dns: Add {to,from}_default_id() to DNSDriver class

Add .to_default_id() and .from_default_id() functions to the DNSDriver
class. These functions support the <type>[:<name>] (e.g. "A:www") record
ID format used by many of the drivers.

Author: Aaron Sierra

libcloud/dns/base.py

@@ -15,10 +15,12 @@
 
 
 import datetime
+import re
+from collections import namedtuple
 from typing import Any, Dict, List, Type, Union, Iterator, Optional
 
 from libcloud import __version__
-from libcloud.dns.types import RecordType
+from libcloud.dns.types import RecordType, RecordDoesNotExistError
 from libcloud.common.base import BaseDriver, Connection, ConnectionUserAndKey
 
 __all__ = ["Zone", "Record", "DNSDriver"]
@@ -277,6 +279,11 @@ class DNSDriver(BaseDriver):
     # Map libcloud record type enum to provider record type name
     RECORD_TYPE_MAP = {}  # type: Dict[RecordType, str]
 
+    # "A"     -> type: "A", prefix: None
+    # "A:www" -> type: "A", prefix: "www"
+    DEFAULT_ID_RE = re.compile(r"(?P<type>[A-Z]+)(\:(?P<name>.+))?")
+    DefaultID = namedtuple("DefaultID", "type,name")
+
     def __init__(
         self,
         key,  # type: str
@@ -640,3 +647,18 @@ def _string_to_record_type(self, string):
         string = string.upper()
         record_type = getattr(RecordType, string)
         return record_type
+
+    @staticmethod
+    def to_default_id(zone, name, type):
+        prefix = zone.prefix(name)
+        return f"{type}:{prefix}" if prefix else str(type)
+
+    @classmethod
+    def from_default_id(cls, zone, record_id):
+        match = cls.DEFAULT_ID_RE.match(record_id)
+        if match is None:
+            raise RecordDoesNotExistError(value="malformed record ID",
+                    driver=cls, record_id=record_id)
+
+        name = match.group("name")
+        return cls.DefaultID(match.group("type"), "" if name is None else zone.prefix(name))

libcloud/test/dns/test_base.py

@@ -180,6 +180,36 @@ def test_get_numeric_id(self):
         result = record._get_numeric_id()
         self.assertEqual(result, "")
 
+    def test_driver_to_default_id(self):
+        data = [
+            # name, type, id (expected)
+            ("", "A", "A"),
+            ("example.com", "A", "A"),
+            ("example.com.", "A", "A"),
+            ("mail", "MX", "MX:mail"),
+            ("mail.example.com", "MX", "MX:mail"),
+            ("mail.example.com.", "MX", "MX:mail"),
+        ]
+        for rname, rtype, rexpect in data:
+            rid = self.driver.to_default_id(self.master_zone, rname, rtype)
+            self.assertEqual(rid, rexpect)
+
+    def test_driver_from_default_id(self):
+        data = [
+            # id, name (expected), type (expected)
+            ("A", "", "A"), # without trailing colon
+            ("A:", "", "A"), # with trailing colon
+            ("A:example.com", "", "A"),
+            ("A:example.com.", "", "A"),
+            ("MX:mail", "mail", "MX"),
+            ("MX:mail.example.com", "mail", "MX"),
+            ("MX:mail.example.com.", "mail", "MX"),
+        ]
+        for rid, rname, rtype in data:
+            rparts = self.driver.from_default_id(self.master_zone, rid)
+            self.assertEqual(rparts.name, rname)
+            self.assertEqual(rparts.type, rtype)
+
 
 def zero_pad(value: int) -> str:
     if value < 10: