opensystemslab / struct.nim

Python-like 'struct' for Nim

struct.nim

Python-like 'struct' for Nim

This library is still under development, use it as yourown risk!

Format String

Byte Order

Character	Byte order
@	native
=	native
<	little-endian
>	big-endian
!	network (= big-endian)

Notes:

• Unlike Python -byte-order can specified once as first character, with this implementation, you can change byte-order anywhere and anytime you want

Format Characters:

integerintegerintegerinteger

Format	C Type	Python Type	Nim Type	Size (bytes)
x	pad byte	no value
b	char	string of length 1	char	1
?	_Bool	bool	bool	1
h	short	integer	int16	2
H	usigned short	integer	uint16	2
i	int	integer	int32	4
I	unsigned int	integer	uint32	4
q	long long	integer	int64	8
Q	unsigned long long	integer	uint64	8
f	float	float	float32	4
d	double	float	float64	8
s	char[]	string	string

Notes:

• Format character can has a number prefix, you can use "3?" instead of "???" for pack/unpack three bool value
• For string , number prefix is the length of value

Usage

# >>> from struct import *
import struct

# >>> pack('hhi', 1, 2, 3)
var output =  pack("hhi", 1, 2, 3)

# alternative way to pack
# output = pack("hhi", newStructInt(1), newStructInt(1), newStructInt(3))

# >>> unpack('hhi', '\x00\x01\x00\x02\x00\x00\x00\x03')
var result = unpack("hhi", output);
echo result[0].getShort
echo result[1].getShort
echo result[2].getInt

struct.nim's Issues

Unexpected Output

Sorry, it's me again.

nim> import struct
nim> var a = unpack(">3I", "Hello World ")
nim> a
@[1214606444, 1864390511, 1919706144] == type seq[StructNode]
nim> pack(">3I", a)
Horld  == type string

Also it would be a useful feature to pass a seq[int32] to pack.

undeclared identifier: 'expr'

for Nim 0.18.1 :

.nimble\pkgs\struct-0.1.1\struct.nim(479, 27) Error: undeclared identifier: 'expr'

calcsize not exported

useful function

Unexpected Output

>>> from struct import unpack
>>> unpack(">3I", b"Hello World ")
(1214606444, 1864390511, 1919706144)

nim> from struct import unpack
nim> unpack(">3I", "Hello World ")
@[(kind: StructInt, num: 1214606444), (kind: StructInt, num: 1214606444), (kind: StructInt, num: 1214606444)] == type seq[StructNode]

packing type 'byte' throws exception

Hi,

This code:

import struct
var packed_byte = pack("b", 5)

throws the following exception:

Traceback (most recent call last)
struct.nim(490)          test
struct.nim(438)          pack
struct.nim(326)          pack_char
system.nim(3535)         failedAssertImpl
system.nim(3527)         raiseAssert
system.nim(2637)         sysFatal
Error: unhandled exception: vars[ctx.offset].kind == StructChar  [AssertionError]