聊聊dubbo-go的tracingFilter

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本文主要研究一下dubbo-go的tracingFilter

tracingFilter

dubbo-go-v1.4.2/filter/filter_impl/tracing_filter.go

const (
	tracingFilterName = "tracing"
)

// this should be executed before users set their own Tracer
func init() {
	extension.SetFilter(tracingFilterName, newTracingFilter)
	opentracing.SetGlobalTracer(opentracing.NoopTracer{})
}

var (
	errorKey   = "ErrorMsg"
	successKey = "Success"
)

// if you wish to using opentracing, please add the this filter into your filter attribute in your configure file.
// notice that this could be used in both client-side and server-side.
type tracingFilter struct {
}

newTracingFilter

dubbo-go-v1.4.2/filter/filter_impl/tracing_filter.go

func newTracingFilter() filter.Filter {
	if tracingFilterInstance == nil {
		tracingFilterInstance = &tracingFilter{}
	}
	return tracingFilterInstance
}

Invoke

dubbo-go-v1.4.2/filter/filter_impl/tracing_filter.go

func (tf *tracingFilter) Invoke(ctx context.Context, invoker protocol.Invoker, invocation protocol.Invocation) protocol.Result {
	var (
		spanCtx context.Context
		span    opentracing.Span
	)
	operationName := invoker.GetUrl().ServiceKey() + "#" + invocation.MethodName()

	wiredCtx := ctx.Value(constant.TRACING_REMOTE_SPAN_CTX)
	preSpan := opentracing.SpanFromContext(ctx)

	if preSpan != nil {
		// it means that someone already create a span to trace, so we use the span to be the parent span
		span = opentracing.StartSpan(operationName, opentracing.ChildOf(preSpan.Context()))
		spanCtx = opentracing.ContextWithSpan(ctx, span)

	} else if wiredCtx != nil {

		// it means that there has a remote span, usually from client side. so we use this as the parent
		span = opentracing.StartSpan(operationName, opentracing.ChildOf(wiredCtx.(opentracing.SpanContext)))
		spanCtx = opentracing.ContextWithSpan(ctx, span)
	} else {
		// it means that there is not any span, so we create a span as the root span.
		span, spanCtx = opentracing.StartSpanFromContext(ctx, operationName)
	}

	defer func() {
		span.Finish()
	}()

	result := invoker.Invoke(spanCtx, invocation)
	span.SetTag(successKey, result.Error() != nil)
	if result.Error() != nil {
		span.LogFields(log.String(errorKey, result.Error().Error()))
	}
	return result
}

OnResponse

dubbo-go-v1.4.2/filter/filter_impl/tracing_filter.go

func (tf *tracingFilter) OnResponse(ctx context.Context, result protocol.Result,
	invoker protocol.Invoker, invocation protocol.Invocation) protocol.Result {
	return result
}

小结

tracingFilter的Invoke方法首先构建operationName,然后使用opentracing.StartSpan开启span,之后defer执行span.Finish(),然后执行invoker.Invoke(spanCtx, invocation),最后设置span.SetTag及span.LogFields

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