def test_unpack_uint32():
a = 12
b = 2**31 + 1
buf = struct.pack('II', a, b)
assert unpack_uint32(buf, 0) == a
assert unpack_uint32(buf, 4) == b
buf = b'abc'
pytest.raises(IndexError, "unpack_uint32(buf, 0)")
def _load_buffer_single_segment(f):
# fast path for the single-segment case. In this scenario, we don't
# even need to compute the padding as we know that we read exactly 4+4
# bytes
buf = f.read(4)
#
# The cost of the len(buf) checks is ~7-8% on CPython, but I don't know
# how to avoid it. However, it's negligible on PyPy
if len(buf) < 4:
raise ValueError("Unexpected EOF when reading the header")
message_size = unpack_uint32(buf, 0)
message_lenght = message_size * 8
buf = f.read(message_lenght)
if len(buf) < message_lenght:
raise ValueError("Unexpected EOF: expected %d bytes, got only %s. "
"Segment size: %s" % (message_lenght, len(buf), message_size))
return Segment(buf)
def _load_message(f):
# read the total number of segments
buf = f.read(4)
if len(buf) < 4:
raise EOFError("No message to load")
n = unpack_uint32(buf, 0) + 1
if n == 1:
capnp_buf = _load_buffer_single_segment(f) # fast path
else:
capnp_buf = _load_buffer_multiple_segments(f, n) # slow path
#
# from the capnproto docs:
#
# The first word of the first segment of the message is always a
# pointer pointing to the message's root struct.
#
# Thus, the root of the message is equivalent to a struct with
# data_size==0 and ptrs_size==1
return struct_from_buffer(Struct, capnp_buf, 0, data_size=0, ptrs_size=1)