Feature 01 task 3: Embed the PWA build with SPA fallback (#4)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

.gitignore

@@ -8,6 +8,11 @@ deploy/secrets/
 # Build artifacts and dependencies
 node_modules
 dist
+bin/
+# Placeholder so the Go embed compiles on a fresh clone; built assets stay ignored.
+!internal/frontend/dist/
+internal/frontend/dist/*
+!internal/frontend/dist/index.html
 
 # Local databases
 *.db

Makefile

@@ -0,0 +1,24 @@
+# Build entry point: build the PWA, embed it, then build the server binary.
+
+FRONTEND_DIST := internal/frontend/dist
+
+.PHONY: build web embed check-embed-clean
+
+build: embed
+	go build -o bin/mealquest ./cmd/server
+
+web:
+	cd web && npm ci && npm run build
+
+# Replace the committed placeholder with the built PWA so go:embed picks it up.
+# Recreate the whole directory: a glob would skip dotfiles, which all:dist embeds.
+embed: web
+	rm -rf $(FRONTEND_DIST)
+	mkdir -p $(FRONTEND_DIST)
+	cp -R web/dist/. $(FRONTEND_DIST)/
+
+# Regression check: a stale hidden file must not survive an embed.
+check-embed-clean:
+	touch $(FRONTEND_DIST)/.stale-embed-check
+	$(MAKE) embed
+	test ! -e $(FRONTEND_DIST)/.stale-embed-check

cmd/server/main.go

@@ -13,6 +13,7 @@ import (
 	"time"
 
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/config"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/frontend"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/server"
 )
 
@@ -37,9 +38,13 @@ func run(cfg config.Config, logger *slog.Logger) error {
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
 
+	router, err := server.NewRouter(logger, version, frontend.Assets())
+	if err != nil {
+		return err
+	}
 	srv := &http.Server{
 		Addr:              cfg.HTTPAddr,
-		Handler:           server.NewRouter(logger, version),
+		Handler:           router,
 		ReadHeaderTimeout: 10 * time.Second,
 		ErrorLog:          slog.NewLogLogger(logger.Handler(), slog.LevelError),
 	}

internal/frontend/dist/index.html

@@ -0,0 +1,11 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <title>MealQuest</title>
+  </head>
+  <body>
+    <!-- Placeholder so the Go embed compiles. The build replaces this directory with web/dist. -->
+    <p>MealQuest web assets have not been built.</p>
+  </body>
+</html>

internal/frontend/frontend.go

@@ -0,0 +1,127 @@
+// Package frontend serves the embedded PWA build with an SPA fallback.
+package frontend
+
+import (
+	"embed"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"log/slog"
+	"net/http"
+	"path"
+	"strings"
+	"time"
+)
+
+// embedded holds the web build. The build copies web/dist over the committed
+// placeholder index.html.
+//
+//go:embed all:dist
+var embedded embed.FS
+
+const (
+	indexFile = "index.html"
+
+	cacheImmutable = "public, max-age=31536000, immutable"
+	cacheNoCache   = "no-cache"
+)
+
+// noCacheFiles must be revalidated on every load: they name the hashed assets
+// (or, for the service worker, control their caching), so a stale copy pins an
+// old release.
+var noCacheFiles = map[string]bool{
+	indexFile:              true,
+	"sw.js":                true,
+	"manifest.webmanifest": true,
+}
+
+// Assets returns the embedded web build rooted at its dist directory.
+func Assets() fs.FS {
+	sub, err := fs.Sub(embedded, "dist")
+	if err != nil {
+		panic(err) // "dist" is a valid path, so Sub cannot fail
+	}
+	return sub
+}
+
+// NewHandler returns a handler that serves files from fsys. A GET or HEAD for a
+// path that is not a file in fsys is answered with index.html so client-side
+// routes load the app. Paths equal to or under a reserved prefix (for example
+// "/api") are never answered with index.html, whether before or after the path
+// is cleaned; they are passed to notFound.
+// fsys must contain index.html.
+func NewHandler(fsys fs.FS, logger *slog.Logger, notFound http.Handler, reserved ...string) (http.Handler, error) {
+	if _, err := fs.Stat(fsys, indexFile); err != nil {
+		return nil, fmt.Errorf("frontend assets: %w", err)
+	}
+	return &handler{fsys: fsys, logger: logger, notFound: notFound, reserved: reserved}, nil
+}
+
+type handler struct {
+	fsys     fs.FS
+	logger   *slog.Logger
+	notFound http.Handler
+	reserved []string
+}
+
+func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	urlPath := path.Clean("/" + r.URL.Path)
+	// Check the uncleaned path too, so dot segments cannot escape a reserved
+	// prefix into the fallback ("/auth/../quests/42" cleans to "/quests/42").
+	if h.isReserved(r.URL.Path) || h.isReserved(urlPath) {
+		h.notFound.ServeHTTP(w, r)
+		return
+	}
+
+	name := strings.TrimPrefix(urlPath, "/")
+	if name == "" || !h.isFile(name) {
+		name = indexFile
+	}
+	h.serveFile(w, r, name)
+}
+
+func (h *handler) isReserved(urlPath string) bool {
+	for _, prefix := range h.reserved {
+		if urlPath == prefix || strings.HasPrefix(urlPath, prefix+"/") {
+			return true
+		}
+	}
+	return false
+}
+
+func (h *handler) isFile(name string) bool {
+	info, err := fs.Stat(h.fsys, name)
+	return err == nil && info.Mode().IsRegular()
+}
+
+func (h *handler) serveFile(w http.ResponseWriter, r *http.Request, name string) {
+	f, err := h.fsys.Open(name)
+	if err != nil {
+		h.fail(w, r, name, err)
+		return
+	}
+	defer f.Close()
+	content, ok := f.(io.ReadSeeker)
+	if !ok {
+		h.fail(w, r, name, errors.New("file does not implement io.Seeker"))
+		return
+	}
+
+	if noCacheFiles[name] {
+		w.Header().Set("Cache-Control", cacheNoCache)
+	} else {
+		w.Header().Set("Cache-Control", cacheImmutable)
+	}
+	if path.Ext(name) == ".webmanifest" {
+		w.Header().Set("Content-Type", "application/manifest+json")
+	}
+	// Embedded files carry no modification time; ServeContent omits
+	// Last-Modified for the zero time.
+	http.ServeContent(w, r, name, time.Time{}, content)
+}
+
+func (h *handler) fail(w http.ResponseWriter, r *http.Request, name string, err error) {
+	h.logger.ErrorContext(r.Context(), "serve frontend asset", "file", name, "error", err)
+	http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+}

internal/frontend/frontend_test.go

@@ -0,0 +1,137 @@
+package frontend
+
+import (
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"testing/fstest"
+)
+
+const (
+	indexBody    = "<!doctype html><title>fixture index</title>"
+	assetBody    = "console.log('fixture asset')"
+	robotsBody   = "User-agent: *"
+	swBody       = "self.addEventListener('fetch', () => {})"
+	manifestBody = `{"name":"MealQuest"}`
+	notFoundBody = "reserved not found"
+)
+
+func fixture() fstest.MapFS {
+	return fstest.MapFS{
+		"index.html":             {Data: []byte(indexBody)},
+		"sw.js":                  {Data: []byte(swBody)},
+		"manifest.webmanifest":   {Data: []byte(manifestBody)},
+		"assets/index-AbC123.js": {Data: []byte(assetBody)},
+		"robots.txt":             {Data: []byte(robotsBody)},
+	}
+}
+
+func newTestHandler(t *testing.T) http.Handler {
+	t.Helper()
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+	notFound := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, notFoundBody, http.StatusNotFound)
+	})
+	h, err := NewHandler(fixture(), logger, notFound, "/api", "/auth", "/media", "/health")
+	if err != nil {
+		t.Fatal(err)
+	}
+	return h
+}
+
+func TestServe(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name      string
+		method    string
+		path      string
+		wantBody  string
+		wantCache string
+	}{
+		{"hashed asset", http.MethodGet, "/assets/index-AbC123.js", assetBody, cacheImmutable},
+		{"unhashed asset", http.MethodGet, "/robots.txt", robotsBody, cacheImmutable},
+		{"root", http.MethodGet, "/", indexBody, cacheNoCache},
+		{"index.html", http.MethodGet, "/index.html", indexBody, cacheNoCache},
+		{"service worker", http.MethodGet, "/sw.js", swBody, cacheNoCache},
+		{"manifest", http.MethodGet, "/manifest.webmanifest", manifestBody, cacheNoCache},
+		{"client route", http.MethodGet, "/quests/42", indexBody, cacheNoCache},
+		{"missing asset", http.MethodGet, "/assets/missing.js", indexBody, cacheNoCache},
+		{"directory", http.MethodGet, "/assets", indexBody, cacheNoCache},
+		{"dot segments", http.MethodGet, "/x/../../sw.js", swBody, cacheNoCache},
+		{"prefix lookalike", http.MethodGet, "/apiary", indexBody, cacheNoCache},
+		{"head", http.MethodHead, "/assets/index-AbC123.js", "", cacheImmutable},
+	}
+	h := newTestHandler(t)
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			rec := httptest.NewRecorder()
+			h.ServeHTTP(rec, httptest.NewRequest(tt.method, tt.path, nil))
+
+			if rec.Code != http.StatusOK {
+				t.Errorf("status = %d, want 200", rec.Code)
+			}
+			if got := rec.Body.String(); got != tt.wantBody {
+				t.Errorf("body = %q, want %q", got, tt.wantBody)
+			}
+			if got := rec.Header().Get("Cache-Control"); got != tt.wantCache {
+				t.Errorf("Cache-Control = %q, want %q", got, tt.wantCache)
+			}
+		})
+	}
+}
+
+func TestManifestContentType(t *testing.T) {
+	t.Parallel()
+
+	rec := httptest.NewRecorder()
+	newTestHandler(t).ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/manifest.webmanifest", nil))
+
+	if got := rec.Header().Get("Content-Type"); got != "application/manifest+json" {
+		t.Errorf("Content-Type = %q, want application/manifest+json", got)
+	}
+}
+
+func TestReservedPrefixesNotServed(t *testing.T) {
+	t.Parallel()
+
+	h := newTestHandler(t)
+	for _, path := range []string{"/api", "/api/unknown", "/auth/login", "/media/x.jpg", "/health", "/health/deep", "/x/../api/unknown", "/auth/../quests/42", "/api%2F..%2Fquests/42"} {
+		t.Run(path, func(t *testing.T) {
+			t.Parallel()
+
+			rec := httptest.NewRecorder()
+			h.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, path, nil))
+
+			if rec.Code != http.StatusNotFound {
+				t.Errorf("status = %d, want 404", rec.Code)
+			}
+			if got := rec.Body.String(); got != notFoundBody+"\n" {
+				t.Errorf("body = %q, want the notFound handler's body", got)
+			}
+		})
+	}
+}
+
+func TestNewHandlerRequiresIndex(t *testing.T) {
+	t.Parallel()
+
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+	fsys := fstest.MapFS{"sw.js": {Data: []byte(swBody)}}
+	if _, err := NewHandler(fsys, logger, http.NotFoundHandler()); err == nil {
+		t.Fatal("NewHandler without index.html: want error, got nil")
+	}
+}
+
+func TestAssetsContainsIndex(t *testing.T) {
+	t.Parallel()
+
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+	if _, err := NewHandler(Assets(), logger, http.NotFoundHandler()); err != nil {
+		t.Fatalf("embedded assets: %v", err)
+	}
+}

internal/server/server.go

@@ -3,20 +3,44 @@ package server
 
 import (
 	"encoding/json"
+	"io/fs"
 	"log/slog"
 	"net/http"
 
 	"github.com/go-chi/chi/v5"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/frontend"
 )
 
+// reservedPrefixes are owned by the API router and are never answered with the
+// SPA's index.html.
+var reservedPrefixes = []string{"/api", "/auth", "/media", "/health"}
+
 // NewRouter returns the HTTP handler for the service. version is reported by
-// GET /health.
-func NewRouter(logger *slog.Logger, version string) http.Handler {
+// GET /health; assets is the web build served for every other GET.
+func NewRouter(logger *slog.Logger, version string, assets fs.FS) (http.Handler, error) {
+	notFound := apiErrorHandler(logger, http.StatusNotFound, "not_found", "not found")
+	methodNotAllowed := apiErrorHandler(logger, http.StatusMethodNotAllowed, "method_not_allowed", "method not allowed")
+
+	web, err := frontend.NewHandler(assets, logger, notFound, reservedPrefixes...)
+	if err != nil {
+		return nil, err
+	}
+
 	r := chi.NewRouter()
+	r.MethodNotAllowed(methodNotAllowed)
+	r.NotFound(notFound)
+
 	r.Get("/health", health(logger, version))
-	r.MethodNotAllowed(apiErrorHandler(logger, http.StatusMethodNotAllowed, "method_not_allowed", "method not allowed"))
-	r.NotFound(apiErrorHandler(logger, http.StatusNotFound, "not_found", "not found"))
-	return r
+	r.Route("/api", func(r chi.Router) {
+		r.MethodNotAllowed(methodNotAllowed)
+		r.NotFound(notFound)
+	})
+	// Catch-all for the PWA. /auth and /media have no routes yet; the frontend
+	// handler passes them to notFound rather than the SPA fallback.
+	r.Method(http.MethodGet, "/*", web)
+	r.Method(http.MethodHead, "/*", web)
+	return r, nil
 }
 
 type errorBody struct {

internal/server/server_test.go

@@ -7,14 +7,35 @@ import (
 	"maps"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
+	"testing/fstest"
 )
 
+const (
+	fixtureIndex = "<!doctype html><title>fixture index</title>"
+	fixtureAsset = "console.log('fixture asset')"
+	notFoundJSON = `{"error":{"code":"not_found","message":"not found","retryable":false}}`
+)
+
+func newTestRouter(t *testing.T, version string) http.Handler {
+	t.Helper()
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+	assets := fstest.MapFS{
+		"index.html":             {Data: []byte(fixtureIndex)},
+		"assets/index-AbC123.js": {Data: []byte(fixtureAsset)},
+	}
+	r, err := NewRouter(logger, version, assets)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return r
+}
+
 func TestHealth(t *testing.T) {
 	t.Parallel()
 
-	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	srv := httptest.NewServer(NewRouter(logger, "1.2.3"))
+	srv := httptest.NewServer(newTestRouter(t, "1.2.3"))
 	t.Cleanup(srv.Close)
 
 	resp, err := http.Get(srv.URL + "/health")
@@ -42,9 +63,8 @@ func TestHealth(t *testing.T) {
 func TestHealthRejectsOtherMethods(t *testing.T) {
 	t.Parallel()
 
-	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
 	rec := httptest.NewRecorder()
-	NewRouter(logger, "dev").ServeHTTP(rec, httptest.NewRequest(http.MethodPost, "/health", nil))
+	newTestRouter(t, "dev").ServeHTTP(rec, httptest.NewRequest(http.MethodPost, "/health", nil))
 
 	if rec.Code != http.StatusMethodNotAllowed {
 		t.Errorf("status = %d, want 405", rec.Code)
@@ -68,21 +88,98 @@ func TestHealthRejectsOtherMethods(t *testing.T) {
 	}
 }
 
-func TestUnknownPathNotFound(t *testing.T) {
+func TestReservedPathsNotFound(t *testing.T) {
 	t.Parallel()
 
-	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	rec := httptest.NewRecorder()
-	NewRouter(logger, "dev").ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/unknown", nil))
+	router := newTestRouter(t, "dev")
+	tests := []struct {
+		method string
+		path   string
+	}{
+		{http.MethodGet, "/api"},
+		{http.MethodGet, "/api/unknown"},
+		{http.MethodPost, "/api/unknown"},
+		{http.MethodGet, "/auth/callback"},
+		{http.MethodGet, "/media/photo.jpg"},
+		{http.MethodGet, "/health/deep"},
+		{http.MethodGet, "/auth/../quests/42"},
+		{http.MethodGet, "/api%2F..%2Fquests/42"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.method+" "+tt.path, func(t *testing.T) {
+			t.Parallel()
 
-	if rec.Code != http.StatusNotFound {
-		t.Errorf("status = %d, want 404", rec.Code)
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, httptest.NewRequest(tt.method, tt.path, nil))
+
+			if rec.Code != http.StatusNotFound {
+				t.Errorf("status = %d, want 404", rec.Code)
+			}
+			if ct := rec.Header().Get("Content-Type"); ct != "application/json" {
+				t.Errorf("Content-Type = %q, want application/json", ct)
+			}
+			if got := rec.Body.String(); got != notFoundJSON {
+				t.Errorf("body = %s, want %s", got, notFoundJSON)
+			}
+		})
 	}
-	if ct := rec.Header().Get("Content-Type"); ct != "application/json" {
-		t.Errorf("Content-Type = %q, want application/json", ct)
+}
+
+func TestFrontend(t *testing.T) {
+	t.Parallel()
+
+	router := newTestRouter(t, "dev")
+	tests := []struct {
+		path      string
+		wantBody  string
+		wantCache string
+	}{
+		{"/", fixtureIndex, "no-cache"},
+		{"/assets/index-AbC123.js", fixtureAsset, "public, max-age=31536000, immutable"},
+		{"/quests/42", fixtureIndex, "no-cache"},
+		{"/quests/42/edit", fixtureIndex, "no-cache"},
 	}
-	const want = `{"error":{"code":"not_found","message":"not found","retryable":false}}`
-	if got := rec.Body.String(); got != want {
-		t.Errorf("body = %s, want %s", got, want)
+	for _, tt := range tests {
+		t.Run(tt.path, func(t *testing.T) {
+			t.Parallel()
+
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, tt.path, nil))
+
+			if rec.Code != http.StatusOK {
+				t.Errorf("status = %d, want 200", rec.Code)
+			}
+			if got := rec.Body.String(); got != tt.wantBody {
+				t.Errorf("body = %q, want %q", got, tt.wantBody)
+			}
+			if got := rec.Header().Get("Cache-Control"); got != tt.wantCache {
+				t.Errorf("Cache-Control = %q, want %q", got, tt.wantCache)
+			}
+		})
+	}
+}
+
+func TestHealthNotShadowed(t *testing.T) {
+	t.Parallel()
+
+	rec := httptest.NewRecorder()
+	newTestRouter(t, "dev").ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/health", nil))
+
+	if body := rec.Body.String(); rec.Code != http.StatusOK || strings.Contains(body, fixtureIndex) {
+		t.Errorf("GET /health = %d %q, want 200 health JSON", rec.Code, body)
+	}
+}
+
+func TestFrontendRejectsOtherMethods(t *testing.T) {
+	t.Parallel()
+
+	rec := httptest.NewRecorder()
+	newTestRouter(t, "dev").ServeHTTP(rec, httptest.NewRequest(http.MethodPost, "/quests/42", nil))
+
+	if rec.Code != http.StatusMethodNotAllowed {
+		t.Errorf("status = %d, want 405", rec.Code)
+	}
+	if strings.Contains(rec.Body.String(), fixtureIndex) {
+		t.Errorf("body = %q, want no index.html", rec.Body.String())
 	}
 }