Forgot to add this in the commit it belongs to

src/calibre/utils/exim.py

@@ -0,0 +1,114 @@
+#!/usr/bin/env python2
+# vim:fileencoding=utf-8
+# License: GPLv3 Copyright: 2015, Kovid Goyal <kovid at kovidgoyal.net>
+
+from __future__ import (unicode_literals, division, absolute_import,
+                        print_function)
+import os, json, struct, hashlib
+
+def send_file(from_obj, to_obj, chunksize=1<<20):
+    m = hashlib.sha1()
+    while True:
+        raw = from_obj.read(chunksize)
+        if not raw:
+            break
+        m.update(raw)
+        to_obj.write(raw)
+    return type('')(m.hexdigest())
+
+class FileDest(object):
+
+    def __init__(self, key, exporter):
+        self.exporter, self.key = exporter, key
+        self.hasher = hashlib.sha1()
+        self.start_pos = exporter.f.tell()
+        self._discard = False
+
+    def discard(self):
+        self._discard = True
+
+    def ensure_space(self, size):
+        if size > 0:
+            self.exporter.ensure_space(size)
+            self.start_pos = self.exporter.f.tell()
+
+    def write(self, data):
+        self.hasher.update(data)
+        self.exporter.f.write(data)
+
+    def flush(self):
+        pass
+
+    def close(self):
+        if not self._discard:
+            size = self.exporter.f.tell() - self.start_pos
+            digest = type('')(self.hasher.hexdigest())
+            self.exporter.file_metadata[self.key] = (len(self.exporter.parts), self.start_pos, size, digest)
+        del self.exporter, self.hasher
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+
+class Exporter(object):
+
+    VERSION = 1
+    TAIL_FMT = b'!II?'  # part_num, version, is_last
+    MDATA_SZ_FMT = b'!Q'
+
+    def __init__(self, path_to_export_dir, part_size=(1 << 30)):
+        self.part_size = part_size
+        self.base = os.path.abspath(path_to_export_dir)
+        self.parts = []
+        self.new_part()
+        self.file_metadata = {}
+        self.metadata = {'file_metadata': self.file_metadata}
+
+    def set_metadata(self, key, val):
+        if key in self.metadata:
+            raise KeyError('The metadata already contains the key: %s' % key)
+        self.metadata[key] = val
+
+    @property
+    def f(self):
+        return self.parts[-1]
+
+    def new_part(self):
+        self.parts.append(open(os.path.join(
+            self.base, 'part-{:04d}.calibre-data'.format(len(self.parts) + 1)), 'wb'))
+
+    def commit_part(self, is_last=False):
+        self.f.write(struct.pack(self.TAIL_FMT, len(self.parts), self.VERSION, is_last))
+        self.f.close()
+        self.parts[-1] = self.f.name
+
+    def ensure_space(self, size):
+        if size + self.f.tell() < self.part_size:
+            return
+        self.commit_part()
+        self.new_part()
+
+    def commit(self):
+        raw = json.dumps(self.metadata, ensure_ascii=False)
+        if not isinstance(raw, bytes):
+            raw = raw.encode('utf-8')
+        self.ensure_space(len(raw))
+        self.f.write(raw)
+        self.f.write(struct.pack(self.MDATA_SZ_FMT, len(raw)))
+        self.commit_part(is_last=True)
+
+    def add_file(self, fileobj, key):
+        fileobj.seek(0, os.SEEK_END)
+        size = fileobj.tell()
+        fileobj.seek(0)
+        self.ensure_space(size)
+        pos = self.f.tell()
+        digest = send_file(fileobj, self.f)
+        size = self.f.tell() - pos
+        self.file_metadata[key] = (len(self.parts), pos, size, digest)
+
+    def start_file(self, key):
+        return FileDest(key, self)