Charm URL type

The following introduces a charm URL, this will help when trying to
ensure that what we get from the API is indeed a valid URL. The code is
pretty much a lift from the juju/charm package, minus the FQDN charm
URLs, which should never have been added to the charm package.

The code is rather procedural and doesn't validate the name or series,
but the controller can do that once we know the pattern is correct.

Essentially we want the charm URL for the schema and the name, so rather
than have methods that sort of do the job, we should replicate the exact
same parsing layout so we don't get it wrong.

Author: SimonRichardson

juju/url.py

@@ -0,0 +1,136 @@
+from enum import Enum
+from .errors import JujuError
+from urllib.parse import urlparse
+
+
+class Schema(Enum):
+    LOCAL = "local"
+    CHARM_STORE = "cs"
+    CHARM_HUB = "ch"
+
+    def matches(self, potential):
+        return self.value == potential
+
+    def __str__(self):
+        return self.value
+
+
+class URL:
+    def __init__(self, schema, user=None, name=None, revision=None, series=None):
+        self.schema = schema
+        self.user = user
+        self.name = name
+        self.series = series
+
+        # 0 can be a valid revision, hence the more verbose check.
+        if revision is None:
+            revision = -1
+        self.revision = revision
+
+    @staticmethod
+    def parse(s):
+        """parse parses the provided charm URL string into its respective
+            structure.
+
+            A missing schema is assumed to be 'ch'.
+
+        """
+        u = urlparse(s)
+        if u.query != "" or u.fragment != "" or u.username or u.password:
+            raise JujuError("charm or bundle URL {} has unrecognized parts".format(u))
+
+        if Schema.LOCAL.matches(u.scheme):
+            c = parse_v1_url(Schema.LOCAL, u, s)
+        elif Schema.CHARM_STORE.matches(u.scheme):
+            c = parse_v1_url(Schema.CHARM_STORE, u, s)
+        else:
+            c = parse_v2_url(u, s)
+
+        if not c.schema:
+            raise JujuError("expected schema for charm or bundle URL {}".format(u))
+        return c
+
+    def with_revision(self, rev):
+        return URL(self.schema, self.user, self.name, rev, self.series)
+
+    def path(self):
+        parts = []
+        if self.user:
+            parts.append("~{}".format(self.user))
+        if self.series:
+            parts.append(self.series)
+        if self.revision is not None and self.revision >= 0:
+            parts.append("{}-{}", self.name, self.revision)
+        else:
+            parts.append(self.name)
+        return "/".join(parts)
+
+    def __eq__(self, other):
+        if isinstance(other, self.__class__):
+            return self.schema == other.schema and \
+                self.user == other.user and \
+                self.name == other.name and \
+                self.revision == other.revision and \
+                self.series == other.series
+        return False
+
+    def __str__(self):
+        return "{}:{}".format(str(self.schema), self.path())
+
+
+def parse_v1_url(schema, u, s):
+    c = URL(schema)
+
+    parts = u.path.split("/")
+    if len(parts) < 1 or len(parts) > 4:
+        raise JujuError("charm or bundle URL has invalid form {}".format(s))
+
+    # ~<username>
+    if parts[0].startswith("~"):
+        if schema == Schema.LOCAL:
+            raise JujuError("local charm or bundle URL with username {}".format(s))
+        c.user = parts[0][1:]
+        parts = parts[1:]
+
+    if len(parts) > 2:
+        raise JujuError("charm or bundle URL has invalid form {}".format(s))
+
+    # <series>
+    if len(parts) == 2:
+        c.series = parts[0]
+        parts = parts[1:]
+        # TODO (stickupkid) - validate the series.
+
+    if len(parts) < 1:
+        raise JujuError("URL without charm or bundle name {}".format(s))
+
+    (c.name, c.revision) = extract_revision(parts[0])
+    # TODO (stickupkid) - validate the name.
+
+    return c
+
+
+def parse_v2_url(u, s):
+    c = URL(Schema.CHARM_HUB)
+
+    parts = u.path.split("/")
+    if len(parts) != 1:
+        raise JujuError("charm or bundle URL {} malformed, expected <name>".format(s))
+
+    (c.name, c.revision) = extract_revision(parts[0])
+    # TODO (stickupkid) - validate the name.
+
+    return c
+
+
+def extract_revision(name):
+    revision = -1
+    for i in range(len(name) - 1, -1, -1):
+        c = name[i]
+        if c.isnumeric():
+            continue
+        if c == "-" and i != (len(name) - 1):
+            revision = int(name[(i + 1):])
+            name = name[:i]
+        break
+    return (name, revision)

tests/unit/test_url.py

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+import unittest
+
+from juju.url import Schema, URL
+
+
+class TestURLV1(unittest.TestCase):
+    def test_parse_charmstore(self):
+        u = URL.parse("cs:mysql")
+        self.assertEqual(u, URL(Schema.CHARM_STORE, name="mysql"))
+
+    def test_parse_local(self):
+        u = URL.parse("local:mysql")
+        self.assertEqual(u, URL(Schema.LOCAL, name="mysql"))
+
+    def test_parse_v1_user(self):
+        u = URL.parse("cs:~fred/mysql")
+        self.assertEqual(u, URL(Schema.CHARM_STORE, name="mysql", user="fred"))
+
+    def test_parse_v1_revision(self):
+        u = URL.parse("cs:~fred/mysql-1")
+        self.assertEqual(u, URL(Schema.CHARM_STORE, name="mysql", user="fred", revision=1))
+
+    def test_parse_v1_large_revision(self):
+        u = URL.parse("cs:~fred/mysql-12345")
+        self.assertEqual(u, URL(Schema.CHARM_STORE, name="mysql", user="fred", revision=12345))
+
+    def test_parse_v1_series(self):
+        u = URL.parse("cs:~fred/bionic/mysql-1")
+        self.assertEqual(u, URL(Schema.CHARM_STORE, name="mysql", user="fred", revision=1, series="bionic"))
+
+
+class TestURLV2(unittest.TestCase):
+    def test_parse_charmhub(self):
+        u = URL.parse("ch:mysql")
+        self.assertEqual(u, URL(Schema.CHARM_HUB, name="mysql"))
+
+    def test_parse_v2_revision(self):
+        u = URL.parse("ch:mysql-1")
+        self.assertEqual(u, URL(Schema.CHARM_HUB, name="mysql", revision=1))
+
+    def test_parse_v2_large_revision(self):
+        u = URL.parse("ch:mysql-12345")
+        self.assertEqual(u, URL(Schema.CHARM_HUB, name="mysql", revision=12345))