I really love the Python construct module's declarative syntax for defining bi-directional (binary|text) parser / builders.
I've recently started focusing on golang and was wondering if anyone has seen (or might be the esteemed author of) a similar library for golang.
If you've never used the construct module, you basically build a declarative tree of Python objects that you can feed Python object trees and get binary blobs out, or parse binary blobs into Python object trees.
A simple example from the construct webpage:
>>> PascalString2 = ExprAdapter(PascalString,
... encoder = lambda obj, ctx: Container(length = len(obj), data = obj),
... decoder = lambda obj, ctx: obj.data
... )
>>> PascalString2.parse("\x05hello")
'hello'
>>> PascalString2.build("i'm a long string")
"\x11i'm a long string"
A slightly more complex example from the source that shows a hard drive MBR parser.
mbr = Struct("mbr",
HexDumpAdapter(Bytes("bootloader_code", 446)),
Array(4,
Struct("partitions",
Enum(Byte("state"),
INACTIVE = 0x00,
ACTIVE = 0x80,
),
BitStruct("beginning",
Octet("head"),
Bits("sect", 6),
Bits("cyl", 10),
),
Enum(UBInt8("type"),
Nothing = 0x00,
FAT12 = 0x01,
XENIX_ROOT = 0x02,
XENIX_USR = 0x03,
FAT16_old = 0x04,
Extended_DOS = 0x05,
FAT16 = 0x06,
FAT32 = 0x0b,
FAT32_LBA = 0x0c,
NTFS = 0x07,
LINUX_SWAP = 0x82,
LINUX_NATIVE = 0x83,
_default_ = Pass,
),
BitStruct("ending",
Octet("head"),
Bits("sect", 6),
Bits("cyl", 10),
),
UBInt32("sector_offset"), # offset from MBR in sectors
UBInt32("size"), # in sectors
)
),
Const("signature", b"\x55\xAA"),
)
There's a TCP/IP stack example that really shows how powerful the construct model is, with the ability to have bite-sized blocks of definitions that you combine into a single parser/generator.
I know there are PEG / EBNF parser generators, but I was hoping for something a little prettier to look at.
This isn't the same as Python's Construct package, but there is a version of Yacc for Go:
Yacc's grammar is similar to EBNF, so it may not meet your criteria, but it's widely used and understood, so I think it's worth mentioning.