Logging to the TUI while developing module

[cyan seal]

This is my first attempt to use dagger and I'm trying to print arbitrary values using fmt.Printf (quick and dirty development logging) to the TUI console but they always get printed on top. I want to print progress values like state changes inside for loops along with the execution of functions like withExec.
Is this possible?
I've checked the documentation, Go SDK and examples but I don't find anything like this, I might be trying to use the framwork in a wrong way but I want to be sure.

Thanks!

[agile quail]

you can use fmt.Printf. In order to see the print statement in the correct place in the TUI, I generally add -vvv to my dagger calls. Let me know if that works for you 🙏

[vocal aurora]

Hey @agile quail do you have an example of that? Here's what I see in my simple test

// Test logging inside of a for loop
func (m *GoLogging) ForLoopTest(ctx context.Context) {
    container := dag.Container().From("alpine:latest")

    for i := 1; i <= 5; i++ {
        fmt.Printf("Inside the loop for Number: %d\n", i)
        container.WithExec([]string{"echo", fmt.Sprintf("Number: %d", i)}).Stdout(ctx)
    }
}

all my fm.Printf lines are grouped together in the log, doing -vvv does not really make a difference in this example.

[cyan seal]

@vocal aurora That's what I'm getting: the output of fmt.Printf always appears on top instead of being alongside the container output

[agile quail]

@vocal aurora @cyan seal you're right. I was testing with a very simple example and I wasn't getting the same output you're getting. I think what's happening here is that whatever the function prints gets assigned as a Log of the function span. That's why you don't see it below each WithExec since those are effectively different spans.

Not sure if there's a "proper" way to handle this. cc @wind zinc ?

[vocal aurora]

I was trying to add otel spans (which I assume is the "right" way to do it) but I couldn't get this to show me anything at all.

// Test logging inside of a for loop
func (m *GoLogging) ForLoopTest(ctx context.Context) {
    container := dag.Container().From("alpine:latest")

    for i := 1; i <= 5; i++ {
        span := trace.SpanFromContext(ctx)
        span.AddEvent(fmt.Sprintf("Inside the loop for Number: %d", i))
        container.WithExec([]string{"echo", fmt.Sprintf("Number: %d", i)}).Stdout(ctx)
    }
}

But its very possible I am not doing otel correctly 😇

[agile quail]

even if you add spans like this, they'll still be children of the forLoopTest parent span. So you're still not gonna see each print before each withExec as you're trying to do.

[vocal aurora]

Yeah I am not 100% sure how to properly make otel spans, but in a perfet world it would be nice if you could easily make a child of the last function for this sort of print debugging

Id love to have some easy way to say WithExec.WithChildSpan(foo) (or something like that)

[wind zinc]

otel spans look like this atm: https://github.com/dagger/dagger/blob/36c79f00884aa4e7d915f2e79b068071f2bdb9b0/modules/go/main.go#L426-L427

            ctx, span := Tracer().Start(ctx, "some name")
            defer telemetry.End(span, func() error { return rerr })

[cyan seal]

@agile quail As you said the output of fmt.Printf becomes part of the output of my function instead of the loog that has the WithExec calls. Is ther a log function or something like that?
@vocal aurora I don't really understand what "otel" means. Could you point me to some documentation about it?

[vocal aurora]

Otel is open telemetry, all the spans and logs that you see in your trace are powered by open telemetry.

https://docs.dagger.io/cookbook/#create-custom-spans

[cyan seal]

thanks! I'm not that familiar with open telemetry

[vocal aurora]

No worries, it takes some getting used to but its really powerful. Allows you to have a single data format that works seamlessly with many different visualization tools (including dagger cloud!)

[cyan seal]

It's good to know because I want to send this outputs to my dashboard 😄

[vocal aurora]

What kind of dashboard?

[cyan seal]

I want to write a custom dashboard but for now I think I'll use grafana or something more lightweight

@wind zinc @vocal aurora the otel code you gave me did what I wanted!

    ctx, span := Tracer().Start(ctx, "running unit tests with Node "+version)
    defer telemetry.End(span, func() error { return rerr })

The only detail I have is that I don't know where rerr comes from so to test I put nil in the End function to make it work

[wind zinc]

nice - that rerr value is just an error that you can return if you want the span (as it's called) to show up with an errored state

[cyan seal]

Thanks!

[agile quail]

as @cyan seal shared above, this works are you were expecting Lev. Looks like the tracer is indeed setting the stdout in the right place. This makes sense given that it's using the span timestamp to effectively render each span in the correct place 🙏