监控扩展

// Tracer is executed at the start and finish of an HTTP.
type Tracer interface {
   Start(ctx context.Context, c *app.RequestContext) context.Context
   Finish(ctx context.Context, c *app.RequestContext)
}

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

// Start record the beginning of an RPC invocation.
func (s *ServerTracer) Start(ctx context.Context, _ *app.RequestContext) context.Context {
	// do nothing
	return ctx
}

// Finish record after receiving the response of server.
func (s *ServerTracer) Finish(ctx context.Context, c *app.RequestContext) {
	ti := c.GetTraceInfo()
	rpcStart := ti.Stats().GetEvent(stats.HTTPStart)
	rpcFinish := ti.Stats().GetEvent(stats.HTTPFinish)
	cost := rpcFinish.Time().Sub(rpcStart.Time())
	// TODO: record the cost of request
}