Plugins: Preserve trailing slash in plugin proxy (#86859)

* Plugins: Preserve trailing slash in plugin proxy

* enable toggle by default

pkg/api/pluginproxy/ds_proxy_test.go

@@ -104,6 +104,10 @@ func TestDataSourceProxy_routeRule(t *testing.T) {
 				URL:  "http://www.test.com",
 				Body: []byte(`{ "url": "{{.JsonData.dynamicUrl}}", "secret": "{{.SecureJsonData.key}}"	}`),
 			},
+			{
+				Path: "mypath",
+				URL:  "https://example.com/api/v1/",
+			},
 		}
 
 		ds := &datasources.DataSource{
@@ -209,6 +213,16 @@ func TestDataSourceProxy_routeRule(t *testing.T) {
 			require.Equal(t, `{ "url": "https://dynamic.grafana.com", "secret": "123"	}`, string(content))
 		})
 
+		t.Run("When matching route path ending with a slash", func(t *testing.T) {
+			ctx, req := setUp()
+			proxy, err := setupDSProxyTest(t, ctx, ds, routes, "mypath/some-route/")
+			require.NoError(t, err)
+			proxy.matchedRoute = routes[6]
+			ApplyRoute(proxy.ctx.Req.Context(), req, proxy.proxyPath, proxy.matchedRoute, dsInfo, proxy.cfg)
+
+			assert.Equal(t, "https://example.com/api/v1/some-route/", req.URL.String())
+		})
+
 		t.Run("Validating request", func(t *testing.T) {
 			t.Run("plugin route with valid role", func(t *testing.T) {
 				ctx, _ := setUp()

pkg/api/pluginproxy/pluginproxy.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"strings"
 
 	"go.opentelemetry.io/otel/attribute"
 
@@ -76,7 +77,12 @@ func (proxy *PluginProxy) HandleRequest() {
 		}
 
 		if path, exists := params["*"]; exists {
+			hasSlash := strings.HasSuffix(proxy.proxyPath, "/")
 			proxy.proxyPath = path
+
+			if hasSlash && !strings.HasSuffix(path, "/") && proxy.features.IsEnabled(proxy.ctx.Req.Context(), featuremgmt.FlagPluginProxyPreserveTrailingSlash) {
+				proxy.proxyPath += "/"
+			}
 		} else {
 			proxy.proxyPath = ""
 		}

pkg/api/pluginproxy/pluginproxy_test.go

@@ -316,10 +316,16 @@ func TestPluginProxyRoutes(t *testing.T) {
 			Method: "GET",
 			URL:    "http://localhost/api/v2/instances",
 		},
+		{
+			Path:   "/mypath/*",
+			Method: "GET",
+			URL:    "https://example.com/api/v1/",
+		},
 	}
 
 	tcs := []struct {
 		proxyPath       string
+		withFeatures    []any
 		expectedURLPath string
 		expectedStatus  int
 	}{
@@ -362,6 +368,17 @@ func TestPluginProxyRoutes(t *testing.T) {
 			expectedURLPath: "/api/v2/instances/instance-one",
 			expectedStatus:  http.StatusOK,
 		},
+		{
+			proxyPath:       "/mypath/some-route/",
+			expectedURLPath: "/api/v1/some-route",
+			expectedStatus:  http.StatusOK,
+		},
+		{
+			proxyPath:       "/mypath/some-route/",
+			withFeatures:    []any{featuremgmt.FlagPluginProxyPreserveTrailingSlash},
+			expectedURLPath: "/api/v1/some-route/",
+			expectedStatus:  http.StatusOK,
+		},
 	}
 
 	for _, tc := range tcs {
@@ -404,7 +421,7 @@ func TestPluginProxyRoutes(t *testing.T) {
 				SecureJSONData: map[string][]byte{},
 			}
 			cfg := &setting.Cfg{}
-			proxy, err := NewPluginProxy(ps, testRoutes, ctx, tc.proxyPath, cfg, secretsService, tracing.InitializeTracerForTest(), &http.Transport{}, acimpl.ProvideAccessControl(featuremgmt.WithFeatures()), featuremgmt.WithFeatures())
+			proxy, err := NewPluginProxy(ps, testRoutes, ctx, tc.proxyPath, cfg, secretsService, tracing.InitializeTracerForTest(), &http.Transport{}, acimpl.ProvideAccessControl(featuremgmt.WithFeatures()), featuremgmt.WithFeatures(tc.withFeatures...))
 			require.NoError(t, err)
 			proxy.HandleRequest()