├── README.md
├── zones
    └── howcode.org.zone
└── dns.py


/README.md:
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1 | howDNS - DNS Server by howCode
2 | ==============================
3 | 
4 | howDNS is a simple DNS Server written in pure Python 3 during the "Make your Own DNS Server" video series on YouTube. You can watch the series here: https://www.youtube.com/playlist?list=PLBOh8f9FoHHhvO5e5HF_6mYvtZegobYX2
5 | 


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/zones/howcode.org.zone:
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 1 | {
 2 |     "$origin": "howcode.org.",
 3 |     "$ttl": 3600,
 4 |     "soa": {
 5 |         "mname": "ns1.howcode.org.",
 6 |         "rname": "admin.howcode.org.",
 7 |         "serial": "{time}",
 8 |         "refresh": 3600,
 9 |         "retry": 600,
10 |         "expire": 604800,
11 |         "minimum": 86400
12 |     },
13 |     "ns": [
14 |         { "host": "ns1.howcode.org." },
15 |         { "host": "ns2.howcode.org." }
16 |     ],
17 |     "a": [
18 |         { "name": "@", "ttl": 400, "value": "255.255.255.255" },
19 |         { "name": "@", "ttl": 400, "value": "127.0.0.1" },
20 |         { "name": "@", "ttl": 400, "value": "127.0.0.1" },
21 |         { "name": "@", "ttl": 400, "value": "127.0.0.1" },
22 |         { "name": "@", "ttl": 400, "value": "10.10.10.10" }
23 |     ]
24 | }
25 | 


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/dns.py:
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  1 | import socket, glob, json
  2 | 
  3 | port = 53
  4 | ip = '127.0.0.1'
  5 | 
  6 | sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
  7 | sock.bind((ip, port))
  8 | 
  9 | def load_zones():
 10 | 
 11 |     jsonzone = {}
 12 |     zonefiles = glob.glob('zones/*.zone')
 13 | 
 14 |     for zone in zonefiles:
 15 |         with open(zone) as zonedata:
 16 |             data = json.load(zonedata)
 17 |             zonename = data["$origin"]
 18 |             jsonzone[zonename] = data
 19 |     return jsonzone
 20 | 
 21 | zonedata = load_zones()
 22 | 
 23 | def getflags(flags):
 24 | 
 25 |     byte1 = bytes(flags[:1])
 26 |     byte2 = bytes(flags[1:2])
 27 | 
 28 |     rflags = ''
 29 | 
 30 |     QR = '1'
 31 | 
 32 |     OPCODE = ''
 33 |     for bit in range(1,5):
 34 |         OPCODE += str(ord(byte1)&(1<<bit))
 35 | 
 36 |     AA = '1'
 37 | 
 38 |     TC = '0'
 39 | 
 40 |     RD = '0'
 41 | 
 42 |     # Byte 2
 43 | 
 44 |     RA = '0'
 45 | 
 46 |     Z = '000'
 47 | 
 48 |     RCODE = '0000'
 49 | 
 50 |     return int(QR+OPCODE+AA+TC+RD, 2).to_bytes(1, byteorder='big')+int(RA+Z+RCODE, 2).to_bytes(1, byteorder='big')
 51 | 
 52 | def getquestiondomain(data):
 53 | 
 54 |     state = 0
 55 |     expectedlength = 0
 56 |     domainstring = ''
 57 |     domainparts = []
 58 |     x = 0
 59 |     y = 0
 60 |     for byte in data:
 61 |         if state == 1:
 62 |             if byte != 0:
 63 |                 domainstring += chr(byte)
 64 |             x += 1
 65 |             if x == expectedlength:
 66 |                 domainparts.append(domainstring)
 67 |                 domainstring = ''
 68 |                 state = 0
 69 |                 x = 0
 70 |             if byte == 0:
 71 |                 domainparts.append(domainstring)
 72 |                 break
 73 |         else:
 74 |             state = 1
 75 |             expectedlength = byte
 76 |         y += 1
 77 | 
 78 |     questiontype = data[y:y+2]
 79 | 
 80 |     return (domainparts, questiontype)
 81 | 
 82 | def getzone(domain):
 83 |     global zonedata
 84 | 
 85 |     zone_name = '.'.join(domain)
 86 |     return zonedata[zone_name]
 87 | 
 88 | def getrecs(data):
 89 |     domain, questiontype = getquestiondomain(data)
 90 |     qt = ''
 91 |     if questiontype == b'\x00\x01':
 92 |         qt = 'a'
 93 | 
 94 |     zone = getzone(domain)
 95 | 
 96 |     return (zone[qt], qt, domain)
 97 | 
 98 | def buildquestion(domainname, rectype):
 99 |     qbytes = b''
100 | 
101 |     for part in domainname:
102 |         length = len(part)
103 |         qbytes += bytes([length])
104 | 
105 |         for char in part:
106 |             qbytes += ord(char).to_bytes(1, byteorder='big')
107 | 
108 |     if rectype == 'a':
109 |         qbytes += (1).to_bytes(2, byteorder='big')
110 | 
111 |     qbytes += (1).to_bytes(2, byteorder='big')
112 | 
113 |     return qbytes
114 | 
115 | def rectobytes(domainname, rectype, recttl, recval):
116 | 
117 |     rbytes = b'\xc0\x0c'
118 | 
119 |     if rectype == 'a':
120 |         rbytes = rbytes + bytes([0]) + bytes([1])
121 | 
122 |     rbytes = rbytes + bytes([0]) + bytes([1])
123 | 
124 |     rbytes += int(recttl).to_bytes(4, byteorder='big')
125 | 
126 |     if rectype == 'a':
127 |         rbytes = rbytes + bytes([0]) + bytes([4])
128 | 
129 |         for part in recval.split('.'):
130 |             rbytes += bytes([int(part)])
131 |     return rbytes
132 | 
133 | def buildresponse(data):
134 | 
135 |     # Transaction ID
136 |     TransactionID = data[:2]
137 | 
138 |     # Get the flags
139 |     Flags = getflags(data[2:4])
140 | 
141 |     # Question Count
142 |     QDCOUNT = b'\x00\x01'
143 | 
144 |     # Answer Count
145 |     ANCOUNT = len(getrecs(data[12:])[0]).to_bytes(2, byteorder='big')
146 | 
147 |     # Nameserver Count
148 |     NSCOUNT = (0).to_bytes(2, byteorder='big')
149 | 
150 |     # Additonal Count
151 |     ARCOUNT = (0).to_bytes(2, byteorder='big')
152 | 
153 |     dnsheader = TransactionID+Flags+QDCOUNT+ANCOUNT+NSCOUNT+ARCOUNT
154 | 
155 |     # Create DNS body
156 |     dnsbody = b''
157 | 
158 |     # Get answer for query
159 |     records, rectype, domainname = getrecs(data[12:])
160 | 
161 |     dnsquestion = buildquestion(domainname, rectype)
162 | 
163 |     for record in records:
164 |         dnsbody += rectobytes(domainname, rectype, record["ttl"], record["value"])
165 | 
166 |     return dnsheader + dnsquestion + dnsbody
167 | 
168 | 
169 | while 1:
170 |     data, addr = sock.recvfrom(512)
171 |     r = buildresponse(data)
172 |     sock.sendto(r, addr)
173 | 


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