VAPI-3163 Replace Transfer SipUri with ReferSipUri in <Refer>

The Transfer SipUri carries ~12 Transfer-specific params (transfer_answer_url,
uui, auth, fallback URLs) that are invalid in a REFER context. A user passing
any of those would silently produce malformed BXML.

ReferSipUri accepts only uri — matching the spec and the C# SDK's nested
Refer.SipUri class design.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: stampercasey

bandwidth/models/bxml/verbs/__init__.py

@@ -12,6 +12,7 @@
 from .play_audio import PlayAudio
 from .record import Record
 from .refer import Refer
+from .refer_sip_uri import ReferSipUri
 from .redirect import Redirect
 from .resume_recording import ResumeRecording
 from .ring import Ring

bandwidth/models/bxml/verbs/refer.py

@@ -6,13 +6,13 @@
 @copyright Bandwidth INC
 """
 from ..nestable_verb import NestableVerb
-from .sip_uri import SipUri
+from .refer_sip_uri import ReferSipUri
 
 
 class Refer(NestableVerb):
 
     def __init__(
-        self, sip_uri: SipUri,
+        self, sip_uri: ReferSipUri,
         refer_complete_url: str=None, refer_complete_method: str=None,
         tag: str=None
     ):
@@ -27,8 +27,10 @@ def __init__(
         handling — there is no live call to act on after success.
 
         Args:
-            sip_uri (SipUri): The SIP URI to refer the call to. Required.
-                Exactly one <SipUri> child element is allowed.
+            sip_uri (ReferSipUri): The SIP URI to refer the call to. Required.
+                Exactly one <SipUri> child element is allowed. Use ReferSipUri,
+                not SipUri — the Transfer SipUri carries callbacks and auth
+                fields that are not valid in a REFER context.
             refer_complete_url (str, optional): URL to send the Refer Complete
                 event to when the REFER flow finishes (success or failure).
                 May be a relative URL. Defaults to None.

bandwidth/models/bxml/verbs/refer_sip_uri.py

@@ -0,0 +1,31 @@
+"""
+refer_sip_uri.py
+
+Bandwidth's ReferSipUri BXML element
+
+@copyright Bandwidth INC
+"""
+from ..verb import Verb
+
+
+class ReferSipUri(Verb):
+
+    def __init__(self, uri: str):
+        """Initialize a <SipUri> child element for use within <Refer>.
+
+        Unlike the SipUri used with <Transfer>, this element carries only the
+        destination URI — no transfer callbacks, auth, or UUI headers apply
+        to a SIP REFER.
+
+        Args:
+            uri (str): The SIP URI to refer the call to (e.g. sip:user@host.example.com).
+        """
+        self.uri = uri
+        super().__init__(
+            tag="SipUri",
+            content=self.uri,
+        )
+
+    @property
+    def _attributes(self):
+        return None

test/unit/models/bxml/test_refer.py

@@ -7,15 +7,13 @@
 """
 import unittest
 
-from bandwidth.models.bxml import Refer, SipUri, Verb, NestableVerb
+from bandwidth.models.bxml import Refer, ReferSipUri, SipUri, Verb, NestableVerb
 
 
 class TestRefer(unittest.TestCase):
 
     def setUp(self):
-        self.sip_uri = SipUri(
-            uri="sip:alice@atlanta.example.com"
-        )
+        self.sip_uri = ReferSipUri(uri="sip:alice@atlanta.example.com")
         self.refer = Refer(
             sip_uri=self.sip_uri,
             refer_complete_url="https://example.com/handleRefer",
@@ -33,6 +31,19 @@ def test_to_bxml(self):
         assert expected == self.refer.to_bxml()
 
     def test_minimal(self):
-        minimal_refer = Refer(sip_uri=SipUri(uri="sip:bob@example.com"))
+        minimal_refer = Refer(sip_uri=ReferSipUri(uri="sip:bob@example.com"))
         expected = '<Refer><SipUri>sip:bob@example.com</SipUri></Refer>'
         assert expected == minimal_refer.to_bxml()
+
+    def test_refer_sip_uri_is_not_transfer_sip_uri(self):
+        """ReferSipUri is a distinct type from the Transfer SipUri — no Transfer-specific
+        attributes (transfer_answer_url, uui, auth, etc.) are accepted."""
+        assert not isinstance(self.sip_uri, SipUri)
+        assert isinstance(self.sip_uri, ReferSipUri)
+
+    def test_refer_sip_uri_has_no_transfer_attributes(self):
+        """ReferSipUri carries only uri — no Transfer baggage."""
+        assert not hasattr(self.sip_uri, 'transfer_answer_url')
+        assert not hasattr(self.sip_uri, 'uui')
+        assert not hasattr(self.sip_uri, 'username')
+        assert not hasattr(self.sip_uri, 'password')