ft

ft – function trace

A lightweight library for tracing function execution with OpenTelemetry integration, structured logging, and metrics collection.

Why?

In most of my projects, I start by relying on simple logs to get quick insights into the application. As the project evolves, I usually add metrics and traces for improved observability, but setting up all the libraries can be time-consuming. This library allows you to enable the observability of your functions with just two lines of code.

Features

• Structured logging using slog.
• OpenTelemetry tracing integration.
• Metrics for execution counts and duration.
• Configurable log level.
• Option to opt out of metrics and tracing.

Usage

Just add two lines to the beginning of the function:

func Do(ctx context.Context) (err error) {
    ctx, span := ft.Start(ctx, "main.Do", ft.WithErr(&err)) // Log when we enter the `Do` function.
    defer span.End()                                        // Log, trace and meter when we exit the `Do` function.

    err = errors.New("unexpected error")
	
    return
}

If you run the code above, you will see the following output:

time=2025-01-25T21:55:27.068+01:00 level=INFO msg="action started" action=main.Do
time=2025-01-25T21:55:27.069+01:00 level=ERROR msg="action ended" action=main.Do duration_ms=0.743 error="unexpected error"

Setup OTEL tracer and meter globally and ft will start sending metrics and traces to the OTLP collector:

mp, _, _ := autometer.NewMeterProvider(context.Background())
otel.SetMeterProvider(mp)
tp, _, _ := autotracer.NewTracerProvider(context.Background())
otel.SetTracerProvider(tp)

ft.SetMetricsEnabled(true)
ft.SetTracingEnabled(true)

[!TIP] In the example above I use go-faster/sdk to setup OTEL based on environment variables.

Configuration

ft package provides many functions to configure its behaviour. See the table below:

Here's a markdown table with all the Set functions and their descriptions: