关于dubbo:聊聊dubbogo的tracingFilter

序

本文次要钻研一下 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 {}

• tracingFilter 的 init 办法设置了 newTracingFilter

newTracingFilter

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

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

• newTracingFilter 办法实例化 tracingFilter

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
}

• Invoke 办法首先构建 operationName，而后应用 opentracing.StartSpan 开启 span，之后 defer 执行 span.Finish()，而后执行 invoker.Invoke(spanCtx, invocation)，最初设置 span.SetTag 及 span.LogFields

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}

• OnResponse 办法间接返回 result

小结

tracingFilter 的 Invoke 办法首先构建 operationName，而后应用 opentracing.StartSpan 开启 span，之后 defer 执行 span.Finish()，而后执行 invoker.Invoke(spanCtx, invocation)，最初设置 span.SetTag 及 span.LogFields

doc

• tracing_filter