Sending events from Go

pkg/client lets a Go process emit GA4 events directly, without going through a browser. Useful for backend-only conversions (refunds, async order completion, webhook-driven events).

Two clients, one per protocol:

• client.GTag — sends form-encoded payloads to a /g/collect endpoint.
• client.MPv2 — sends JSON to a /mp/collect endpoint with API secret + measurement ID.

MPv2 client (recommended for server-side)

import (
	"github.com/foomo/sesamy-go/pkg/client"
	"github.com/foomo/sesamy-go/pkg/sesamy"
)

c := client.NewMPv2(l, "https://www.google-analytics.com",
	client.MPv2WithAPISecret("YOUR_SECRET"),
	client.MPv2WithMeasurementID("G-XXXXXXXXX"),
)

err := c.Collect(r,
	sesamy.NewEvent(sesamy.EventNamePurchase, map[string]any{
		"transaction_id": "T-123",
		"value":          42.0,
		"currency":       "EUR",
	}).AnyEvent(),
)

Options

Option	Purpose
MPv2WithHTTPClient(*http.Client)	Override the HTTP client (timeouts, transports).
MPv2WithPath(string)	Override the upstream path (default /mp/collect).
MPv2WithCookies(...string)	Cookie names to forward from the inbound request.
MPv2WithAPISecret(string)	GA4 Measurement Protocol API secret.
MPv2WithMeasurementID(string)	G-XXXXXXXXX from GA4 Admin → Data Streams.
MPv2WithMiddlewares(...MPv2Middleware)	Pre-send enrichment middleware.

Methods

c.Collect(r, events...)              // wraps events into a Payload and sends
c.SendPayload(r, payload)            // sends a fully built mpv2.Payload[any]
c.HTTPClient()                        // exposes underlying *http.Client

The constructor implicitly appends MPv2MiddlewarClientID so missing client IDs are sourced from the inbound _ga cookie.

GTag client

c := client.NewGTag(l, "https://www.google-analytics.com", "G-XXXXXXXXX",
	client.GTagWithCookies("gtm_auth"),
)

err := c.Send(r, &gtag.Payload{...})

Options

Option	Purpose
GTagWithHTTPClient(*http.Client)	Override HTTP client.
GTagWithPath(string)	Override upstream path (default /g/collect).
GTagWithCookies(...string)	Cookie names to forward.
GTagWithMiddlewares(...GTagMiddleware)	Pre-send middleware.

Built-in middlewares appended in the constructor:

• GTagMiddlewareRichsstsse — populates the richsstsse parameter.
• GTagMiddlewarTrackingID — fills tracking ID if missing.
• GTagMiddlewarProtocolVersion — sets v=2.
• GTagMiddlewarIsDebug — preserves debug flag.
• GTagMiddlewarClientID — fills client ID from _ga.
• GTagMiddlewarSessionID — fills session ID from _ga_<id>.

Choosing between them

• Use MPv2 for new server-side code — it's the typed JSON protocol GA4 recommends and the easiest to compose middleware against.
• Use GTag only if you must mimic exact gtag.js behavior (e.g. when fronting a tagging server that expects gtag traffic).