a working backend

.gitignore

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+*.ipr
+*.iml
+*.iws

src/backend.conf

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+[main]
+# main domain
+domain=lcl.io
+
+# default ttl
+ttl=432000
+
+# default IP address for non-wildcard entries
+ipaddress=127.0.0.1
+
+
+# SOA
+[soa]
+# serial number
+id=1
+# Hostmaster email address
+hostmaster=hostmaster@lcl.io
+# Name server
+ns=ns1.lcl.io
+
+
+# nameservers
+[nameservers]
+ns1.lcl.io=127.0.0.1
+ns2.lcl.io=127.0.0.1
+
+

src/backend.py

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+#!/usr/bin/python
+
+import sys
+import re
+import os
+import ConfigParser
+
+DEBUG=0
+
+def log(msg):
+    sys.stderr.write('backend: %s\n' % msg)
+
+def write(*l):
+    args=len(l)
+    c = 0
+    for a in l:
+        c += 1
+        if DEBUG: log('writing: %s' % a)
+        sys.stdout.write(a)
+        if c < args:
+            if DEBUG: log('writetab')
+            sys.stdout.write('\t')
+    if DEBUG: log('writenewline')
+    sys.stdout.write('\n')
+    sys.stdout.flush()
+
+def get_next():
+    if DEBUG: log('reading now')
+    l = sys.stdin.readline()
+    if DEBUG: log('read line: %s' % l)
+    return l.strip().split('\t')
+
+
+class DynamicBackend:
+    def __init__(self):
+        self.id = ''
+        self.soa = ''
+        self.domain = ''
+        self.ip_address = ''
+        self.ttl = ''
+        self.name_servers = {}
+
+    def configure(self):
+        fname = os.path.join(os.path.dirname(os.path.realpath(__file__)), 'backend.conf')
+        if not os.path.exists(fname):
+            log('%s does not exist' % fname)
+            sys.exit(1)
+    
+        fp = open(fname)
+        config = ConfigParser.ConfigParser()
+        config.readfp(fp)
+        fp.close()
+
+        self.id = config.get('soa', 'id')
+        self.soa = '%s %s %s' % (config.get('soa', 'ns'), config.get('soa','hostmaster'), self.id)
+        self.domain = config.get('main', 'domain')
+        self.ip_address = config.get('main', 'ipaddress')
+        self.ttl = config.get('main', 'ttl')
+    
+        for entry in config.items('nameservers'):
+            self.name_servers[entry[0]] = entry[1]
+
+        log('Name servers: %s' % self.name_servers)
+        log('ID: %s' % self.id)
+        log('TTL %s' % self.ttl)
+        log('SOA: %s' % self.soa)
+        log('IP Address: %s' % self.ip_address)
+        log('DOMAIN: %s' % self.domain)
+
+    def run(self):
+        log('starting up')
+        handshake = get_next()
+        if handshake[1] != '1':
+            log('Not version 1: %s' % handshake)
+            sys.exit(1)
+        write('OK', 'We are good')
+        log('Done handshake')
+
+        while True:
+            cmd = get_next()
+            if DEBUG: log(cmd)
+
+            if len(cmd) < 6:
+                log('did not understand: %s' % cmd)
+                write('FAIL')
+                continue
+
+            qname = cmd[1]
+            qtype = cmd[3]
+
+            if (qtype == 'A' or qtype == 'ANY') and qname.endswith(self.domain):
+                if qname == self.domain:
+                    self.handle_self(self.domain)
+                elif qname in self.name_servers:
+                    self.handle_nameservers(qname)
+                else:
+                    self.handle_subdomains(qname)
+            elif qtype == 'SOA':
+                self.handle_soa(qname)
+            else:
+                self.handle_unknown(qtype, qname)
+
+    def handle_self(self, name):
+        write('DATA', name, 'IN', 'A', self.ttl, self.id, self.ip_address)
+        self.write_name_servers(name)
+        write('END')
+
+    def handle_subdomains(self, qname):
+        subdomain = qname[0:qname.find(self.domain)-1]
+
+        subparts = subdomain.split('.')
+        if len(subparts) < 4:
+            if DEBUG: log('subparts less than 4')
+            self.handle_self(qname)
+            return
+
+        ipaddress = subparts[-4:]
+        if DEBUG: log('ip: %s' % ipaddress)
+        for part in ipaddress:
+            if re.match('^\d{1,3}$', part) is None:
+                if DEBUG: log('%s is not a number' % part)
+                self.handle_self(qname)
+                return
+            parti = int(part)
+            if parti < 0 or parti > 255:
+                if DEBUG: log('%d is too big/small' % parti)
+                self.handle_self(qname)
+                return
+
+        write('DATA', qname, 'IN', 'A', self.ttl, self.id, '%s.%s.%s.%s' % (ipaddress[0], ipaddress[1], ipaddress[2], ipaddress[3]))
+        self.write_name_servers(qname)
+        write('END')
+
+    def handle_nameservers(self, qname):
+        ip = self.name_servers[qname]
+        write('DATA', qname, 'IN', 'A', self.ttl, self.id, ip)
+        write('END')
+
+    def write_name_servers(self, qname):
+        for nameServer in self.name_servers:
+            write('DATA', qname, 'IN', 'NS', self.ttl, self.id, nameServer)
+
+    def handle_soa(self, qname):
+        write('DATA', qname, 'IN', 'SOA', self.ttl, self.id, self.soa)
+        write('END')
+
+    def handle_unknown(self, qtype, qname):
+        write('LOG', 'Unknown type: %s, domain: %s' % (qtype, qname))
+        write('FAIL')
+
+
+if __name__ == '__main__':
+
+    backend = DynamicBackend()
+    backend.configure()
+    backend.run()
+