Encoding

GA4 traffic comes in two protocols and sesamy-go round-trips between them.

GTag (pkg/encoding/gtag)

Form-encoded querystring protocol used by gtag.js. Each field maps to a short key (e.g. tid, cid, en, dl).

import "github.com/foomo/sesamy-go/pkg/encoding/gtag"

var p gtag.Payload
if err := gtag.Decode(url.Values{...}, &p); err != nil { /* ... */ }

values, body, err := gtag.Encode(&p)  // re-encode to url.Values + body
qs := gtag.EncodeValues(values)

Payload struct (selected fields)

Field	GTag key	Description
ProtocolVersion	v	Protocol version (always 2).
TrackingID	tid	Measurement / stream ID (G-XXXXXXXXX).
ClientID	cid	GA client ID (281344611.1635634925).
UserID	uid	Custom user ID.
SessionID	sid	Session ID.
EventName	en	Event name (e.g. page_view).
DocumentLocation	dl	Current page URL.
DocumentTitle	dt	Current page title.
DocumentReferrer	dr	Referrer.
IsDebug	_dbg	Debug flag.
GTMHashInfo	gtm	GTM container fingerprint.

Embedded sub-structs (with ,inline,squash):

• Consent — consent-mode signals.
• Campaign — UTM-style campaign fields.
• ECommerce — items, value, currency.
• ClientHints — UA-CH derived.

Full field list lives in pkg/encoding/gtag/payload.go.

Helpers

gtag.Get[T any](*T, T) T              // safe deref with fallback
gtag.GetDefault[T any](*T, T) T       // alias

MPv2 (pkg/encoding/mpv2)

JSON body protocol used by GA4's Measurement Protocol v2.

import "github.com/foomo/sesamy-go/pkg/encoding/mpv2"

p := mpv2.NewPayload[any]()
p.Events = append(p.Events, sesamy.NewEvent(sesamy.EventNamePageView, params).AnyEvent())
body, _ := json.Marshal(p)

Payload[P] (selected fields)

Field	JSON key	Description
ClientID	client_id	GA client ID.
UserID	user_id	Custom user ID.
SessionID	(per event param)	Session ID lives on each event's params.
TimestampMicros	timestamp_micros	Hit timestamp in microseconds.
Events	events	Slice of sesamy.Event[P].
UserProperties	user_properties	User-scoped properties.
Consent	consent	Consent flags.
UserData	user_data	Enhanced conversions (SHA-256 hashed).

Also: userdata.go, userdataaddress.go, sha256hash.go — helpers for enhanced conversions (server-side hashing of email/phone/address).

Conversion

GTag → MPv2

import "github.com/foomo/sesamy-go/pkg/encoding/gtagencode"

var p *mpv2.Payload[any]
err := gtagencode.MPv2(gtagPayload, &p)

MPv2 → GTag

import "github.com/foomo/sesamy-go/pkg/encoding/mpv2encode"

var p *gtag.Payload
err := mpv2encode.GTag[any](mpv2Payload, &p)

Used internally by gtaghttp.MiddlewareEventHandler so cross-protocol handlers can write MPv2-shaped logic regardless of inbound wire format.