Enable picking truly random port in serve mode

[ptrdom]

Currently there is no way to tell esbuild to pick a truly random port in serve mode - if port is unset or set to 0 then port in 8000-8009 range gets picked up. Ideally if port is set to 0 then this would just be passed to Go listen implementation and it would pick a free random port.

[ghost]

So I just have to modify this right:
if serveOptions.Port == 0 { // Default to picking a "800X" port if result, err := net.Listen(network, net.JoinHostPort(host, ":0")); err == nil { listener = result break } }
This will allow us to use random port can anybody check if my understanding is true

[ptrdom]

It is somewhat tricky - I think we want to preserve default behavior of keeping the port in familiar range of 8000-8009, but also allow passing 0. Problem here comes mainly from the fact that Go does not have nullable variables, so 0 expressed both user setting port to 0 and user not setting the port. The code likely needs a separate variable to track whether user has set the port or not.

[ghost]

Thanks for the feedback, should i pr my changes or leave it
PS: am a beginner

[ptrdom]

Not sure, @evanw could you comment on this issue? Need your confirmation before exploring solutions.

[ghost]

Hey yo i did this pr #3693 and i also tested locally which was confusing to setup and test but it has the random functionality

[evanw]

I can do this but making the port nullable in the Go API is a breaking change, so it'll have to wait until a breaking change release to do it. Adding the breaking label for now to track this.

[ghost]

K