add Proxy.AddHTTPHostRouteFunc to match routes by hosts dynamically.

http.go

@@ -38,16 +38,34 @@ func (p *Proxy) AddHTTPHostRoute(ipPort, httpHost string, dest Target) {
 //
 // The ipPort is any valid net.Listen TCP address.
 func (p *Proxy) AddHTTPHostMatchRoute(ipPort string, match Matcher, dest Target) {
-	p.addRoute(ipPort, httpHostMatch{match, dest})
+	p.addRoute(ipPort, httpHostMatch{matcher: match, target: dest})
+}
+
+// HTTPHostTargetFunc is the func callback used by Proxy.AddHTTPHostRouteFunc.
+type HTTPHostTargetFunc func(ctx context.Context, httpHost string) (t Target, ok bool)
+
+// AddHTTPHostRouteFunc adds a route to ipPort that matches an HTTP request and calls
+// fn to map it to a target.
+func (p *Proxy) AddHTTPHostRouteFunc(ipPort string, fn HTTPHostTargetFunc) {
+	p.addRoute(ipPort, httpHostMatch{targetFunc: fn})
 }
 
 type httpHostMatch struct {
 	matcher Matcher
 	target  Target
+
+	// Alternatively, if targetFunc is non-nil, it's used instead:
+	targetFunc HTTPHostTargetFunc
 }
 
 func (m httpHostMatch) match(br *bufio.Reader) (Target, string) {
 	hh := httpHostHeader(br)
+	if m.targetFunc != nil {
+		if t, ok := m.targetFunc(context.TODO(), hh); ok {
+			return t, hh
+		}
+		return nil, ""
+	}
 	if m.matcher(context.TODO(), hh) {
 		return m.target, hh
 	}

tcpproxy_test.go

@@ -72,7 +72,7 @@ func TestMatchHTTPHost(t *testing.T) {
 		}
 		t.Run(name, func(t *testing.T) {
 			br := bufio.NewReader(tt.r)
-			r := httpHostMatch{equals(tt.host), noopTarget{}}
+			r := httpHostMatch{matcher: equals(tt.host), target: noopTarget{}}
 			m, name := r.match(br)
 			got := m != nil
 			if got != tt.want {
@@ -247,6 +247,50 @@ func TestProxyHTTP(t *testing.T) {
 	}
 }
 
+func TestProxyHTTPFunc(t *testing.T) {
+	front := newLocalListener(t)
+	defer front.Close()
+
+	backFoo := newLocalListener(t)
+	defer backFoo.Close()
+	backBar := newLocalListener(t)
+	defer backBar.Close()
+
+	p := testProxy(t, front)
+	p.AddHTTPHostRouteFunc(testFrontAddr, func(ctx context.Context, httpHost string) (_ Target, ok bool) {
+		if httpHost == "bar.com" {
+			return To(backBar.Addr().String()), true
+		}
+		t.Fatalf("failed to match %q", httpHost)
+		return nil, false
+	})
+	if err := p.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	toFront, err := net.Dial("tcp", front.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer toFront.Close()
+
+	const msg = "GET / HTTP/1.1\r\nHost: bar.com\r\n\r\n"
+	io.WriteString(toFront, msg)
+
+	fromProxy, err := backBar.Accept()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	buf := make([]byte, len(msg))
+	if _, err := io.ReadFull(fromProxy, buf); err != nil {
+		t.Fatal(err)
+	}
+	if string(buf) != msg {
+		t.Fatalf("got %q; want %q", buf, msg)
+	}
+}
+
 func TestProxySNI(t *testing.T) {
 	front := newLocalListener(t)
 	defer front.Close()