feat: add image thumbnails support (#980)

* set max image preview size to 1080x1080px

http/preview.go

@@ -0,0 +1,94 @@
+package http
+
+import (
+	"fmt"
+	"image"
+	"net/http"
+
+	"github.com/disintegration/imaging"
+	"github.com/gorilla/mux"
+
+	"github.com/filebrowser/filebrowser/v2/files"
+)
+
+const (
+	sizeThumb = "thumb"
+	sizeBig   = "big"
+)
+
+type imageProcessor func(src image.Image) (image.Image, error)
+
+var previewHandler = withUser(func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {
+	if !d.user.Perm.Download {
+		return http.StatusAccepted, nil
+	}
+	vars := mux.Vars(r)
+	size := vars["size"]
+	if size != sizeBig && size != sizeThumb {
+		return http.StatusNotImplemented, nil
+	}
+
+	file, err := files.NewFileInfo(files.FileOptions{
+		Fs:      d.user.Fs,
+		Path:    "/" + vars["path"],
+		Modify:  d.user.Perm.Modify,
+		Expand:  true,
+		Checker: d,
+	})
+	if err != nil {
+		return errToStatus(err), err
+	}
+
+	setContentDisposition(w, r, file)
+
+	switch file.Type {
+	case "image":
+		return handleImagePreview(w, r, file, size)
+	default:
+		return http.StatusNotImplemented, fmt.Errorf("can't create preview for %s type", file.Type)
+	}
+})
+
+func handleImagePreview(w http.ResponseWriter, r *http.Request, file *files.FileInfo, size string) (int, error) {
+	format, err := imaging.FormatFromExtension(file.Extension)
+	if err != nil {
+		// Unsupported extensions directly return the raw data
+		if err == imaging.ErrUnsupportedFormat {
+			return rawFileHandler(w, r, file)
+		}
+		return errToStatus(err), err
+	}
+
+	var imgProcessor imageProcessor
+	switch size {
+	case sizeBig:
+		imgProcessor = func(img image.Image) (image.Image, error) {
+			return imaging.Fit(img, 1080, 1080, imaging.Lanczos), nil
+		}
+	case sizeThumb:
+		imgProcessor = func(img image.Image) (image.Image, error) {
+			return imaging.Thumbnail(img, 128, 128, imaging.Box), nil
+		}
+	default:
+		return http.StatusBadRequest, fmt.Errorf("unsupported preview size %s", size)
+	}
+
+	fd, err := file.Fs.Open(file.Path)
+	if err != nil {
+		return errToStatus(err), err
+	}
+	defer fd.Close()
+
+	img, err := imaging.Decode(fd, imaging.AutoOrientation(true))
+	if err != nil {
+		return errToStatus(err), err
+	}
+	img, err = imgProcessor(img)
+	if err != nil {
+		return errToStatus(err), err
+	}
+	if imaging.Encode(w, img, format) != nil {
+		return errToStatus(err), err
+	}
+	return 0, nil
+}