How to Implement API Versioning in Go

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2026-04-17T14:12:14+00:00
Implement API versioning in Go using URL path prefixes and GODEBUG directives to manage different API behaviors.

Implement API versioning in Go by using URL path prefixes (e.g., /v1/) and conditional logic based on the GODEBUG environment variable or go.mod directives to control behavior. Use the //go:debug directive in your source files to toggle specific behaviors for different versions without changing the core logic.

//go:debug default=go1.21
//go:debug panicnil=1

package main

import (
	"net/http"
	"os"
)

func main() {
	// Check GODEBUG for version-specific behavior
	if os.Getenv("GODEBUG") != "" {
		http.HandleFunc("/v1/", handleV1)
		http.HandleFunc("/v2/", handleV2)
	} else {
		http.HandleFunc("/", handleDefault)
	}
	http.ListenAndServe(":8080", nil)
}

func handleV1(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("API v1"))
}

func handleV2(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("API v2"))
}

func handleDefault(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Default API"))
}