contrib/net/http: Upgrade from v1.64.0 to v1.74.6 caused regression when setting tags

[agis]

Update: I think this has to do with the contrib import path change.

After upgrading to v1.74.6, some code that was setting tags started panicking. Before drilling down further, I wanted to ask here just in case this rings any bell.

The code that set the tags was like this:

import (
	trace "gopkg.in/DataDog/dd-trace-go.v1/contrib/net/http"
	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
)

func foo() {
	tagger := func(cfg *ddtrace.StartSpanConfig) {
			cfg.Tags["x"] = "foo"
	}

	rt.base = trace.WrapRoundTripper(
		rt.base,
		trace.RTWithServiceName("xxx"),
		trace.RTWithResourceNamer(xxx),
		trace.RTWithSpanOptions(tagger),
	)
}

After the upgrade, this code started panicking with:

runtime.plainError: assignment to entry in nil map
WithSentry.func2.1.1.1()
    /app/jobs/middleware.go:70
NewRoundTripper.func2()
    /app/pkg/httptrace/httptrace.go:56
NewRoundTripper.RTWithSpanOptions.ApplyV1Options.ApplyV1Options.func6()
    /go/pkg/mod/gopkg.in/!data!dog/[email protected]/ddtrace/internal/v2.go:83
spanStart()
    /go/pkg/mod/github.com/!data!dog/dd-trace-go/[email protected]/ddtrace/tracer/tracer.go:596
(*tracer).StartSpan()
    /go/pkg/mod/github.com/!data!dog/dd-trace-go/[email protected]/ddtrace/tracer/tracer.go:697
StartSpan()
    /go/pkg/mod/github.com/!data!dog/dd-trace-go/[email protected]/ddtrace/tracer/tracer.go:288
StartSpanFromContext()
    /go/pkg/mod/github.com/!data!dog/dd-trace-go/[email protected]/ddtrace/tracer/context.go:52
ObserveRoundTrip()
    /go/pkg/mod/github.com/!data!dog/dd-trace-go/contrib/net/http/[email protected]/internal/wrap/roundtrip.go:67
(*roundTripper).RoundTrip()
    /go/pkg/mod/github.com/!data!dog/dd-trace-go/contrib/net/http/[email protected]/roundtripper.go:21
(*RoundTripper).RoundTrip()
    /app/pkg/httptrace/httptrace.go:80

Thanks in advance.

[genesor]

Hi @agis

Thanks for the report. I checked the code to understand what could be causing this and this is indeed a bug.

As v1.74.x are transitional releases (v1 with v2 under the hood) we are transforming the options passed to RTWithSpanOptions into v2 StartSpanOption.

In pure v1 or v2 the cfg *StartSpanConfig param of a StartSpanOption func has already been tagged when the options funcs of RTWithSpanOptions are called but that is not the case for the v1.74.x, it's an empty StartSpanConfig used only for executing the options and then backfilled into the v2 StartSpanConfig.

I wrote a fix in #3956

[agis]

Thanks!