lmdrouter

Go HTTP router library for AWS API Gateway-invoked Lambda Functions

Table of Contents

• Overview
  • Use Case
  • Features
• Installation
• Usage
• Static Compilation for AWS Lambda
• License

Overview

lmdrouter is a simple-to-use library for writing AWS Lambda functions in Go that listen to events of type API Gateway Proxy Request. It allows creating a lambda function that can match requests based on their URI, just like an HTTP server would.

The library provides an interface not unlike the standard net/http.Mux type or community libraries such as httprouter and chi.

Use Case

When building large cloud-native applications, there's a certain balance to strike when it comes to deployment of APIs. On one side of the scale, each API endpoint has its own lambda function. This provides the greatest flexibility, but is extremely difficult to maintain. On the other side of the scale, there can be one lambda function for the entire API. This provides the least flexibility, but is the easiest to maintain. Both are probably not a good idea.

With lmdrouter, one can create small lambda functions for different aspects of the API. For example, if your application model contains multiple domains (e.g. articles, authors, topics, etc…), you can create one lambda function for each domain, and deploy these independently (e.g. everything below "/api/articles" is one lambda function, everything below "/api/authors" is another function). This is also useful for applications where different teams are in charge of different parts of the API.

Features

• Supports all HTTP methods.
• Supports middleware at a global and per-resource level.
• Supports path parameters with a simple ":" format (e.g. "/posts/:id").
• Provides ability to automatically "unmarshal" an API Gateway request to an arbitrary Go struct, with data coming from the request path, the query string, the headers and the request body (only JSON requests are currently supported).
• Provides ability to automatically "marshal" responses of any type to an API Gateway response (only JSON responses are currently generated).
• Implements net/http.Handler for running locally or as a simple HTTP server.

Installation

go get github.com/aquasecurity/lmdrouter

Usage

lmdrouter is meant to be used inside Go Lambda functions.

package main

import (
    "github.com/aws/aws-lambda-go/lambda"
    "github.com/aquasecurity/lmdrouter"
)

var router *lmdrouter.Router

func init() {
    router = lmdrouter.NewRouter("/api", loggerMiddleware, authMiddleware)
    router.Route("GET", "/", listSomethings)
    router.Route("POST", "/", postSomething, someOtherMiddleware)
    router.Route("GET", "/:id", getSomething)
    router.Route("PUT", "/:id", updateSomething)
    router.Route("DELETE", "/:id", deleteSomething)
}

func main() {
    lambda.Start(router.Handler)
}

// the rest of the code is a redacted example, it will probably reside in a
// separate package inside your project

type listSomethingsInput struct {
    ID                string   `lambda:"path.id"`                // a path parameter declared as :id
    ShowSomething     bool     `lambda:"query.show_something"`   // a query parameter named "show_something"
    AcceptedLanguages []string `lambda:"header.Accept-Language"` // a multi-value header parameter
}

type postSomethingInput struct {
    Title   string    `json:"title"`
    Date    time.Time `json:"date"`
}

func listSomethings(ctx context.Context, req events.APIGatewayProxyRequest) (
    res events.APIGatewayProxyResponse,
    err error,
) {
    // parse input from request and path parameters
    var input listSomethingsInput
    err = lmdrouter.UnmarshalRequest(req, false, &input)
    if err != nil {
        return lmdrouter.HandleError(err)
    }

    // call some business logic that generates an output struct
    // ...

    return lmdrouter.MarshalResponse(http.StatusOK, nil, output)
}

func postSomethings(ctx context.Context, req events.APIGatewayProxyRequest) (
    res events.APIGatewayProxyResponse,
    err error,
) {
    // parse input from request body
    var input postSomethingsInput
    err = lmdrouter.UnmarshalRequest(req, true, &input)
    if err != nil {
        return lmdrouter.HandleError(err)
    }

    // call some business logic that generates an output struct
    // ...

    return lmdrouter.MarshalResponse(http.StatusCreated, nil, output)
}

func loggerMiddleware(next lmdrouter.Handler) lmdrouter.Handler {
    return func(ctx context.Context, req events.APIGatewayProxyRequest) (
        res events.APIGatewayProxyResponse,
        err error,
    ) {
        // [LEVEL] [METHOD PATH] [CODE] EXTRA
        format := "[%s] [%s %s] [%d] %s"
    	level := "INF"
    	var code int
    	var extra string

    	res, err = next(ctx, req)
    	if err != nil {
    	    level = "ERR"
    	    code = http.StatusInternalServerError
    	    extra = " " + err.Error()
    	} else {
    	    code = res.StatusCode
    	    if code >= 400 {
    	        level = "ERR"
    	    }
        }

        log.Printf(format, level, req.HTTPMethod, req.Path, code, extra)

        return res, err
    }
}

Note that for requests with a body (e.g. POST, PUT, PATCH), the struct types of your inputs can contain parameters from all sources: path parameters, query string parameters, request headers and the JSON body. Anything that doesn't have a lambda struct tag is taken from the body. Regular json tags can be used for that.

Static Compilation for AWS Lambda

To ensure Lambda applications using lmdrouter (or any Lambda applications written in Go, for that matter) will properly work in AWS's Go runtime, make sure to compile your applications statically. You can either disable CGO completely using CGO_ENABLED=0, or use the following build flags:

go build -tags netgo -ldflags "-s -w"

License

This library is distributed under the terms of the Apache License 2.0.