Smithy AWS Core

Common errors

• ModuleNotFoundError: No module named 'smithy_aws_core.config'

  cause The 'smithy-aws-core' library or its core dependencies ('smithy-python', 'aiobotocore') are not installed, or your virtual environment is not active.
  fix Ensure you have installed the necessary packages: `pip install smithy-aws-core smithy-python aiobotocore`. Verify your virtual environment is correctly activated.

• TypeError: __init__ missing 1 required positional argument: 'config'

  cause When initializing components like `AwsSigner` or `AwsEndpointResolver`, an `AwsUserConfig` (or similar configuration object) is a required argument.
  fix Always create an instance of `AwsUserConfig` (specifying region, credentials, etc.) and pass it as the `config` argument to `smithy-aws-core` component constructors.

• TypeError: argument 'credentials': Expected Credentials, got NoneType

  cause The `credentials` parameter provided to a component (e.g., `AwsUserConfig`, `AwsSigner`) was `None`, indicating that AWS credentials could not be loaded or were not provided.
  fix Ensure that AWS credentials are available in your environment (e.g., `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY` environment variables), in a shared credentials file, or explicitly passed as a `smithy_python.types.Credentials` object.

Warnings

• gotcha Smithy AWS Core is currently pre-1.0 (version 0.5.0). This means its API is not yet stable, and breaking changes may occur in minor versions without deprecation cycles.
  Fix: Refer to the `smithy-python` repository's changelog or release notes for specific breaking changes when upgrading.
• gotcha AWS credential and session management within the Smithy Python ecosystem heavily relies on 'aiobotocore'. If you are accustomed to 'boto3', you might need to adapt your credential provider to work with 'aiobotocore' sessions.
  Fix: Utilize `aiobotocore.session.get_session()` to retrieve `Credentials` objects compatible with `smithy-aws-core` components, or convert credentials from other sources to `smithy_python.types.Credentials`.
• gotcha Direct instantiation of abstract base classes like `AwsHttpClient` is not typically the way to make HTTP requests. These components are usually integrated into generated Smithy clients.
  Fix: For making actual HTTP calls, rely on a generated Smithy client, which will provide a concrete HTTP client implementation, or instantiate a specific implementation like `smithy_python.http.aiohttp.AiohttpHttpClient`.

Install

• pip install smithy-aws-core Install smithy-aws-core

Imports

• AwsUserConfig

  from smithy_aws_core.config import AwsUserConfig

• AwsSigner

  from smithy_aws_core.signing import AwsSigner

• AwsHttpClient

  from smithy_aws_core.http import AwsHttpClient

  AwsHttpClient is an abstract base class; concrete implementations like aiohttp.AiohttpHttpClient are typically used via generated clients.
• AwsEndpointResolver

  from smithy_aws_core.endpoint import AwsEndpointResolver

Quickstart

This quickstart demonstrates how to initialize core Smithy AWS components like `AwsUserConfig` for regional and credential settings, and how to use `AwsSigner` to sign a basic HTTP request, which is a fundamental step in interacting with AWS services. It uses environment variables for AWS credentials.

import asyncio
import os
import datetime
from smithy_aws_core.config import AwsUserConfig
from smithy_aws_core.signing import AwsSigner
from smithy_python.types import Credentials, UnresolvedUrl
from smithy_python.http import HttpRequest

async def main():
    # In a real application, consider using aiobotocore.session.get_session()
    # for robust credential discovery. For this quickstart, we use environment variables.
    aws_access_key_id = os.environ.get("AWS_ACCESS_KEY_ID", "AKIAIOSFODNN7EXAMPLE")
    aws_secret_access_key = os.environ.get("AWS_SECRET_ACCESS_KEY", "wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY")
    aws_session_token = os.environ.get("AWS_SESSION_TOKEN", None)

    if aws_access_key_id == "AKIAIOSFODNN7EXAMPLE" or aws_secret_access_key == "wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY":
        print("Warning: Using dummy AWS credentials. Set AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY environment variables for real usage.")

    credentials = Credentials(
        access_key_id=aws_access_key_id,
        secret_access_key=aws_secret_access_key,
        token=aws_session_token
    )

    config = AwsUserConfig(
        region="us-east-1",
        credentials=credentials,
        endpoint_url=UnresolvedUrl("https://s3.us-east-1.amazonaws.com") # Example S3 endpoint
    )
    print(f"\nCreated AWS User Config for region: {config.region}")

    # Demonstrate an AWS Signer
    signer = AwsSigner(service_id="s3", config=config) # 's3' is the service ID for S3
    print(f"Created AWS Signer for service: {signer.service_id}")

    # Prepare a dummy HTTP request to be signed
    request = HttpRequest(
        method="GET",
        url="https://s3.us-east-1.amazonaws.com/my-bucket", # Example URL, typically resolved by client
        headers={
            "Host": "s3.us-east-1.amazonaws.com",
            "User-Agent": "smithy-python-quickstart/1.0"
        },
        body=b""
    )

    # Sign the request
    # Note: The 'url' in HttpRequest must be a concrete string, not UnresolvedUrl, for signing.
    # In a real client, endpoint resolution would convert UnresolvedUrl to a string.
    signed_request = await signer.sign(request, credentials, datetime.datetime.now(datetime.timezone.utc))

    print(f"\n--- Signed Request Details ---")
    print(f"Method: {signed_request.method}")
    print(f"URL: {signed_request.url}")
    print(f"Headers: {signed_request.headers}")
    if 'Authorization' in signed_request.headers:
        print(f"Authorization header present (truncated): {signed_request.headers['Authorization'][:50]}...")
    else:
        print("Authorization header NOT found.")

asyncio.run(main())