plugins: googledomains: Use configured authentication source.

After merging #23 the actual source for credentials could be
something else than the .netrc file. To cope with this, the library
function get_netrc_auth should be used despite that it has a bad
nam).

Re-factor the bundled get_netrc_auth to use the library function
instead of just the .netrc file.

plugins/googledomains.py

@@ -9,8 +9,8 @@
 import os.path
 import urllib.parse
 import urllib.request
-from ddupdate.ddplugin import ServiceError, ServicePlugin, \
-    get_response
+from ddupdate.ddplugin import ServiceError, ServicePlugin
+from ddupdate.ddplugin import AuthError, get_response, get_netrc_auth
 
 
 # See https://github.com/leamas/ddupdate/pull/56
@@ -20,7 +20,7 @@ def http_basic_auth_setup(url, *, providerhost=None, targethost=None):
     """
     Configure urllib to provide basic authentication.
 
-    See get_netrc_auth for how providerhost and targethost
+    See get_auth for how providerhost and targethost
     are resolved to credentials stored in netrc.
 
     Parameters:
@@ -33,18 +33,16 @@ def http_basic_auth_setup(url, *, providerhost=None, targethost=None):
     """
     if not providerhost:
         providerhost = urllib.parse.urlparse(url).hostname
-    user, password = get_netrc_auth(providerhost, targethost)
+    user, password = get_auth(providerhost, targethost)
     pwmgr = urllib.request.HTTPPasswordMgrWithDefaultRealm()
     pwmgr.add_password(None, url, user, password)
     auth_handler = urllib.request.HTTPBasicAuthHandler(pwmgr)
     opener = urllib.request.build_opener(auth_handler)
     urllib.request.install_opener(opener)
 
-def get_netrc_auth(providerhost, targethost=None):
+def get_auth(providerhost, targethost=None):
     """
-    Retrieve data from  ~/-netrc or /etc/netrc.
-
-    Will look for matching identifiers in the netrc file.
+    Retrieve credentials from configured source.
 
     If a targethost is passed, the first machine name we look for
     is targethost.providerhost.ddupdate, falling back to providerhost.
@@ -57,28 +55,18 @@ def get_netrc_auth(providerhost, targethost=None):
     Returns:
       - A (user, password) tuple. User might be None.
     Raises:
-      - ServiceError if .netrc or password is not found.
-    See:
-      - netrc(5)
+      - AuthError password is not found.
 
     """
-    if os.path.exists(os.path.expanduser('~/.netrc')):
-        path = os.path.expanduser('~/.netrc')
-    elif os.path.exists('/etc/netrc'):
-        path = '/etc/netrc'
-    else:
-        raise ServiceError("Cannot locate the netrc file (see manpage).")
-    netrcdata = netrc.netrc(path)
     if targethost is not None:
         machine1 = "%s.%s.ddupdate" % (targethost, providerhost)
-        auth = netrcdata.authenticators(machine1) or netrcdata.authenticators(providerhost)
+        try:
+            credentials = get_netrc_auth(machine1)
+        except AuthError:
+            credentials = get_netrc_auth(providerhost)
     else:
-        auth = netrcdata.authenticators(providerhost)
-    if not auth:
-        raise ServiceError("No .netrc data found for " + providerhost)
-    if not auth[2]:
-        raise ServiceError("No password found for " + providerhost)
-    return auth[0], auth[2]
+        credentials = get_netrc_auth(providerhost)
+    return credentials
 
 
 class GoogleDomainsPlugin(ServicePlugin):