[handlers] add link response headers

api/requests.http

@@ -277,6 +277,10 @@ Content-Type: application/json
     "messageTypes": ["SMS", "MMS"]
 }
 
+###
+# @no-redirect
+GET http://localhost:3000/ HTTP/1.1
+
 ###
 GET http://localhost:3000/metrics HTTP/1.1
 

internal/sms-gateway/handlers/root.go

@@ -1,6 +1,7 @@
 package handlers
 
 import (
+	"fmt"
 	"path"
 	"strings"
 
@@ -16,6 +17,8 @@ type rootHandler struct {
 }
 
 func (h *rootHandler) Register(app *fiber.App) {
+	app.Get("/", h.handleRoot)
+
 	if h.config.PublicPath != "/api" {
 		app.Use(func(c *fiber.Ctx) error {
 			err := c.Next()
@@ -34,13 +37,34 @@ func (h *rootHandler) Register(app *fiber.App) {
 	h.registerOpenAPI(app)
 }
 
+func (h *rootHandler) handleRoot(c *fiber.Ctx) error {
+	h.setLinkHeaders(c)
+
+	if err := c.Redirect(h.config.PublicPath, fiber.StatusMovedPermanently); err != nil {
+		return fmt.Errorf("redirect to public path %q: %w", h.config.PublicPath, err)
+	}
+	return nil
+}
+
+func (h *rootHandler) setLinkHeaders(c *fiber.Ctx) {
+	publicPath := strings.TrimRight(h.config.PublicPath, "/")
+	c.Set(fiber.HeaderLink,
+		`</.well-known/api-catalog>; rel="api-catalog", `+
+			`<`+publicPath+`/docs/doc.json>; rel="service-desc", `+
+			`<https://docs.sms-gate.app/>; rel="service-doc", `+
+			`</.well-known/api-catalog>; rel="describedby"`,
+	)
+}
+
 func (h *rootHandler) registerOpenAPI(router fiber.Router) {
 	if !h.config.OpenAPIEnabled {
 		return
 	}
 
 	router.Use(func(c *fiber.Ctx) error {
 		if c.Path() == "/api" || c.Path() == "/api/" {
+			h.setLinkHeaders(c)
+
 			return c.Redirect("/api/docs", fiber.StatusMovedPermanently)
 		}