Tolerate empty structured payloads

This updates http bindings deserializers to tolerate empty
payloads when the payload is a collection.

Author: JordonPhillips

packages/smithy-http/src/smithy_http/deserializers.py

@@ -84,17 +84,44 @@ def read_struct(
                     )
                 case Binding.PAYLOAD:
                     assert binding_matcher.payload_member is not None  # noqa: S101
-                    deserializer = self._create_payload_deserializer(
-                        binding_matcher.payload_member
-                    )
-                    consumer(binding_matcher.payload_member, deserializer)
+                    if self._should_read_payload(binding_matcher.payload_member):
+                        deserializer = self._create_payload_deserializer(
+                            binding_matcher.payload_member
+                        )
+                        consumer(binding_matcher.payload_member, deserializer)
                 case _:
                     pass
 
-        if binding_matcher.has_body:
+        if binding_matcher.has_body and not self._has_empty_body(
+            self._response, self._body
+        ):
             deserializer = self._create_body_deserializer()
             deserializer.read_struct(schema, consumer)
 
+    def _should_read_payload(self, schema: Schema) -> bool:
+        if schema.shape_type not in (
+            ShapeType.LIST,
+            ShapeType.MAP,
+            ShapeType.UNION,
+            ShapeType.STRUCTURE,
+        ):
+            return True
+        return not self._has_empty_body(self._response, self._body)
+
+    def _has_empty_body(
+        self, response: HTTPResponse, body: "SyncStreamingBlob | None"
+    ) -> bool:
+        if "content-length" in response.fields:
+            return int(response.fields["content-length"].as_string()) == 0
+        if isinstance(body, bytes | bytearray):
+            return len(body) == 0
+        if (seek := getattr(self._body, "seek", None)) is not None:
+            content_length = seek(0, 2)
+            if content_length == 0:
+                return True
+            seek(0, 0)
+        return False
+
     def _create_payload_deserializer(self, payload_member: Schema) -> ShapeDeserializer:
         if payload_member.shape_type in (ShapeType.BLOB, ShapeType.STRING):
             body = self._body if self._body is not None else self._response.body

packages/smithy-http/tests/unit/test_serializers.py

@@ -581,7 +581,7 @@ def _consumer(schema: Schema, de: ShapeDeserializer) -> None:
 
 @dataclass
 class HTTPStringPayload:
-    payload: str
+    payload: str | None = None
 
     ID: ClassVar[ShapeID] = ShapeID("com.smithy#HTTPStringPayload")
     SCHEMA: ClassVar[Schema] = Schema.collection(
@@ -594,7 +594,8 @@ def serialize(self, serializer: ShapeSerializer) -> None:
             self.serialize_members(s)
 
     def serialize_members(self, serializer: ShapeSerializer) -> None:
-        serializer.write_string(self.SCHEMA.members["payload"], self.payload)
+        if self.payload is not None:
+            serializer.write_string(self.SCHEMA.members["payload"], self.payload)
 
     @classmethod
     def deserialize(cls, deserializer: ShapeDeserializer) -> Self:
@@ -684,7 +685,7 @@ def _consumer(schema: Schema, de: ShapeDeserializer) -> None:
 
 @dataclass
 class HTTPStructuredPayload:
-    payload: HTTPStringPayload
+    payload: HTTPStringPayload | None = None
 
     ID: ClassVar[ShapeID] = ShapeID("com.smithy#HTTPStructuredPayload")
     SCHEMA: ClassVar[Schema] = Schema.collection(
@@ -702,7 +703,8 @@ def serialize(self, serializer: ShapeSerializer) -> None:
             self.serialize_members(s)
 
     def serialize_members(self, serializer: ShapeSerializer) -> None:
-        serializer.write_struct(self.SCHEMA.members["payload"], self.payload)
+        if self.payload is not None:
+            serializer.write_struct(self.SCHEMA.members["payload"], self.payload)
 
     @classmethod
     def deserialize(cls, deserializer: ShapeDeserializer) -> Self:
@@ -1548,6 +1550,53 @@ def payload_cases() -> list[HTTPMessageTestCase]:
             HTTPStructuredPayload(payload=HTTPStringPayload(payload="foo")),
             HTTPMessage(body=BytesIO(b'{"payload":"foo"}')),
         ),
+        HTTPMessageTestCase(
+            HTTPStructuredPayload(HTTPStringPayload()),
+            HTTPMessage(body=BytesIO(b"{}")),
+        ),
+    ]
+
+
+class NonSeekableBytesReader:
+    def __init__(self, data: bytes) -> None:
+        self._wrapped = BytesIO(data)
+
+    def read(self, size: int = -1, /) -> bytes:
+        return self._wrapped.read(size)
+
+
+def response_payload_cases() -> list[HTTPMessageTestCase]:
+    return [
+        HTTPMessageTestCase(
+            HTTPStructuredPayload(),
+            HTTPMessage(body=b""),
+        ),
+        HTTPMessageTestCase(
+            HTTPStructuredPayload(),
+            HTTPMessage(body=BytesIO(b"")),
+        ),
+        HTTPMessageTestCase(
+            HTTPStructuredPayload(),
+            HTTPMessage(
+                body=NonSeekableBytesReader(b""),
+                fields=tuples_to_fields([("content-length", "0")]),
+            ),
+        ),
+        HTTPMessageTestCase(
+            HTTPImplicitPayload(),
+            HTTPMessage(body=b""),
+        ),
+        HTTPMessageTestCase(
+            HTTPImplicitPayload(),
+            HTTPMessage(body=BytesIO(b"")),
+        ),
+        HTTPMessageTestCase(
+            HTTPImplicitPayload(),
+            HTTPMessage(
+                body=NonSeekableBytesReader(b""),
+                fields=tuples_to_fields([("content-length", "0")]),
+            ),
+        ),
     ]
 
 
@@ -1664,7 +1713,10 @@ async def test_serialize_response_omitting_empty_payload() -> None:
 
 
 RESPONSE_DESER_CASES: list[HTTPMessageTestCase] = (
-    header_cases() + empty_prefix_header_deser_cases() + payload_cases()
+    header_cases()
+    + empty_prefix_header_deser_cases()
+    + payload_cases()
+    + response_payload_cases()
 )