dnsserver

--DNS Server by Cynagen (for CC1.6+)

--Settings:
--Honor zone transfer requests (default: false) (Setting: true = Permit this instance of dnsserver to share records in bulk)
local allowZoneTransfers=false
--Only transfer authorized records (default: true) (Setting: false = Permit the sharing of records which were copied from other servers)
local onlyAuthZone=true

--Find and open all modems
for _,v in ipairs(peripheral.getNames()) do
  if peripheral.getType(v) == "modem" then
    rednet.open(v)
  end
end

--Configuring static host records; String(hostname)={Boolean(local),Int(computerID)}
hosts={}
if fs.exists("data/hosts") then
  file=fs.open("data/hosts","r")
  if file then
    write("Importing records...")
    imports=0
    line=""
    while true do
      line=file.readLine()
      if not line then break end
      splitAt=string.find(line,":")
      if string.len(line) > 0 and splitAt > 1 then
        hosts[tostring(string.sub(line,0,splitAt-1))]={true,tonumber(string.sub(line,splitAt+1))}
        imports=imports+1
      end
    end
    print("imported "..imports.." records")
  end
  file.close()
end

--Checking for any other root DNS servers
write("Searching for other DNS servers... ")
rednet.broadcast({root=true},"dns")
servers={}
id,msg = rednet.receive("dns",2)
while id do
  write(id.." ")
  if type(msg) == "table" and msg["root"] == true then servers[#servers+1]=id end
  id,msg = rednet.receive("dns",2)
end
print()

--Scanning other DNS servers for additional records
for _,v in ipairs(servers) do
  rednet.send(v,{zonetrans="request"},"dns")
  write("Polling server @ "..v)
  id,msg = rednet.receive("dns",2)
  if id == v and type(msg) == "table" then
    recvRecords=0
    if type(msg.zonetrans) == "table" then
      for hname,htable in pairs(msg.zonetrans) do
        if not hosts[hname] then
          htable[1]=false --Flip authoritative flag to "no" since we received a copy of this record
          hosts[hname]=htable --Inject into hosts table
          recvRecords=recvRecords+1
        end
      end
    end
    print(" - Received "..recvRecords.." records")
  end
  sleep(1)
end

--Daemon loop, listen to rednet, etc, etc...
while true do
  term.clear()
  term.setCursorPos(1,1)
  hostcount=0
  for _,_ in pairs(hosts) do hostcount=hostcount+1 end
  term.setTextColor(colors.green)
  print("Known hosts: "..hostcount)
  if hostcount > 0 then
    hostTable={}
    hostTable[#hostTable+1]=colors.white
    hostTable[#hostTable+1]={"Hostname","Address","Static"}
    i = 1
    for name,record in pairs(hosts) do
      if i == 1 then
        hostTable[#hostTable+1]=colors.lightGray
        i = 2
      else
        hostTable[#hostTable+1]=colors.gray
        i = 1
      end
      hostTable[#hostTable+1]={name,record[2],tostring(record[1])}
    end
    i = nil
    textutils.tabulate(unpack(hostTable))
  end
  id,msg = rednet.receive("dns",1)
  if id and type(msg) == "table" then
    if msg.query then
      if not hosts[msg.query.host] then
        rednet.send(id,{query=false},"dns")
      else
        rednet.send(id,{query=hosts[msg.query.host]},"dns")
      end
    elseif msg.create then
      if hosts[msg.create.host] then
        rednet.send(id,{create=false},"dns")
      else
        hosts[msg.create.host] = {false,id}
        rednet.send(id,{create=hosts[msg.create.host]},"dns")
      end
    elseif msg.remove then
      if type(hosts[msg.remove.host]) ~= "table" then
        rednet.send(id,{remove=false},"dns")
      elseif hosts[msg.remove.host][1] or hosts[msg.remove.host][2] ~= id then
        rednet.send(id,{remove=false},"dns")
      else
        hosts[msg.remove.host]=nil
        rednet.send(id,{remove={}},"dns")
      end
    elseif msg.zonetrans == "request" then
      if not allowZoneTransfers then
        rednet.send(id,{zonetrans=false},"dns")
      else
        if not onlyAuthZone then
          rednet.send(id,{zonetrans=hosts},"dns")
        else
          transfer={}
          for hostname,record in pairs(hosts) do
            if record[1] then transfer[hostname]=record end
          end
          rednet.send(id,{zonetrans=transfer},"dns")
        end
      end
    elseif msg.root then
      rednet.send(id,{root=true},"dns")
    end
  end
end