reqtrace is a package for simple request tracing. It requires nothing of its user except:

• They must use golang.org/x/net/context.
• They must add a single line to each function they want to be visible in traces.

In particular, reqtrace is console-based and doesn't require an HTTP server.

Warning: This package is still barebones and in its early days. I reserve the right to make backwards-incompatible changes to its API. But if it's useful to you in your current form, have at it.

Use

Call reqtrace.Trace anywhere you want to start a new root trace. (This is probably where you create your root context.) This returns a new context that you should pass to child operations, and a reporting function that you must use to inform reqtrace when the trace is complete.

For example:

func HandleRequest(r *someRequest) (err error) {
  ctx, report := reqtrace.Trace(context.Background(), "HandleRequest")
  defer func() { report(err) }()

  // Do two things for this request.
  DoSomething(ctx, r)
  DoSomethingElse(ctx, r)
}

Within other functions that you want to show up in the trace, you reqtrace.StartSpan (or its more convenient sibling reqtrace.StartSpanWithError):

func DoSomething(ctx context.Context, r *someRequest) (err error) {
  defer reqtrace.StartSpanWithError(&ctx, &err, "DoSomething")()

  // Process the request somehow using ctx. If downstream code also annotes
  // using reqtrace, reqtrace will know that its spans are descendants of
  // this one.
  CallAnotherLibrary(ctx, r.Param)
}

When --reqtrace.enable is set, the completion of a trace will cause helpful ASCII art to be spit out.