| 1 | // Package pwa supplies installability and offline-fallback assets for a web app. |
| 2 | // The app owns its manifest identity, worker entrypoint and update UI. |
| 3 | package pwa |
| 4 | |
| 5 | import ( |
| 6 | "embed" |
| 7 | "encoding/json" |
| 8 | "fmt" |
| 9 | "io/fs" |
| 10 | "net/http" |
| 11 | "net/url" |
| 12 | "strings" |
| 13 | ) |
| 14 | |
| 15 | //go:embed js/client.mjs js/worker.js |
| 16 | var assets embed.FS |
| 17 | |
| 18 | // Assets serves client.mjs and worker.js. Mount with http.StripPrefix at |
| 19 | // an app-owned path; keep sw.js at the scope it should control. |
| 20 | func Assets() http.Handler { |
| 21 | f, _ := fs.Sub(assets, "js") |
| 22 | files := http.FileServer(http.FS(f)) |
| 23 | return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { |
| 24 | if r.Method != http.MethodGet && r.Method != http.MethodHead { |
| 25 | w.Header().Set("Allow", "GET, HEAD") |
| 26 | http.Error(w, "Method not allowed", http.StatusMethodNotAllowed) |
| 27 | return |
| 28 | } |
| 29 | if r.URL.Path != "/client.mjs" && r.URL.Path != "/worker.js" { |
| 30 | http.NotFound(w, r) |
| 31 | return |
| 32 | } |
| 33 | w.Header().Set("Content-Type", "text/javascript; charset=utf-8") |
| 34 | w.Header().Set("Cache-Control", "no-cache") |
| 35 | w.Header().Set("X-Content-Type-Options", "nosniff") |
| 36 | files.ServeHTTP(w, r) |
| 37 | }) |
| 38 | } |
| 39 | |
| 40 | type Icon struct { |
| 41 | Src string `json:"src"` |
| 42 | Sizes string `json:"sizes"` |
| 43 | Type string `json:"type"` |
| 44 | Purpose string `json:"purpose,omitempty"` |
| 45 | } |
| 46 | |
| 47 | // Manifest is application identity. Keep ID stable across start URL changes, |
| 48 | // or browsers may treat an update as a different installed app. |
| 49 | type Manifest struct { |
| 50 | ID string `json:"id"` |
| 51 | Name string `json:"name"` |
| 52 | ShortName string `json:"short_name,omitempty"` |
| 53 | StartURL string `json:"start_url"` |
| 54 | Scope string `json:"scope"` |
| 55 | Display string `json:"display"` |
| 56 | ThemeColor string `json:"theme_color,omitempty"` |
| 57 | BackgroundColor string `json:"background_color,omitempty"` |
| 58 | Icons []Icon `json:"icons"` |
| 59 | } |
| 60 | |
| 61 | // Handler validates the manifest at boot so an invalid scope cannot silently |
| 62 | // turn an installed app's first launch into a browser navigation. |
| 63 | func (m Manifest) Handler() (http.Handler, error) { |
| 64 | if strings.TrimSpace(m.Name) == "" { |
| 65 | return nil, fmt.Errorf("pwa: name is required") |
| 66 | } |
| 67 | if !localPath(m.ID) || !localPath(m.StartURL) || !localPath(m.Scope) || |
| 68 | !strings.HasSuffix(m.Scope, "/") || strings.ContainsAny(m.Scope, "?#") || |
| 69 | !strings.HasPrefix(m.StartURL, m.Scope) { |
| 70 | return nil, fmt.Errorf("pwa: use root-relative paths and a start URL within a scope ending in /") |
| 71 | } |
| 72 | if m.Display == "" { |
| 73 | m.Display = "standalone" |
| 74 | } |
| 75 | switch m.Display { |
| 76 | case "standalone", "minimal-ui", "fullscreen", "browser": |
| 77 | default: |
| 78 | return nil, fmt.Errorf("pwa: unsupported display mode") |
| 79 | } |
| 80 | if len(m.Icons) == 0 { |
| 81 | return nil, fmt.Errorf("pwa: supply app icons, including 192x192 and 512x512 PNGs") |
| 82 | } |
| 83 | for _, icon := range m.Icons { |
| 84 | if !localPath(icon.Src) || icon.Sizes == "" || icon.Type == "" { |
| 85 | return nil, fmt.Errorf("pwa: icons need a root-relative src, sizes and type") |
| 86 | } |
| 87 | } |
| 88 | body, err := json.Marshal(m) |
| 89 | if err != nil { |
| 90 | return nil, err |
| 91 | } |
| 92 | return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { |
| 93 | if r.Method != http.MethodGet && r.Method != http.MethodHead { |
| 94 | w.Header().Set("Allow", "GET, HEAD") |
| 95 | http.Error(w, "Method not allowed", http.StatusMethodNotAllowed) |
| 96 | return |
| 97 | } |
| 98 | w.Header().Set("Content-Type", "application/manifest+json") |
| 99 | w.Header().Set("Cache-Control", "no-cache") |
| 100 | w.Header().Set("X-Content-Type-Options", "nosniff") |
| 101 | if r.Method != http.MethodHead { |
| 102 | _, _ = w.Write(body) |
| 103 | } |
| 104 | }), nil |
| 105 | } |
| 106 | |
| 107 | func localPath(raw string) bool { |
| 108 | if !strings.HasPrefix(raw, "/") || strings.HasPrefix(raw, "//") || strings.ContainsAny(raw, "\\\r\n\t#") { |
| 109 | return false |
| 110 | } |
| 111 | u, err := url.Parse(raw) |
| 112 | if err != nil || u.Host != "" || u.Scheme != "" || u.Opaque != "" { |
| 113 | return false |
| 114 | } |
| 115 | // Browsers normalize escaped dots and backslashes before scope matching. |
| 116 | // Refuse ambiguous forms so Go and the browser cannot disagree about scope. |
| 117 | if strings.Contains(u.Path, "\\") || strings.Contains(u.Path, "//") { |
| 118 | return false |
| 119 | } |
| 120 | for _, part := range strings.Split(u.Path, "/") { |
| 121 | if part == "." || part == ".." { |
| 122 | return false |
| 123 | } |
| 124 | } |
| 125 | return true |
| 126 | } |
| 127 | |
amadan