feat(handlers): add file icons with standard and retro variants

Introduce file icon support to the file browser. Icons are loaded on
startup and mapped based on file name and content type.

- Load file icon mappings in the App handler initialization.
- Add `HasThumbnail`, `IconURL`, and `IconRetroURL` to the file view.
- Update CSS to support displaying file icons alongside thumbnails.
- Add retro theme support to swap standard icons with pixelated retro
  variants when the retro theme is active.

backend/libs/handlers/app.go

@@ -20,9 +20,14 @@ type App struct {
 	banService      *services.BanService
 	rateLimiter     *rateLimiter
 	uploadGroups    *uploadGrouper
+	fileIcons       *fileIconSet
 }
 
 func NewApp(cfg config.Config, logger *slog.Logger, renderer *web.Renderer, uploadService *services.UploadService, authService *services.AuthService, settingsService *services.SettingsService, reactionService *services.ReactionService, banService *services.BanService) *App {
+	fileIcons, err := loadFileIcons(cfg.StaticDir)
+	if err != nil {
+		logger.Warn("failed to load file icon map", "source", "handlers", "severity", "warn", "error", err.Error())
+	}
 	return &App{
 		cfg:             cfg,
 		logger:          logger,
@@ -34,6 +39,7 @@ func NewApp(cfg config.Config, logger *slog.Logger, renderer *web.Renderer, uplo
 		banService:      banService,
 		rateLimiter:     newRateLimiter(),
 		uploadGroups:    newUploadGrouper(),
+		fileIcons:       fileIcons,
 	}
 }
 

backend/libs/handlers/download.go

@@ -45,6 +45,9 @@ type fileView struct {
 	URL          string
 	DownloadURL  string
 	ThumbnailURL string
+	HasThumbnail bool
+	IconURL      string
+	IconRetroURL string
 	ReactURL     string
 	Reactions    []reactionView
 	Reacted      bool
@@ -350,6 +353,7 @@ func (a *App) fileView(box services.Box, file services.File) fileView {
 }
 
 func (a *App) fileViewWithReactions(box services.Box, file services.File, reactions []services.ReactionSummary, reacted bool) fileView {
+	icon := a.fileIcons.lookup(file.Name, file.ContentType)
 	return fileView{
 		ID:           file.ID,
 		Name:         file.Name,
@@ -359,6 +363,9 @@ func (a *App) fileViewWithReactions(box services.Box, file services.File, reacti
 		URL:          fmt.Sprintf("/d/%s/f/%s", box.ID, file.ID),
 		DownloadURL:  fmt.Sprintf("/d/%s/f/%s/download", box.ID, file.ID),
 		ThumbnailURL: fmt.Sprintf("/d/%s/thumb/%s", box.ID, file.ID),
+		HasThumbnail: file.Thumbnail != "",
+		IconURL:      fileIconURL("standard", icon.Standard),
+		IconRetroURL: fileIconURL("retro", icon.Retro),
 		ReactURL:     fmt.Sprintf("/d/%s/f/%s/react", box.ID, file.ID),
 		Reactions:    a.reactionViews(reactions),
 		Reacted:      reacted,

backend/libs/handlers/icons.go

@@ -0,0 +1,152 @@
+package handlers
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// fileIcon holds the two icon filenames for a file type: the standard (modern)
+// icon and the retro (Win98) icon. The filenames are resolved against
+// static/file-icons/standard and static/file-icons/retro respectively.
+type fileIcon struct {
+	Standard string `json:"standard"`
+	Retro    string `json:"retro"`
+}
+
+type iconType struct {
+	Mime       string   `json:"mime"`
+	Standard   string   `json:"standard"`
+	Retro      string   `json:"retro"`
+	Extensions []string `json:"extensions"`
+}
+
+type iconMapFile struct {
+	Default iconType   `json:"default"`
+	Types   []iconType `json:"types"`
+}
+
+type mimeRule struct {
+	pattern string // exact mime ("application/pdf") or major prefix ("image/")
+	prefix  bool
+	icon    fileIcon
+}
+
+// fileIconSet is the loaded icon map: an extension lookup plus content-type
+// rules and a fallback. It is built once at startup from icon-map.json.
+type fileIconSet struct {
+	byExt    map[string]fileIcon
+	byMime   []mimeRule
+	fallback fileIcon
+}
+
+// loadFileIcons reads static/file-icons/icon-map.json and indexes it by
+// extension and content type so icons can be assigned at render time.
+func loadFileIcons(staticDir string) (*fileIconSet, error) {
+	data, err := os.ReadFile(filepath.Join(staticDir, "file-icons", "icon-map.json"))
+	if err != nil {
+		return nil, err
+	}
+	var raw iconMapFile
+	if err := json.Unmarshal(data, &raw); err != nil {
+		return nil, err
+	}
+
+	set := &fileIconSet{
+		byExt:    make(map[string]fileIcon),
+		fallback: fileIcon{Standard: raw.Default.Standard, Retro: raw.Default.Retro},
+	}
+	if err := validateFileIcon(staticDir, set.fallback); err != nil {
+		return nil, err
+	}
+	for _, t := range raw.Types {
+		icon := fileIcon{Standard: t.Standard, Retro: t.Retro}
+		if err := validateFileIcon(staticDir, icon); err != nil {
+			return nil, err
+		}
+		for _, ext := range t.Extensions {
+			set.byExt[strings.ToLower(strings.TrimPrefix(ext, "."))] = icon
+		}
+		if t.Mime == "" {
+			continue
+		}
+		if strings.HasSuffix(t.Mime, "/*") {
+			set.byMime = append(set.byMime, mimeRule{pattern: strings.TrimSuffix(t.Mime, "*"), prefix: true, icon: icon})
+		} else {
+			set.byMime = append(set.byMime, mimeRule{pattern: strings.ToLower(t.Mime), icon: icon})
+		}
+	}
+	return set, nil
+}
+
+func validateFileIcon(staticDir string, icon fileIcon) error {
+	if icon.Standard != "" {
+		if err := validateFileIconPath(staticDir, "standard", icon.Standard); err != nil {
+			return err
+		}
+	}
+	if icon.Retro != "" {
+		if err := validateFileIconPath(staticDir, "retro", icon.Retro); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func validateFileIconPath(staticDir, theme, name string) error {
+	if strings.Contains(name, "/") || strings.Contains(name, "\\") || strings.Contains(name, "..") {
+		return fmt.Errorf("invalid %s file icon path %q", theme, name)
+	}
+	path := filepath.Join(staticDir, "file-icons", theme, name)
+	info, err := os.Stat(path)
+	if err != nil {
+		return fmt.Errorf("missing %s file icon %q: %w", theme, name, err)
+	}
+	if info.IsDir() {
+		return fmt.Errorf("%s file icon %q is a directory", theme, name)
+	}
+	return nil
+}
+
+// lookup resolves a file's icon from its name (extension) first, falling back to
+// its content type, then to the default icon. Extension wins because stored
+// content types are often the generic application/octet-stream.
+func (s *fileIconSet) lookup(name, contentType string) fileIcon {
+	if s == nil {
+		return fileIcon{}
+	}
+	if ext := strings.ToLower(strings.TrimPrefix(filepath.Ext(name), ".")); ext != "" {
+		if icon, ok := s.byExt[ext]; ok {
+			return icon
+		}
+	}
+
+	ct := strings.ToLower(strings.TrimSpace(contentType))
+	if i := strings.IndexByte(ct, ';'); i >= 0 {
+		ct = strings.TrimSpace(ct[:i])
+	}
+	if ct != "" && ct != "application/octet-stream" {
+		for _, rule := range s.byMime { // exact matches first
+			if !rule.prefix && rule.pattern == ct {
+				return rule.icon
+			}
+		}
+		for _, rule := range s.byMime { // then major-type prefixes
+			if rule.prefix && strings.HasPrefix(ct, rule.pattern) {
+				return rule.icon
+			}
+		}
+	}
+	return s.fallback
+}
+
+// fileIconURL builds the /static URL for an icon filename in the given theme
+// directory ("standard" or "retro").
+func fileIconURL(theme, name string) string {
+	if name == "" {
+		return ""
+	}
+	return "/static/file-icons/" + theme + "/" + name
+}

backend/libs/handlers/icons_test.go

@@ -0,0 +1,54 @@
+package handlers
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestFileIconMapLoadsAndResolvesCommonTypes(t *testing.T) {
+	icons, err := loadFileIcons(filepath.Join("..", "..", "static"))
+	if err != nil {
+		t.Fatalf("loadFileIcons returned error: %v", err)
+	}
+
+	tests := []struct {
+		name         string
+		contentType  string
+		wantStandard string
+		wantRetro    string
+	}{
+		{
+			name:         "photo.jpg",
+			contentType:  "application/octet-stream",
+			wantStandard: "image-document-svgrepo-com.svg",
+			wantRetro:    "shimgvw.dll_14_1-2.png",
+		},
+		{
+			name:         "movie.mkv",
+			contentType:  "",
+			wantStandard: "video-document-svgrepo-com.svg",
+			wantRetro:    "wmploc.dll_14_504-2.png",
+		},
+		{
+			name:         "archive.7z",
+			contentType:  "",
+			wantStandard: "zip-document-svgrepo-com.svg",
+			wantRetro:    "zipfldr.dll_14_101-2.png",
+		},
+		{
+			name:         "unknown.bin",
+			contentType:  "application/octet-stream",
+			wantStandard: "txt-document-svgrepo-com.svg",
+			wantRetro:    "shell32.dll_14_152-2.png",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := icons.lookup(tt.name, tt.contentType)
+			if got.Standard != tt.wantStandard || got.Retro != tt.wantRetro {
+				t.Fatalf("lookup returned %+v, want standard=%q retro=%q", got, tt.wantStandard, tt.wantRetro)
+			}
+		})
+	}
+}