Server Sent Events in Go

Gurleen Sethi — Tue, 14 Mar 2023 02:59:45 +0000

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Introduction

In this article, I will demonstrate how to set up a basic SSE (Server Sent Events) endpoint in Go. The complete code related to this article is available in this GitHub repository.

Example: We are going to assume an example of a live crypto price api.

Project Setup

Initialize a new go project.

mkdir go-server-send-events-examples
cd go-server-send-events-examples
go mod init github.com/gurleensethi/go-server-send-events-examples

Create a main.go file with basic http server setup.

package main

import (
    "net/http"
)

func main() {
    http.ListenAndServe(":4444", nil)
}

Mocking live data

Write a function that generates random integers every second. This function will simulate live crypto price data that you will send back to the client.

func main() {
    ...
}

// generateCryptoPrice generates price as random integer and sends it the
// provided channel every 1 second.
func generateCryptoPrice(ctx context.Context, priceCh chan<- int) {
    r := rand.New(rand.NewSource(time.Now().Unix()))

    ticker := time.NewTicker(time.Second)

outerloop:
    for {
        select {
        case <-ctx.Done():
            break outerloop
        case <-ticker.C:
            p := r.Intn(100)
            priceCh <- p
        }
    }

    ticker.Stop()

    close(priceCh)
}

The generateCryptoPrice function accepts a one-way write-only channel to which it sends the live price. It uses time.Ticker with a duration of 1 second to send a price update.

Furthermore, we receive a context that we can use to stop sending price updates. For instance, if the client disconnects, the context is cancelled, and price updates cease.

math/rand package is used to generate random integers.

...

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Print all routes in Chi router

Gurleen Sethi — Mon, 15 Aug 2022 05:08:10 +0000

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Getting Started

If you have been writing Go you probably have heard of the popular http router chi. In this article you are going to learn how to print all the routes registered in a router, this is very helpful for debugging purposes.

If you want to learn about chi, please read Restful routing with Chi.

Setting up a router

I assume you have a project with chi setup (if not please install chi).

Let's assume an application that has a router with 3 routes registered.

package main

import (
    "fmt"
    "github.com/go-chi/chi/v5"
    "net/http"
)

func main() {
    router := chi.NewRouter()

    router.Get("/articles", sayHello)
    router.Get("/articles/{articleID}", sayHello)

    router.With(func(next http.Handler) http.Handler {
        return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
            next.ServeHTTP(w, r)
        })
    }).Post("/articles", sayHello) // 👈 route with middleware
}

func sayHello(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("Hello World"))
}

Look closely one of these routes (POST route) has a middleware setup as well. So now we want to print out all the routes and the number of middlewares setup on each routes.

Print routes with chi.Walk

We want to print each route in the format: [<method>]: '<route>' has <x> middlewares.

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