gojuno / tracegen

Simple tool to generate opentracing decorators

Tracegen

Generates interface decorators with opentracing support.

Installation

go get github.com/gojuno/tracegen

Example

type Cache interface {
	Set(ctx context.Context, key, value []byte) error
	Get(ctx context.Context, key []byte) (value []byte, err error)
}

tracegen -i Cache -o example/cache_trace.go ./example

Will generate:

type CacheTracer struct {
	next   Cache
	prefix string
}

func NewCacheTracer(next Cache, prefix string) *CacheTracer {
	return &CacheTracer{
		next:   next,
		prefix: prefix,
	}
}

func (t *CacheTracer) Get(in context.Context, in1 []byte) (out []byte, out1 error) {
	span, in := opentracing.StartSpanFromContext(in, t.prefix+".Cache.Get")
	defer func() {
		if out1 != nil {
			ext.Error.Set(span, true)
			span.LogFields(
				log.String("event", "error"),
				log.String("message", out1.Error()),
			)
		}
		span.Finish()
	}()

	return t.next.Get(in, in1)
}

func (t *CacheTracer) Set(in context.Context, in1 []byte, in2 []byte) (out error) {
	span, in := opentracing.StartSpanFromContext(in, t.prefix+".Cache.Set")
	defer func() {
		if out != nil {
			ext.Error.Set(span, true)
			span.LogFields(
				log.String("event", "error"),
				log.String("message", out.Error()),
			)
		}
		span.Finish()
	}()

	return t.next.Set(in, in1, in2)
}

tracegen's Issues

Generated code fails lint because public structs and methods aren't commented

Observed
Generated code fails lint because the structs and methods in the template do not have comments, this causes go lint to fail.

Expected
Generated code does not have lint warnings

Recommendation
Use the existing template logic to generate some basic comments:
https://github.com/gojuno/tracegen/blob/master/main.go#L24

// {{ $structName }} provides tracing for a {{ $interfaceName}}

// New{{$structName}} creates a {{$structName}}

// {{$methodName}} is a tracing decorator for {{$methodName}}

Support usage with explicit tracer

Hi,

It would be nice to support an opentracing.Tracer given in constructor instead of using opentracing.StartSpanFromContext() which uses opentracing.GlobalTracer() underneath. This could be an optional feature controlled by an extra flag. I'd be happy to fork the project, add that functionality and make a PR if you would think something like that would be useful.

As an implementation detail, that tracer would be added as an extra field to the generated struct and be used when starting new spans.

Adrian

Support unnamed parameters in interfaces

Go supports unnamed parameters for interfaces. This looks like the following.

type FooService interface {
    Bar(context.Context, string) error
}

When I use tracegen to generate a decorator with an interface with unnamed parameters I get the following

return t.next.Bar(, , )

It would be a nice to have to support this, though the work around is trivial. Also thanks for opensourcing such a wonderful little utility!