better network boot host, by PaymentionOption --
VERSION = 1.0
-----------

-- NOTE:
-- All OS' must have a file titled with their name and another file titled: <osname>_version containing the version of the OS.

-- Variables --
local tOS_List = {} -- Holds all of the OS'.
-- ^^ Format: tOS_List[n] = { Name, Version, Path }
---------------

-- Drawing Functions --
-----------------------

-- File functions --
function LoadOS_List() -- Load all of the OS' and their respective information from the OS directory.
    if fs.exists( "OS_Directory" ) and fs.isDir( "OS_Directory" ) then -- If the OS directory exists.
        local tOS = fs.list( "OS_Directory" ) -- Get the contents of the OS directory.

        if #tOS % 2 == 0 then -- If the amount of files in the OS directory is even.
            local File = nil -- Setup a variable to hold a file instance.
            local FileVersion = nil -- Setup a variable to hold the version of an OS.

            for i=1, #tOS, 2 do -- Loop through all of the files in the OS directory.
                File = fs.open( "OS_Directory/" .. tOS[i+1], "r" ) -- Open the current OS version file.
                FileVersion = File.readAll() -- Get the version.
                File.close() -- Close the file instance.

                tOS_List[#tOS_List+1] = { Name = tOS[i], Version = tonumber( FileVersion ), Path = "OS_Directory/" .. tOS[i] }
                -- ^^ Add the OS to the table.
            end
        else -- If there are too many version files over OS' or vice versa.
            error( "OS Directory format error." ) -- Throw an error.
        end
    else -- If the OS directory does not exist.
        error( "OS Directory not found." ) -- Throw an error.
    end
end

function GetOS_FromFile( Index ) -- Gets the OS from the passed index and returns it as a string.
    local File = fs.open( tOS_List[Index].Path, "r" ) -- Open the OS file in read mode.
    local FileContents = File.readAll() -- Get the OS from the file into a string.
    File.close() -- Close the file.

    return FileContents -- Return the OS that was read from the file.
end
--------------------

-- Networking functions --
function OpenExistantModem() -- Opens any modem that is found on the computer. Returns false if no modem was found.
    local tSides = rs.getSides()

    for i=1, #tSides do
        if peripheral.isPresent( tSides[i] ) and peripheral.getType( tSides[i] ) == "modem" then
            rednet.open( tSides[i] )
            return true
        end
    end

    return false
end

function RespondToPings() -- Waits and responds to any ping received.
    local sender, message = rednet.receive() -- Wait forever for a message.

    if message == "PingingYou" then -- If the message was a ping.
        rednet.send( sender, "PingingYouBack" ) -- Respond to the ping to inform the user of our communication.
        return true, sender -- Return true and the sender that pinged us.
    else -- If the message was not a ping.
        return false, nil -- Return false and nil for the sender did not send a valid request.
    end
end

function SendOS_List( Reciever ) -- Sends the list of available OS'.
    local sOS_List = "" -- Setup a variable to hold all of the OS' in a string.

    for i=1, #tOS_List do -- Iterate through the OS List table.
        sOS_List = sOS_List .. tOS_List[i].Name .. "@#DS!" .. tostring( tOS_List[i].Version ) .. "@#DS!"
        -- ^^ Create the OS List string and build upon it very iteration.
    end

    rednet.send( Receiver, sOS_List ) -- Send the list to the intended receiver.
end

function SendOS( Receiver, Index ) -- Packages and sends the requested OS to the requester.
    local OS = GetOS_FromFile( Index ) -- Get the OS.

    if OS then -- If the OS is not nil.
        rednet.send( Receiver, tostring( OS ) ) -- Send the OS.
        return true -- Report a success.
    else -- If the OS is nil.
        return false -- Report a failure.
    end
end
--------------------------

-- Main Loop --
function MainLoop()
    local bPinged, Sender = RespondToPings()

    if bPinged then
        local sender, request = rednet.receive( 0.4 )
        -- Handle the request --
        if sender == Sender then
            if request == "AllPlease" then -- Get the list of OS'.
                SendOS_List( Sender )
            elseif string.find( request, "OS_Number_" ) then -- Request a specific OS.
                SendOS( Sender, tonumber( string.sub( request, 11, string.len( request ) ) ) )
            end
        else
            return
        end
        ------------------------
    else
        return
    end
end
---------------

-- The program --
if not OpenExistantModem() then
    error( "No modem found." )
end

LoadOS_List() -- Load all of the OS' in the OS directory.

while true do
    MainLoop()
end
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