Improve error for thumbnails during dimension checks

CHANGELOG.md

@@ -21,6 +21,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 * Swap out the HEIF library for better support towards [ARM64 Docker Images](https://github.com/turt2live/matrix-media-repo/issues/365).
 * The development environment now uses Synapse as a homeserver. Test accounts will need recreating.
 * Updated to Go 1.18
+* Improved error message when thumbnailer cannot determine image dimensions.
 
 ### Fixed
 

thumbnailing/thumbnail.go

@@ -2,11 +2,12 @@ package thumbnailing
 
 import (
 	"errors"
-	"github.com/turt2live/matrix-media-repo/common"
 	"io"
 	"io/ioutil"
 	"reflect"
 
+	"github.com/turt2live/matrix-media-repo/common"
+
 	"github.com/turt2live/matrix-media-repo/common/rcontext"
 	"github.com/turt2live/matrix-media-repo/thumbnailing/i"
 	"github.com/turt2live/matrix-media-repo/thumbnailing/m"
@@ -45,7 +46,7 @@ func GenerateThumbnail(imgStream io.ReadCloser, contentType string, width int, h
 	// https://github.com/turt2live/matrix-media-repo/security/advisories/GHSA-j889-h476-hh9h
 	dimensional, w, h, err := generator.GetOriginDimensions(b, contentType, ctx)
 	if err != nil {
-		return nil, err
+		return nil, errors.New("error getting dimensions: " + err.Error())
 	}
 	if dimensional && (w*h) >= ctx.Config.Thumbnails.MaxPixels {
 		ctx.Log.Warn("Image too large: too many pixels")