def unpack(fmt, s):
tfmt, fmt = __get_type(fmt)
if not fmt:
return ()
if tfmt != '.':
raise ValueError(
'Only variable-length encoding is currently supported')
result = []
for offset, havesize, size, f in __unpack_iter_fmt(fmt):
if f == 'x':
s = s[size:]
# Note: no value, don't increment i
elif f in 'SsUu':
if not havesize:
if f == 's':
pass
elif f == 'S':
size = s.find(x00)
elif f == 'u' and offset == len(fmt) - 1:
# A WT_ITEM with a NULL data field will be appear as None.
if s == None:
s = empty_pack
size = len(s)
else:
# Note: 'U' is used internally, and may be exposed to us.
# It indicates that the size is always stored unless there
# is a size in the format.
size, s = unpack_int(s)
if f in 'Ss':
result.append(_string_result(s[:size]))
if f == 'S' and not havesize:
size += 1
else:
result.append(s[:size])
s = s[size:]
elif f in 't':
# bit type, size is number of bits
result.append(_ord(s[0]))
s = s[1:]
elif f in 'Bb':
# byte type
for i in range(size):
v = _ord(s[0])
if f != 'B':
v -= 0x80
result.append(v)
s = s[1:]
else:
# integral type
for j in range(size):
v, s = unpack_int(s)
result.append(v)
return result
def unpack_int(b):
marker = _ord(b[0])
if marker < NEG_2BYTE_MARKER:
sz = 8 - getbits(marker, 4)
return ((-1 << (sz << 3)) | get_int(b[1:], sz), b[sz+1:])
elif marker < NEG_1BYTE_MARKER:
return (NEG_2BYTE_MIN + ((getbits(marker, 5) << 8) | _ord(b[1])), b[2:])
elif marker < POS_1BYTE_MARKER:
return (NEG_1BYTE_MIN + getbits(marker, 6), b[1:])
elif marker < POS_2BYTE_MARKER:
return (getbits(marker, 6), b[1:])
elif marker < POS_MULTI_MARKER:
return (POS_1BYTE_MAX + 1 +
((getbits(marker, 5) << 8) | _ord(b[1])), b[2:])
else:
sz = getbits(marker, 4)
return (POS_2BYTE_MAX + 1 + get_int(b[1:], sz), b[sz+1:])
def get_int(b, size):
r = 0
for i in range(size):
r = (r << 8) | _ord(b[i])
return r