Book polishing: Do not scan book for font usage when subsetting if no embedded fonts are available. Fixes #1737400 [Ebook edit: Subset embedded fonts does something even if there are no fonts](https://bugs.launchpad.net/calibre/+bug/1737400)

src/calibre/ebooks/oeb/polish/main.py

@@ -13,7 +13,7 @@ from functools import partial
 
 from calibre.ebooks.oeb.polish.container import get_container
 from calibre.ebooks.oeb.polish.stats import StatsCollector
-from calibre.ebooks.oeb.polish.subset import subset_all_fonts
+from calibre.ebooks.oeb.polish.subset import subset_all_fonts, iter_subsettable_fonts
 from calibre.ebooks.oeb.polish.images import compress_images
 from calibre.ebooks.oeb.polish.embed import embed_all_fonts
 from calibre.ebooks.oeb.polish.cover import set_cover
@@ -145,8 +145,12 @@ def polish_one(ebook, opts, report, customization=None):
     jacket = None
     changed = False
     customization = customization or CUSTOMIZATION.copy()
+    has_subsettable_fonts = False
+    for x in iter_subsettable_fonts(ebook):
+        has_subsettable_fonts = True
+        break
 
-    if opts.subset or opts.embed:
+    if (opts.subset and has_subsettable_fonts) or opts.embed:
         stats = StatsCollector(ebook, do_embed=opts.embed)
 
     if opts.opf:
@@ -196,12 +200,16 @@ def polish_one(ebook, opts, report, customization=None):
         rt(_('Embedding referenced fonts'))
         if embed_all_fonts(ebook, stats, report):
             changed = True
+            has_subsettable_fonts = True
         report('')
 
     if opts.subset:
-        rt(_('Subsetting embedded fonts'))
+        if has_subsettable_fonts:
-        if subset_all_fonts(ebook, stats.font_stats, report):
+            rt(_('Subsetting embedded fonts'))
-            changed = True
+            if subset_all_fonts(ebook, stats.font_stats, report):
+                changed = True
+        else:
+            rt(_('No embedded fonts to subset'))
         report('')
 
     if opts.remove_unused_css:

src/calibre/ebooks/oeb/polish/subset.py

@@ -34,52 +34,57 @@ def remove_font_face_rules(container, sheet, remove_names, base):
     return changed
 
 
+def iter_subsettable_fonts(container):
+    for name, mt in container.mime_map.iteritems():
+        if (mt in OEB_FONTS or name.rpartition('.')[-1].lower() in {'otf', 'ttf'}) and mt != guess_type('a.woff'):
+            yield name, mt
+
+
 def subset_all_fonts(container, font_stats, report):
     remove = set()
     total_old = total_new = 0
     changed = False
-    for name, mt in container.mime_map.iteritems():
+    for name, mt in iter_subsettable_fonts(container):
-        if (mt in OEB_FONTS or name.rpartition('.')[-1].lower() in {'otf', 'ttf'}) and mt != guess_type('a.woff'):
+        chars = font_stats.get(name, set())
-            chars = font_stats.get(name, set())
+        with container.open(name, 'rb') as f:
-            with container.open(name, 'rb') as f:
+            f.seek(0, os.SEEK_END)
-                f.seek(0, os.SEEK_END)
+            total_old += f.tell()
-                total_old += f.tell()
+        if not chars:
-            if not chars:
+            remove.add(name)
-                remove.add(name)
+            report(_('Removed unused font: %s')%name)
-                report(_('Removed unused font: %s')%name)
+            continue
+        with container.open(name, 'r+b') as f:
+            raw = f.read()
+            try:
+                font_name = get_font_names(raw)[-1]
+            except Exception as e:
+                container.log.warning(
+                    'Corrupted font: %s, ignoring.  Error: %s'%(
+                        name, as_unicode(e)))
+                continue
+            warnings = []
+            container.log('Subsetting font: %s'%(font_name or name))
+            try:
+                nraw, old_sizes, new_sizes = subset(raw, chars,
+                                                warnings=warnings)
+            except UnsupportedFont as e:
+                container.log.warning(
+                    'Unsupported font: %s, ignoring.  Error: %s'%(
+                        name, as_unicode(e)))
                 continue
-            with container.open(name, 'r+b') as f:
-                raw = f.read()
-                try:
-                    font_name = get_font_names(raw)[-1]
-                except Exception as e:
-                    container.log.warning(
-                        'Corrupted font: %s, ignoring.  Error: %s'%(
-                            name, as_unicode(e)))
-                    continue
-                warnings = []
-                container.log('Subsetting font: %s'%(font_name or name))
-                try:
-                    nraw, old_sizes, new_sizes = subset(raw, chars,
-                                                   warnings=warnings)
-                except UnsupportedFont as e:
-                    container.log.warning(
-                        'Unsupported font: %s, ignoring.  Error: %s'%(
-                            name, as_unicode(e)))
-                    continue
 
-                for w in warnings:
+            for w in warnings:
-                    container.log.warn(w)
+                container.log.warn(w)
-                olen = sum(old_sizes.itervalues())
+            olen = sum(old_sizes.itervalues())
-                nlen = sum(new_sizes.itervalues())
+            nlen = sum(new_sizes.itervalues())
-                total_new += len(nraw)
+            total_new += len(nraw)
-                if nlen == olen:
+            if nlen == olen:
-                    report(_('The font %s was already subset')%font_name)
+                report(_('The font %s was already subset')%font_name)
-                else:
+            else:
-                    report(_('Decreased the font {0} to {1} of its original size').format(
+                report(_('Decreased the font {0} to {1} of its original size').format(
-                        font_name, ('%.1f%%' % (nlen/olen * 100))))
+                    font_name, ('%.1f%%' % (nlen/olen * 100))))
-                    changed = True
+                changed = True
-                f.seek(0), f.truncate(), f.write(nraw)
+            f.seek(0), f.truncate(), f.write(nraw)
 
     for name in remove:
         container.remove_item(name)