Janus
7 years ago
committed by
ThomasV
4 changed files with 164 additions and 153 deletions
@ -0,0 +1,155 @@
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import json |
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import os |
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from typing import Callable, Tuple |
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from collections import OrderedDict |
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def _eval_length_term(x, ma: dict) -> int: |
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""" |
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Evaluate a term of the simple language used |
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to specify lightning message field lengths. |
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If `x` is an integer, it is returned as is, |
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otherwise it is treated as a variable and |
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looked up in `ma`. |
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If the value in `ma` was no integer, it is |
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assumed big-endian bytes and decoded. |
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Returns evaluated result as int |
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""" |
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try: |
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x = int(x) |
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except ValueError: |
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x = ma[x] |
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try: |
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x = int(x) |
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except ValueError: |
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x = int.from_bytes(x, byteorder='big') |
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return x |
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def _eval_exp_with_ctx(exp, ctx: dict) -> int: |
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""" |
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Evaluate simple mathematical expression given |
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in `exp` with context (variables assigned) |
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from the dict `ctx`. |
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Returns evaluated result as int |
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""" |
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exp = str(exp) |
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if "*" in exp: |
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assert "+" not in exp |
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result = 1 |
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for term in exp.split("*"): |
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result *= _eval_length_term(term, ctx) |
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return result |
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return sum(_eval_length_term(x, ctx) for x in exp.split("+")) |
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def _make_handler(k: str, v: dict) -> Callable[[bytes], Tuple[str, dict]]: |
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""" |
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Generate a message handler function (taking bytes) |
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for message type `k` with specification `v` |
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Check lib/lightning.json, `k` could be 'init', |
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and `v` could be |
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{ type: 16, payload: { 'gflen': ..., ... }, ... } |
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Returns function taking bytes |
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""" |
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def handler(data: bytes) -> Tuple[str, dict]: |
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nonlocal k, v |
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ma = {} |
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pos = 0 |
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for fieldname in v["payload"]: |
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poslenMap = v["payload"][fieldname] |
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if "feature" in poslenMap and pos == len(data): |
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continue |
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assert pos == _eval_exp_with_ctx(poslenMap["position"], ma) |
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length = poslenMap["length"] |
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length = _eval_exp_with_ctx(length, ma) |
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ma[fieldname] = data[pos:pos+length] |
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pos += length |
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assert pos == len(data), (k, pos, len(data)) |
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return k, ma |
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return handler |
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class LNSerializer: |
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def __init__(self): |
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message_types = {} |
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path = os.path.join(os.path.dirname(__file__), 'lightning.json') |
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with open(path) as f: |
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structured = json.loads(f.read(), object_pairs_hook=OrderedDict) |
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for k in structured: |
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v = structured[k] |
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# these message types are skipped since their types collide |
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# (for example with pong, which also uses type=19) |
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# we don't need them yet |
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if k in ["final_incorrect_cltv_expiry", "final_incorrect_htlc_amount"]: |
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continue |
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if len(v["payload"]) == 0: |
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continue |
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try: |
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num = int(v["type"]) |
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except ValueError: |
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#print("skipping", k) |
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continue |
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byts = num.to_bytes(2, 'big') |
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assert byts not in message_types, (byts, message_types[byts].__name__, k) |
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names = [x.__name__ for x in message_types.values()] |
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assert k + "_handler" not in names, (k, names) |
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message_types[byts] = _make_handler(k, v) |
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message_types[byts].__name__ = k + "_handler" |
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assert message_types[b"\x00\x10"].__name__ == "init_handler" |
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self.structured = structured |
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self.message_types = message_types |
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def encode_msg(self, msg_type : str, **kwargs) -> bytes: |
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""" |
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Encode kwargs into a Lightning message (bytes) |
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of the type given in the msg_type string |
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""" |
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typ = self.structured[msg_type] |
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data = int(typ["type"]).to_bytes(2, 'big') |
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lengths = {} |
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for k in typ["payload"]: |
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poslenMap = typ["payload"][k] |
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if "feature" in poslenMap: continue |
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leng = _eval_exp_with_ctx(poslenMap["length"], lengths) |
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try: |
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clone = dict(lengths) |
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clone.update(kwargs) |
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leng = _eval_exp_with_ctx(poslenMap["length"], clone) |
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except KeyError: |
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pass |
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try: |
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param = kwargs[k] |
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except KeyError: |
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param = 0 |
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try: |
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if not isinstance(param, bytes): |
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assert isinstance(param, int), "field {} is neither bytes or int".format(k) |
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param = param.to_bytes(leng, 'big') |
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except ValueError: |
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raise Exception("{} does not fit in {} bytes".format(k, leng)) |
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lengths[k] = len(param) |
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if lengths[k] != leng: |
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raise Exception("field {} is {} bytes long, should be {} bytes long".format(k, lengths[k], leng)) |
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data += param |
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return data |
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def decode_msg(self, data : bytes) -> Tuple[str, dict]: |
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""" |
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Decode Lightning message by reading the first |
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two bytes to determine message type. |
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Returns message type string and parsed message contents dict |
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""" |
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typ = data[:2] |
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k, parsed = self.message_types[typ](data[2:]) |
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return k, parsed |
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_inst = LNSerializer() |
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encode_msg = _inst.encode_msg |
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decode_msg = _inst.decode_msg |
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