Hot reload for a Go app using Air and Makefile

I've been learning Go via Alex Edwards' excellent books, Let's Go and Let's Go Further. It's been an enjoyable experience so far, and in some ways the development experience is nicer than what I'm accustomed to coming from JavaScript-world. But one thing that I missed was having the server automatically restart on changes to the source code, which is built-in to frontend tools like Vite or Live Server, and trivial to set up on the backend with nodemon.

I have found setting it up in a Go app to be rather more difficult, but I've managed to work something out. I'm making use of the Air module, which you can install globally with

go install github.com/cosmtrek/air@latest

Then put an .air.toml file in your project's root with the following content:

root = "."
tmp_dir = "tmp"

[build]
  cmd = "go build -o ./tmp/main ./cmd/web && chmod +x ./tmp/main"
  bin = "./tmp/main -db-dsn=${YOUR_DB_DSN} -port=${PORT}"
  include_ext = ["go", "tmpl", "html", "css", "js"]
  exclude_dir = ["assets", "tmp"]

[log]
  time_format = "15:04:05"
  log_file = "air.log"

[color]
  main = "yellow"
  watcher = "cyan"
  build = "green"
  runner = "magenta"

Full disclosure: this is mostly provided by ChatGPT, with a few suitable modifications. Adjust the include_ext and exclude_dir fields to suit the needs of your project. A few notes:

• cmd is the command that builds the binary, saves it as ./tmp/main, makes it executable with chmod, then runs it
• bin is the command that runs the binary. Adjust the flags as needed (if needed). More on this soon.

Now, I'm sure there is a way that you can run this command successfully by supplying flags. For example:

air -- -db-dsn=your-dsn-string -port=4000

But I ran in to issues with escaping my dsn and I don't feel like figuring them out. But I got it to work as follows. I already had a Makefile like this:

include .envrc

## run/web: run the cmd/web application
.PHONY: run/web
run/web:
	@go run ./cmd/web -db-dsn=${CONTACTS_DB_DSN} -port=4000

For this to work, I have a gitignored .envrc file, like so:

CONTACTS_DB_DSN=my-dsn-string
PORT=4000

So I added the following:

## run/air: run server using air for live reloading
.PHONY: run/air
run/air:
	@export CONTACTS_DB_DSN=$(CONTACTS_DB_DSN) && export PORT=$(PORT) && air

And now I can run my app with

make run/air

Great! There is one smallish issue: all this does is restart the server, it doesn't automatically refresh the browser. To implement this I believe I need to use some client-side JavaScript that uses WebSockets to listen for a reload signal sent by my Go application. Might be an interesting project for a later day.