Use exiffix library to fix image orientation

If you upload an unedited image from an iPhone, the EXIF data
indicates how it should be oriented. Oddmu used to resize images strip
the EXIF data, resulting in resized images that were not oriented
correctly. If the EXIF data is stripped, the image has to be rotated.
In order to do this, the exiffix single-function library is used to
work around "image/jpeg: correct for EXIF orientation? #4341", opened
in 2012. See golang/go#4341 for more
information and a link to https://github.com/edwvee/exiffix.

go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/bashdrew/goheif v0.0.0-20230406184952-7a08ca9c9bdd
 	github.com/charmbracelet/lipgloss v0.9.1
 	github.com/disintegration/imaging v1.6.2
+	github.com/edwvee/exiffix v0.0.0-20210922235313-0f6cbda5e58f
 	github.com/fsnotify/fsnotify v1.7.0
 	github.com/gomarkdown/markdown v0.0.0-20231222211730-1d6d20845b47
 	github.com/google/subcommands v1.2.0

go.sum

@@ -11,6 +11,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/disintegration/imaging v1.6.2 h1:w1LecBlG2Lnp8B3jk5zSuNqd7b4DXhcjwek1ei82L+c=
 github.com/disintegration/imaging v1.6.2/go.mod h1:44/5580QXChDfwIclfc/PCwrr44amcmDAg8hxG0Ewe4=
+github.com/edwvee/exiffix v0.0.0-20210922235313-0f6cbda5e58f h1:RMnUwTnNR070mFAEIoqMYjNirHj8i0h79VXTYyBCyVA=
+github.com/edwvee/exiffix v0.0.0-20210922235313-0f6cbda5e58f/go.mod h1:KoE3Ti1qbQXCb3s/XGj0yApHnbnNnn1bXTtB5Auq/Vc=
 github.com/fsnotify/fsnotify v1.7.0 h1:8JEhPFa5W2WU7YfeZzPNqzMP6Lwt7L2715Ggo0nosvA=
 github.com/fsnotify/fsnotify v1.7.0/go.mod h1:40Bi/Hjc2AVfZrqy+aj+yEI+/bRxZnMJyTJwOpGvigM=
 github.com/gomarkdown/markdown v0.0.0-20231222211730-1d6d20845b47 h1:k4Tw0nt6lwro3Uin8eqoET7MDA4JnT8YgbCjc/g5E3k=

upload_drop.go

@@ -6,6 +6,7 @@ package main
 import (
 	_ "github.com/bashdrew/goheif"
 	"github.com/disintegration/imaging"
+	"github.com/edwvee/exiffix"
 	"io"
 	"log"
 	"net/http"
@@ -160,22 +161,23 @@ func dropHandler(w http.ResponseWriter, r *http.Request, dir string) {
 		}
 		defer dst.Close()
 		if mw > 0 {
-			img, err := imaging.Decode(file)
+			// do not use imaging.Decode(file, imaging.AutoOrientation(true)) because that only works for JPEG files
+			img, fmt, err := exiffix.Decode(file)
 			if err != nil {
 				http.Error(w, "The image could not be decoded (only PNG, JPG and HEIC formats are supported for resizing)", http.StatusBadRequest)
 				return
 			}
-			rect := img.Bounds()
-			if rect.Max.X - rect.Min.X > mw {
-				img = imaging.Resize(img, mw, 0, imaging.Lanczos) // preserve aspect ratio
-				imaging.Encode(dst, img, format, imaging.JPEGQuality(quality))
-				if err != nil {
-					log.Println(err)
-					http.Error(w, err.Error(), http.StatusInternalServerError)
-					return
-				}
-			} else {
-				http.Error(w, "The file is too small for this", http.StatusBadRequest)
+			log.Println("Decoded", fmt, "file")
+			res := imaging.Resize(img, mw, 0, imaging.Lanczos) // preserve aspect ratio
+			// imaging functions don't return errors but empty images…
+			if !res.Rect.Empty() {
+				img = res
+			}
+			// images are always reencoded, so image quality goes down
+			err = imaging.Encode(dst, img, format, imaging.JPEGQuality(quality))
+			if err != nil {
+				log.Println(err)
+				http.Error(w, err.Error(), http.StatusInternalServerError)
 				return
 			}
 		} else {