cleanup and simplify middleware implementations, refactor some other code

internal/net/http/middleware/set_upstream_headers.go

@@ -0,0 +1,34 @@
+package middleware
+
+import (
+	"net/http"
+
+	gphttp "github.com/yusing/go-proxy/internal/net/http"
+)
+
+// internal use only.
+type setUpstreamHeaders struct {
+	Scheme, Host, Port string
+}
+
+var suh = NewMiddleware[setUpstreamHeaders]()
+
+func newSetUpstreamHeaders(rp *gphttp.ReverseProxy) *Middleware {
+	m, err := suh.New(OptionsRaw{
+		"scheme": rp.TargetURL.Scheme,
+		"host":   rp.TargetURL.Hostname(),
+		"port":   rp.TargetURL.Port(),
+	})
+	if err != nil {
+		panic(err)
+	}
+	return m
+}
+
+// before implements RequestModifier.
+func (s setUpstreamHeaders) before(w http.ResponseWriter, r *http.Request) (proceed bool) {
+	r.Header.Set(gphttp.HeaderUpstreamScheme, s.Scheme)
+	r.Header.Set(gphttp.HeaderUpstreamHost, s.Host)
+	r.Header.Set(gphttp.HeaderUpstreamPort, s.Port)
+	return true
+}