Add an encodable version of the APIGatewayResponse

[sebsto]

Add a convenience initializer to the APIGatewayResponse v2 that accepts an Encodable object

Motivation:

Most Lambda developers will return a JSON object when exposing their function through the API Gateway. The current initializer only accepts a String body as per the AWS message definition.

This obliges all developers to write two lines of code + error handling to encode their object and transform the Data to a string.

Modifications:

Add a new initializer that accepts a body as Encodable

public init<Input: Encodable> (
        statusCode: HTTPResponse.Status,
        headers: HTTPHeaders? = nil,
        body: Input,
        isBase64Encoded: Bool? = nil,
        cookies: [String]? = nil
) throws { ... }

Result:

Developers can now pass a Swift struct to the APIGatewayResponse.

let businessResponse = BusinessResponse(message: "Hello World", code: 200)
return APIGatewayV2Response(statusCode: .ok, body: businessResponse)

[sebsto]

Thank you @adam-fowler
I simplified the code, removed the isBase64Encoded argument, and added the same initializer to APIGatewayResponse

[0xTim]

Have we broken/confused the API before? Since String automatically conforms to Encodable does the new API take precedence over the existing String one meaning it always throws when it doesn't need to? (And always add an extra hop through the encoder that isn't needed, or potentially double encode a JSON body)

[adam-fowler]

Yeah would be good to ensure we have a different signature for the Codable version

[sebsto]

Good point.
What type of difference would be acceptable ?

What about changing the order of the parameters. We sacrifice consistency for compatibility.

extension APIGatewayV2Response {

    public init<Input: Encodable>(
        body: Input,
        statusCode: HTTPResponse.Status,
        headers: HTTPHeaders? = nil,
        cookies: [String]? = nil
    ) throws {
        self.init(
            statusCode: statusCode,
            headers: headers,
            body: try body.string(),
            isBase64Encoded: nil,
            cookies: cookies
        )
    }
}

[0xTim]

Yeah I'd keep the ordering and make the body parameter different to be explicit

[sebsto]

done. I kept the original order and renamed body to encodableBody

[sebsto]

@0xTim @adam-fowler would this be acceptable ? I changed the order of the args.

[adam-fowler]

@0xTim @adam-fowler would this be acceptable ? I changed the order of the args.

I'd prefer you changed the name of the body parameter.