server.lua

local channels = {
  atm = 1,
  db = 2,
}

os.loadAPI("/common.lua")
os.loadAPI("/sha256.lua")

local database = {}
local dbpath = "/bank.db"
local logpath = "/bank.log"
local maintenance_pass = "test"
local modem = peripheral.find("modem")

local function loadDB(path)
  local ret = {}
  if fs.exists(path) then
    local f = fs.open(path, "r")
    local c = f.readAll()
    ret = textutils.unserialise(c)
    if not ret then return false end
  end
  return ret
end
local function saveDB(path, db)
  local f = fs.open(path, "w")
  local s = textutils.serialise(db)
  f.write(s)
  f.close()
  return true
end
local function printHeader(str, ny)
  local w, h = term.getSize()
  local x, y = term.getCursorPos()
  term.setCursorPos(math.ceil(w/2) - math.floor(#str/2), ny or 1)
  term.clearLine()
  term.write(str)
  term.setCursorPos(x, y)
end
local logfile = fs.open(logpath, "a")
local function log(top, str, nosave)
  local form = (top and ("["..top.."] ") or "")..(str)
  print(form)
  printHeader("Database running with "..dbpath)
  if not nosave then
    logfile.writeLine(form)
    logfile.flush()
  end
end

database = loadDB(dbpath)
saveDB(dbpath, database)

modem.open(channels.db)
term.clear()
term.setCursorPos(1,2)
logfile.writeLine()
log("Init", "Database started")

while true do
  local event, side, chan, reply, msg = os.pullEvent()
  if event == "modem_message" and chan == channels.db and reply == channels.atm and type(msg) == "table" then

    if msg[1] == "auth" then
      local user = msg[2]:lower()
      local userdata = database[user]
      if userdata then
        modem.transmit(reply, channels.db, {true, userdata.salt})
        local resp = common.waitForMsg(reply, 2)
        if resp and resp[1] then
          local ok = resp[2] == userdata.passwd
          modem.transmit(reply, channels.db, {ok, not ok and "Wrong password" or nil})
          log("Auth", (ok and "Valid" or "Invalid").." auth: "..user)
        else log("Auth", user.." timed out")
        end
      else
        log("Auth", "User not found: "..user)
        modem.transmit(reply, channels.db, {false, "User not found"})
      end

    elseif msg[1] == "register" then
      local user = msg[2]:lower()
      local ok = true
      if user:find("%s") then ok = false log("Register", "Tried registering with a space: "..user) modem.transmit(reply, channels.db, {false, "Username cannot contain spaces"}) end
      if database[user] then ok = false log("Register", "User already exists: "..user) modem.transmit(reply, channels.db, {false, "User already exists"}) end
      if ok then
        local salt = common.genSalt(16)
        modem.transmit(reply, channels.db, {true, salt})
        local r = common.waitForMsg(reply, 2)
        if r and r[1] and type(r[2]) == "string" and #r[2] == 64 then
          database[user] = {}
          database[user].balance = 0
          database[user].passwd = r[2]
          database[user].salt = salt
          saveDB(dbpath, database)
          log("Register", user.." created")
          modem.transmit(reply, channels.db, {true})
        else
          log("Register", user.." timed out")
        end
      end

    elseif msg[1] == "balance" then
      local user = msg[2]:lower()
      local userdata = database[user]
      if msg[3] == userdata.passwd then
        modem.transmit(reply, channels.db, {true, userdata.balance})
        log("Balance", "Sent balance: "..user)
      else
        modem.transmit(reply, channels.db, {false, "Invalid hash"})
        log("Balance", "Invalid hash from: "..user)
      end

    elseif msg[1] == "transfer" then
      local user = msg[2]:lower()
      local recip = msg[4]:lower()
      local hash = msg[3]
      local amt = tonumber(msg[5]) or math.huge
      amt = math.abs(amt)
      local userdat = database[user]
      local recipdat = database[recip]
      local ok = true

      if not recipdat then ok = false log("Transfer", user.." tried to send to invalid: "..recip) modem.transmit(reply, channels.db, {false, "Recipient doesn't exist"}) end
      if userdat.passwd ~= hash then ok = false log("Transfer", "Invalid hash from: "..user) modem.transmit(reply, channels.db, {false, "Invalid hash"}) end
      if userdat.balance < amt then ok = false log("Transfer", user.." tried to send "..amt.." but has "..userdat.balance.." to "..recip) modem.transmit(reply, channels.db, {false, "Insufficent funds"}) end
      if ok then
        database[user].balance = userdat.balance - amt
        database[recip].balance = recipdat.balance + amt
        saveDB(dbpath, database)
        modem.transmit(reply, channels.db, {true, userdat.balance})
        log("Transfer", user.." transfered "..amt.." to "..recip)
      end
    end

  elseif event == "key" and side == keys.enter then
    log("Admin", "Enter password")
    write("> ")
    local pswd = read("*")
    if pswd == maintenance_pass then
      log("Admin", "Entering maintenance mode")
      while true do
        write("> ")
        local cmd = read()
        cmd = common.split(cmd, "%s")
        if cmd[1] == "set" then
          local user = cmd[2]
          local amt = tonumber(cmd[3]) or 0
          if type(user) ~= "string" or type(amt) ~= "number" then
            log("Error", "Usage: set <user> <balance>")
          else
            user = user:lower()
            if database[user] then
              database[user].balance = amt
              saveDB(dbpath, database)
              log("Admin", "Set "..user.." balance to "..amt)
            else
              log("Admin", "Cannot set balance of "..user)
            end
          end

        elseif cmd[1] == "add" then
          local user = cmd[2]
          local amt = tonumber(cmd[3]) or 0
          if type(user) ~= "string" or type(amt) ~= "number" then
            log("Error", "Usage: add <user> <amount>")
          else
            user = user:lower()
            if database[user] then
              database[user].balance = database[user].balance + amt
              saveDB(dbpath, database)
              log("Admin", (amt >= 0 and "Added " or "Removed ")..amt.." to "..user.."'s balance")
            else
              log("Admin", "Cannot add to balance of "..user)
            end
          end

        elseif cmd[1] == "create" then
          local user = cmd[2]
          if type(user) ~= "string" then
            log("Error", "Usage: create <user>")
          else
            user = user:lower()
            local ok = true
            if user:find("%s") then ok = false log("Admin", "Tried registering with a space: "..user) end
            if database[user] then ok = false log("Admin", "User already exists: "..user) end
            if ok then
              log("Admin", "Enter password: ")
              write("> ")
              local pass = read()
              local salt = common.genSalt(16)
              local hash = sha256.pbkdf2(pass, salt, 64):toHex()
              database[user] = {}
              database[user].balance = 0
              database[user].passwd = hash
              database[user].salt = salt
              saveDB(dbpath, database)
              log("Admin", user.." created")
            end
          end

        elseif cmd[1] == "delete" then
          local user = cmd[2]
          if type(user) ~= "string" then
            log("Error", "Usage: delete <user>")
          else
            user = user:lower()
            if database[user] then
              database[user] = nil
              saveDB(dbpath, database)
              log("Admin", user.." deleted from database")
            else
              log("Admin", "Tried to delete invalid user: "..user)
            end
          end

        elseif cmd[1] == "recover" then
          local user = cmd[2]
          if type(user) ~= "string" then
            log("Error", "Usage: recover <user>")
          else
            user = user:lower()
            if database[user] then
              log("Admin", "Enter new password: ")
              write("> ")
              local pass = read()
              local salt = common.genSalt(16)
              local hash = sha256.pbkdf2(pass, salt, 64):toHex()
              database[user].passwd = hash
              database[user].salt = salt
              saveDB(dbpath, database)
              log("Admin", user.." password changed")
            else
              log("Admin", user.." does not exists")
            end
          end

        elseif cmd[1] == "list" then
          local users = {}
          for user, userdat in pairs(database) do
            log(nil, user..": "..userdat.balance, true)
          end
        elseif cmd[1] == "help" then
          log(nil, "set <user> <balance> \16 Sets a user balance", true)
          log(nil, "add <user> <amount> \16 Add/Remove from user balance", true)
          log(nil, "create <user> \16 Adds account to database", true)
          log(nil, "delete <user> \16 Removes account from database", true)
          log(nil, "recover <user> \16 Changes account's password", true)
          log(nil, "list \16 Lists registered accounts", true)
          log(nil, "quit \16 Quits maintenance mode", true)
          log(nil, "stop \16 Stops the database", true)

        elseif cmd[1] == "quit" then break
        elseif cmd[1] == "stop" then return

        else log("Command", "Invalid command: "..(cmd[1] or ""), true)
        end
        repeat event, side = os.pullEvent("key") until side == keys.enter
      end
      log("Admin", "Exiting maintenance")
    else
      log("Admin", "Wrong password")
    end
  end
end
log("Admin", "Database shutting down")