Add purepython fallback. (Merge branch 'purepython')

5 files changed, 588 insertions, 8 deletions

diff --git a/.travis.yml b/.travis.yml
index 2e6fc56..e536fdc 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,4 +12,4 @@ install:
     - cython --cplus msgpack/_packer.pyx
     - cython --cplus msgpack/_unpacker.pyx
 
-script: "tox"
+script: "tox && MSGPACK_PUREPYTHON=x tox"
diff --git a/msgpack/__init__.py b/msgpack/__init__.py
index 0bfe6fe..77f6b81 100644
--- a/msgpack/__init__.py
+++ b/msgpack/__init__.py
@@ -1,8 +1,16 @@
 # coding: utf-8
 from msgpack._version import version
 from msgpack.exceptions import *
-from msgpack._packer import pack, packb, Packer
-from msgpack._unpacker import unpack, unpackb, Unpacker
+
+import os
+if os.environ.get('MSGPACK_PUREPYTHON'):
+    from msgpack.fallback import pack, packb, Packer, unpack, unpackb, Unpacker
+else:
+    try:
+        from msgpack._packer import pack, packb, Packer
+        from msgpack._unpacker import unpack, unpackb, Unpacker
+    except ImportError:
+        from msgpack.fallback import pack, packb, Packer, unpack, unpackb, Unpacker
 
 # alias for compatibility to simplejson/marshal/pickle.
 load = unpack
diff --git a/msgpack/fallback.py b/msgpack/fallback.py
new file mode 100644
index 0000000..ac6dbf9
--- /dev/null
+++ b/msgpack/fallback.py
@@ -0,0 +1,550 @@
+"""Fallback pure Python implementation of msgpack"""
+
+import sys
+import array
+import struct
+
+if sys.version_info[0] == 3:
+    PY3 = True
+    int_types = int
+    Unicode = str
+    xrange = range
+    def dict_iteritems(d):
+        return d.items()
+else:
+    PY3 = False
+    int_types = (int, long)
+    Unicode = unicode
+    def dict_iteritems(d):
+        return d.iteritems()
+
+
+if hasattr(sys, 'pypy_version_info'):
+    # cStringIO is slow on PyPy, StringIO is faster.  However: PyPy's own
+    # StringBuilder is fastest.
+    from __pypy__.builders import StringBuilder
+    USING_STRINGBUILDER = True
+    class StringIO(object):
+        def __init__(self, s=b''):
+            if s:
+                self.builder = StringBuilder(len(s))
+                self.builder.append(s)
+            else:
+                self.builder = StringBuilder()
+        def write(self, s):
+            self.builder.append(s)
+        def getvalue(self):
+            return self.builder.build()
+else:
+    USING_STRINGBUILDER = False
+    from io import BytesIO as StringIO
+
+from msgpack.exceptions import (
+        BufferFull,
+        OutOfData,
+        UnpackValueError,
+        PackValueError,
+        ExtraData)
+
+EX_SKIP                 = 0 
+EX_CONSTRUCT            = 1
+EX_READ_ARRAY_HEADER    = 2
+EX_READ_MAP_HEADER      = 3
+
+TYPE_IMMEDIATE          = 0
+TYPE_ARRAY              = 1
+TYPE_MAP                = 2
+TYPE_RAW                = 3
+
+DEFAULT_RECURSE_LIMIT=511
+
+def pack(o, stream, default=None, encoding='utf-8', unicode_errors='strict'):
+    """ Pack object `o` and write it to `stream` """
+    packer = Packer(default=default, encoding=encoding,
+                    unicode_errors=unicode_errors)
+    stream.write(packer.pack(o))
+
+def packb(o, default=None, encoding='utf-8', unicode_errors='struct',
+          use_single_float=False):
+    """ Pack object `o` and return packed bytes """
+    packer = Packer(default=default,
+                    encoding=encoding,
+                    unicode_errors=unicode_errors,
+                    use_single_float=use_single_float)
+    return packer.pack(o)
+
+def unpack(stream, object_hook=None, list_hook=None, use_list=True,
+           encoding=None, unicode_errors='strict',
+           object_pairs_hook=None):
+    """ Unpack an object from `stream`.
+
+    Raises `ExtraData` when `stream` has extra bytes. """
+    unpacker = Unpacker(stream, object_hook=object_hook, list_hook=list_hook,
+                        use_list=use_list,
+                        encoding=encoding, unicode_errors=unicode_errors,
+                        object_pairs_hook=object_pairs_hook)
+    ret = unpacker._fb_unpack()
+    if unpacker._fb_got_extradata():
+        raise ExtraData(ret, unpacker._fb_get_extradata())
+    return ret
+
+def unpackb(packed, object_hook=None, list_hook=None, use_list=True,
+            encoding=None, unicode_errors='strict',
+            object_pairs_hook=None):
+    """ Unpack an object from `packed`.
+
+    Raises `ExtraData` when `packed` contains extra bytes. """
+    unpacker = Unpacker(None, object_hook=object_hook, list_hook=list_hook,
+                        use_list=use_list,
+                        encoding=encoding, unicode_errors=unicode_errors,
+                        object_pairs_hook=object_pairs_hook)
+    unpacker.feed(packed)
+    ret = unpacker._fb_unpack()
+    if unpacker._fb_got_extradata():
+        raise ExtraData(ret, unpacker._fb_get_extradata())
+    return ret
+
+class Unpacker(object):
+    """
+    Streaming unpacker.
+
+    `file_like` is a file-like object having a `.read(n)` method.
+    When `Unpacker` is initialized with a `file_like`, `.feed()` is not
+    usable.
+
+    `read_size` is used for `file_like.read(read_size)`.
+
+    If `use_list` is True (default), msgpack lists are deserialized to Python
+    lists.  Otherwise they are deserialized to tuples.
+
+    `object_hook` is the same as in simplejson.  If it is not None, it should
+    be callable and Unpacker calls it with a dict argument after deserializing
+    a map.
+
+    `object_pairs_hook` is the same as in simplejson.  If it is not None, it
+    should be callable and Unpacker calls it with a list of key-value pairs
+    after deserializing a map.
+
+    `encoding` is the encoding used for decoding msgpack bytes.  If it is
+    None (default), msgpack bytes are deserialized to Python bytes.
+
+    `unicode_errors` is used for decoding bytes.
+
+    `max_buffer_size` limits the buffer size.  0 means INT_MAX (default).
+
+    Raises `BufferFull` exception when it is unsufficient.
+
+    You should set this parameter when unpacking data from an untrustred source.
+
+    example of streaming deserialization from file-like object::
+
+        unpacker = Unpacker(file_like)
+        for o in unpacker:
+            do_something(o)
+
+    example of streaming deserialization from socket::
+
+        unpacker = Unapcker()
+        while 1:
+            buf = sock.recv(1024*2)
+            if not buf:
+                break
+            unpacker.feed(buf)
+            for o in unpacker:
+                do_something(o)
+    """
+
+    def __init__(self, file_like=None, read_size=0, use_list=True,
+                 object_hook=None, object_pairs_hook=None, list_hook=None,
+                 encoding=None, unicode_errors='strict', max_buffer_size=0):
+        if file_like is None:
+            self._fb_feeding = True
+        else:
+            if not callable(file_like.read):
+                raise ValueError("`file_like.read` must be callable")
+            self.file_like = file_like
+            self._fb_feeding = False
+        self._fb_buffers = []
+        self._fb_buf_o = 0
+        self._fb_buf_i = 0
+        self._fb_buf_n = 0
+        self.max_buffer_size = (2**31-1 if max_buffer_size == 0
+                                        else max_buffer_size)
+        self.read_size = (read_size if read_size != 0
+                            else min(self.max_buffer_size, 2048))
+        if read_size > self.max_buffer_size:
+            raise ValueError("read_size must be smaller than max_buffer_size")
+        self.encoding = encoding
+        self.unicode_errors = unicode_errors
+        self.use_list = use_list
+        self.list_hook = list_hook
+        self.object_hook = object_hook
+        self.object_pairs_hook = object_pairs_hook
+
+        if list_hook is not None and not callable(list_hook):
+            raise ValueError('`list_hook` is not callable')
+        if object_hook is not None and not callable(object_hook):
+            raise ValueError('`object_hook` is not callable')
+        if object_pairs_hook is not None and not callable(object_pairs_hook):
+            raise ValueError('`object_pairs_hook` is not callable')
+        if object_hook is not None and object_pairs_hook is not None:
+            raise ValueError("object_pairs_hook and object_hook are mutually "
+                             "exclusive")
+
+    def feed(self, next_bytes):
+        if isinstance(next_bytes, array.array):
+            next_bytes = next_bytes.tostring()
+        assert self._fb_feeding
+        if self._fb_buf_n + len(next_bytes) > self.max_buffer_size:
+            raise BufferFull
+        self._fb_buf_n += len(next_bytes)
+        self._fb_buffers.append(next_bytes)
+
+    def _fb_consume(self):
+        self._fb_buffers = self._fb_buffers[self._fb_buf_i:]
+        if self._fb_buffers:
+            self._fb_buffers[0] = self._fb_buffers[0][self._fb_buf_o:]
+        self._fb_buf_o = 0
+        self._fb_buf_i = 0
+        self._fb_buf_n = sum(map(len, self._fb_buffers))
+
+    def _fb_got_extradata(self):
+        if self._fb_buf_i != len(self._fb_buffers):
+            return True
+        if self._fb_feeding:
+            return False
+        if not self.file_like:
+            return False
+        if self.file_like.read(1):
+            return True
+        return False
+
+    def __iter__(self):
+        return self
+
+    def read_bytes(self, n):
+        return self._fb_read(n)
+
+    def _fb_rollback(self):
+        self._fb_buf_i = 0
+        self._fb_buf_o = 0
+
+    def _fb_get_extradata(self):
+        bufs = self._fb_buffers[self._fb_buf_i:]
+        if bufs:
+            bufs[0] = bufs[0][self._fb_buf_o:]
+        return b''.join(bufs)
+
+    def _fb_read(self, n, write_bytes=None):
+        if (write_bytes is None and self._fb_buf_i < len(self._fb_buffers)
+                and self._fb_buf_o + n < len(self._fb_buffers[self._fb_buf_i])):
+            self._fb_buf_o += n
+            return self._fb_buffers[self._fb_buf_i][
+                    self._fb_buf_o-n:self._fb_buf_o]
+        ret = b''
+        while len(ret) != n:
+            if self._fb_buf_i == len(self._fb_buffers):
+                if self._fb_feeding:
+                    break
+                tmp = self.file_like.read(self.read_size)
+                if not tmp:
+                    break
+                self._fb_buffers.append(tmp)
+                continue
+            sliced = n - len(ret)
+            ret += self._fb_buffers[self._fb_buf_i][
+                        self._fb_buf_o:self._fb_buf_o + sliced]
+            self._fb_buf_o += sliced
+            if self._fb_buf_o >= len(self._fb_buffers[self._fb_buf_i]):
+                self._fb_buf_o = 0
+                self._fb_buf_i += 1
+        if len(ret) != n:
+            self._fb_rollback()
+            raise OutOfData
+        if write_bytes is not None:
+            write_bytes(ret)
+        return ret
+
+    def _fb_unpack(self, execute=EX_CONSTRUCT, write_bytes=None):
+        typ = TYPE_IMMEDIATE
+        c = self._fb_read(1, write_bytes)
+        b = ord(c)
+        if   b & 0b10000000 == 0:
+            obj = b
+        elif b & 0b11100000 == 0b11100000:
+            obj = struct.unpack("b", c)[0]
+        elif b & 0b11100000 == 0b10100000:
+            n = b & 0b00011111
+            obj = self._fb_read(n, write_bytes)
+            typ = TYPE_RAW
+        elif b & 0b11110000 == 0b10010000:
+            n = b & 0b00001111
+            typ = TYPE_ARRAY
+        elif b & 0b11110000 == 0b10000000:
+            n = b & 0b00001111
+            typ = TYPE_MAP
+        elif b == 0xc0:
+            obj = None
+        elif b == 0xc2:
+            obj = False
+        elif b == 0xc3:
+            obj = True
+        elif b == 0xca:
+            obj = struct.unpack(">f", self._fb_read(4, write_bytes))[0]
+        elif b == 0xcb:
+            obj = struct.unpack(">d", self._fb_read(8, write_bytes))[0]
+        elif b == 0xcc:
+            obj = struct.unpack("B", self._fb_read(1, write_bytes))[0]
+        elif b == 0xcd:
+            obj = struct.unpack(">H", self._fb_read(2, write_bytes))[0]
+        elif b == 0xce:
+            obj = struct.unpack(">I", self._fb_read(4, write_bytes))[0]
+        elif b == 0xcf:
+            obj = struct.unpack(">Q", self._fb_read(8, write_bytes))[0]
+        elif b == 0xd0:
+            obj = struct.unpack("b", self._fb_read(1, write_bytes))[0]
+        elif b == 0xd1:
+            obj = struct.unpack(">h", self._fb_read(2, write_bytes))[0]
+        elif b == 0xd2:
+            obj = struct.unpack(">i", self._fb_read(4, write_bytes))[0]
+        elif b == 0xd3:
+            obj = struct.unpack(">q", self._fb_read(8, write_bytes))[0]
+        elif b == 0xda:
+            n = struct.unpack(">H", self._fb_read(2, write_bytes))[0]
+            obj = self._fb_read(n, write_bytes)
+            typ = TYPE_RAW
+        elif b == 0xdb:
+            n = struct.unpack(">I", self._fb_read(4, write_bytes))[0]
+            obj = self._fb_read(n, write_bytes)
+            typ = TYPE_RAW
+        elif b == 0xdc:
+            n = struct.unpack(">H", self._fb_read(2, write_bytes))[0]
+            typ = TYPE_ARRAY
+        elif b == 0xdd:
+            n = struct.unpack(">I", self._fb_read(4, write_bytes))[0]
+            typ = TYPE_ARRAY
+        elif b == 0xde:
+            n = struct.unpack(">H", self._fb_read(2, write_bytes))[0]
+            typ = TYPE_MAP
+        elif b == 0xdf:
+            n = struct.unpack(">I", self._fb_read(4, write_bytes))[0]
+            typ = TYPE_MAP
+        else:
+            raise UnpackValueError("Unknown header: 0x%x" % b)
+        if execute == EX_READ_ARRAY_HEADER:
+            if typ != TYPE_ARRAY:
+                raise UnpackValueError("Expected array")
+            return n
+        if execute == EX_READ_MAP_HEADER:
+            if typ != TYPE_MAP:
+                raise UnpackValueError("Expected map")
+            return n
+        # TODO should we eliminate the recursion?
+        if typ == TYPE_ARRAY:
+            if execute == EX_SKIP:
+                for i in xrange(n):
+                    # TODO check whether we need to call `list_hook`
+                    self._fb_unpack(EX_SKIP, write_bytes)
+                return
+            ret = []
+            for i in xrange(n):
+                ret.append(self._fb_unpack(EX_CONSTRUCT, write_bytes))
+            if self.list_hook is not None:
+                ret = self.list_hook(ret)
+            # TODO is the interaction between `list_hook` and `use_list` ok?
+            return ret if self.use_list else tuple(ret)
+        if typ == TYPE_MAP:
+            if execute == EX_SKIP:
+                for i in xrange(n):
+                    # TODO check whether we need to call hooks
+                    self._fb_unpack(EX_SKIP, write_bytes)
+                    self._fb_unpack(EX_SKIP, write_bytes)
+                return
+            ret = []
+            for i in xrange(n):
+                ret.append((self._fb_unpack(EX_CONSTRUCT, write_bytes),
+                            self._fb_unpack(EX_CONSTRUCT, write_bytes)))
+            if self.object_pairs_hook is not None:
+                ret = self.object_pairs_hook(ret)
+            else:
+                ret = dict(ret)
+            if self.object_hook is not None:
+                ret = self.object_hook(ret)
+            return ret
+        if execute == EX_SKIP:
+            return
+        if typ == TYPE_RAW:
+            if self.encoding is not None:
+                obj = obj.decode(self.encoding, self.unicode_errors)
+            return obj
+        assert typ == TYPE_IMMEDIATE
+        return obj
+
+    def next(self):
+        try:
+            ret = self._fb_unpack(EX_CONSTRUCT, None)
+            self._fb_consume()
+            return ret
+        except OutOfData:
+            raise StopIteration
+    __next__ = next
+
+    def skip(self, write_bytes=None):
+        self._fb_unpack(EX_SKIP, write_bytes)
+        self._fb_consume()
+
+    def unpack(self, write_bytes=None):
+        ret = self._fb_unpack(EX_CONSTRUCT, write_bytes)
+        self._fb_consume()
+        return ret
+
+    def read_array_header(self, write_bytes=None):
+        ret = self._fb_unpack(EX_READ_ARRAY_HEADER, write_bytes)
+        self._fb_consume()
+        return ret
+
+    def read_map_header(self, write_bytes=None):
+        ret = self._fb_unpack(EX_READ_MAP_HEADER, write_bytes)
+        self._fb_consume()
+        return ret
+
+class Packer(object):
+    def __init__(self, default=None, encoding='utf-8', unicode_errors='strict',
+                 use_single_float=False, autoreset=True):
+        self.use_float = use_single_float
+        self.autoreset = autoreset
+        self.encoding = encoding
+        self.unicode_errors = unicode_errors
+        self.buffer = StringIO()
+        if default is not None:
+            if not callable(default):
+                raise TypeError("default must be callable")
+        self._default = default
+
+    def _pack(self, obj, nest_limit=DEFAULT_RECURSE_LIMIT):
+        if nest_limit < 0:
+            raise PackValueError("recursion limit exceeded")
+        if obj is None:
+            return self.buffer.write(b"\xc0")
+        if isinstance(obj, bool):
+            if obj:
+                return self.buffer.write(b"\xc3")
+            return self.buffer.write(b"\xc2")
+        if isinstance(obj, int_types):
+            if 0 <= obj < 0x80:
+                return self.buffer.write(struct.pack("B", obj))
+            if -0x20 <= obj < 0:
+                return self.buffer.write(struct.pack("b", obj))
+            if 0x80 <= obj <= 0xff:
+                return self.buffer.write(struct.pack("BB", 0xcc, obj))
+            if -0x80 <= obj < 0:
+                return self.buffer.write(struct.pack(">Bb", 0xd0, obj))
+            if 0xff < obj <= 0xffff:
+                return self.buffer.write(struct.pack(">BH", 0xcd, obj))
+            if -0x8000 <= obj < -0x80:
+                return self.buffer.write(struct.pack(">Bh", 0xd1, obj))
+            if 0xffff < obj <= 0xffffffff:
+                return self.buffer.write(struct.pack(">BI", 0xce, obj))
+            if -0x80000000 <= obj < -0x8000:
+                return self.buffer.write(struct.pack(">Bi", 0xd2, obj))
+            if 0xffffffff < obj <= 0xffffffffffffffff:
+                return self.buffer.write(struct.pack(">BQ", 0xcf, obj))
+            if -0x8000000000000000 <= obj < -0x80000000:
+                return self.buffer.write(struct.pack(">Bq", 0xd3, obj))
+            raise PackValueError("Integer value out of range")
+        if isinstance(obj, (Unicode, bytes)):
+            if isinstance(obj, Unicode):
+                obj = obj.encode(self.encoding, self.unicode_errors)
+            n = len(obj)
+            if n <= 0x1f:
+                self.buffer.write(struct.pack('B', 0xa0 + n))
+                return self.buffer.write(obj)
+            if n <= 0xffff:
+                self.buffer.write(struct.pack(">BH", 0xda, n))
+                return self.buffer.write(obj)
+            if n <= 0xffffffff:
+                self.buffer.write(struct.pack(">BI", 0xdb, n))
+                return self.buffer.write(obj)
+            raise PackValueError("String is too large")
+        if isinstance(obj, float):
+            if self.use_float:
+                return self.buffer.write(struct.pack(">Bf", 0xca, obj))
+            return self.buffer.write(struct.pack(">Bd", 0xcb, obj))
+        if isinstance(obj, list) or isinstance(obj, tuple):
+            n = len(obj)
+            self._fb_pack_array_header(n)
+            for i in xrange(n):
+                self._pack(obj[i], nest_limit - 1)
+            return
+        if isinstance(obj, dict):
+            return self._fb_pack_map_pairs(len(obj), dict_iteritems(obj),
+                                           nest_limit - 1)
+        if self._default is not None:
+            return self._pack(self._default(obj), nest_limit - 1)
+        raise TypeError("Cannot serialize %r" % obj)
+
+    def pack(self, obj):
+        self._pack(obj)
+        ret = self.buffer.getvalue()
+        if self.autoreset:
+            self.buffer = StringIO()
+        elif USING_STRINGBUILDER:
+            self.buffer = StringIO(ret)
+        return ret
+
+    def pack_map_pairs(self, pairs):
+        self._fb_pack_map_pairs(len(pairs), pairs)
+        ret = self.buffer.getvalue()
+        if self.autoreset:
+            self.buffer = StringIO()
+        elif USING_STRINGBUILDER:
+            self.buffer = StringIO(ret)
+        return ret
+
+    def pack_array_header(self, n):
+        self._fb_pack_array_header(n)
+        ret = self.buffer.getvalue()
+        if self.autoreset:
+            self.buffer = StringIO()
+        elif USING_STRINGBUILDER:
+            self.buffer = StringIO(ret)
+        return ret
+
+    def pack_map_header(self, n):
+        self._fb_pack_map_header(n)
+        ret = self.buffer.getvalue()
+        if self.autoreset:
+            self.buffer = StringIO()
+        elif USING_STRINGBUILDER:
+            self.buffer = StringIO(ret)
+        return ret
+
+    def _fb_pack_array_header(self, n):
+        if n <= 0x0f:
+            return self.buffer.write(struct.pack('B', 0x90 + n))
+        if n <= 0xffff:
+            return self.buffer.write(struct.pack(">BH", 0xdc, n))
+        if n <= 0xffffffff:
+            return self.buffer.write(struct.pack(">BI", 0xdd, n))
+        raise PackValueError("Array is too large")
+
+    def _fb_pack_map_header(self, n):
+        if n <= 0x0f:
+            return self.buffer.write(struct.pack('B', 0x80 + n))
+        if n <= 0xffff:
+            return self.buffer.write(struct.pack(">BH", 0xde, n))
+        if n <= 0xffffffff:
+            return self.buffer.write(struct.pack(">BI", 0xdf, n))
+        raise PackValueError("Dict is too large")
+
+    def _fb_pack_map_pairs(self, n, pairs, nest_limit=DEFAULT_RECURSE_LIMIT):
+        self._fb_pack_map_header(n)
+        for (k, v) in pairs:
+            self._pack(k, nest_limit - 1)
+            self._pack(v, nest_limit - 1)
+
+    def bytes(self):
+        return self.buffer.getvalue()
+
+    def reset(self):
+        self.buffer = StringIO()
diff --git a/setup.py b/setup.py
index ac3eeb5..d4808d6 100644
--- a/setup.py
+++ b/setup.py
@@ -8,6 +8,9 @@ from setuptools import setup, Extension
 
 from distutils.command.build_ext import build_ext
 
+class NoCython(Exception):
+    pass
+
 try:
     import Cython.Compiler.Main as cython_compiler
     have_cython = True
@@ -24,10 +27,7 @@ def ensure_source(src):
 
     if not os.path.exists(src):
         if not have_cython:
-            raise Exception("""\
-Cython is required for building extension from checkout.
-Install Cython >= 0.16 or install msgpack from PyPI.
-""")
+            raise NoCython
         cythonize(pyx)
     elif (os.path.exists(pyx) and
           os.stat(src).st_mtime < os.stat(pyx).st_mtime and
@@ -38,7 +38,14 @@ Install Cython >= 0.16 or install msgpack from PyPI.
 
 class BuildExt(build_ext):
     def build_extension(self, ext):
-        ext.sources = list(map(ensure_source, ext.sources))
+        try:
+            ext.sources = list(map(ensure_source, ext.sources))
+        except NoCython:
+            print("WARNING")
+            print("Cython is required for building extension from checkout.")
+            print("Install Cython >= 0.16 or install msgpack from PyPI.")
+            print("Falling back to pure Python implementation.")
+            return
         return build_ext.build_extension(self, ext)
 
 
diff --git a/test/test_sequnpack.py b/test/test_sequnpack.py
index fc1f712..9db14ca 100644
--- a/test/test_sequnpack.py
+++ b/test/test_sequnpack.py
@@ -7,6 +7,21 @@ from msgpack.exceptions import OutOfData
 from pytest import raises
 
 
+def test_partialdata():
+    unpacker = Unpacker()
+    unpacker.feed(b'\xa5')
+    with raises(StopIteration): next(iter(unpacker))
+    unpacker.feed(b'h')
+    with raises(StopIteration): next(iter(unpacker))
+    unpacker.feed(b'a')
+    with raises(StopIteration): next(iter(unpacker))
+    unpacker.feed(b'l')
+    with raises(StopIteration): next(iter(unpacker))
+    unpacker.feed(b'l')
+    with raises(StopIteration): next(iter(unpacker))
+    unpacker.feed(b'o')
+    assert next(iter(unpacker)) == b'hallo'
+
 def test_foobar():
     unpacker = Unpacker(read_size=3, use_list=1)
     unpacker.feed(b'foobar')