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Event Source Data Classes

Event Source Data Classes utility provides classes self-describing Lambda event sources.

Key Features

  • Type hinting and code completion for common event types
  • Helper functions for decoding/deserializing nested fields
  • Docstrings for fields contained in event schemas

Background

When authoring Lambda functions, you often need to understand the schema of the event dictionary which is passed to the handler. There are several common event types which follow a specific schema, depending on the service triggering the Lambda function.

Getting started

Utilizing the data classes

The classes are initialized by passing in the Lambda event object into the constructor of the appropriate data class or by using the event_source decorator.

For example, if your Lambda function is being triggered by an API Gateway proxy integration, you can use the APIGatewayProxyEvent class.

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from aws_lambda_powertools.utilities.data_classes import APIGatewayProxyEvent

def lambda_handler(event: dict, context):
    event = APIGatewayProxyEvent(event)
    if 'helloworld' in event.path and event.http_method == 'GET':
        do_something_with(event.body, user)

Same example as above, but using the event_source decorator

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from aws_lambda_powertools.utilities.data_classes import event_source, APIGatewayProxyEvent

@event_source(data_class=APIGatewayProxyEvent)
def lambda_handler(event: APIGatewayProxyEvent, context):
    if 'helloworld' in event.path and event.http_method == 'GET':
        do_something_with(event.body, user)

Autocomplete with self-documented properties and methods

Utilities Data Classes

Supported event sources

Event Source Data_class
API Gateway Proxy APIGatewayProxyEvent
API Gateway Proxy V2 APIGatewayProxyEventV2
Application Load Balancer ALBEvent
AppSync Resolver AppSyncResolverEvent
CloudWatch Logs CloudWatchLogsEvent
CodePipeline Job Event CodePipelineJobEvent
Cognito User Pool Multiple available under cognito_user_pool_event
Connect Contact Flow ConnectContactFlowEvent
DynamoDB streams DynamoDBStreamEvent, DynamoDBRecordEventName
EventBridge EventBridgeEvent
Kinesis Data Stream KinesisStreamEvent
S3 S3Event
S3 Object Lambda S3ObjectLambdaEvent
SES SESEvent
SNS SNSEvent
SQS SQSEvent

Info

The examples provided below are far from exhaustive - the data classes themselves are designed to provide a form of documentation inherently (via autocompletion, types and docstrings).

API Gateway Proxy

It is used for either API Gateway REST API or HTTP API using v1 proxy event.

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from aws_lambda_powertools.utilities.data_classes import event_source, APIGatewayProxyEvent

@event_source(data_class=APIGatewayProxyEvent)
def lambda_handler(event: APIGatewayProxyEvent, context):
    if "helloworld" in event.path and event.http_method == "GET":
        request_context = event.request_context
        identity = request_context.identity
        user = identity.user
        do_something_with(event.json_body, user)

API Gateway Proxy V2

It is used for HTTP API using v2 proxy event.

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from aws_lambda_powertools.utilities.data_classes import event_source, APIGatewayProxyEventV2

@event_source(data_class=APIGatewayProxyEventV2)
def lambda_handler(event: APIGatewayProxyEventV2, context):
    if "helloworld" in event.path and event.http_method == "POST":
        do_something_with(event.json_body, event.query_string_parameters)

Application Load Balancer

Is it used for Application load balancer event.

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from aws_lambda_powertools.utilities.data_classes import event_source, ALBEvent

@event_source(data_class=ALBEvent)
def lambda_handler(event: ALBEvent, context):
    if "helloworld" in event.path and event.http_method == "POST":
        do_something_with(event.json_body, event.query_string_parameters)

AppSync Resolver

New in 1.12.0

Used when building Lambda GraphQL Resolvers with Amplify GraphQL Transform Library (@function), and AppSync Direct Lambda Resolvers.

In this example, we also use the new Logger correlation_id and built-in correlation_paths to extract, if available, X-Ray Trace ID in AppSync request headers:

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from aws_lambda_powertools.logging import Logger, correlation_paths
from aws_lambda_powertools.utilities.data_classes.appsync_resolver_event import (
    AppSyncResolverEvent,
    AppSyncIdentityCognito
)

logger = Logger()

def get_locations(name: str = None, size: int = 0, page: int = 0):
    """Your resolver logic here"""

@logger.inject_lambda_context(correlation_id_path=correlation_paths.APPSYNC_RESOLVER)
def lambda_handler(event, context):
    event: AppSyncResolverEvent = AppSyncResolverEvent(event)

    # Case insensitive look up of request headers
    x_forwarded_for = event.get_header_value("x-forwarded-for")

    # Support for AppSyncIdentityCognito or AppSyncIdentityIAM identity types
    assert isinstance(event.identity, AppSyncIdentityCognito)
    identity: AppSyncIdentityCognito = event.identity

    # Logging with correlation_id
    logger.debug({
        "x-forwarded-for": x_forwarded_for,
        "username": identity.username
    })

    if event.type_name == "Merchant" and event.field_name == "locations":
        return get_locations(**event.arguments)

    raise ValueError(f"Unsupported field resolver: {event.field_name}")

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{
  "typeName": "Merchant",
  "fieldName": "locations",
  "arguments": {
    "page": 2,
    "size": 1,
    "name": "value"
  },
  "identity": {
    "claims": {
      "iat": 1615366261
      ...
    },
    "username": "mike",
    ...
  },
  "request": {
    "headers": {
      "x-amzn-trace-id": "Root=1-60488877-0b0c4e6727ab2a1c545babd0",
      "x-forwarded-for": "127.0.0.1"
      ...
    }
  },
  ...
}

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{
    "level":"DEBUG",
    "location":"lambda_handler:22",
    "message":{
        "x-forwarded-for":"127.0.0.1",
        "username":"mike"
    },
    "timestamp":"2021-03-10 12:38:40,062",
    "service":"service_undefined",
    "sampling_rate":0.0,
    "cold_start":true,
    "function_name":"func_name",
    "function_memory_size":512,
    "function_arn":"func_arn",
    "function_request_id":"6735a29c-c000-4ae3-94e6-1f1c934f7f94",
    "correlation_id":"Root=1-60488877-0b0c4e6727ab2a1c545babd0"
}

CloudWatch Logs

CloudWatch Logs events by default are compressed and base64 encoded. You can use the helper function provided to decode, decompress and parse json data from the event.

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from aws_lambda_powertools.utilities.data_classes import event_source, CloudWatchLogsEvent
from aws_lambda_powertools.utilities.data_classes.cloud_watch_logs_event import CloudWatchLogsDecodedData

@event_source(data_class=CloudWatchLogsEvent)
def lambda_handler(event: CloudWatchLogsEvent, context):
    decompressed_log: CloudWatchLogsDecodedData = event.parse_logs_data
    log_events = decompressed_log.log_events
    for event in log_events:
        do_something_with(event.timestamp, event.message)

CodePipeline Job

Data classes and utility functions to help create continuous delivery pipelines tasks with AWS Lambda

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from aws_lambda_powertools import Logger
from aws_lambda_powertools.utilities.data_classes import event_source, CodePipelineJobEvent

logger = Logger()

@event_source(data_class=CodePipelineJobEvent)
def lambda_handler(event, context):
    """The Lambda function handler

    If a continuing job then checks the CloudFormation stack status
    and updates the job accordingly.

    If a new job then kick of an update or creation of the target
    CloudFormation stack.
    """

    # Extract the Job ID
    job_id = event.get_id

    # Extract the params
    params: dict = event.decoded_user_parameters
    stack = params["stack"]
    artifact_name = params["artifact"]
    template_file = params["file"]

    try:
        if event.data.continuation_token:
            # If we're continuing then the create/update has already been triggered
            # we just need to check if it has finished.
            check_stack_update_status(job_id, stack)
        else:
            template = event.get_artifact(artifact_name, template_file)
            # Kick off a stack update or create
            start_update_or_create(job_id, stack, template)
    except Exception as e:
        # If any other exceptions which we didn't expect are raised
        # then fail the job and log the exception message.
        logger.exception("Function failed due to exception.")
        put_job_failure(job_id, "Function exception: " + str(e))

    logger.debug("Function complete.")
    return "Complete."

Cognito User Pool

Cognito User Pools have several different Lambda trigger sources, all of which map to a different data class, which can be imported from aws_lambda_powertools.data_classes.cognito_user_pool_event:

Trigger/Event Source Data Class
Custom message event data_classes.cognito_user_pool_event.CustomMessageTriggerEvent
Post authentication data_classes.cognito_user_pool_event.PostAuthenticationTriggerEvent
Post confirmation data_classes.cognito_user_pool_event.PostConfirmationTriggerEvent
Pre authentication data_classes.cognito_user_pool_event.PreAuthenticationTriggerEvent
Pre sign-up data_classes.cognito_user_pool_event.PreSignUpTriggerEvent
Pre token generation data_classes.cognito_user_pool_event.PreTokenGenerationTriggerEvent
User migration data_classes.cognito_user_pool_event.UserMigrationTriggerEvent
Define Auth Challenge data_classes.cognito_user_pool_event.DefineAuthChallengeTriggerEvent
Create Auth Challenge data_classes.cognito_user_pool_event.CreateAuthChallengeTriggerEvent
Verify Auth Challenge data_classes.cognito_user_pool_event.VerifyAuthChallengeResponseTriggerEvent

Post Confirmation Example

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from aws_lambda_powertools.utilities.data_classes.cognito_user_pool_event import PostConfirmationTriggerEvent

def lambda_handler(event, context):
    event: PostConfirmationTriggerEvent = PostConfirmationTriggerEvent(event)

    user_attributes = event.request.user_attributes
    do_something_with(user_attributes)

Define Auth Challenge Example

NOTE

In this example we are modifying the wrapped dict response fields, so we need to return the json serializable wrapped event in event.raw_event

This example is based on the AWS Cognito docs for Define Auth Challenge Lambda Trigger.

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from aws_lambda_powertools.utilities.data_classes.cognito_user_pool_event import DefineAuthChallengeTriggerEvent

def handler(event: dict, context) -> dict:
    event: DefineAuthChallengeTriggerEvent = DefineAuthChallengeTriggerEvent(event)
    if (
        len(event.request.session) == 1
        and event.request.session[0].challenge_name == "SRP_A"
    ):
        event.response.issue_tokens = False
        event.response.fail_authentication = False
        event.response.challenge_name = "PASSWORD_VERIFIER"
    elif (
        len(event.request.session) == 2
        and event.request.session[1].challenge_name == "PASSWORD_VERIFIER"
        and event.request.session[1].challenge_result
    ):
        event.response.issue_tokens = False
        event.response.fail_authentication = False
        event.response.challenge_name = "CUSTOM_CHALLENGE"
    elif (
        len(event.request.session) == 3
        and event.request.session[2].challenge_name == "CUSTOM_CHALLENGE"
        and event.request.session[2].challenge_result
    ):
        event.response.issue_tokens = True
        event.response.fail_authentication = False
    else:
        event.response.issue_tokens = False
        event.response.fail_authentication = True

    return event.raw_event

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{
    "version": "1",
    "region": "us-east-1",
    "userPoolId": "us-east-1_example",
    "userName": "UserName",
    "callerContext": {
        "awsSdkVersion": "awsSdkVersion",
        "clientId": "clientId"
    },
    "triggerSource": "DefineAuthChallenge_Authentication",
    "request": {
        "userAttributes": {
            "sub": "4A709A36-7D63-4785-829D-4198EF10EBDA",
            "email_verified": "true",
            "name": "First Last",
            "email": "define-auth@mail.com"
        },
        "session": [
            {
                "challengeName": "SRP_A",
                "challengeResult": true
            }
        ]
    },
    "response": {
        "issueTokens": false,
        "failAuthentication": false,
        "challengeName": "PASSWORD_VERIFIER"
    }
}

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{
    "version": "1",
    "region": "us-east-1",
    "userPoolId": "us-east-1_example",
    "userName": "UserName",
    "callerContext": {
        "awsSdkVersion": "awsSdkVersion",
        "clientId": "clientId"
    },
    "triggerSource": "DefineAuthChallenge_Authentication",
    "request": {
        "userAttributes": {
            "sub": "4A709A36-7D63-4785-829D-4198EF10EBDA",
            "email_verified": "true",
            "name": "First Last",
            "email": "define-auth@mail.com"
        },
        "session": [
            {
                "challengeName": "SRP_A",
                "challengeResult": true
            },
            {
                "challengeName": "PASSWORD_VERIFIER",
                "challengeResult": true
            }
        ]
    },
    "response": {
        "issueTokens": false,
        "failAuthentication": false,
        "challengeName": "CUSTOM_CHALLENGE"
    }
}

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{
    "version": "1",
    "region": "us-east-1",
    "userPoolId": "us-east-1_example",
    "userName": "UserName",
    "callerContext": {
        "awsSdkVersion": "awsSdkVersion",
        "clientId": "clientId"
    },
    "triggerSource": "DefineAuthChallenge_Authentication",
    "request": {
        "userAttributes": {
            "sub": "4A709A36-7D63-4785-829D-4198EF10EBDA",
            "email_verified": "true",
            "name": "First Last",
            "email": "define-auth@mail.com"
        },
        "session": [
            {
                "challengeName": "SRP_A",
                "challengeResult": true
            },
            {
                "challengeName": "PASSWORD_VERIFIER",
                "challengeResult": true
            },
            {
                "challengeName": "CUSTOM_CHALLENGE",
                "challengeResult": true
            }
        ]
    },
    "response": {
        "issueTokens": true,
        "failAuthentication": false
    }
}

Create Auth Challenge Example

This example is based on the AWS Cognito docs for Create Auth Challenge Lambda Trigger.

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from aws_lambda_powertools.utilities.data_classes import event_source
from aws_lambda_powertools.utilities.data_classes.cognito_user_pool_event import CreateAuthChallengeTriggerEvent

@event_source(data_class=CreateAuthChallengeTriggerEvent)
def handler(event: CreateAuthChallengeTriggerEvent, context) -> dict:
    if event.request.challenge_name == "CUSTOM_CHALLENGE":
        event.response.public_challenge_parameters = {"captchaUrl": "url/123.jpg"}
        event.response.private_challenge_parameters = {"answer": "5"}
        event.response.challenge_metadata = "CAPTCHA_CHALLENGE"
    return event.raw_event

Verify Auth Challenge Response Example

This example is based on the AWS Cognito docs for Verify Auth Challenge Response Lambda Trigger.

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from aws_lambda_powertools.utilities.data_classes import event_source
from aws_lambda_powertools.utilities.data_classes.cognito_user_pool_event import VerifyAuthChallengeResponseTriggerEvent

@event_source(data_class=VerifyAuthChallengeResponseTriggerEvent)
def handler(event: VerifyAuthChallengeResponseTriggerEvent, context) -> dict:
    event.response.answer_correct = (
        event.request.private_challenge_parameters.get("answer") == event.request.challenge_answer
    )
    return event.raw_event

Connect Contact Flow

New in 1.11.0

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from aws_lambda_powertools.utilities.data_classes.connect_contact_flow_event import (
    ConnectContactFlowChannel,
    ConnectContactFlowEndpointType,
    ConnectContactFlowEvent,
    ConnectContactFlowInitiationMethod,
)

def lambda_handler(event, context):
    event: ConnectContactFlowEvent = ConnectContactFlowEvent(event)
    assert event.contact_data.attributes == {"Language": "en-US"}
    assert event.contact_data.channel == ConnectContactFlowChannel.VOICE
    assert event.contact_data.customer_endpoint.endpoint_type == ConnectContactFlowEndpointType.TELEPHONE_NUMBER
    assert event.contact_data.initiation_method == ConnectContactFlowInitiationMethod.API

DynamoDB Streams

The DynamoDB data class utility provides the base class for DynamoDBStreamEvent, a typed class for attributes values (AttributeValue), as well as enums for stream view type (StreamViewType) and event type (DynamoDBRecordEventName).

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from aws_lambda_powertools.utilities.data_classes.dynamo_db_stream_event import (
    DynamoDBStreamEvent,
    DynamoDBRecordEventName
)

def lambda_handler(event, context):
    event: DynamoDBStreamEvent = DynamoDBStreamEvent(event)

    # Multiple records can be delivered in a single event
    for record in event.records:
        if record.event_name == DynamoDBRecordEventName.MODIFY:
            do_something_with(record.dynamodb.new_image)
            do_something_with(record.dynamodb.old_image)

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from aws_lambda_powertools.utilities.data_classes import event_source, DynamoDBStreamEvent
from aws_lambda_powertools.utilities.data_classes.dynamo_db_stream_event import AttributeValueType, AttributeValue
from aws_lambda_powertools.utilities.typing import LambdaContext


@event_source(data_class=DynamoDBStreamEvent)
def lambda_handler(event: DynamoDBStreamEvent, context: LambdaContext):
    for record in event.records:
        key: AttributeValue = record.dynamodb.keys["id"]
        if key == AttributeValueType.Number:
            # {"N": "123.45"} => "123.45"
            assert key.get_value == key.n_value
            print(key.get_value)
        elif key == AttributeValueType.Map:
            assert key.get_value == key.map_value
            print(key.get_value)

EventBridge

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from aws_lambda_powertools.utilities.data_classes import event_source, EventBridgeEvent

@event_source(data_class=EventBridgeEvent)
def lambda_handler(event: EventBridgeEvent, context):
    do_something_with(event.detail)

Kinesis streams

Kinesis events by default contain base64 encoded data. You can use the helper function to access the data either as json or plain text, depending on the original payload.

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from aws_lambda_powertools.utilities.data_classes import event_source, KinesisStreamEvent

@event_source(data_class=KinesisStreamEvent)
def lambda_handler(event: KinesisStreamEvent, context):
    kinesis_record = next(event.records).kinesis

    # if data was delivered as text
    data = kinesis_record.data_as_text()

    # if data was delivered as json
    data = kinesis_record.data_as_json()

    do_something_with(data)

S3

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from urllib.parse import unquote_plus
from aws_lambda_powertools.utilities.data_classes import event_source, S3Event

@event_source(data_class=S3Event)
def lambda_handler(event: S3Event, context):
    bucket_name = event.bucket_name

    # Multiple records can be delivered in a single event
    for record in event.records:
        object_key = unquote_plus(record.s3.get_object.key)

        do_something_with(f"{bucket_name}/{object_key}")

S3 Object Lambda

This example is based on the AWS Blog post Introducing Amazon S3 Object Lambda – Use Your Code to Process Data as It Is Being Retrieved from S3.

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import boto3
import requests

from aws_lambda_powertools import Logger
from aws_lambda_powertools.logging.correlation_paths import S3_OBJECT_LAMBDA
from aws_lambda_powertools.utilities.data_classes.s3_object_event import S3ObjectLambdaEvent

logger = Logger()
session = boto3.Session()
s3 = session.client("s3")

@logger.inject_lambda_context(correlation_id_path=S3_OBJECT_LAMBDA, log_event=True)
def lambda_handler(event, context):
    event = S3ObjectLambdaEvent(event)

    # Get object from S3
    response = requests.get(event.input_s3_url)
    original_object = response.content.decode("utf-8")

    # Make changes to the object about to be returned
    transformed_object = original_object.upper()

    # Write object back to S3 Object Lambda
    s3.write_get_object_response(
        Body=transformed_object, RequestRoute=event.request_route, RequestToken=event.request_token
    )

    return {"status_code": 200}

SES

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from aws_lambda_powertools.utilities.data_classes import event_source, SESEvent

@event_source(data_class=SESEvent)
def lambda_handler(event: SESEvent, context):
    # Multiple records can be delivered in a single event
    for record in event.records:
        mail = record.ses.mail
        common_headers = mail.common_headers

        do_something_with(common_headers.to, common_headers.subject)

SNS

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from aws_lambda_powertools.utilities.data_classes import event_source, SNSEvent

@event_source(data_class=SNSEvent)
def lambda_handler(event: SNSEvent, context):
    # Multiple records can be delivered in a single event
    for record in event.records:
        message = record.sns.message
        subject = record.sns.subject

        do_something_with(subject, message)

SQS

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from aws_lambda_powertools.utilities.data_classes import event_source, SQSEvent

@event_source(data_class=SQSEvent)
def lambda_handler(event: SQSEvent, context):
    # Multiple records can be delivered in a single event
    for record in event.records:
        do_something_with(record.body)
Last update: 2021-06-08
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