lambda – Shawn

This post is for whom want to use AWS Lambda with OpenAPI Generator. Official guide is useful but I felt there are some missing information. So I wrote this post. You can successfully run AWS Lambda function on your local machine and debug your code.

Let’s start from very simple example. You only need 4 files. I’ll explain details. (Ignore Tests folder, no need it in this tutorial)

Package.swift
NativeMobileServer.swift
openapi.yaml
openapi-generator-config.yaml

Step 1. Define OpenAPI Spec

This OpenAPI spec is for tutorial.

Please check folder and file structure. Create an openapi.yaml

openapi: 3.1.0
info:
  title: MobileJobService
  version: 1.0.0

paths:
  /jobs/fetch:
    post:
      summary: Fetch job data from external source
      description: >
        This endpoint is called by a scheduled Lambda or backend service.
        It fetches job data from the given URL and processes it using the provided prompt.
      operationId: fetchJobs
      tags:
        - jobs
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/FetchJobsRequest'
      responses:
        '200':
          description: Successfully fetched and processed job data
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/JobListResponse'
        '400':
          description: Invalid input parameters
        '500':
          description: Internal error during job fetch or processing

components:
  schemas:
    FetchJobsRequest:
      type: object
      required:
        - url
        - prompt
      properties:
        url:
          type: string
          format: uri
          description: Target URL to scrape or fetch job data from
        prompt:
          type: string
          description: Instruction / extraction prompt used to parse the fetched page

    JobListResponse:
      type: array
      items:
        $ref: '#/components/schemas/Job'

    Job:
      type: object
      required:
        - id
        - title
      properties:
        id:
          type: string
          description: Unique identifier for the job
        title:
          type: string
          description: Job title
        country:
          type: string
          description: Country code (e.g. SG, US, TW)
        city:
          type: string
          description: City name (e.g. Singapore)
        postedAt:
          type: string
          format: date-time
          description: When this job was posted, if known
        company:
          type: string
          description: Company name
        team:
          type: string
          description: Team / department (e.g. Mobile, Backend, Growth)
        jobDescriptionLink:
          type: string
          format: uri
          description: Public link to full job description
        jobApplyLink:
          type: string
          format: uri
          description: Public link to apply
        salary:
          $ref: '#/components/schemas/Salary'
        description:
          type: string
          description: Cleaned / extracted full-text description for the role

    Salary:
      type: object
      properties:
        min:
          type: number
          description: Minimum compensation
        max:
          type: number
          description: Maximum compensation
        basis:
          type: string
          enum: [year, month]
          description: Salary period basis (yearly or monthly)

And then create openapi-generator-config.yaml

generate:
  - types
  - server

Step 2. Create Swift Package Manger

Package.swift

// swift-tools-version: 6.2
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "NativeMobileServer",
    platforms: [
        .macOS(.v15)
    ],
    products: [
        .executable(name: "NativeMobileServer", targets: ["NativeMobileServer"])
    ],
    dependencies: [
        .package(url: "https://github.com/apple/swift-openapi-generator.git", from: "1.10.3"),
        .package(url: "https://github.com/apple/swift-openapi-runtime.git", from: "1.8.2"),

        .package(url: "https://github.com/awslabs/swift-aws-lambda-runtime.git", from: "2.0.0"),
        .package(url: "https://github.com/awslabs/swift-aws-lambda-events.git", from: "1.2.0"),
        .package(url: "https://github.com/awslabs/swift-openapi-lambda.git", from: "2.0.0"),

        .package(url: "https://github.com/swift-server/swift-service-lifecycle.git", from: "2.0.0"),
    ],
    targets: [
        .executableTarget(
            name: "NativeMobileServer",
            dependencies: [
                .product(name: "OpenAPIRuntime", package: "swift-openapi-runtime"),

                .product(name: "AWSLambdaRuntime", package: "swift-aws-lambda-runtime"),
                .product(name: "AWSLambdaEvents", package: "swift-aws-lambda-events"),

                .product(name: "OpenAPILambda", package: "swift-openapi-lambda"),
                .product(name: "ServiceLifecycle", package: "swift-service-lifecycle"),
            ],
            path: "Sources/NativeMobileServer",
            resources: [
                .copy("openapi.yaml"),
                .copy("openapi-generator-config.yaml")
            ],
            plugins: [
                .plugin(name: "OpenAPIGenerator", package: "swift-openapi-generator")
            ]
        ),
        .testTarget(
            name: "NativeMobileServerTests",
            dependencies: ["NativeMobileServer"]
        ),
    ]
)

You can remove .testTarget if you don’t need to write test cases.

Step 3. Write a main function

//
//  NativeMobileServer.swift
//  NativeMobileServer
//
//  Created by Shawn Sungwook Baek on 10/26/25.
//

import Foundation
import Logging
import OpenAPILambda
import OpenAPIRuntime

@main
struct JobServiceImpl: APIProtocol, OpenAPILambdaHttpApi {
    func fetchJobs(_ input: Operations.fetchJobs.Input) async throws -> Operations.fetchJobs.Output
    {
        logger.info("fetchJobs invoked")
        let requestBody = input
       
        if case let .json(request) = requestBody.body {
            logger.info("Fetching jobs from \(request.url) with prompt: \(request.prompt)")
        }

        let mockJobs: [Components.Schemas.Job] = [
            .init(
                id: "job-001",
                title: "iOS Developer",
                country: "SG",
                postedAt: Date(),
                company: "Apple",
                team: "Mobile",
                jobDescriptionLink: "https://example.com/job/1",
                jobApplyLink: "https://example.com/apply/1",
                salary: .init(min: 6000, max: 9000, basis: .month),
                description: "Develop and maintain the iOS application."
            ),
            .init(
                id: "job-002",
                title: "Backend Engineer",
                country: "TW",
                postedAt: Date(),
                company: "Uber",
                team: "Server",
                jobDescriptionLink: "https://example.com/job/2",
                jobApplyLink: "https://example.com/apply/2",
                salary: .init(min: 7000, max: 10000, basis: .month),
                description: "Build API services and integrations."
            ),
        ]
        return .ok(.init(body: .json(mockJobs)))
    }

    let logger: Logger

    func register(transport: OpenAPILambdaTransport) throws {
        try transport.router.get("/health") { _, _ in
            "OK"
        }
        logger.trace("Available Routes\n\(transport.router)")
        // to log all requests and their responses, add a logging middleware
        let loggingMiddleware = LoggingMiddleware(logger: logger)

        // MANDATORY (middlewares are optional)
        try self.registerHandlers(on: transport, middlewares: [loggingMiddleware])
    }

    static func main() async throws {
        let openAPIService = JobServiceImpl(loggerLabel: "JobService")
        try await openAPIService.run()

    }

    init(loggerLabel: String) {
        var logger = Logger(label: loggerLabel)
        logger.logLevel = .trace
        self.logger = logger
    }
}

Step 4. Check Scheme in Xcode

Check Executable Target.

Important!

You need to set Environment Variables

LOCAL_LAMBDA_SERVER_ENABLED
LOCAL_LAMBDA_PORT <- Optional! Default port is 7000

Try build and run and check which pid is using 7000 port.

lsof -i :7000

If other program uses that port, you can change default port by setting LOCAL_LAMBDA_PORT

When you run it, you will see the message. (In my case, I changed the default port 8000)

Step 5. Invoke Lambda function

This part you may confusing because you can’t call lambda like

curl -v -X POST http://127.0.0.1:8000/jobs/fetch \
  -H "Content-Type: application/json" \
  -d '{
    "url": "https://example.com/jobs",
    "prompt": "Extract latest mobile job listings"
  }'

If you want to see more detail information, check this out

https://github.com/awslabs/swift-openapi-lambda?tab=readme-ov-file#testing

To invoke and debug our code, we should invoke function like this.

If you want to learn more about this payload structure v2.0 in API Gateway check here

https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-develop-integrations-lambda.html

curl -X "POST" "http://127.0.0.1:8000/invoke" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -d $'{
  "requestContext": {
    "accountId": "",
    "time": "",
    "http": {
      "path": "/jobs/fetch",
      "userAgent": "",
      "method": "POST",
      "protocol": "HTTP/1.1",
      "sourceIp": "127.0.0.1"
    },
    "domainName": "",
    "timeEpoch": 0,
    "domainPrefix": "",
    "apiId": "",
    "requestId": "",
    "stage": "$default"
  },
  "rawPath": "/jobs/fetch",
  "rawQueryString": "",
  "version": "2.0",
  "routeKey": "$default",
  "isBase64Encoded": true,
  "body": "{\\"url\\":\\"https://jobs.apple.com/en-sg/search\\", \\"prompt\\":\\"Extract latest mobile job listings\\"}"
}'

I’ve set breakpoint at here.

Let’s invoke function.

Ok, breakpoint is working.

And I can see the results from AWS Lambda function

Conclusion

Swift is very powerful for developing server-side applications. There a lot of great open source projects. In Part 2, I’ll explain how to deploy AWS Lambda Swift function to the AWS using SAM CLI.

Tag: lambda

Server-Side Swift – AWS Lambda with OpenAPI Generator Part 1