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#!/usr/bin/env python
#
# Copyright (c) 2008-2012 WiredTiger, Inc.
# All rights reserved.
#
# See the file LICENSE for redistribution information.
#
# WiredTiger fixed-size packing and unpacking functions, using the Python
# struct library.
import struct
def __wt2struct(fmt):
if not fmt:
return None, fmt
# Big endian with no alignment is the default
if fmt[0] in '@=<>!':
tfmt = fmt[0]
fmt = fmt[1:]
else:
tfmt = '>'
return tfmt, fmt.replace('r', 'Q')
def unpack(fmt, s):
tfmt, fmt = __wt2struct(fmt)
if not fmt:
return ()
result = ()
pfmt = tfmt
sizebytes = 0
for offset, f in enumerate(fmt):
if f.isdigit():
sizebytes += 1
# With a fixed size, everything is encoded as a string
if f in 'Su' and sizebytes > 0:
f = 's'
if f not in 'Su':
pfmt += f
sizebytes = 0
continue
# We've hit something that needs special handling, split any fixed-size
# values we've already passed
if len(pfmt) > 1:
size = struct.calcsize(pfmt)
result += struct.unpack_from(pfmt, s)
s = s[size:]
if f == 'S':
l = s.find('\0')
result += (s[:l],)
s = s[l+1:]
if f == 'u':
if offset == len(fmt) - 1:
result += (s,)
else:
l = struct.unpack_from(tfmt + 'l', s)[0]
s = s[struct.calcsize(tfmt + 'l'):]
result += (s[:l],)
s = s[l:]
pfmt = tfmt
sizebytes = 0
if len(pfmt) > 1:
result += struct.unpack(pfmt, s)
return result
def pack(fmt, *values):
pfmt, fmt = __wt2struct(fmt)
if not fmt:
return ''
i = sizebytes = 0
for offset, f in enumerate(fmt):
if f == 'S':
# Note: this code is being careful about embedded NUL characters
if sizebytes == 0:
l = values[i].find('\0') + 1
if not l:
l = len(values[i]) + 1
pfmt += str(l)
sizebytes = len(str(l))
f = 's'
elif f == 'u':
if sizebytes == 0 and offset != len(fmt) - 1:
l = len(values[i])
pfmt += 'l' + str(l)
values = values[:i] + (l,) + values[i:]
sizebytes = len(str(l))
f = 's'
pfmt += f
if f.isdigit():
sizebytes += 1
continue
if f != 's' and sizebytes > 0:
i += int(pfmt[-sizebytes:])
else:
i += 1
sizebytes = 0
return struct.pack(pfmt, *values)
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