traefik_x_request_start.go

// Package traefikxrequeststart adds X-Request-Start header in "t=<seconds.millis>" format.
package traefikxrequeststart

import (
	"context"
	"fmt"
	"net/http"
	"time"
)

type Config struct {
	// Optional: override header name and include "t=" prefix
	HeaderName string
	WithPrefix bool
}

func CreateConfig() *Config {
	return &Config{
		HeaderName: "X-Request-Start",
		WithPrefix: true, // matches common NGINX/Heroku style: "t=<value>"
	}
}

type XRequestStart struct {
	next       http.Handler
	name       string
	headerName string
	withPrefix bool
}

func New(_ context.Context, next http.Handler, cfg *Config, name string) (http.Handler, error) {
	if cfg == nil {
		cfg = CreateConfig()
	}
	return &XRequestStart{
		next:       next,
		name:       name,
		headerName: cfg.HeaderName,
		withPrefix: cfg.WithPrefix,
	}, nil
}

func (a *XRequestStart) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
	val := makeUnixSecMillis(time.Now())
	if a.withPrefix {
		val = "t=" + val
	}

	// Forward to backend
	req.Header.Set(a.headerName, val)
	// Also expose on response (handy for debugging/clients)
	rw.Header().Set(a.headerName, val)

	a.next.ServeHTTP(rw, req)
}

// makeUnixSecMillis returns "seconds.mmm" (UTC) with millisecond precision.
func makeUnixSecMillis(t time.Time) string {
	t = t.UTC()
	sec := t.Unix()
	msec := t.Nanosecond() / int(time.Millisecond) // 0..999
	return fmt.Sprintf("%d.%03d", sec, msec)
}