ServeFromSubPath: Redirect to URL with subpath when subpath missing (#66724)

* ServeFromSubPath: Redirect to URL with subpath when subpath missing

* Review fixes

* Added tests

* Use constant

* change to useMiddleware

* Update pkg/middleware/subpath_redirect.go

---------

Co-authored-by: Carl Bergquist <carl.bergquist@gmail.com>

pkg/api/http_server.go

@@ -602,6 +602,7 @@ func (hs *HTTPServer) addMiddlewaresAndStaticRoutes() {
 
 	if hs.Cfg.ServeFromSubPath && hs.Cfg.AppSubURL != "" {
 		m.SetURLPrefix(hs.Cfg.AppSubURL)
+		m.UseMiddleware(middleware.SubPathRedirect(hs.Cfg))
 	}
 
 	m.UseMiddleware(web.Renderer(filepath.Join(hs.Cfg.StaticRootPath, "views"), "[[", "]]"))
@@ -616,6 +617,7 @@ func (hs *HTTPServer) addMiddlewaresAndStaticRoutes() {
 
 	m.UseMiddleware(hs.ContextHandler.Middleware)
 	m.Use(middleware.OrgRedirect(hs.Cfg, hs.userService))
+
 	if !hs.Features.IsEnabled(featuremgmt.FlagAuthnService) {
 		m.Use(accesscontrol.LoadPermissionsMiddleware(hs.accesscontrolService))
 	}

pkg/middleware/subpath_redirect.go

@@ -0,0 +1,26 @@
+package middleware
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/grafana/grafana/pkg/setting"
+	"github.com/grafana/grafana/pkg/web"
+)
+
+// SubPathRedirect Redirects URLs that are missing the configured subpath to an URL that contains the subpath.
+func SubPathRedirect(cfg *setting.Cfg) web.Middleware {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+			// Direct to url with subpath if the request is missing the subpath and is not an API request.
+			if !strings.HasPrefix(req.RequestURI, cfg.AppSubURL) && !strings.HasPrefix(req.RequestURI, "/api") {
+				newURL := fmt.Sprintf("%s%s", cfg.AppURL, strings.TrimPrefix(req.RequestURI, "/"))
+				http.Redirect(rw, req, newURL, http.StatusMovedPermanently)
+				return
+			}
+
+			next.ServeHTTP(rw, req)
+		})
+	}
+}

pkg/middleware/subpath_redirect_test.go

@@ -0,0 +1,43 @@
+package middleware
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSubPathRedirect(t *testing.T) {
+	testSubPathRedirect(t, "/", "http://localhost:3000/subpath/")
+	testSubPathRedirect(t, "/admin/my/page", "http://localhost:3000/subpath/admin/my/page")
+	testSubPathRedirect(t, "/api/users", "")
+}
+
+func testSubPathRedirect(t *testing.T, url string, expectedRedirect string) {
+	middlewareScenario(t, "GET url without subpath", func(t *testing.T, sc *scenarioContext) {
+		sc.cfg.AppSubURL = "/subpath"
+		sc.cfg.AppURL = "http://localhost:3000/subpath/"
+
+		sc.m.UseMiddleware(SubPathRedirect(sc.cfg))
+		sc.m.Get("/api/users", sc.defaultHandler)
+
+		sc.fakeReqWithParams("GET", url, map[string]string{}).exec()
+
+		if expectedRedirect != "" {
+			assert.Equal(t, 301, sc.resp.Code)
+
+			// nolint:bodyclose
+			resp := sc.resp.Result()
+			t.Cleanup(func() {
+				err := resp.Body.Close()
+				assert.NoError(t, err)
+			})
+			redirectURL, err := resp.Location()
+			require.NoError(t, err)
+
+			assert.Equal(t, expectedRedirect, redirectURL.String())
+		} else {
+			assert.Equal(t, 200, sc.resp.Code)
+		}
+	})
+}

pkg/middleware/testing.go

@@ -99,7 +99,10 @@ func (sc *scenarioContext) fakeReqWithParams(method, url string, queryParams map
 	for k, v := range queryParams {
 		q.Add(k, v)
 	}
+
 	req.URL.RawQuery = q.Encode()
+	req.RequestURI = req.URL.RequestURI()
+
 	require.NoError(sc.t, err)
 
 	reqCtx := &contextmodel.ReqContext{