聊聊dubbo-go的metricsFilter

const (
    metricFilterName = "metrics"
)
​
var (
    metricFilterInstance filter.Filter
)
​
// must initialized before using the filter and after loading configuration
func init() {
    extension.SetFilter(metricFilterName, newMetricsFilter)
}
​
// metricFilter will calculate the invocation's duration and the report to the reporters
// If you want to use this filter to collect the metrics,
// Adding this into your configuration file, like:
// filter: "metrics"
// metrics:
//   reporter:
//     - "your reporter" # here you should specify the reporter, for example 'prometheus'
// more info please take a look at dubbo-samples projects
type metricsFilter struct {
    reporters []metrics.Reporter
}

func newMetricsFilter() filter.Filter {
    if metricFilterInstance == nil {
        reporterNames := config.GetMetricConfig().Reporters
        reporters := make([]metrics.Reporter, 0, len(reporterNames))
        for _, name := range reporterNames {
            reporters = append(reporters, extension.GetMetricReporter(name))
        }
        metricFilterInstance = &metricsFilter{
            reporters: reporters,
        }
    }
​
    return metricFilterInstance
}

func (p *metricsFilter) Invoke(ctx context.Context, invoker protocol.Invoker, invocation protocol.Invocation) protocol.Result {
    start := time.Now()
    res := invoker.Invoke(ctx, invocation)
    end := time.Now()
    duration := end.Sub(start)
    go func() {
        for _, reporter := range p.reporters {
            reporter.Report(ctx, invoker, invocation, duration, res)
        }
    }()
    return res
}

func (p *metricsFilter) OnResponse(ctx context.Context, res protocol.Result, invoker protocol.Invoker, invocation protocol.Invocation) protocol.Result {
    return res
}