A helper for collecting and emitting metadata throughout a request lifecycle.
When a new request arrives in your program, HTTP server, etc., use the New constructor with the incoming request's context to construct a new, empty Data.
func handler(w http.ResponseWriter, r *http.Request) {
ctx, d := ctxdata.New(r.Context())Use the returned context for all further operations on that request.
otherHandler(w, r.WithContext(ctx))
result, err := process(ctx, r.Header.Get("X-My-Key"))
// etc.Whenever you want to add metadata to the request Data, use the From helper to fetch the Data from the context, and call whatever method is appropriate.
func otherHandler(w http.ResponseWriter, r *http.Request) {
d := ctxdata.From(r.Context())
d.Set("user", r.URL.Query().Get("user"))
d.Set("corrleation_id", r.Header.Get("X-Correlation-ID"))
// ...
}
func process(ctx context.Context, key string) {
begin := time.Now()
// ...
ctxdata.From(ctx).Set("process_duration", time.Since(begin).String())
}At the end of the request, all of the metadata collected throughout the request's lifecycle will be available.
fmt.Fprintln(w, "OK")
for k, v := range d {
log.Printf("%s: %s", k, v)
}
}Here is an example middleware that writes a so-called wide event in JSON to the dst at the end of each request.
func logMiddleware(next http.Handler, dst io.Writer) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
ctx, d := ctxdata.New(r.Context())
defer func() { json.NewEncoder(dst).Encode(d.GetAll()) }()
next.ServeHTTP(w, r.WithContext(ctx))
})
}