Enable automasq service to permit using Dnsmasq as global resolver without losing upstream DNS

Library/LaunchAgents/org.insectsarerubbish.automasq.plist

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>KeepAlive</key>
+	<true/>
+	<key>Label</key>
+	<string>org.insectsarerubbish.automasq</string>
+	<key>ProgramArguments</key>
+	<array>
+		<string>/Users/dani/.local/bin/automasq</string>
+		<string>/usr/local/etc/resolv.conf</string>
+	</array>
+	<key>RunAtLoad</key>
+	<true/>
+</dict>
+</plist>

local/bin/automasq

@@ -0,0 +1,104 @@
+#!/usr/bin/python
+"""OSX-based script to watch for changes to network state and write out a
+second resolv.conf file containing the DHCP provided nameservers, intended
+for use with a local resolver such as dnsmasq. This is to workaround the
+changes in Snow Leopard from Leopard with regards to DNS resolution.
+
+ie: the inability to have both manually configured nameservers and
+DHCP provided ones as well as the issues with split-DNS.
+
+usage: python automasq.py /path/to/second/resolv.conf
+
+original source: https://gist.github.com/edwardgeorge/270506
+
+"""
+import optparse
+import sys
+
+from SystemConfiguration import *
+
+GLOBAL_KEY = 'State:/Network/Global/IPv4'
+
+
+class Watcher(object):
+    def __init__(self, filename, defaults_filename=None,
+                append_defaults=False):
+        self.filename = filename
+        self.defaults = defaults_filename
+        self.append = append_defaults
+
+        store = self.store = SCDynamicStoreCreate(None, "automasq",
+            self.dynamicStoreChanged, None)
+        SCDynamicStoreSetNotificationKeys(store, None, [GLOBAL_KEY])
+        source = self.source = SCDynamicStoreCreateRunLoopSource(None,
+            store, 0)
+
+        self.write_file(self.get_primary_dns(store))
+
+        loop = self.loop = CFRunLoopGetCurrent()
+        CFRunLoopAddSource(loop, source, kCFRunLoopCommonModes)
+        CFRunLoopRun()
+
+    def write_file(self, servers=[]):
+        with open(self.filename, 'w+') as f:
+            for server in servers:
+                f.write('nameserver %s\n' % server)
+            if (self.append or not servers) and self.defaults is not None:
+                with open(self.defaults) as d:
+                    f.write(d.read())
+
+    def process_dns_for_service(self, store, service):
+        key = 'State:/Network/Service/%s/DNS' % service
+        val = SCDynamicStoreCopyValue(store, key)
+        data = list(dict(val)['ServerAddresses'])
+        return data
+
+    def get_primary_dns(self, store=None):
+        store = store or self.store
+        val = SCDynamicStoreCopyValue(store, GLOBAL_KEY)
+        if val:
+            data = dict(val)
+            svcid = data['PrimaryService']
+            return self.process_dns_for_service(store, svcid)
+        else:
+            return []
+
+    def dynamicStoreChanged(self, store, changedKeys, info):
+        servers = []
+        for key in list(changedKeys):
+            #if key == GLOBAL_KEY:
+            servers = self.get_primary_dns(store)
+            self.write_file(servers)
+
+
+def dummy_timer(*args):
+    pass
+
+
+def main(filename, options):
+    # this gives us a callback into python every 1s for signal handling
+    CFRunLoopAddTimer(CFRunLoopGetCurrent(),
+        CFRunLoopTimerCreate(None, CFAbsoluteTimeGetCurrent(), 1.0, 0, 0,
+            dummy_timer, None),
+        kCFRunLoopCommonModes)
+    try:
+        watcher = Watcher(filename, defaults_filename=options.default,
+            append_defaults=options.append_defaults)
+    except KeyboardInterrupt, e:
+        # exiting
+        pass
+
+if __name__ == '__main__':
+    usage = "usage: %prog [options] output-file"
+    parser = optparse.OptionParser(usage)
+    parser.add_option('-d', '--default-conf', dest='default',
+        help='default conf if no resolvers provided', metavar='RESOLVCONF')
+    parser.add_option('-a', '--append', dest='append_defaults',
+        action='store_true',
+        help='always append defaults to generated resolv.conf')
+    opts, args = parser.parse_args()
+    if len(args) != 1:
+        parser.error("specify a single output-file")
+    if opts.append_defaults and not opts.default:
+        parser.error("default conf must be specified to be able to append")
+    main(args[0], opts)