Quick helper functions when testing local serverless applications (Typescript + AWS Lambda) to translate `express` req/res objects into the appropriate types for API Gateway

apigw-express.ts

const apiGWEventFromReq = (req: Request): APIGatewayEvent => {
    const [headers, multiValueHeaders] = Object.keys(req.headers).reduce((parts, key) => {
        const val = req.headers[key]
        if (!val) {
            return parts
        }
        const [headers, multiValueHeaders] = parts
        if (Array.isArray(val)) {
            multiValueHeaders[key] = val;
        } else {
            headers[key] = val
        }

        return [headers, multiValueHeaders]
    }, [<Record<string, string>>{}, <Record<string, string[]>>{}])

    return {
        body: req.body,
        headers,
        multiValueHeaders,
        httpMethod: req.method,
        isBase64Encoded: false,
        path: req.path,
        resource: '',
        pathParameters: null,
        queryStringParameters: null,
        multiValueQueryStringParameters: null,
        stageVariables: null,
        requestContext: {
            accountId: '',
            apiId: '',
            protocol: '',
            httpMethod: '',
            authorizer: null,
            identity: {
                accessKey: null,
                accountId: null,
                apiKey: null,
                apiKeyId: null,
                caller: null,
                clientCert: null,
                cognitoAuthenticationProvider: null,
                cognitoAuthenticationType: null,
                cognitoIdentityId: null,
                cognitoIdentityPoolId: null,
                principalOrgId: null,
                user: null,
                userAgent: null,
                userArn: null,
                sourceIp: '',
            },
            path: '',
            stage: '',
            requestId: '',
            requestTimeEpoch: 0,
            resourceId: '',
            resourcePath: '',
        },
    }
}

export const sendAPIGWResponse = (apiGWResponse: APIGatewayProxyResult, res: Response) => {
    return res.status(apiGWResponse.statusCode).send(apiGWResponse.body)
}