[gimp/gimp-2-10] libgimp: fix issue #6050 Phantom comments on pictures.

[Jacob Boerema <jboerema src gnome org>]

commit e10517dcccedd3534cd50c6dd8e69448b69c81d5
Author: Jacob Boerema <jgboerema gmail com>
Date:   Mon Mar 22 16:06:54 2021 -0400

    libgimp: fix issue #6050 Phantom comments on pictures.
    
    Since version 0.27.3 exiv2 has changed how it returns
    comments for Exif.Photo.UserComment. We now get
    the comment including the charset=Ascii value.
    
    Let's remove anything that's not part of the actual
    comment. To not complicate things we will  only
    handle charset=Ascii for now since I've never seen
    any other charset used.
    
    (cherry picked from commit 352b5885b19a65322013407ca2670a6af25da7bb)
    
    # Conflicts:
    #       libgimp/gimpimagemetadata.c

 libgimp/gimpimagemetadata.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
---
diff --git a/libgimp/gimpimagemetadata.c b/libgimp/gimpimagemetadata.c
index 1697010015..52fad728c0 100644
--- a/libgimp/gimpimagemetadata.c
+++ b/libgimp/gimpimagemetadata.c
@@ -39,6 +39,7 @@ typedef struct
   gint  type;
 } XmpStructs;
 
+static gchar *     gimp_image_metadata_interpret_comment    (gchar *comment);
 
 static void        gimp_image_metadata_rotate        (gint32             image_ID,
                                                       GExiv2Orientation  orientation);
@@ -92,6 +93,37 @@ gimp_image_metadata_load_prepare (gint32        image_ID,
   return metadata;
 }
 
+static gchar *
+gimp_image_metadata_interpret_comment (gchar *comment)
+{
+  /* Exiv2 can return unwanted text at the start of a comment
+   * taken from Exif.Photo.UserComment since 0.27.3.
+   * Let's remove that part and return NULL if there
+   * is nothing else left as comment. */
+
+  if (comment && g_str_has_prefix (comment, "charset=Ascii "))
+    {
+      gchar *real_comment;
+
+      /* Skip "charset=Ascii " (length 14) to find the real comment */
+      real_comment = comment + 14;
+      if (real_comment[0] == '\0' ||
+          ! g_strcmp0 (real_comment, "binary comment"))
+        {
+          g_free (comment);
+          return NULL;
+        }
+      else
+        {
+          real_comment = g_strdup (real_comment);
+          g_free (comment);
+          return real_comment;
+        }
+    }
+
+  return comment;
+}
+
 /**
  * gimp_image_metadata_load_finish:
  * @image_ID:    The image
@@ -123,6 +155,8 @@ gimp_image_metadata_load_finish (gint32                 image_ID,
 
       comment = gexiv2_metadata_get_tag_interpreted_string (GEXIV2_METADATA (metadata),
                                                             "Exif.Photo.UserComment");
+      comment = gimp_image_metadata_interpret_comment (comment);
+
       if (! comment)
         comment = gexiv2_metadata_get_tag_interpreted_string (GEXIV2_METADATA (metadata),
                                                               "Exif.Image.ImageDescription");