From d1b0579a41c8215487a17317851f01756a1d938d Mon Sep 17 00:00:00 2001
From: jaseg <code@jaseg.net>
Date: Tue, 29 Dec 2020 13:08:13 +0100
Subject: Add dns, dyndns services

---
 dyndns.py | 149 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 149 insertions(+)
 create mode 100644 dyndns.py

(limited to 'dyndns.py')

diff --git a/dyndns.py b/dyndns.py
new file mode 100644
index 0000000..2546dce
--- /dev/null
+++ b/dyndns.py
@@ -0,0 +1,149 @@
+#!/usr/bin/env python3
+
+import time
+from contextlib import contextmanager
+import re
+import os
+import os.path
+import random
+import string
+import subprocess
+import sqlite3
+import hmac
+from ipaddress import IPv4Address, IPv6Address
+
+from flask import Flask, request, abort
+import uwsgidecorators
+
+app = Flask(__name__)
+app.config.update(dict(
+    RECORD_EXPIRY_S = 86400,
+    NSD_CONTROL = 'nsd-control'
+    ))
+app.config.from_pyfile('config.py')
+
+
+ZONEFILE_TEMPLATE = '''\
+; #################################################### ;
+; THIS FILE IS AUTOMATICALLY GENERATED! DO NOT MODIFY! ;
+; #################################################### ;
+
+$ORIGIN {zone}.
+$TTL 1800
+@       IN      SOA     {ns}.      {mail}. (
+                        {serial}                ; serial number
+                        60                      ; refresh
+                        60                      ; retry
+                        {expire}                ; expire
+                        60                      ; ttl
+                        )
+; Name servers
+                    IN      NS      {ns}.
+
+; Additional A records from template
+; @                   IN      A       192.0.2.3
+; www                 IN      A       192.0.2.3
+
+; Dynamically generated records
+{dynamic_records}
+'''
+
+db = sqlite3.connect(app.config['SQLITE_DB'], check_same_thread=False)
+with db as conn:
+    conn.execute('''CREATE TABLE IF NOT EXISTS zone_versions (date TEXT)''')
+    conn.execute('''CREATE TABLE IF NOT EXISTS records
+            (name TEXT PRIMARY KEY, ipv4 TEXT, ipv6 TEXT, last_update INTEGER)''')
+
+def purge_expired_records():
+    with db as conn:
+        conn.execute('DELETE FROM records WHERE last_update < ?',
+                (int(time.time()) - app.config['RECORD_EXPIRY_S'],))
+
+def update_record(record, ipv4=None, ipv6=None):
+    with db as conn:
+        old_v4, old_v6 = conn.execute('SELECT ipv4, ipv6 FROM records WHERE name=?', (record,)).fetchone() or (None, None)
+        conn.execute('INSERT OR REPLACE INTO records VALUES (?, ?, ?, ?)', (record, ipv4, ipv6, int(time.time())))
+        return ipv4 != old_v4 or ipv6 != old_v6
+
+@contextmanager
+def inplace_rewrite(filename, cleanup=True):
+    print('Writing', filename)
+    filename = os.path.abspath(filename)
+    if cleanup:
+        basename = os.path.basename(filename)
+        for entry in os.scandir(os.path.dirname(filename)):
+            if entry.name.startswith(basename) and re.match(r'\.tmp-[a-zA-Z0-9]{8}', entry.name[len(basename):]):
+                os.remove(entry.path)
+
+    tmp_fn = filename + f'.tmp-' + ''.join(random.choices(string.ascii_letters + string.digits, k=8))
+    with open(tmp_fn, 'w') as tmp_f:
+        yield tmp_f
+        tmp_f.flush()
+        os.fsync(tmp_f.fileno())
+    os.rename(tmp_fn, filename)
+
+def write_zonefile():
+    # Find the next free zonefile version number
+    with db as conn:
+        conn.execute('INSERT INTO zone_versions VALUES (DATE())')
+        date, version_num, = conn.execute('SELECT zone_versions.date, COUNT(*) FROM zone_versions WHERE zone_versions.date = DATE()').fetchone()
+    zone_version = f'{date.replace("-", "")}{version_num:02d}'
+
+    # Generate dynamic record block
+    with db as conn:
+        records = db.execute('SELECT name, "A", ipv4 FROM records UNION SELECT name, "AAAA", ipv6 FROM records')
+        dynamic_records = '\n'.join(f'{name:<20} IN {rtype:<4} {value}' for name, rtype, value in records if value is not None)
+
+    # Template zone file content
+    content = ZONEFILE_TEMPLATE.format(
+            zone = app.config['ZONE'],
+            ns = app.config['NAMESERVER'],
+            mail = app.config['NAMESERVER_MAIL'].replace('@', '.'),
+            serial = zone_version,
+            dynamic_records = dynamic_records,
+            expire = app.config['RECORD_EXPIRY_S']
+            )
+
+    with inplace_rewrite(app.config['ZONEFILE'], cleanup=True) as f:
+        f.write(content)
+
+def kick_nsd():
+    prog = app.config['NSD_CONTROL']
+    if isinstance(prog, str):
+        prog = [prog]
+    subprocess.run([*prog, 'reload', app.config['ZONE']], check=True)
+
+@app.before_first_request
+@uwsgidecorators.timer(300)
+def update_zonefile():
+    purge_expired_records()
+    write_zonefile()
+    kick_nsd()
+
+@app.route('/update', methods=['POST'])
+def route_update():
+    if request.authorization is None:
+        abort(403)
+
+    record = request.authorization['username']
+    record_config = app.config['DYNAMIC_RECORDS'].get(record)
+    if record_config is None:
+        abort(403)
+
+    *supported_formats, password = record_config
+    if not hmac.compare_digest(request.authorization['password'], password):
+        abort(403)
+
+    ipv4 = request.args.get('ipv4', '127.0.0.1')
+    ipv6 = request.args.get('ipv6', '::1')
+    ipv4 = str(IPv4Address(ipv4)) if 'v4' in supported_formats else None
+    ipv6 = str(IPv6Address(ipv6)) if 'v6' in supported_formats else None
+    if update_record(record, ipv4=ipv4, ipv6=ipv6):
+        update_zonefile()
+
+    return 'success'
+
+
+if __name__ == '__main__':
+    app.run()
+
-- 
cgit