Begin work on reference resolution

rfc3986/exceptions.py

@@ -7,3 +7,9 @@ class InvalidAuthority(RFC3986Exception):
     def __init__(self, authority):
         super(InvalidAuthority, self).__init__(
             "The authority ({0}) is not valid.".format(authority))
+
+
+class ResolutionError(RFC3986Exception):
+    def __init__(self, uri):
+        super(ResolutionError, self).__init__(
+            "{0} is not an absolute URI.".format(uri.unsplit()))

rfc3986/uri.py

@@ -15,10 +15,11 @@
 from collections import namedtuple
 
 from .compat import to_str
-from .exceptions import InvalidAuthority
+from .exceptions import InvalidAuthority, ResolutionError
 from .misc import (
-    FRAGMENT_MATCHER, IPv4_MATCHER, PATH_MATCHER, QUERY_MATCHER,
-    SCHEME_MATCHER, SUBAUTHORITY_MATCHER, URI_MATCHER, URI_COMPONENTS
+    ABSOLUTE_URI_MATCHER, FRAGMENT_MATCHER, IPv4_MATCHER, PATH_MATCHER,
+    QUERY_MATCHER, SCHEME_MATCHER, SUBAUTHORITY_MATCHER, URI_MATCHER,
+    URI_COMPONENTS
     )
 from .normalizers import (
     encode_component, normalize_scheme, normalize_authority, normalize_path,
@@ -139,6 +140,18 @@ class URIReference(namedtuple('URIReference', URI_COMPONENTS)):
             return None
         return authority['userinfo']
 
+    def is_absolute(self):
+        """Determine if this URI Reference is an absolute URI.
+
+        See http://tools.ietf.org/html/rfc3986#section-4.3 for explanation.
+
+        :returns: ``True`` if it is an absolute URI, ``False`` otherwise.
+        :rtype: bool
+        """
+        if ABSOLUTE_URI_MATCHER.match(self.unsplit()):
+            return True
+        return False
+
     def is_valid(self, **kwargs):
         """Determines if the URI is valid.
 
@@ -266,6 +279,28 @@ class URIReference(namedtuple('URIReference', URI_COMPONENTS)):
         """
         return tuple(self.normalize()) == tuple(other_ref.normalize())
 
+    def resolve(self, base_uri, strict=False):
+        """Use an absolute URI Reference to resolve this relative reference.
+
+        See http://tools.ietf.org/html/rfc3986#section-5 for more information.
+
+        :param base_uri: Either a string or URIReference. It must be an
+            absolute URI or it will raise an exception.
+        :returns: A new URIReference which is the result of resolving this
+            reference using ``base_uri``.
+        :rtype: :class:`URIReference`
+        :raises ResolutionError: If the ``base_uri`` is not an absolute URI.
+        """
+        if not isinstance(base_uri, URIReference):
+            base_uri = URIReference.from_string(base_uri)
+
+        if not base_uri.is_absolute():
+            raise ResolutionError(base_uri)
+
+        # This is optional per
+        # http://tools.ietf.org/html/rfc3986#section-5.2.1
+        base_uri = base_uri.normalize()
+
     def unsplit(self):
         """Create a URI string from the components.