What

A small application to demonstrate how an OpenAPI v3.0 API can be implemented in Go and deployed to AWS using the HTTP API.

Check out this medium post FIXME for more information.

Requirements

• Modern go toolchain - I used go 1.14.6
• oapi-codegen
• AWS SAM application management tool
• Basic utilities: zip for function upload to AWS, curl and jq for testing

Install

Clone this repo somewhere on your filesystem.

git clone github.com/seanrmurphy/lambda-openapi3-test

Build, deploy, test, clean up

• Generate the types and server-side stub code

cd api
go generate

This generates two files api-server.gen.go and api-types.gen.go which contain the server code and the types defined in the OAS3 specification respectively.

• Build the application

This application supports 2 modes: one in which the application runs locally and one in which the application runs in AWS. main.go provides a boolean lambdaMode which determines whether the resulting binary should be run locally or as a Lamdba function. Set lambdaMode to false to build a binary which can offer the API locally.

go build

This builds the application in the top level directory of the repo.

• Run the application locally (optional)

If the application was built with lambdaMode set to false, you can run the binary directly

./lambda-openapi3-test

You can then run the curl based tests in the tests directory.

• Deploy the application to AWS

If the binary is compiled with lambdaMode set to true, then it can be deployed to AWS. Assuming your AWS credentials are configured and SAM is set up

cd deploy
./deploy.sh

This zips the executable and uploads it to AWS using the sam tool and associated configuration file (sam-deploy.toml). On successful completion, it prints the identifier for the Lambda function and the endpoint of the HTTP API.

• Run the tests

cd ../tests
export RESTAPI=<ENDPOINT OUTPUT FROM DEPLOYMENT PROCESS>
./tests.sh

The tests demonstrate both successful and unsuccessful calling of all of the endpoints defined in the API.

• Removing the API

The easiest way to remove the application is via the AWS CloudFormations dashboard.

Improved Request Validation

As noted in the medium post, oapi-codegen does not perform validation of the body of requests. This should be evident from the test suite provided.

One way of dealing with that is to apply this pull request. This makes a new capability available to the oapi-codegen tool, that of validating the unmarshall of objects. It operates by creating an UnmarshalJSON() function for schemas which are used as input parameters. You can achieve the same by copying the code below to the api-types.gen.go file and rebuilding.

Now, if you run the API locally, the tests generate an error when and incorrect JSON object is supplied and there is similar behaviour when the function is uploaded to AWS.

func (t *InputObject) UnmarshalJSON(data []byte) error {
	inner := struct {
		Descriptor *string `json:"descriptor,omitempty"`
		IntVal     *int    `json:"int_val,omitempty"`
		String     *string `json:"string,omitempty"`
	}{}
	err := json.Unmarshal(data, &inner)
	if err != nil {
		return err
	}
	if inner.Descriptor == nil {
		return errors.New("descriptor is required")
	}
	if inner.IntVal == nil {
		return errors.New("int_val is required")
	}
	if inner.String == nil {
		return errors.New("string is required")
	}
	*t = InputObject{
		Descriptor: *inner.Descriptor,
		IntVal:     *inner.IntVal,
		String:     *inner.String,
	}
	return nil
}