Add serverless handler for Vercel deployments

README.md

@@ -57,6 +57,20 @@ Health check path: `/widget`.
 
 ---
 
+## Deploy to Vercel
+
+The repository ships with a serverless handler under `api/index.go` and a
+`vercel.json` rewrite that forwards every request to it. Deploying through the
+"Deploy with Vercel" button or via `vercel deploy` builds a Go Serverless
+Function, so no Docker support is required. Once deployed, the instance exposes
+the same routes described above.
+
+You can set `HOST`, `PORT`, or `ADDR` environment variables if you want to run
+the binary locally with `vercel dev`, but they are not required for production
+deployments on Vercel.
+
+---
+
 ## Deploy to a generic VPS
 
 ### Option A: Docker on VPS

api/index.go

@@ -0,0 +1,24 @@
+package handler
+
+import (
+	"net/http"
+	"time"
+
+	"giscus-proxy/internal/cache"
+	"giscus-proxy/internal/proxy"
+)
+
+var defaultHandler http.Handler
+
+func init() {
+	p := proxy.New(proxy.Config{
+		Client: &http.Client{Timeout: 25 * time.Second},
+		Cache:  cache.NewMemoryCache(256),
+	})
+	defaultHandler = p.Handler()
+}
+
+// Handler is the entry point for Vercel's Go runtime.
+func Handler(w http.ResponseWriter, r *http.Request) {
+	defaultHandler.ServeHTTP(w, r)
+}

cmd/giscus-proxy/main.go

@@ -19,6 +19,7 @@ func main() {
 		Cache:  cache.NewMemoryCache(512),
 	})
 
+	handler := p.Handler()
 	mux := http.NewServeMux()
 	p.Register(mux)
 
@@ -34,6 +35,7 @@ func main() {
 
 	srv := &http.Server{
 		Addr:              addr,
+		Handler:           handler,
 		Handler:           mux,
 		ReadHeaderTimeout: 5 * time.Second,
 		ErrorLog:          log.New(os.Stdout, "", 0),

internal/proxy/proxy.go

@@ -77,6 +77,13 @@ func (p *Proxy) Register(mux *http.ServeMux) {
 	mux.HandleFunc("/", p.handlePassthrough)
 }
 
+// Handler returns a ready-to-use HTTP handler that serves the proxy.
+func (p *Proxy) Handler() http.Handler {
+	mux := http.NewServeMux()
+	p.Register(mux)
+	return mux
+}
+
 func (p *Proxy) logf(format string, args ...any) {
 	if p.logger == nil {
 		log.Printf(format, args...)

vercel.json

@@ -1,8 +1,8 @@
 {
-    "builds": [
-      {
-        "src": "Dockerfile",
-        "use": "@vercel/docker"
-      }
-    ]
-  }
+  "rewrites": [
+    {
+      "source": "/(.*)",
+      "destination": "/api/index"
+    }
+  ]
+}