Implement basic query handling
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198
lib/dns.nim
198
lib/dns.nim
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@ -1,4 +1,5 @@
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from std/strutils import join
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from std/strutils import join, split
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import std/sequtils
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import utils
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type
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@ -10,10 +11,30 @@ type
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NO_ERROR = 0, FORMAT_ERROR = 1, SERVER_FAULURE = 2, NAME_ERROR = 3,
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NOT_IMPLEMENTED = 4, REFUSED = 5
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type
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DnsType* = enum
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A = 1, NS = 2, MD = 3, MF =4, CNAME = 5, SOA = 6, MB = 7, MG = 8,
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MR = 9, NULL = 10, WKS = 11, PTR = 12, HINFO = 13, MINFO = 14, MX = 15,
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TXT = 16, AXFR = 252, MAILB = 253, MAILA = 254, ANY = 255
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type
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DnsClass* = enum
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IN = 1, CS = 2, CH = 3, HS = 4
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type
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DnsQr* = enum
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REQUEST = false, RESPONSE = true
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type
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DnsQuestion* = object
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qname*: string
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qtype*: DnsType
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qclass*: DnsClass
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type
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DnsHeader* = object
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id*: uint16
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qr*: bool
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qr*: DnsQr
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opcode*: Opcode
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aa*: bool
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tc*: bool
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@ -26,12 +47,55 @@ type
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nscount*: uint16
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arcount*: uint16
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proc parseHeader*(data: string): DnsHeader =
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type
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DnsRecord* = object
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name*: string
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rtype*: DnsType
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class*: DnsClass
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ttl*: uint32
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rdlength*: uint16
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rdata*: string
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type
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DnsMessage* = object
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header*: DnsHeader
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questions*: seq[DnsQuestion]
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answer*: seq[DnsRecord]
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authroity*: seq[DnsRecord]
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additional*: seq[DnsRecord]
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func parseNameField*(data: string, startOffset: uint16): (seq[string], uint16) =
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var names: seq[string] = @[]
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var len = toUint8(data[startOffset])
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var offset: uint16 = startOffset + 1
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while len > 0:
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names.add(data[offset .. offset + len - 1])
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offset += len + 1
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len = toUint8(data[offset - 1])
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return (names, offset)
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func packNameField*(input: string): string =
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let names = input.split(".")
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var finalName = newStringofCap(len(input) + 1)
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for name in names:
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finalName.add(chr(len(name)))
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finalName = finalName & name
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if len(finalName) mod 2 != 0:
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finalName.add(chr(0))
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return finalName
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func parseHeader*(data: string): DnsHeader =
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assert len(data) >= 12
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return DnsHeader(
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id: toUInt16(data[1], data[0]),
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qr: sliceBit(data[2], 0),
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qr: DnsQr(sliceBit(data[2], 0)),
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opcode: Opcode((toUint8(data[2]) shr 3) and 0b00001111),
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aa: sliceBit(data[2], 5),
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tc: sliceBit(data[2], 6),
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@ -45,52 +109,104 @@ proc parseHeader*(data: string): DnsHeader =
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arcount: toUint16(data[11], data[10])
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)
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type
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DnsType* = enum
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A = 1, NS = 2, MD =3, MF =4, CNAME = 5, SOA = 6, MB = 7, MG = 8,
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MR = 9, NULL = 10, WKS = 11, PTR = 12, HINFO = 13, MINFO = 14, MX = 15,
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TXT = 16, AXFR = 252, MAILB = 253, MAILA = 254, ANY = 255
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func packHeader*(data: DnsHeader): string =
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var header = newStringOfCap(12)
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type
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DnsClass* = enum
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IN = 1, CS = 2, CH = 3, HS = 4
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header.add(uint16ToString(data.id))
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header.add(chr(
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(data.qr.uint8 shl 7) or
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(data.opcode.uint8 shl 3) or
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(data.aa.uint8 shl 2) or
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(data.tc.uint8 shl 1) or
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data.rd.uint8
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))
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type
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DnsQuestion* = object
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qname*: string
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qtype*: DnsType
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qclass*: DnsClass
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header.add(chr(
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(data.ra.uint8 shl 7) or
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(data.z.uint8 shl 4) or
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data.rcode.uint8
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))
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proc parseQuestion*(data: string): (DnsQuestion, uint16) =
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var qname: seq[string] = @[]
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var len = toUint8(data[0])
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var offset: uint16 = 1
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header.add(uint16ToString(data.qdcount))
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header.add(uint16ToString(data.ancount))
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header.add(uint16ToString(data.nscount))
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header.add(uint16ToString(data.arcount))
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while len > 0:
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qname.add(data[offset .. offset + len - 1])
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return header
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offset += len + 1
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len = toUint8(data[offset - 1])
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func parseQuestion*(data: string, startOffset: uint16): (DnsQuestion, uint16) =
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let (qnames, offset) = parseNameField(data, startOffset)
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return (DnsQuestion(
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qname: qname.join("."),
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qname: qnames.join("."),
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qtype: DnsType(toUint16(data[offset + 1], data[offset])),
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qclass: DnsClass(toUint16(data[offset + 3], data[offset + 2]))
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), offset + 4)
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type
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DnsRecord* = object
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name*: string
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rtype*: DnsType
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class*: DnsClass
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ttl*: uint32
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rdlength*: uint16
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rdata: string
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# BROKEN
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func parseResourceRecord*(data: string, startOffset: uint16): (DnsRecord, uint16) =
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let (names, offset) = parseNameField(data, startOffset)
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let dataLength = toUint16(data[offset + 9], data[offset + 8])
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type
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DnsMessage* = object
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header*: DnsHeader
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questions*: seq[DnsQuestion]
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answer*: seq[DnsRecord]
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authroity*: seq[DnsRecord]
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additional*: seq[DnsRecord]
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return (DnsRecord(
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name: names.join("."),
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rtype: DnsType(toUint16(data[offset + 1], data[offset])),
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class: DnsClass(toUint16(data[offset + 3], data[offset + 2])),
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ttl: toUint32(data[offset + 5], data[offset + 4], data[offset + 7], data[offset + 6]),
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rdlength: dataLength,
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rdata: data[offset + 10 .. offset + 10 + dataLength]
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), offset)
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func packResourceRecord*(data: DnsRecord): string =
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var record = ""
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record.add(packNameField(data.name))
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record.add(uint16ToString(data.rtype.uint16))
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record.add(uint16ToString(data.class.uint16))
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record.add(uint32ToString(data.ttl.uint32))
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record.add(uint16ToString(data.rdlength.uint16))
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record.add(data.rdata)
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return record
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func parseMessage*(data: string): DnsMessage =
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let header = parseHeader(data[0 .. 11])
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var questions: seq[DnsQuestion] = @[]
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var offset: uint16 = 12
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for i in (1.uint32)..header.qdcount:
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let parsed = parseQuestion(data, offset)
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questions.add(parsed[0])
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offset = parsed[1]
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return DnsMessage(header: header, questions: questions)
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func packMessage*(message: DnsMessage): string =
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var encoded = packHeader(message.header)
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for answer in message.answer:
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encoded.add(packResourceRecord(answer))
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return encoded
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func mkRecord*(rtype: DnsType, question: string, answer: string): DnsRecord =
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return DnsRecord(
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name: question,
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rtype: rtype,
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class: DnsClass.IN,
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ttl: 60,
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rdLength: (if rtype == DnsType.TXT: len(answer) + 1 else: len(answer)).uint16,
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rdata: (if rtype == DnsType.TXT: chr(len(answer)) & answer else: answer)
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)
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func mkResponse*(id: uint16, question: DnsQuestion, answer: seq[string]): DnsMessage =
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return DnsMessage(
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header: DnsHeader(
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id: id,
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qr: DnsQr.RESPONSE,
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aa: true,
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rcode: Rcode.NO_ERROR,
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ancount: len(answer).uint16
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),
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answer: answer.map(proc (a: string): DnsRecord = mkRecord(question.qtype, question.qname, a))
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)
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@ -1,9 +1,18 @@
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proc toUint8*(l: char): uint8 =
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func toUint8*(l: char): uint8 =
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return ord(l).uint8
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proc toUint16*(l: char, h: char): uint16 =
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func toUint16*(l: char, h: char): uint16 =
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return ord(l).uint16 or (ord(h).uint16 shl 8);
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proc sliceBit*(s: char, i: uint8): bool =
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func uint16ToString*(n: uint16): string =
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return chr(n shr 8) & chr(n and 0b11111111)
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func toUint32*(a: char, b: char, d: char, c: char): uint32 =
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return toUint16(a, b).uint32 or (toUint16(d, c).uint32 shl 16)
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func uint32ToString*(n: uint32): string =
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return uint16ToString((n shr 16).uint16) & uint16ToString((n and 0b1111111111111111).uint16)
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func sliceBit*(s: char, i: uint8): bool =
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assert i < 8
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return ((toUint8(s) shr (8 - i)) and 1) == 1
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39
server.nim
39
server.nim
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@ -1,17 +1,24 @@
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import asyncnet, asyncdispatch, nativesockets, strutils, lib/dns
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import asyncnet, asyncdispatch, nativesockets
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import strutils, options, tables
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import lib/dns
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proc handleDnsRequest(data: string) =
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let header = parseHeader(data[0 .. 11])
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var questions: seq[DnsQuestion] = @[]
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var offset = 12
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const records = {
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DnsType.A: {"m5w.de": @["\127\0\0\1"]}.toTable,
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DnsType.TXT: {"m5w.de": @["hello world", "abc"]}.toTable
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}.toTable
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for i in (1.uint32)..header.qdcount:
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let (question, read) = parseQuestion(data[offset .. len(data) - 1])
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questions.add(question)
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offset += read.int
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proc handleDnsRequest(data: string): Option[string] =
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let msg = parseMessage(data)
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let msg = DnsMessage(header: header, questions: questions)
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echo msg
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if len(msg.questions) == 0:
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return
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let question = msg.questions[0]
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# todo: handle missing record
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let answer = records[question.qtype][question.qname]
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let response = mkResponse(msg.header.id, question, answer)
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return some(packMessage(response))
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proc serve() {.async.} =
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let server = newAsyncSocket(sockType=SockType.SOCK_DGRAM, protocol=Protocol.IPPROTO_UDP, buffered = false)
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@ -19,10 +26,14 @@ proc serve() {.async.} =
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server.bindAddr(Port(12345))
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while true:
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echo "start loop"
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try:
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let request = await server.recvFrom(size=512)
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echo "received"
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handleDnsRequest(request.data)
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let response = handleDnsRequest(request.data)
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if (response.isSome):
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await server.sendTo(request.address, request.port, response.unsafeGet)
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except:
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continue
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proc main() =
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asyncCheck serve()
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