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diff --git a/swh/core/bencode.py b/swh/core/bencode.py
new file mode 100644
--- /dev/null
+++ b/swh/core/bencode.py
@@ -0,0 +1,58 @@
+# Copyright (C) 2019 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+"""Provides a bencode encoder.
+
+This allows encoding a nested bytes/int/list/dict structure
+into its bencode representation."""
+
+from typing import Dict, Callable, Any, Generator
+
+
+def _encode_bytes(obj: bytes) -> Generator[bytes, None, None]:
+ yield b'%d:' % len(obj)
+ yield obj
+
+
+def _encode_int(obj: int) -> Generator[bytes, None, None]:
+ yield b'i%de' % obj
+
+
+def _encode_list(obj: list) -> Generator[bytes, None, None]:
+ yield b'l'
+ for item in obj:
+ yield from _encode(item)
+ yield b'e'
+
+
+def _encode_dict(obj: dict) -> Generator[bytes, None, None]:
+ yield b'd'
+ for (key, value) in sorted(obj.items()):
+ assert type(key) == bytes
+ yield from _encode_bytes(key)
+ yield from _encode(value)
+ yield b'e'
+
+
+_ENCODERS = {
+ bytes: _encode_bytes,
+ int: _encode_int,
+ list: _encode_list,
+ dict: _encode_dict,
+} # type: Dict[type, Callable[[Any], Generator[bytes, None, None]]]
+
+
+def _encode(obj: Any) -> Generator[bytes, None, None]:
+ encoder = _ENCODERS.get(type(obj), None)
+ if not encoder:
+ raise TypeError('Unsupported type for bencoding: {}'.format(type(obj)))
+ yield from encoder(obj)
+
+
+def encode(obj) -> bytes:
+ """Encodes a nested bytes/int/list/dict structure into its bencode
+ representation.
+ """
+ return b''.join(_encode(obj))
diff --git a/swh/core/tests/test_bencode.py b/swh/core/tests/test_bencode.py
new file mode 100644
--- /dev/null
+++ b/swh/core/tests/test_bencode.py
@@ -0,0 +1,54 @@
+# Copyright (C) 2019 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+import unittest
+
+from swh.core.bencode import encode
+
+
+class SpecificationTestCase(unittest.TestCase):
+ """These examples are from the specification:
+ https://wiki.theory.org/index.php/BitTorrentSpecification#Bencoding"""
+
+ def test_bencode_bytes(self):
+ self.assertEqual(b'4:spam', encode(b'spam'))
+
+ self.assertEqual(b'0:', encode(b''))
+
+ def test_encode_int(self):
+ self.assertEqual(b'i3e', encode(3))
+
+ self.assertEqual(b'i-3e', encode(-3))
+
+ self.assertEqual(b'i0e', encode(0))
+
+ def test_encode_list(self):
+ self.assertEqual(b'l4:spam4:eggse', encode([b'spam', b'eggs']))
+
+ self.assertEqual(b'le', encode([]))
+
+ def test_encode_dict(self):
+ self.assertEqual(
+ b'd3:cow3:moo4:spam4:eggse',
+ encode({b'cow': b'moo', b'spam': b'eggs'}))
+
+ self.assertEqual(
+ b'd4:spaml1:a1:bee',
+ encode({b'spam': [b'a', b'b']}))
+
+ self.assertEqual(
+ b'd9:publisher3:bob17:publisher-webpage15:www.example.com'
+ b'18:publisher.location4:homee',
+ encode({b'publisher': b'bob',
+ b'publisher-webpage': b'www.example.com',
+ b'publisher.location': b'home'}))
+
+ self.assertEqual(b'de', encode({}))
+
+
+class TypeTestCase(unittest.TestCase):
+ def test_invalid_type(self):
+ with self.assertRaises(TypeError):
+ encode('string')

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