Add exec-env to User-Agent and warn on long app IDs

packages/smithy-aws-core/.changes/next-release/smithy-aws-core-enhancement-7976d8dcd859490ab10c8b5c5876e21d.json

@@ -0,0 +1,4 @@
+{
+  "type": "enhancement",
+  "description": "Add the `exec-env/` field to the User-Agent header from the `AWS_EXECUTION_ENV` environment variable, and log a warning when `sdk_ua_app_id` is longer than 50 characters."
+}

packages/smithy-aws-core/src/smithy_aws_core/aio/config/aws_config.py

@@ -27,6 +27,7 @@
     validate_profile,
     validate_region,
     validate_retry_mode,
+    validate_sdk_ua_app_id,
 )
 from .context import AsyncSharedConfigContext
 from .filesystem import AsyncFileSystem
@@ -184,6 +185,7 @@ class AsyncAwsConfig:
         "sdk_ua_app_id": FieldSpec(
             default=None,
             resolver=resolve_sdk_ua_app_id,
+            validator=validate_sdk_ua_app_id,
         ),
         "user_agent_extra": FieldSpec(
             default=None,

packages/smithy-aws-core/src/smithy_aws_core/config/validators.py

@@ -1,6 +1,7 @@
 # Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 # SPDX-License-Identifier: Apache-2.0
 
+import logging
 import re
 from collections.abc import Collection
 from typing import get_args
@@ -15,8 +16,13 @@
     "validate_profile",
     "validate_region",
     "validate_retry_mode",
+    "validate_sdk_ua_app_id",
 ]
 
+logger = logging.getLogger(__name__)
+
+_SDK_UA_APP_ID_MAX_LENGTH = 50
+
 _REGION_PATTERN = re.compile(r"^(?![0-9]+$)(?!-)[a-zA-Z0-9-]{1,63}(?<!-)$")
 
 
@@ -110,3 +116,18 @@ def validate_profile(
         raise ProfileNotFoundError(
             f"Profile {profile_name!r} from {source_str} was not found in config file."
         )
+
+
+def validate_sdk_ua_app_id(value: object) -> None:
+    """Warn when the SDK user agent app ID is longer than recommended.
+
+    The app ID is still used. Config is resolved once, so the warning is logged once.
+
+    :param value: The resolved app ID value.
+    """
+    if isinstance(value, str) and len(value) > _SDK_UA_APP_ID_MAX_LENGTH:
+        logger.warning(
+            "The configured value for sdk_ua_app_id exceeds the recommended maximum "
+            "length of %d characters.",
+            _SDK_UA_APP_ID_MAX_LENGTH,
+        )

packages/smithy-aws-core/src/smithy_aws_core/interceptors/user_agent.py

@@ -1,6 +1,7 @@
 #  Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 #  SPDX-License-Identifier: Apache-2.0
 # pyright: reportMissingTypeStubs=false
+import os
 from typing import Any
 
 import smithy_core
@@ -39,6 +40,7 @@ def __init__(
         self._ua_app_id = ua_app_id
         self._sdk_version = sdk_version
         self._service_id = service_id
+        self._execution_env = os.environ.get("AWS_EXECUTION_ENV")
 
     def read_after_serialization(self, context: RequestContext[Any, Any]) -> None:
         if USER_AGENT in context.properties:
@@ -48,6 +50,11 @@ def read_after_serialization(self, context: RequestContext[Any, Any]) -> None:
                 UserAgentComponent("api", self._service_id, self._sdk_version)
             )
 
+            if self._execution_env:
+                user_agent.env_metadata.append(
+                    UserAgentComponent("exec-env", self._execution_env)
+                )
+
             if self._ua_app_id is not None:
                 user_agent.additional_metadata.append(
                     UserAgentComponent("app", self._ua_app_id)

packages/smithy-aws-core/tests/unit/config/test_validators.py

@@ -9,6 +9,7 @@
     validate_max_attempts,
     validate_region,
     validate_retry_mode,
+    validate_sdk_ua_app_id,
 )
 
 
@@ -89,3 +90,14 @@ def test_valid_values(self, value: int):
     def test_invalid_values(self, value: int):
         with pytest.raises(ConfigValidationError, match="max_attempts"):
             validate_max_attempts(value)
+
+
+class TestValidateSdkUaAppId:
+    def test_warns_when_too_long(self, caplog: pytest.LogCaptureFixture):
+        validate_sdk_ua_app_id("a" * 51)
+        assert "exceeds the recommended maximum length of 50" in caplog.text
+
+    @pytest.mark.parametrize("value", [None, "a" * 50])
+    def test_no_warning(self, value: str | None, caplog: pytest.LogCaptureFixture):
+        validate_sdk_ua_app_id(value)
+        assert caplog.text == ""

packages/smithy-aws-core/tests/unit/interceptors/test_user_agent.py

@@ -0,0 +1,36 @@
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0
+from typing import Any
+from unittest.mock import Mock
+
+import pytest
+from smithy_aws_core.interceptors.user_agent import UserAgentInterceptor
+from smithy_core.interceptors import RequestContext
+from smithy_core.types import TypedProperties
+from smithy_http.interceptors.user_agent import USER_AGENT
+from smithy_http.user_agent import UserAgent, UserAgentComponent
+
+
+def _user_agent_string() -> str:
+    interceptor = UserAgentInterceptor(
+        ua_suffix=None, ua_app_id=None, sdk_version="1.0.0", service_id="svc"
+    )
+    properties = TypedProperties()
+    properties[USER_AGENT] = UserAgent(
+        language_metadata=[UserAgentComponent("lang", "python", "3.12")]
+    )
+    context = RequestContext[Any, Any](
+        request=Mock(), transport_request=Mock(), properties=properties
+    )
+    interceptor.read_after_serialization(context)
+    return str(properties[USER_AGENT])
+
+
+def test_adds_execution_env(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("AWS_EXECUTION_ENV", "AWS_Lambda_python3.12")
+    assert "lang/python#3.12 exec-env/AWS_Lambda_python3.12" in _user_agent_string()
+
+
+def test_omits_execution_env_when_unset(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.delenv("AWS_EXECUTION_ENV", raising=False)
+    assert "exec-env/" not in _user_agent_string()

scripts/api-snapshot/api.json

@@ -126,7 +126,8 @@
     "validate_max_attempts": "rex-function",
     "validate_profile": "rex-function",
     "validate_region": "rex-function",
-    "validate_retry_mode": "rex-function"
+    "validate_retry_mode": "rex-function",
+    "validate_sdk_ua_app_id": "rex-function"
   },
   "smithy_aws_core.aio.config.context": {
     "AsyncDefaultFileSystem": "rex-class[async]",
@@ -465,10 +466,12 @@
     "ConfigSource": "rex-class",
     "ConfigValidationError": "rex-exception",
     "ProfileNotFoundError": "rex-exception",
+    "logger": "Logger",
     "validate_max_attempts": "function",
     "validate_profile": "function",
     "validate_region": "function",
-    "validate_retry_mode": "function"
+    "validate_retry_mode": "function",
+    "validate_sdk_ua_app_id": "function"
   },
   "smithy_aws_core.endpoints": {
     "PropertyKey": "rex-class",