Wrapping a request with libhoney

libhoney_example.go

func (a *App) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
    // we wrap the writer to gain access to the status field later
    w := api.NewResponseWrapper(writer)
    builder := libhoney.NewBuilder()
    // we wrap libhoney in an interface to abstract events vs. builders
    hnyWrapper := &libhoneyWrapper{builder: builder}
    // Embed the libhoney wrapper in a context to give the rest of the code access
    ctx := context.WithValue(request.Context(), CtxKeyLibhoney, hnyWrapper)
    r := request.WithContext(ctx)

    // send the event at the end of the request, even if it panics
    defer func() {
        // this evt will have all fields added throughout the request's lifetime
        evt := builder.NewEvent()
        if p := recover(); p != nil {
            w.WriteHeader(http.StatusInternalServerError)
            evt.AddField("panic", p)
        }
        evt.AddField("status", w.Status())

        // apply dynamic sampling to make sure all customers are represented
        // while discarding most high volume successful traffic
        if a.DynamicSampler != nil {
            key := fmt.Sprintf("%s,%s,%v,%v", r.Method, r.URL.Path,
                hnyWrapper.datasetID, w.Status())
            evt.AddField("dynsample_key", key)
            rate := a.DynamicSampler.GetSampleRate(key)
            evt.AddField("dynsample_rate", rate)
            evt.SampleRate = uint(rate)
        }
        evt.Send()
    }()

    // add a timer for the entire request
    defer trackTimer(hnyWrapper, "request", time.Now())
    
    // go on and actually handle the request
}