監(jiān)控?cái)U(kuò)展

用戶如果需要更詳細(xì)的打點(diǎn)，例如包大小，或者想要更換其他數(shù)據(jù)源，例如 influxDB，用戶可以根據(jù)自己的需求實(shí)現(xiàn) ?Trace ?接口，并通過(guò) ?WithTracer ?Option來(lái)注入。

// Tracer is executed at the start and finish of an RPC.
type Tracer interface {
    Start(ctx context.Context) context.Context
    Finish(ctx context.Context)
}

從 ctx 中可以獲得 RPCInfo，進(jìn)一步的從 RPCInfo 中獲取請(qǐng)求耗時(shí)、包大小和請(qǐng)求返回的錯(cuò)誤信息等，舉例：

type clientTracer struct {
    // contain entities which recording metric
}

// Start record the beginning of an RPC invocation.
func (c *clientTracer) Start(ctx context.Context) context.Context {
    // do nothing
	return ctx
}

// Finish record after receiving the response of server.
func (c *clientTracer) Finish(ctx context.Context) {
	ri := rpcinfo.GetRPCInfo(ctx)
	rpcStart := ri.Stats().GetEvent(stats.RPCStart)
	rpcFinish := ri.Stats().GetEvent(stats.RPCFinish)
	cost := rpcFinish.Time().Sub(rpcStart.Time())
	// TODO: record the cost of request
}