Implement serialization of Metadata instances

src/calibre/db/tests/reading.py

@@ -237,6 +237,17 @@ class ReadingTest(BaseTest):
             self.compare_metadata(mi1, mi2)
     # }}}
 
+    def test_serialize_metadata(self):  # {{{
+        from calibre.utils.serialize import json_dumps, json_loads, msgpack_dumps, msgpack_loads
+        cache = self.init_cache(self.library_path)
+        for i in xrange(1, 4):
+            mi = cache.get_metadata(i, get_cover=True, cover_as_data=True)
+            rmi = msgpack_loads(msgpack_dumps(mi))
+            self.compare_metadata(mi, rmi, exclude='format_metadata has_cover formats id'.split())
+            rmi = json_loads(json_dumps(mi))
+            self.compare_metadata(mi, rmi, exclude='format_metadata has_cover formats id'.split())
+    # }}}
+
     def test_get_cover(self):  # {{{
         'Test cover() returns the same data for both backends'
         from calibre.library.database2 import LibraryDatabase2

src/calibre/ebooks/metadata/book/serialize.py

@@ -0,0 +1,66 @@
+#!/usr/bin/env python2
+# vim:fileencoding=utf-8
+# License: GPLv3 Copyright: 2017, Kovid Goyal <kovid at kovidgoyal.net>
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import base64
+
+from calibre.constants import preferred_encoding
+from calibre.ebooks.metadata.book import SERIALIZABLE_FIELDS
+from calibre.ebooks.metadata.book.base import Metadata
+from calibre.utils.imghdr import what
+
+
+def ensure_unicode(obj, enc=preferred_encoding):
+    if isinstance(obj, unicode):
+        return obj
+    if isinstance(obj, bytes):
+        return obj.decode(enc, 'replace')
+    if isinstance(obj, (list, tuple)):
+        return [ensure_unicode(x) for x in obj]
+    if isinstance(obj, dict):
+        return {ensure_unicode(k): ensure_unicode(v) for k, v in obj.iteritems()}
+    return obj
+
+
+def read_cover(mi):
+    if mi.cover_data and mi.cover_data[1]:
+        return
+    if mi.cover:
+        try:
+            with lopen(mi.cover, 'rb') as f:
+                cd = f.read()
+            mi.cover_data = what(cd), cd
+        except EnvironmentError:
+            pass
+    return mi
+
+
+def metadata_as_dict(mi, encode_cover_data=False):
+    if hasattr(mi, 'to_book_metadata'):
+        mi = mi.to_book_metadata()
+    ans = {}
+    for field in SERIALIZABLE_FIELDS:
+        if field != 'cover' and not mi.is_null(field):
+            val = getattr(mi, field)
+            ans[field] = ensure_unicode(val)
+    if mi.cover_data and mi.cover_data[1]:
+        if encode_cover_data:
+            ans['cover_data'] = [mi.cover_data[0], base64.standard_b64encode(bytes(mi.cover_data[1]))]
+        else:
+            ans['cover_data'] = mi.cover_data
+    um = mi.get_all_user_metadata(False)
+    if um:
+        ans['user_metadata'] = um
+    return ans
+
+
+def metadata_from_dict(src):
+    ans = Metadata('Unknown')
+    for key, value in src.iteritems():
+        if key == 'user_metadata':
+            ans.set_all_user_metadata(value)
+        else:
+            setattr(ans, key, value)
+    return ans

src/calibre/utils/serialize.py

@@ -4,17 +4,23 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-import json
+import json, base64
+from functools import partial
 from datetime import datetime
-from calibre.utils.iso8601 import parse_iso8601
 
+from calibre.utils.iso8601 import parse_iso8601
 
 MSGPACK_MIME = 'application/x-msgpack'
 
 
-def encoder(obj):
+def encoder(obj, for_json=False):
     if isinstance(obj, datetime):
-        return {'__datetime__': obj.isoformat()}
+        return {'__datetime__': unicode(obj.isoformat())}
+    if obj.__class__.__name__ == 'Metadata':
+        from calibre.ebooks.metadata.book.base import Metadata
+        if isinstance(obj, Metadata):
+            from calibre.ebooks.metadata.book.serialize import metadata_as_dict
+            obj = {'__metadata__': metadata_as_dict(obj, encode_cover_data=for_json)}
     return obj
 
 
@@ -24,7 +30,7 @@ def msgpack_dumps(data):
 
 
 def json_dumps(data, **kw):
-    kw['default'] = encoder
+    kw['default'] = partial(encoder, for_json=True)
     kw['ensure_ascii'] = False
     ans = json.dumps(data, **kw)
     if not isinstance(ans, bytes):
@@ -32,19 +38,24 @@ def json_dumps(data, **kw):
     return ans
 
 
-def decoder(obj):
+def decoder(obj, for_json=False):
     dt = obj.get('__datetime__')
     if dt is not None:
-        obj = parse_iso8601(dt, assume_utc=True)
+        return parse_iso8601(dt, assume_utc=True)
+    m = obj.get('__metadata__')
+    if m is not None:
+        from calibre.ebooks.metadata.book.serialize import metadata_from_dict
+        obj = metadata_from_dict(m)
+        if for_json and obj.cover_data and obj.cover_data[1]:
+            obj.cover_data = obj.cover_data[0], base64.standard_b64decode(obj.cover_data[1])
+            return obj
     return obj
 
 
 def msgpack_loads(data):
     import msgpack
-    return msgpack.unpackb(
-        data, encoding='utf-8', use_list=False, object_hook=decoder
-    )
+    return msgpack.unpackb(data, encoding='utf-8', object_hook=decoder)
 
 
 def json_loads(data):
-    return json.loads(data, object_hook=decoder)
+    return json.loads(data, object_hook=partial(decoder, for_json=True))