feat: reverse proxy handler with event stream

Author: ArpitRajputGithub

proxy.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"time"
+)
+
+// Event is a single request going through the proxy.
+// It is published to a channel and consumed by whichever UI is active.
+type Event struct {
+	Method   string
+	Path     string
+	Status   int
+	Duration time.Duration
+	Time     time.Time
+}
+
+// newProxyHandler returns an http.Handler that reverse-proxies to the given target
+// and publishes an Event for each request to the events channel.
+// events may be nil (drops events on the floor).
+func newProxyHandler(targetPort int, events chan<- Event) http.Handler {
+	target, _ := url.Parse(fmt.Sprintf("http://127.0.0.1:%d", targetPort))
+	proxy := httputil.NewSingleHostReverseProxy(target)
+
+	// Preserve client's Host header — dev servers (Vite HMR, Next) check it.
+	originalDirector := proxy.Director
+	proxy.Director = func(r *http.Request) {
+		host := r.Host
+		originalDirector(r)
+		r.Host = host
+	}
+
+	proxy.ErrorHandler = func(w http.ResponseWriter, r *http.Request, err error) {
+		w.WriteHeader(http.StatusBadGateway)
+		fmt.Fprintf(w, "upstream unreachable at localhost:%d\n", targetPort)
+	}
+
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+		sw := &statusWriter{ResponseWriter: w, status: http.StatusOK}
+		proxy.ServeHTTP(sw, r)
+		if events != nil {
+			// Non-blocking send — never let a slow UI stall the proxy.
+			select {
+			case events <- Event{
+				Method:   r.Method,
+				Path:     r.URL.Path,
+				Status:   sw.status,
+				Duration: time.Since(start),
+				Time:     start,
+			}:
+			default:
+			}
+		}
+	})
+}
+
+// statusWriter captures the status code from an http.ResponseWriter.
+// Also implements http.Hijacker so WebSocket upgrades work.
+type statusWriter struct {
+	http.ResponseWriter
+	status int
+}
+
+func (s *statusWriter) WriteHeader(code int) {
+	s.status = code
+	s.ResponseWriter.WriteHeader(code)
+}
+
+func (s *statusWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	if h, ok := s.ResponseWriter.(http.Hijacker); ok {
+		return h.Hijack()
+	}
+	return nil, nil, errors.New("hijacking not supported")
+}
+
+func (s *statusWriter) Flush() {
+	if f, ok := s.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	}
+}