Use TypedProperty for UserAgent (#425)

Author: alextwoods

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

@@ -6,6 +6,7 @@
 import smithy_aws_core
 import smithy_core
 from smithy_core.interceptors import Interceptor, InterceptorContext
+from smithy_http.interceptors.user_agent import USER_AGENT
 from smithy_http.user_agent import UserAgentComponent, RawStringUserAgentComponent
 
 _USERAGENT_SDK_NAME = "aws-sdk-python"
@@ -39,8 +40,8 @@ def __init__(
     def read_after_serialization(
         self, context: InterceptorContext[Any, Any, Any, Any]
     ) -> None:
-        if "user_agent" in context.properties:
-            user_agent = context.properties["user_agent"]
+        if USER_AGENT in context.properties:
+            user_agent = context.properties[USER_AGENT]
             user_agent.sdk_metadata = self._build_sdk_metadata()
             user_agent.api_metadata.append(
                 UserAgentComponent("api", self._service_id, self._sdk_version)

packages/smithy-http/src/smithy_http/interceptors/user_agent.py

@@ -5,10 +5,13 @@
 
 import smithy_core
 from smithy_core.interceptors import Interceptor, InterceptorContext
+from smithy_core.types import PropertyKey
 from smithy_http import Field
 from smithy_http.aio.interfaces import HTTPRequest
 from smithy_http.user_agent import UserAgent, UserAgentComponent
 
+USER_AGENT = PropertyKey(key="user_agent", value_type=UserAgent)
+
 
 class UserAgentInterceptor(Interceptor[Any, None, HTTPRequest, None]):
     """Adds interceptors that initialize UserAgent in the context and add the user-agent
@@ -17,12 +20,12 @@ class UserAgentInterceptor(Interceptor[Any, None, HTTPRequest, None]):
     def read_before_execution(
         self, context: InterceptorContext[Any, None, None, None]
     ) -> None:
-        context.properties["user_agent"] = _UserAgentBuilder.from_environment().build()
+        context.properties[USER_AGENT] = _UserAgentBuilder.from_environment().build()
 
     def modify_before_signing(
         self, context: InterceptorContext[Any, None, HTTPRequest, None]
     ) -> HTTPRequest:
-        user_agent = context.properties["user_agent"]
+        user_agent = context.properties[USER_AGENT]
         request = context.transport_request
         request.fields.set_field(Field(name="User-Agent", values=[str(user_agent)]))
         return context.transport_request