Edit Book: Check Book: Add a test to check if the embedded fonts in the book have their embedding permissions enabled

src/calibre/ebooks/oeb/polish/check/fonts.py

@@ -14,7 +14,7 @@ from calibre.ebooks.oeb.polish.check.base import BaseError, WARN
 from calibre.ebooks.oeb.polish.container import OEB_FONTS
 from calibre.ebooks.oeb.polish.pretty import pretty_script_or_style
 from calibre.ebooks.oeb.polish.fonts import change_font_in_declaration
-from calibre.utils.fonts.utils import get_all_font_names
+from calibre.utils.fonts.utils import get_all_font_names, is_font_embeddable, UnsupportedFont
 from tinycss.fonts3 import parse_font_family
 
 
@@ -32,6 +32,17 @@ def fix_sheet(sheet, css_name, font_name):
     return changed
 
 
+class NotEmbeddable(BaseError):
+
+    level = WARN
+
+    def __init__(self, name, fs_type):
+        BaseError.__init__(self, _('The font {} is not allowed to be embedded').format(name), name)
+        self.HELP = _('The font has a flag in its metadata ({:09b}) set indicating that it is'
+                      ' not licensed for embedding. You can ignore this warning, if you are'
+                      ' sure you have permission to embed this font.').format(fs_type)
+
+
 class FontAliasing(BaseError):
 
     level = WARN
@@ -83,6 +94,12 @@ def check_fonts(container):
                 errors.append(InvalidFont(_('Not a valid font: %s') % e, name))
                 continue
             font_map[name] = name_map.get('family_name', None) or name_map.get('preferred_family_name', None) or name_map.get('wws_family_name', None)
+            try:
+                embeddable, fs_type = is_font_embeddable(raw)
+            except UnsupportedFont:
+                embeddable = True
+            if not embeddable:
+                errors.append(NotEmbeddable(name, fs_type))
 
     sheets = []
     for name, mt in container.mime_map.iteritems():

src/calibre/utils/fonts/utils.py

@@ -328,6 +328,26 @@ def remove_embed_restriction(raw):
     return raw
 
 
+def is_font_embeddable(raw):
+    # https://www.microsoft.com/typography/otspec/os2.htm#fst
+    ok, sig = is_truetype_font(raw)
+    if not ok:
+        raise UnsupportedFont('Not a supported font, sfnt_version: %r'%sig)
+
+    table, table_index, table_offset = get_table(raw, 'os/2')[:3]
+    if table is None:
+        raise UnsupportedFont('Not a supported font, has no OS/2 table')
+    fs_type_offset = struct.calcsize(b'>HhHH')
+    fs_type = struct.unpack_from(b'>H', table, fs_type_offset)[0]
+    if fs_type == 0 or fs_type & 0x8:
+        return True, fs_type
+    if fs_type & 1:
+        return False, fs_type
+    if fs_type & 0x200:
+        return False, fs_type
+    return True, fs_type
+
+
 def read_bmp_prefix(table, bmp):
     length, language, segcount = struct.unpack_from(b'>3H', table, bmp+2)
     array_len = segcount //2
@@ -479,4 +499,3 @@ def main():
 
 if __name__ == '__main__':
     main()
-