"""Provides functions for decoding WASM modules and bytecode."""

from __future__ import print_function, absolute_import, division, unicode_literals

from collections import namedtuple

from .modtypes import ModuleHeader, Section, SEC_UNK, SEC_NAME, NameSubSection

from .opcodes import OPCODE_MAP

from .compat import byte2int

Instruction = namedtuple('Instruction', 'op imm len')

ModuleFragment = namedtuple('ModuleFragment', 'type data')

def decode_bytecode(bytecode):

"""Decodes raw bytecode, yielding `Instruction`s."""

bytecode_wnd = memoryview(bytecode)

while bytecode_wnd:

opcode_id = byte2int(bytecode_wnd[0])

opcode = OPCODE_MAP[opcode_id]

if opcode.imm_struct is not None:

offs, imm, _ = opcode.imm_struct.from_raw(None, bytecode_wnd[1:])

else:

imm = None

offs = 0

insn_len = 1 + offs

yield Instruction(opcode, imm, insn_len)

bytecode_wnd = bytecode_wnd[insn_len:]

def decode_module(module, decode_name_subsections=False):

"""Decodes raw WASM modules, yielding `ModuleFragment`s."""

module_wnd = memoryview(module)

# Read & yield module header.

hdr = ModuleHeader()

hdr_len, hdr_data, _ = hdr.from_raw(None, module_wnd)

yield ModuleFragment(hdr, hdr_data)

module_wnd = module_wnd[hdr_len:]

# Read & yield sections.

while module_wnd:

sec = Section()

sec_len, sec_data, _ = sec.from_raw(None, module_wnd)

# If requested, decode name subsections when encountered.

if (

decode_name_subsections and

sec_data.id == SEC_UNK and

sec_data.name == SEC_NAME

):

sec_wnd = sec_data.payload

while sec_wnd:

subsec = NameSubSection()

subsec_len, subsec_data, _ = subsec.from_raw(None, sec_wnd)

yield ModuleFragment(subsec, subsec_data)

sec_wnd = sec_wnd[subsec_len:]

else:

yield ModuleFragment(sec, sec_data)

module_wnd = module_wnd[sec_len:]