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Collect ​

pkg/collect. High-level server that fronts GA4 traffic and forwards it to a tagging server.

Constructor ​

go
func New(l *zap.Logger, opts ...Option) (*Collect, error)

Options ​

go
WithTagging(url string)                                  // downstream tagging server URL
WithTaggingClient(c *http.Client)                        // override HTTP client
WithGTagHTTPMiddlewares(v ...gtaghttp.Middleware)        // /g/collect middleware chain
WithMPv2HTTPMiddlewares(v ...mpv2http.Middleware)        // /mp/collect middleware chain

Methods ​

go
func (c *Collect) GTagHTTPHandler(w http.ResponseWriter, r *http.Request)
func (c *Collect) MPv2HTTPHandler(w http.ResponseWriter, r *http.Request)

Both have signature http.HandlerFunc so they mount on any router.

Behavior ​

For each request:

  1. Decode payload using the per-protocol Handler(...) — invalid requests get an HTTP error and never reach middleware.
  2. Run the configured middleware chain.
  3. Re-encode the payload and POST it to ${taggingURL}${path}, where path is /g/collect for GTag and /mp/collect for MPv2. Inbound r.Header is cloned to the upstream request.
  4. Map upstream non-200 responses to 500 Internal Server Error on the inbound side.

Defaults ​

  • taggingClient defaults to http.DefaultClient (override with WithTaggingClient).
  • No middlewares by default. The chain is purely opt-in via the With…Middlewares options.

Example ​

go
c, err := collect.New(l,
	collect.WithTagging("https://sgtm.example.com"),
	collect.WithMPv2HTTPMiddlewares(
		mpv2http.MiddlewareLogger,
		mpv2http.MiddlewareClientID,
		mpv2http.MiddlewareIPOverride,
		mpv2http.MiddlewareUserAgent,
		mpv2http.MiddlewarePageLocation,
		mpv2http.MiddlewareEngagementTime,
		mpv2http.MiddlewareWithTimeout(2 * time.Second),
	),
)

http.HandleFunc("/g/collect", c.GTagHTTPHandler)
http.HandleFunc("/mp/collect", c.MPv2HTTPHandler)