CODE-1845: Always serving index.html for static resources which are not found in dist folder (#2033)

web/dist.go

@@ -18,20 +18,23 @@ package web
 import (
 	"bytes"
 	"embed"
+	"fmt"
 	"io"
 	"io/fs"
 	"net/http"
 	"os"
 	"path"
-	"path/filepath"
-	"strings"
 	"time"
-
-	"github.com/rs/zerolog/log"
 )
 
 //go:embed dist/*
 var UI embed.FS
+var remoteEntryContent []byte
+var fileMap map[string]bool
+
+const distPath = "dist"
+const remoteEntryJS = "remoteEntry.js"
+const remoteEntryJSFullPath = "/" + remoteEntryJS
 
 // Handler returns an http.HandlerFunc that servers the
 // static content from the embedded file system.
@@ -39,84 +42,104 @@ var UI embed.FS
 //nolint:gocognit // refactor if required.
 func Handler() http.HandlerFunc {
 	// Load the files subdirectory
-	fs, err := fs.Sub(UI, "dist")
+	fs, err := fs.Sub(UI, distPath)
 	if err != nil {
 		panic(err)
 	}
+
 	// Create an http.FileServer to serve the
 	// contents of the files subdiretory.
 	handler := http.FileServer(http.FS(fs))
 
-	// Create an http.HandlerFunc that wraps the
-	// http.FileServer to always load the index.html
-	// file if a directory path is being requested.
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		// because this is a single page application,
-		// we need to always load the index.html file
-		// in the root of the project, unless the path
-		// points to a file with an extension (css, js, etc)
-		// No ext: (1) a browser URL request, not a static asset request
-		if filepath.Ext(r.URL.Path) == "" ||
-			// "..." : (2a) browser URL with ... in it
-			(strings.Contains(r.URL.Path, "...") &&
-				// (2b) filter out static asset URLs that browsers make along with it
-				filepath.Ext(strings.ReplaceAll(r.URL.Path, "...", "")) == "") {
-			// HACK: alter the path to point to the
-			// root of the project.
+		// Get the file base path
+		basePath := path.Base(r.URL.Path)
+
+		// If the file exists in dist/ then serve it from "/".
+		// Otherwise, rewrite the request to "/" so /index.html is served
+		if fileNotFoundInDist(basePath) {
 			r.URL.Path = "/"
 		} else {
-			// All static assets are served from the root path
-			r.URL.Path = "/" + path.Base(r.URL.Path)
+			r.URL.Path = "/" + basePath
 		}
 
 		// Disable caching and sniffing via HTTP headers for UI main entry resources
-		if r.URL.Path == "/" || r.URL.Path == "/remoteEntry.js" || r.URL.Path == "/index.html" {
+		if r.URL.Path == "/" || r.URL.Path == remoteEntryJSFullPath || r.URL.Path == "/index.html" {
 			w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate, max-age=0")
 			w.Header().Set("pragma", "no-cache")
 			w.Header().Set("X-Content-Type-Options", "nosniff")
 		}
 
-		if r.URL.Path == "/remoteEntry.js" {
-			if readerRemoteEntry, errFetch := fetchRemoteEntryJS(fs); errFetch == nil {
-				http.ServeContent(w, r, r.URL.Path, time.Now(), readerRemoteEntry)
-			} else {
-				log.Error().Msgf("Failed to fetch remoteEntry.js %v", err)
-				http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
-			}
+		// Serve /remoteEntry.js from memory
+		if r.URL.Path == remoteEntryJSFullPath {
+			http.ServeContent(w, r, r.URL.Path, time.Now(), bytes.NewReader(remoteEntryContent))
 		} else {
-			// and finally serve the file.
 			handler.ServeHTTP(w, r)
 		}
 	})
 }
 
-var remoteEntryContent *bytes.Reader
-
-func fetchRemoteEntryJS(fs fs.FS) (*bytes.Reader, error) {
-	if remoteEntryContent == nil {
-		path := "remoteEntry.js"
-
-		file, err := fs.Open(path)
-		if err != nil {
-			log.Error().Msgf("Failed to open file %v", path)
-			return nil, err
-		}
-
-		buf, err := io.ReadAll(file)
-		if err != nil {
-			log.Error().Msgf("Failed to read file %v", path)
-			return nil, err
-		}
-
-		enableCDN := os.Getenv("ENABLE_CDN")
-		if len(enableCDN) == 0 {
-			enableCDN = "false"
-		}
-
-		modBuf := bytes.Replace(buf, []byte("__ENABLE_CDN__"), []byte(enableCDN), 1)
-
-		remoteEntryContent = bytes.NewReader(modBuf)
+func init() {
+	err := readRemoteEntryJSContent()
+	if err != nil {
+		panic(err)
 	}
 
-	return remoteEntryContent, nil
+	err = createFileMapForDistFolder()
+	if err != nil {
+		panic(err)
+	}
+}
+
+func readRemoteEntryJSContent() error {
+	fs, err := fs.Sub(UI, distPath)
+
+	if err != nil {
+		return fmt.Errorf("failed to open /dist: %w", err)
+	}
+
+	file, err := fs.Open(remoteEntryJS)
+
+	if err != nil {
+		return fmt.Errorf("failed to open remoteEntry.js: %w", err)
+	}
+
+	defer file.Close()
+	buf, err := io.ReadAll(file)
+
+	if err != nil {
+		return fmt.Errorf("failed to read remoteEntry.js: %w", err)
+	}
+
+	enableCDN := os.Getenv("ENABLE_CDN")
+
+	if len(enableCDN) == 0 {
+		enableCDN = "false"
+	}
+
+	remoteEntryContent = bytes.Replace(buf, []byte("__ENABLE_CDN__"), []byte(enableCDN), 1)
+
+	return nil
+}
+
+func createFileMapForDistFolder() error {
+	fileMap = make(map[string]bool)
+
+	err := fs.WalkDir(UI, distPath, func(path string, _ fs.DirEntry, err error) error {
+		if err != nil {
+			return fmt.Errorf("failed to build file map for path %q: %w", path, err)
+		}
+
+		if path != distPath { // exclude "dist" from file map
+			fileMap[path] = true
+		}
+
+		return nil
+	})
+
+	return err
+}
+
+func fileNotFoundInDist(path string) bool {
+	return !fileMap[distPath+"/"+path]
 }