Simple client for the Google Analytics Measurement Protocol (https://developers.google.com/analytics/devguides/collection/protocol/v1/parameters), to report events to Google Analytics. Also a half-baked example of using reflection and struct tags to generate URL query parameters.

analytics.go

// See https://developers.google.com/analytics/devguides/collection/protocol/v1/parameters
//
// Usage:
// req, _ := analytics.Request{
// 	HitType:    analytics.PageView,
//	TrackingID: "UA-XXXX-Y",
//	ClientID:   "35009a79-1a05-49d7-b876-2b884d0f825b",
//      // ...
// }.Request()
// resp, _ := req.Do()

package analytics

import (
	"fmt"
	"net/http"
	"net/url"
	"reflect"
	"time"
)

var required = []string{"t", "tid", "cid"}

type HitType string

const (
	PageView    HitType = "pageview"
	AppView     HitType = "appview"
	Event       HitType = "event"
	Transaction HitType = "transaction"
	Item        HitType = "item"
	Social      HitType = "social"
	Exception   HitType = "exception"
	Timing      HitType = "timing"
)

type SessionEvent string

const (
	Start SessionEvent = "start"
	End   SessionEvent = "end"
)

type Request struct {
	// TODO: Custom dimensions and metrics

	Version                          string        `url:"v"`
	TrackingID                       string        `url:"tid"`
	ClientID                         string        `url:"cid"`
	HitType                          HitType       `url:"t"`
	AnonymizeIP                      bool          `url:"aip"`
	QueueTimeMilliseconds            time.Duration `url:"qt"`
	CacheBuster                      string        `url:"z"`
	SessionControl                   SessionEvent  `url:"sc"`
	DocumentReferrer                 string        `url:"dr"`
	CampaignName                     string        `url:"cn"`
	CampaignSource                   string        `url:"cs"`
	CampaignMedium                   string        `url:"cm"`
	CampaignKeyword                  string        `url:"ck"`
	CampaignContent                  string        `url:"cc"`
	CampaignID                       string        `url:"ci"`
	GoogleAdwordsID                  string        `url:"gclid"`
	GoogleDisplayAdsID               string        `url:"gclid"`
	ScreenResolution                 string        `url:"sc"`
	ViewportSize                     string        `url:"vp"`
	DocumentEncoding                 string        `url:"de"`
	ScreenColors                     string        `url:"sd"`
	UserLanguage                     string        `url:"ul"`
	JavaEnabled                      bool          `url:"je"`
	FlashVersion                     string        `url:"fl"`
	NonInteractionHit                bool          `url:"ni"`
	DocumentLocation                 string        `url:"dl"`
	DocumentHost                     string        `url:"dh"`
	DocumentPath                     string        `url:"dp"`
	DocumentTitle                    string        `url:"dt"`
	ContentDescription               string        `url:"cd"`
	LinkID                           string        `url:"linkid"`
	ApplicationName                  string        `url:"an"`
	ApplicationVersion               string        `url:"av"`
	EventCategory                    string        `url:"ec"`
	EventAction                      string        `url:"ea"`
	EventLabel                       string        `url:"el"`
	EventValue                       int           `url:"ev"`
	TransactionID                    string        `url:"ti"`
	TransactionAffiliation           string        `url:"ta"`
	TransactionRevenue               float64       `url:"tr"`
	TransactionShipping              float64       `url:"ts"`
	TransactionTax                   float64       `url:"tt"`
	ItemName                         string        `url:"in"`
	ItemPrice                        float64       `url:"ip"`
	ItemQuantity                     int           `url:"iq"`
	ItemCode                         string        `url:"ic"`
	ItemCategory                     string        `url:"iv"`
	CurrencyCode                     string        `url:"cc"`
	SocialNetwork                    string        `url:"sn"`
	SocialAction                     string        `url:"sa"`
	SocialActionTarget               string        `url:"st"`
	UserTimingCategory               string        `url:"utc"`
	UserTimingVariable               string        `url:"utv"`
	UserTimingTimeMilliseconds       time.Duration `url:"utt"`
	UserTimingLabel                  string        `url:"utl"`
	PageLoadTimeMilliseconds         time.Duration `url:"ptl"`
	DNSTimeMilliseconds              time.Duration `url:"dns"`
	PageDownloadTimeMilliseconds     time.Duration `url:"pdt"`
	RedirectResponseTimeMilliseconds time.Duration `url:"rrt"`
	TCPConnectTimeMilliseconds       time.Duration `url:"tcp"`
	ServerResponseTimeMilliseconds   time.Duration `url:"srt"`
	ExceptionDescription             string        `url:"exd"`
	ExceptionFatal                   bool          `url:"exf"`
	ExperimentID                     string        `url:"xid"`
	ExperimentVariant                string        `url:"xvar"`
}

func NewRequest(tid, cid string, t HitType) Request {
	return Request{
		TrackingID: tid,
		ClientID:   cid,
		HitType:    t,
	}
}

func (r Request) encode() url.Values {
	vals := url.Values{}
	rt := reflect.TypeOf(r)
	rv := reflect.ValueOf(r)
	for i := 0; i < rt.NumField(); i++ {
		f := rt.Field(i)
		fv := rv.FieldByName(f.Name)
		sv := ""
		switch f.Type.Kind() {
		case reflect.Bool:
			if fv.Bool() {
				sv = "1"
			}
		case reflect.Int:
			fi := fv.Int()
			if fi == 0 {
				continue
			}
			sv = string(fi)
		case reflect.Float64:
			ff := fv.Float()
			if ff == 0 {
				continue
			}
			sv = fmt.Sprintf("%d", ff)
		case reflect.Int64:
			// Fields of type int64 are probably time.Durations, and we want the millisecond value
			fi := fv.Int()
			if fi == 0 {
				continue
			}
			sv = string(fv.Int() / 1000)
		default:
			sv = fv.String()
		}
		if sv != "" {
			vals.Set(f.Tag.Get("url"), sv)
		}
	}
	return vals
}

func (r Request) Validate() error {
	v := r.encode()
	if v.Get("v") == "" {
		v.Set("v", "1")
	}
	for _, req := range required {
		if v.Get(req) == "" {
			return fmt.Errorf("%s is required\n", req)
		}
	}
	return nil
}

func (r Request) Request() (*http.Request, error) {
	u := url.URL{
		Scheme:   "https",
		Host:     "www.google-analytics.com",
		Path:     "collect",
		RawQuery: r.encode().Encode(),
	}
	req, err := http.NewRequest("POST", u.String(), nil)
	if err != nil {
		return nil, err
	}
	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
	return req, nil
}