From: Ralf Jung <post@ralfj.de>
Date: Tue, 7 Jul 2020 08:23:05 +0000 (+0200)
Subject: resolve domains directly against dyn nameserver (instead of system resolver)
X-Git-Url: https://git.ralfj.de/dyn-nsupdate.git/commitdiff_plain/35c48c1c12c7c9c4bcafd74fcaa74dd8ba00c51a

resolve domains directly against dyn nameserver (instead of system resolver)
---

diff --git a/README.md b/README.md
index 8c81015..05cf527 100644
--- a/README.md
+++ b/README.md
@@ -86,16 +86,16 @@ setup::
 
 ## Client setup (using the script)
 
-You can find the client script at `client-scripts/dyn-ns-client`. It requires 
-Python 3. Copy that script to the machine that should be available under the 
-dynamic domain. Also copy the sample configuration file 
-`dyn-ns-client.conf.dist` to `$HOME/.config/dyn-nsupdate/dyn-ns-client.conf`.
-You can choose another name, but then you will have to tell the script about it. 
-Call `dyn-ns-client --help` for this and other options the script accepts. An 
-important aspect of configuration is how to detect the current addresses of the 
-machine the script is running on. For IPv4, this can only be "web", which can 
-deal with NAT. For IPv6, the script can alternatively attempt to detect the 
-correct local address to use. The sample file contains comments that should 
+You can find the client script at `client-scripts/dyn-ns-client`. It requires
+Python 3 and the `dnspython` package. Copy that script to the machine that
+should be available under the dynamic domain. Also copy the sample configuration
+file `dyn-ns-client.conf.dist` to `$HOME/.config/dyn-nsupdate/dyn-ns-client.conf`.
+You can choose another name, but then you will have to tell the script about it.
+Call `dyn-ns-client --help` for this and other options the script accepts. An
+important aspect of configuration is how to detect the current addresses of the
+machine the script is running on. For IPv4, this can only be "web", which can
+deal with NAT. For IPv6, the script can alternatively attempt to detect the
+correct local address to use. The sample file contains comments that should
 explain everything.
 
 Note that the script can update a list of domain names, in case you need the 
diff --git a/client-scripts/dyn-ns-client b/client-scripts/dyn-ns-client
index e5eb56e..124498a 100755
--- a/client-scripts/dyn-ns-client
+++ b/client-scripts/dyn-ns-client
@@ -24,6 +24,7 @@
 #==============================================================================
 
 import urllib.request, socket, sys, argparse, os, configparser, itertools, subprocess, re, ssl
+import dns, dns.resolver
 
 VERBOSE_CHANGE = 1
 VERBOSE_FULL   = 2
@@ -99,22 +100,21 @@ def getMyIPv6(config, verbose = 0):
         raise Exception("Unable to detect correct local IPv6 address")
     return getMyIP("IPv6", config, methods={'local': local}, verbose=verbose)
 
-def getCurIP(domain, family):
-    '''Return the current IP of the given <domain>. <family> can be socket.AF_INET or socket.AF_INET6.'''
+def getResolver(server):
+    '''Return a resovler with the given server (defined by DNS name)'''
+    addr = socket.getaddrinfo(server, None, family=socket.AF_INET)
+    addr = addr[0][4][0]
+    res = dns.resolver.Resolver()
+    res.nameservers = [addr]
+    return res
+
+def getCurIP(domain, rtype, res):
+    '''Return the current IP of the given <domain>. <rtype> can be A or AAAA.'''
     try:
-        addr = socket.getaddrinfo(domain, None, family=family)
-        return addr[0][4][0]
-    except socket.gaierror: # domain not found
+        return res.query(domain, rtype)[0].address
+    except dns.exception.DNSException: # domain not found
         return ""
 
-def getCurIPv4(domain):
-    '''Returns the current IPv4 address of the given domain'''
-    return getCurIP(domain, socket.AF_INET)
-
-def getCurIPv6(domain):
-    '''Returns the current IPv6 address of the given domain'''
-    return getCurIP(domain, socket.AF_INET6)
-
 def updateDomain(server, domain, ipv4, ipv6, password, config, verbose):
     '''Update the given domain, using the server, password. ipv4 or ipv6 can be None to not update that record, or strings with the respective addresses.
        Updates ae only performed if necessary.
@@ -122,8 +122,11 @@ def updateDomain(server, domain, ipv4, ipv6, password, config, verbose):
     assert ipv4 is not None or ipv6 is not None
     
     # check what the domain is currently mapped to
-    curIPv4 = getCurIPv4(domain)
-    curIPv6 = getCurIPv6(domain)
+    res = getResolver(server)
+    if verbose >= VERBOSE_FULL:
+        print("Resolving names using {}".format(res.nameservers))
+    curIPv4 = getCurIP(domain, 'A', res)
+    curIPv6 = getCurIP(domain, 'AAAA', res)
     if verbose >= VERBOSE_FULL:
         print("Current status of domain {} is: IPv4 address '{}', IPv6 address '{}'".format(domain, curIPv4, curIPv6))