ui: serve files from embedded ./assets/ directory

Static assets that are embedded within CRDB were traditionally served
from the ./assets/ directory (relative to the root of the embed.FS
instance built at compile time). Commit fcd385c (ui: serve ETag
header and respect If-None-Match req. header for assets, 2022-03-24)
served files directly from the root of that embed.FS instance, which
caused browser requests for `/bundle.js` to fail with a 404 response
code (the correct path would have been `/assets/bundle.js` in that
commit). Serve static assets from ./assets/ again, so that browsers can
load `/bundle.js` and the admin UI can be successfully loaded.

fixes #79657

Release note: None

pkg/server/server_test.go

@@ -42,6 +42,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/security"
 	"github.com/cockroachdb/cockroach/pkg/server/serverpb"
 	"github.com/cockroachdb/cockroach/pkg/server/status/statuspb"
+	"github.com/cockroachdb/cockroach/pkg/server/testdata"
 	"github.com/cockroachdb/cockroach/pkg/sql"
 	"github.com/cockroachdb/cockroach/pkg/sql/catalog/catalogkeys"
 	"github.com/cockroachdb/cockroach/pkg/sql/catalog/dbdesc"
@@ -68,10 +69,6 @@ import (
 	"google.golang.org/grpc/status"
 )
 
-// embedFsys is a small instance of embed.FS used for testing purposes only
-//go:embed doc.go
-var embedFsys embed.FS
-
 // TestSelfBootstrap verifies operation when no bootstrap hosts have
 // been specified.
 func TestSelfBootstrap(t *testing.T) {
@@ -1163,7 +1160,7 @@ Binary built without web UI.
 		linkInFakeUI()
 		defer unlinkFakeUI()
 
-		ui.Assets = embedFsys
+		ui.Assets = testdata.TestAssets
 
 		// Clear fake asset FS when we're done
 		defer func() {
@@ -1196,7 +1193,7 @@ Binary built without web UI.
 		for _, testCase := range cases {
 			t.Run(fmt.Sprintf("bundle caching for %s", testCase.desc), func(t *testing.T) {
 				// Request bundle.js without an If-None-Match header first, to simulate the initial load
-				uncachedReq, err := http.NewRequestWithContext(ctx, "GET", s.AdminURL()+"/doc.go", nil)
+				uncachedReq, err := http.NewRequestWithContext(ctx, "GET", s.AdminURL()+"/bundle.js", nil)
 				require.NoError(t, err)
 
 				uncachedResp, err := testCase.client.Do(uncachedReq)
@@ -1208,7 +1205,7 @@ Binary built without web UI.
 				require.NotEmpty(t, etag, "Server must provide ETag response header with asset responses")
 
 				// Use that ETag header on the next request to simulate a client reload
-				cachedReq, err := http.NewRequestWithContext(ctx, "GET", s.AdminURL()+"/doc.go", nil)
+				cachedReq, err := http.NewRequestWithContext(ctx, "GET", s.AdminURL()+"/bundle.js", nil)
 				require.NoError(t, err)
 				cachedReq.Header.Add("If-None-Match", etag)
 

pkg/server/testdata/assets/bundle.js

@@ -0,0 +1,10 @@
+// Copyright 2022 The Cockroach Authors.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+console.log("This is a test-only bundle.js, meant for embedding in server_test.go.");

pkg/server/testdata/embedded_assets.go

@@ -0,0 +1,17 @@
+// Copyright 2022 The Cockroach Authors.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+package testdata
+
+import "embed"
+
+// TestAssets is a test-only embed.FS, and should not be used for any other purposes.
+//go:embed assets
+var TestAssets embed.FS

pkg/ui/ui.go

@@ -22,6 +22,7 @@ import (
 	"embed"
 	"fmt"
 	"html/template"
+	"io/fs"
 	"net/http"
 
 	"github.com/cockroachdb/cockroach/pkg/base"
@@ -113,13 +114,17 @@ type Config struct {
 // including index.html, which has some login-related variables
 // templated into it, as well as static assets.
 func Handler(cfg Config) http.Handler {
+	// assetsFsys is an io/fs instance rooted at `./assets`, relative to the Assets embedded in
+	// the CRDB binary.
+	assetsFsys, _ := fs.Sub(Assets, "assets")
+
 	// etags is used to provide a unique per-file checksum for each served file,
 	// which enables client-side caching using Cache-Control and ETag headers.
 	etags := make(map[string]string)
 
 	if HaveUI {
 		// Only compute hashes for UI-enabled builds
-		err := httputil.ComputeEtags(Assets, etags)
+		err := httputil.ComputeEtags(assetsFsys, etags)
 		if err != nil {
 			log.Errorf(context.Background(), "Unable to compute asset hashes: %+v", err)
 		}
@@ -128,7 +133,7 @@ func Handler(cfg Config) http.Handler {
 	fileHandlerChain := httputil.EtagHandler(
 		etags,
 		http.FileServer(
-			http.FS(Assets),
+			http.FS(assetsFsys),
 		),
 	)
 	buildInfo := build.GetInfo()