add prefix from X-Forwarded-Prefix in redirectTrailingSlash (#1238)

* add prefix from X-Forwarded-Prefix in redirectTrailingSlash

* added test

* fix path import

gin.go

@@ -10,6 +10,7 @@ import (
 	"net"
 	"net/http"
 	"os"
+	"path"
 	"sync"
 
 	"github.com/gin-gonic/gin/render"
@@ -438,17 +439,20 @@ func serveError(c *Context, code int, defaultMessage []byte) {
 
 func redirectTrailingSlash(c *Context) {
 	req := c.Request
-	path := req.URL.Path
+	p := req.URL.Path
+	if prefix := path.Clean(c.Request.Header.Get("X-Forwarded-Prefix")); prefix != "." {
+		p = prefix + "/" + req.URL.Path
+	}
 	code := http.StatusMovedPermanently // Permanent redirect, request with GET method
 	if req.Method != "GET" {
 		code = http.StatusTemporaryRedirect
 	}
 
-	req.URL.Path = path + "/"
-	if length := len(path); length > 1 && path[length-1] == '/' {
-		req.URL.Path = path[:length-1]
+	req.URL.Path = p + "/"
+	if length := len(p); length > 1 && p[length-1] == '/' {
+		req.URL.Path = p[:length-1]
 	}
-	debugPrint("redirecting request %d: %s --> %s", code, path, req.URL.String())
+	debugPrint("redirecting request %d: %s --> %s", code, p, req.URL.String())
 	http.Redirect(c.Writer, req, req.URL.String(), code)
 	c.writermem.WriteHeaderNow()
 }

routes_test.go

@@ -16,8 +16,16 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func performRequest(r http.Handler, method, path string) *httptest.ResponseRecorder {
+type header struct {
+	Key   string
+	Value string
+}
+
+func performRequest(r http.Handler, method, path string, headers ...header) *httptest.ResponseRecorder {
 	req, _ := http.NewRequest(method, path, nil)
+	for _, h := range headers {
+		req.Header.Add(h.Key, h.Value)
+	}
 	w := httptest.NewRecorder()
 	r.ServeHTTP(w, req)
 	return w
@@ -170,6 +178,13 @@ func TestRouteRedirectTrailingSlash(t *testing.T) {
 	w = performRequest(router, "PUT", "/path4/")
 	assert.Equal(t, http.StatusOK, w.Code)
 
+	w = performRequest(router, "GET", "/path2", header{Key: "X-Forwarded-Prefix", Value: "/api"})
+	assert.Equal(t, "/api/path2/", w.Header().Get("Location"))
+	assert.Equal(t, 301, w.Code)
+
+	w = performRequest(router, "GET", "/path2/", header{Key: "X-Forwarded-Prefix", Value: "/api/"})
+	assert.Equal(t, 200, w.Code)
+
 	router.RedirectTrailingSlash = false
 
 	w = performRequest(router, "GET", "/path/")