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List Amazon S3 Buckets with the AWS SDK for Swift

This is a simple example of an AWS Lambda function that uses the AWS SDK for Swift to read data from Amazon S3.

Code

The Lambda function reads all bucket names from your AWS account and returns them as a String.

The code creates a LambdaRuntime struct. In it's simplest form, the initializer takes a function as argument. The function is the handler that will be invoked when the API Gateway receives an HTTP request.

The handler is (event: APIGatewayV2Request, context: LambdaContext) -> APIGatewayV2Response. The function takes two arguments:

  • the event argument is a APIGatewayV2Request. It is the parameter passed by the API Gateway. It contains all data passed in the HTTP request and some meta data.
  • the context argument is a Lambda Context. It is a description of the runtime context.

The function must return a APIGatewayV2Response.

APIGatewayV2Request and APIGatewayV2Response are defined in the Swift AWS Lambda Events library.

The handler creates an S3 client and ListBucketsInput object. It passes the input object to the client and receives an output response. It then extracts the list of bucket names from the output and creates a \n-separated list of names, as a String

Build & Package

To build the package, type the following commands.

swift build
swift package archive --allow-network-connections docker

If there is no error, there is a ZIP file ready to deploy. The ZIP file is located at .build/plugins/AWSLambdaPackager/outputs/AWSLambdaPackager/AWSSDKExample/AWSSDKExample.zip

Deploy

The deployment must include the Lambda function and an API Gateway. We use the Serverless Application Model (SAM) to deploy the infrastructure.

Prerequisites : Install the SAM CLI

The example directory contains a file named template.yaml that describes the deployment.

To actually deploy your Lambda function and create the infrastructure, type the following sam command.

sam deploy \
--resolve-s3 \
--template-file template.yaml \
--stack-name AWSSDKExample \
--capabilities CAPABILITY_IAM

At the end of the deployment, the script lists the API Gateway endpoint. The output is similar to this one.

-----------------------------------------------------------------------------------------------------------------------------
Outputs                                                                                                                     
-----------------------------------------------------------------------------------------------------------------------------
Key                 APIGatewayEndpoint                                                                                      
Description         API Gateway endpoint URL"                                                                                
Value               https://a5q74es3k2.execute-api.us-east-1.amazonaws.com                                                  
-----------------------------------------------------------------------------------------------------------------------------

Invoke your Lambda function

To invoke the Lambda function, use this curl command line.

curl https://a5q74es3k2.execute-api.us-east-1.amazonaws.com

Be sure to replace the URL with the API Gateway endpoint returned in the previous step.

This should print text similar to

my_bucket_1
my_bucket_2
...

Delete the infrastructure

When done testing, you can delete the infrastructure with this command.

sam delete