Remove enum usage for header/trailer in smithy-http and aws-sdk-signers (#670)

* Remove enum usage for header/trailer in smithy-http and aws-sdk-signers

Author: ubaskota

packages/aws-sdk-signers/.changes/next-release/aws-sdk-signers-breaking-9b52e1c29eb541999e2239be4c725d00.json

@@ -0,0 +1,4 @@
+{
+  "type": "breaking",
+  "description": "Replace `FieldPosition` enum values with string literals for `Field.kind`. Use \"header\" and \"trailer\" instead of `FieldPosition.HEADER` and `FieldPosition.TRAILER`."
+}

packages/aws-sdk-signers/src/aws_sdk_signers/_http.py

@@ -15,11 +15,13 @@
 from copy import deepcopy
 from dataclasses import dataclass
 from functools import cached_property
-from typing import TypedDict
+from typing import TypedDict, get_args
 from urllib.parse import urlunparse
 
 import aws_sdk_signers.interfaces.http as interfaces_http
 
+_VALID_FIELD_POSITIONS = frozenset(get_args(interfaces_http.FieldPosition))
+
 
 class Field(interfaces_http.Field):
     """A name-value pair representing a single field in an HTTP Request or Response.
@@ -36,10 +38,12 @@ def __init__(
         *,
         name: str,
         values: Iterable[str] | None = None,
-        kind: interfaces_http.FieldPosition = interfaces_http.FieldPosition.HEADER,
+        kind: interfaces_http.FieldPosition = "header",
     ):
         self.name = name
         self.values: list[str] = list(values) if values is not None else []
+        if kind not in _VALID_FIELD_POSITIONS:
+            raise ValueError(f"Unknown field kind: {kind!r}")
         self.kind = kind
 
     def add(self, value: str) -> None:
@@ -92,7 +96,7 @@ def __eq__(self, other: object) -> bool:
             return False
         return (
             self.name == other.name
-            and self.kind is other.kind
+            and self.kind == other.kind
             and self.values == other.values
         )
 
@@ -168,7 +172,7 @@ def get_by_type(
 
         Used to grab all headers or all trailers.
         """
-        return [entry for entry in self.entries.values() if entry.kind is kind]
+        return [entry for entry in self.entries.values() if entry.kind == kind]
 
     def extend(self, other: interfaces_http.Fields) -> None:
         """Merges ``entries`` of ``other`` into the current ``entries``.

packages/aws-sdk-signers/src/aws_sdk_signers/interfaces/http.py

@@ -5,29 +5,18 @@
 
 from collections import OrderedDict
 from collections.abc import AsyncIterable, Iterable, Iterator
-from enum import Enum
-from typing import Protocol, runtime_checkable
+from typing import Literal, Protocol, runtime_checkable
 
+FieldPosition = Literal["header", "trailer"]
+"""The type of a field.
 
-class FieldPosition(Enum):
-    """The type of a field.
+Defines its placement in a request or response.
 
-    Defines its placement in a request or response.
-    """
-
-    HEADER = 0
-    """Header field.
-
-    In HTTP this is a header as defined in RFC 9110 Section 6.3. Implementations of
-    other protocols may use this FieldPosition for similar types of metadata.
-    """
-
-    TRAILER = 1
-    """Trailer field.
+header: Header field. In HTTP this is a header as defined in RFC 9110 Section 6.3.
+trailer: Trailer field. In HTTP this is a trailer as defined in RFC 9110 Section 6.5.
 
-    In HTTP this is a trailer as defined in RFC 9110 Section 6.5. Implementations of
-    other protocols may use this FieldPosition for similar types of metadata.
-    """
+Implementations of other protocols may use this FieldPosition for similar types of metadata.
+"""
 
 
 class Field(Protocol):
@@ -43,7 +32,7 @@ class Field(Protocol):
 
     name: str
     values: list[str]
-    kind: FieldPosition = FieldPosition.HEADER
+    kind: FieldPosition = "header"
 
     def add(self, value: str) -> None:
         """Append a value to a field."""

packages/aws-sdk-signers/tests/unit/test_fields.py

@@ -3,22 +3,21 @@
 
 import pytest
 from aws_sdk_signers import Field, Fields
-from aws_sdk_signers.interfaces.http import FieldPosition
 
 
 def test_field_single_valued_basics() -> None:
-    field = Field(name="fname", values=["fval"], kind=FieldPosition.HEADER)
+    field = Field(name="fname", values=["fval"], kind="header")
     assert field.name == "fname"
-    assert field.kind == FieldPosition.HEADER
+    assert field.kind == "header"
     assert field.values == ["fval"]
     assert field.as_string() == "fval"
     assert field.as_tuples() == [("fname", "fval")]
 
 
 def test_field_multi_valued_basics() -> None:
-    field = Field(name="fname", values=["fval1", "fval2"], kind=FieldPosition.HEADER)
+    field = Field(name="fname", values=["fval1", "fval2"], kind="header")
     assert field.name == "fname"
-    assert field.kind == FieldPosition.HEADER
+    assert field.kind == "header"
     assert field.values == ["fval1", "fval2"]
     assert field.as_string() == "fval1,fval2"
     assert field.as_tuples() == [("fname", "fval1"), ("fname", "fval2")]
@@ -62,16 +61,16 @@ def test_field_serialization(values: list[str], expected: str) -> None:
     "field,expected_repr",
     [
         (
-            Field(name="fname", values=["fval1", "fval2"], kind=FieldPosition.HEADER),
-            "Field(name='fname', value=['fval1', 'fval2'], kind=<FieldPosition.HEADER: 0>)",
+            Field(name="fname", values=["fval1", "fval2"], kind="header"),
+            "Field(name='fname', value=['fval1', 'fval2'], kind='header')",
         ),
         (
-            Field(name="fname", kind=FieldPosition.TRAILER),
-            "Field(name='fname', value=[], kind=<FieldPosition.TRAILER: 1>)",
+            Field(name="fname", kind="trailer"),
+            "Field(name='fname', value=[], kind='trailer')",
         ),
         (
             Field(name="fname"),
-            "Field(name='fname', value=[], kind=<FieldPosition.HEADER: 0>)",
+            "Field(name='fname', value=[], kind='header')",
         ),
     ],
 )
@@ -83,8 +82,8 @@ def test_field_repr(field: Field, expected_repr: str) -> None:
     "f1,f2",
     [
         (
-            Field(name="fname", values=["fval1", "fval2"], kind=FieldPosition.TRAILER),
-            Field(name="fname", values=["fval1", "fval2"], kind=FieldPosition.TRAILER),
+            Field(name="fname", values=["fval1", "fval2"], kind="trailer"),
+            Field(name="fname", values=["fval1", "fval2"], kind="trailer"),
         ),
         (
             Field(name="fname", values=["fval1", "fval2"]),
@@ -104,20 +103,20 @@ def test_field_equality(f1: Field, f2: Field) -> None:
     "f1,f2",
     [
         (
-            Field(name="fname", values=["fval1", "fval2"], kind=FieldPosition.HEADER),
-            Field(name="fname", values=["fval1", "fval2"], kind=FieldPosition.TRAILER),
+            Field(name="fname", values=["fval1", "fval2"], kind="header"),
+            Field(name="fname", values=["fval1", "fval2"], kind="trailer"),
         ),
         (
-            Field(name="fname", values=["fval1", "fval2"], kind=FieldPosition.HEADER),
-            Field(name="fname", values=["fval2", "fval1"], kind=FieldPosition.HEADER),
+            Field(name="fname", values=["fval1", "fval2"], kind="header"),
+            Field(name="fname", values=["fval2", "fval1"], kind="header"),
         ),
         (
-            Field(name="fname", values=["fval1", "fval2"], kind=FieldPosition.HEADER),
-            Field(name="fname", values=["fval1"], kind=FieldPosition.HEADER),
+            Field(name="fname", values=["fval1", "fval2"], kind="header"),
+            Field(name="fname", values=["fval1"], kind="header"),
         ),
         (
-            Field(name="fname1", values=["fval1", "fval2"], kind=FieldPosition.HEADER),
-            Field(name="fname2", values=["fval1", "fval2"], kind=FieldPosition.HEADER),
+            Field(name="fname1", values=["fval1", "fval2"], kind="header"),
+            Field(name="fname2", values=["fval1", "fval2"], kind="header"),
         ),
     ],
 )
@@ -211,7 +210,7 @@ def test_fields_length_value(fields: Fields, expected_length: int) -> None:
             Fields([Field(name="fname1")]),
             (
                 "Fields(OrderedDict({'fname1': Field(name='fname1', value=[], "
-                "kind=<FieldPosition.HEADER: 0>)}))"
+                "kind='header')}))"
             ),
         ),
     ],
@@ -314,3 +313,8 @@ def test_fields_delitem_missing() -> None:
     fields = Fields([Field(name="fname1")])
     with pytest.raises(KeyError):
         del fields["fname2"]
+
+
+def test_field_invalid_kind() -> None:
+    with pytest.raises(ValueError, match="Unknown field kind"):
+        Field(name="fname", kind="metadata")  # type: ignore

packages/smithy-http/.changes/next-release/smithy-http-breaking-f567cc46e12d4f61ac5f85b65a0e4426.json

@@ -0,0 +1,4 @@
+{
+  "type": "breaking",
+  "description": "Replace `FieldPosition` enum values with string literals for `Field.kind`. Use \"header\" and \"trailer\" instead of `FieldPosition.HEADER` and `FieldPosition.TRAILER`."
+}

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

@@ -2,12 +2,15 @@
 # SPDX-License-Identifier: Apache-2.0
 from collections import Counter, OrderedDict
 from collections.abc import Iterable, Iterator
+from typing import get_args
 
 from . import interfaces
 from .interfaces import FieldPosition
 
 __version__ = "0.3.1"
 
+_VALID_FIELD_POSITIONS = frozenset(get_args(FieldPosition))
+
 
 class Field(interfaces.Field):
     """A name-value pair representing a single field in an HTTP Request or Response.
@@ -24,10 +27,12 @@ def __init__(
         *,
         name: str,
         values: Iterable[str] | None = None,
-        kind: FieldPosition = FieldPosition.HEADER,
+        kind: FieldPosition = "header",
     ):
         self.name = name
         self.values: list[str] = list(values) if values is not None else []
+        if kind not in _VALID_FIELD_POSITIONS:
+            raise ValueError(f"Unknown field kind: {kind!r}")
         self.kind = kind
 
     def add(self, value: str) -> None:
@@ -79,7 +84,7 @@ def __eq__(self, other: object) -> bool:
             return False
         return (
             self.name == other.name
-            and self.kind is other.kind
+            and self.kind == other.kind
             and self.values == other.values
         )
 
@@ -153,7 +158,7 @@ def get_by_type(self, kind: FieldPosition) -> list[interfaces.Field]:
 
         Used to grab all headers or all trailers.
         """
-        return [entry for entry in self.entries.values() if entry.kind is kind]
+        return [entry for entry in self.entries.values() if entry.kind == kind]
 
     def extend(self, other: interfaces.Fields) -> None:
         """Merges ``entries`` of ``other`` into the current ``entries``.
@@ -225,8 +230,6 @@ def tuples_to_fields(
         try:
             fields[name].add(value)
         except KeyError:
-            fields[name] = Field(
-                name=name, values=[value], kind=kind or FieldPosition.HEADER
-            )
+            fields[name] = Field(name=name, values=[value], kind=kind or "header")
 
     return fields

packages/smithy-http/src/smithy_http/aio/aiohttp.py

@@ -28,7 +28,6 @@
 
 from .. import Field, Fields
 from ..interfaces import (
-    FieldPosition,
     HTTPClientConfiguration,
     HTTPRequestConfiguration,
 )
@@ -125,7 +124,7 @@ async def _marshal_response(
                 headers[header_name] = Field(
                     name=header_name,
                     values=[header_val],
-                    kind=FieldPosition.HEADER,
+                    kind="header",
                 )
 
         return HTTPResponse(

packages/smithy-http/src/smithy_http/aio/crt.py

@@ -41,7 +41,6 @@
 from .. import Field, Fields
 from .. import interfaces as http_interfaces
 from ..exceptions import SmithyHTTPError
-from ..interfaces import FieldPosition
 from . import interfaces as http_aio_interfaces
 
 # Default buffer size for reading from streams (8 KB)
@@ -203,7 +202,7 @@ async def _await_response(
                 fields[header_name] = Field(
                     name=header_name,
                     values=[header_val],
-                    kind=FieldPosition.HEADER,
+                    kind="header",
                 )
         return AWSCRTHTTPResponse(
             status=status_code,
@@ -294,8 +293,7 @@ def _marshal_request(
             request.fields.set_field(Field(name="accept", values=["*/*"]))
 
         for fld in request.fields.entries.values():
-            # TODO: Use literal values for "header"/"trailer".
-            if fld.kind.value != FieldPosition.HEADER.value:
+            if fld.kind != "header":
                 continue
             for val in fld.values:
                 headers_list.append((fld.name, val))

packages/smithy-http/src/smithy_http/interfaces/__init__.py

@@ -2,29 +2,18 @@
 #  SPDX-License-Identifier: Apache-2.0
 from collections.abc import Iterator
 from dataclasses import dataclass
-from enum import Enum
-from typing import Protocol
+from typing import Literal, Protocol
 
+FieldPosition = Literal["header", "trailer"]
+"""The type of a field.
 
-class FieldPosition(Enum):
-    """The type of a field.
+Defines its placement in a request or response.
 
-    Defines its placement in a request or response.
-    """
-
-    HEADER = 0
-    """Header field.
-
-    In HTTP this is a header as defined in RFC 9110 Section 6.3. Implementations of
-    other protocols may use this FieldPosition for similar types of metadata.
-    """
-
-    TRAILER = 1
-    """Trailer field.
+header: Header field. In HTTP this is a header as defined in RFC 9110 Section 6.3.
+trailer: Trailer field. In HTTP this is a trailer as defined in RFC 9110 Section 6.5.
 
-    In HTTP this is a trailer as defined in RFC 9110 Section 6.5. Implementations of
-    other protocols may use this FieldPosition for similar types of metadata.
-    """
+Implementations of other protocols may use this FieldPosition for similar types of metadata.
+"""
 
 
 class Field(Protocol):
@@ -40,7 +29,7 @@ class Field(Protocol):
 
     name: str
     values: list[str]
-    kind: FieldPosition = FieldPosition.HEADER
+    kind: FieldPosition = "header"
 
     def add(self, value: str) -> None:
         """Append a value to a field."""