dev_agent
85569b451f
Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com> Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>
128 lines
3.5 KiB
Go
128 lines
3.5 KiB
Go
// Package frontend serves the embedded PWA build with an SPA fallback.
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package frontend
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import (
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"embed"
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"errors"
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"fmt"
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"io"
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"io/fs"
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"log/slog"
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"net/http"
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"path"
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"strings"
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"time"
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)
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// embedded holds the web build. The build copies web/dist over the committed
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// placeholder index.html.
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//
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//go:embed all:dist
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var embedded embed.FS
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const (
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indexFile = "index.html"
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cacheImmutable = "public, max-age=31536000, immutable"
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cacheNoCache = "no-cache"
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)
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// noCacheFiles must be revalidated on every load: they name the hashed assets
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// (or, for the service worker, control their caching), so a stale copy pins an
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// old release.
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var noCacheFiles = map[string]bool{
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indexFile: true,
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"sw.js": true,
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"manifest.webmanifest": true,
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}
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// Assets returns the embedded web build rooted at its dist directory.
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func Assets() fs.FS {
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sub, err := fs.Sub(embedded, "dist")
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if err != nil {
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panic(err) // "dist" is a valid path, so Sub cannot fail
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}
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return sub
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}
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// NewHandler returns a handler that serves files from fsys. A GET or HEAD for a
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// path that is not a file in fsys is answered with index.html so client-side
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// routes load the app. Paths equal to or under a reserved prefix (for example
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// "/api") are never answered with index.html, whether before or after the path
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// is cleaned; they are passed to notFound.
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// fsys must contain index.html.
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func NewHandler(fsys fs.FS, logger *slog.Logger, notFound http.Handler, reserved ...string) (http.Handler, error) {
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if _, err := fs.Stat(fsys, indexFile); err != nil {
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return nil, fmt.Errorf("frontend assets: %w", err)
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}
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return &handler{fsys: fsys, logger: logger, notFound: notFound, reserved: reserved}, nil
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}
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type handler struct {
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fsys fs.FS
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logger *slog.Logger
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notFound http.Handler
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reserved []string
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}
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func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
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urlPath := path.Clean("/" + r.URL.Path)
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// Check the uncleaned path too, so dot segments cannot escape a reserved
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// prefix into the fallback ("/auth/../quests/42" cleans to "/quests/42").
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if h.isReserved(r.URL.Path) || h.isReserved(urlPath) {
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h.notFound.ServeHTTP(w, r)
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return
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}
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name := strings.TrimPrefix(urlPath, "/")
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if name == "" || !h.isFile(name) {
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name = indexFile
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}
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h.serveFile(w, r, name)
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}
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func (h *handler) isReserved(urlPath string) bool {
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for _, prefix := range h.reserved {
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if urlPath == prefix || strings.HasPrefix(urlPath, prefix+"/") {
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return true
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}
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}
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return false
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}
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func (h *handler) isFile(name string) bool {
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info, err := fs.Stat(h.fsys, name)
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return err == nil && info.Mode().IsRegular()
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}
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func (h *handler) serveFile(w http.ResponseWriter, r *http.Request, name string) {
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f, err := h.fsys.Open(name)
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if err != nil {
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h.fail(w, r, name, err)
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return
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}
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defer f.Close()
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content, ok := f.(io.ReadSeeker)
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if !ok {
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h.fail(w, r, name, errors.New("file does not implement io.Seeker"))
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return
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}
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if noCacheFiles[name] {
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w.Header().Set("Cache-Control", cacheNoCache)
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} else {
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w.Header().Set("Cache-Control", cacheImmutable)
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}
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if path.Ext(name) == ".webmanifest" {
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w.Header().Set("Content-Type", "application/manifest+json")
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}
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// Embedded files carry no modification time; ServeContent omits
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// Last-Modified for the zero time.
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http.ServeContent(w, r, name, time.Time{}, content)
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}
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func (h *handler) fail(w http.ResponseWriter, r *http.Request, name string, err error) {
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h.logger.ErrorContext(r.Context(), "serve frontend asset", "file", name, "error", err)
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http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
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}
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