commit d80a398e67e4262d73f31b794d14f2041f3efd33
Author: mawalu <web@mawalabs.de>
Date:   Sun Jan 23 18:29:13 2022 +0100

    Add question parser

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..56bf7c6
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+server
+.idea
diff --git a/lib/dns.nim b/lib/dns.nim
new file mode 100644
index 0000000..9607048
--- /dev/null
+++ b/lib/dns.nim
@@ -0,0 +1,96 @@
+from std/strutils import join
+import utils
+
+type
+  Opcode* = enum
+    QUERY = 0, IQUERY = 1, STATUS = 2
+
+type
+  Rcode* = enum
+    NO_ERROR = 0, FORMAT_ERROR = 1, SERVER_FAULURE = 2, NAME_ERROR = 3,
+    NOT_IMPLEMENTED = 4, REFUSED = 5
+
+type
+  DnsHeader* = object
+    id*: uint16
+    qr*: bool
+    opcode*: Opcode
+    aa*: bool
+    tc*: bool
+    rd*: bool
+    ra*: bool
+    z*: uint8
+    rcode*: Rcode
+    qdcount*: uint16
+    ancount*: uint16
+    nscount*: uint16
+    arcount*: uint16
+
+proc parseHeader*(data: string): DnsHeader =
+  assert len(data) >= 12
+
+  return DnsHeader(
+    id: toUInt16(data[1], data[0]),
+    qr: sliceBit(data[2], 0),
+    opcode: Opcode((toUint8(data[2]) shr 3) and 0b00001111),
+    aa: sliceBit(data[2], 5),
+    tc: sliceBit(data[2], 6),
+    rd: sliceBit(data[2], 7),
+    ra: sliceBit(data[3], 0),
+    z: (toUint8(data[3]) shr 4) and 0b00000111,
+    rcode: Rcode(toUint8(data[3]) and 0b00001111),
+    qdcount: toUint16(data[5], data[4]),
+    ancount: toUint16(data[7], data[6]),
+    nscount: toUint16(data[9], data[8]),
+    arcount: toUint16(data[11], data[10])
+  )
+
+type
+  DnsType* = enum
+    A = 1, NS = 2, MD =3, MF =4, CNAME = 5, SOA = 6, MB = 7, MG = 8,
+    MR = 9, NULL = 10, WKS = 11, PTR = 12, HINFO = 13, MINFO = 14, MX = 15,
+    TXT = 16, AXFR = 252, MAILB = 253,  MAILA = 254, ANY = 255
+
+type
+  DnsClass* = enum
+    IN = 1, CS = 2, CH = 3, HS = 4
+
+type
+  DnsQuestion* = object
+    qname*: string
+    qtype*: DnsType
+    qclass*: DnsClass
+
+proc parseQuestion*(data: string): (DnsQuestion, uint16) =
+  var qname: seq[string] = @[]
+  var len = toUint8(data[0])
+  var offset: uint16 = 1
+
+  while len > 0:
+    qname.add(data[offset .. offset + len - 1])
+
+    offset += len + 1
+    len = toUint8(data[offset - 1])
+
+  return (DnsQuestion(
+    qname: qname.join("."),
+    qtype: DnsType(toUint16(data[offset + 1], data[offset])),
+    qclass: DnsClass(toUint16(data[offset + 3], data[offset + 2]))
+  ), offset + 4)
+
+type
+  DnsRecord* = object
+    name*: string
+    rtype*: DnsType
+    class*: DnsClass
+    ttl*: uint32
+    rdlength*: uint16
+    rdata: string
+
+type
+  DnsMessage* = object
+    header*: DnsHeader
+    questions*: seq[DnsQuestion]
+    answer*: seq[DnsRecord]
+    authroity*: seq[DnsRecord]
+    additional*: seq[DnsRecord]
\ No newline at end of file
diff --git a/lib/utils.nim b/lib/utils.nim
new file mode 100644
index 0000000..368e9d0
--- /dev/null
+++ b/lib/utils.nim
@@ -0,0 +1,9 @@
+proc toUint8*(l: char): uint8 =
+  return ord(l).uint8
+
+proc toUint16*(l: char, h: char): uint16 =
+  return ord(l).uint16 or (ord(h).uint16 shl 8);
+
+proc sliceBit*(s: char, i: uint8): bool =
+  assert i < 8
+  return ((toUint8(s) shr (8 - i)) and 1) == 1
diff --git a/server.nim b/server.nim
new file mode 100644
index 0000000..291e686
--- /dev/null
+++ b/server.nim
@@ -0,0 +1,31 @@
+import asyncnet, asyncdispatch, nativesockets, strutils, lib/dns
+
+proc handleDnsRequest(data: string) =
+  let header = parseHeader(data[0 .. 11])
+  var questions: seq[DnsQuestion] = @[]
+  var offset = 12
+
+  for i in (1.uint32)..header.qdcount:
+    let (question, read) = parseQuestion(data[offset .. len(data) - 1])
+    questions.add(question)
+    offset += read.int
+
+  let msg = DnsMessage(header: header, questions: questions)
+  echo msg
+
+proc serve() {.async.} =
+  let server = newAsyncSocket(sockType=SockType.SOCK_DGRAM, protocol=Protocol.IPPROTO_UDP, buffered = false)
+  server.setSockOpt(OptReuseAddr, true)
+  server.bindAddr(Port(12345))
+
+  while true:
+    echo "start loop"
+    let request = await server.recvFrom(size=512)
+    echo "received"
+    handleDnsRequest(request.data)
+
+proc main() =
+  asyncCheck serve()
+  runForever()
+
+main()
\ No newline at end of file