Unpacker: add tell() (#227)

test/test_sequnpack.py

@@ -3,6 +3,7 @@
 
 import io
 from msgpack import Unpacker, BufferFull
+from msgpack import pack
 from msgpack.exceptions import OutOfData
 from pytest import raises
 
@@ -96,3 +97,22 @@ def test_issue124():
     unpacker.feed(b"!")
     assert tuple(unpacker) == (b'!',)
     assert tuple(unpacker) == ()
+
+
+def test_unpack_tell():
+    stream = io.BytesIO()
+    messages = [2**i-1 for i in range(65)]
+    messages += [-(2**i) for i in range(1, 64)]
+    messages += [b'hello', b'hello'*1000, list(range(20)),
+                 {i: bytes(i)*i for i in range(10)},
+                 {i: bytes(i)*i for i in range(32)}]
+    offsets = []
+    for m in messages:
+        pack(m, stream)
+        offsets.append(stream.tell())
+    stream.seek(0)
+    unpacker = Unpacker(stream)
+    for m, o in zip(messages, offsets):
+        m2 = next(unpacker)
+        assert m == m2
+        assert o == unpacker.tell()