105 lines
3.0 KiB
Python
105 lines
3.0 KiB
Python
import itertools
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import math
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from libp2p.exceptions import ParseError
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from libp2p.io.abc import Reader
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# Unsigned LEB128(varint codec)
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# Reference: https://github.com/ethereum/py-wasm/blob/master/wasm/parsers/leb128.py
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LOW_MASK = 2 ** 7 - 1
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HIGH_MASK = 2 ** 7
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# The maximum shift width for a 64 bit integer. We shouldn't have to decode
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# integers larger than this.
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SHIFT_64_BIT_MAX = int(math.ceil(64 / 7)) * 7
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def encode_uvarint(number: int) -> bytes:
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"""Pack `number` into varint bytes"""
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buf = b""
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while True:
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towrite = number & 0x7F
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number >>= 7
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if number:
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buf += bytes((towrite | 0x80,))
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else:
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buf += bytes((towrite,))
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break
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return buf
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async def decode_uvarint_from_stream(reader: Reader) -> int:
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"""
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https://en.wikipedia.org/wiki/LEB128
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"""
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res = 0
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for shift in itertools.count(0, 7):
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if shift > SHIFT_64_BIT_MAX:
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raise ParseError("TODO: better exception msg: Integer is too large...")
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byte = await reader.read(1)
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try:
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value = byte[0]
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except IndexError:
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raise ParseError(
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"Unexpected end of stream while parsing LEB128 encoded integer"
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)
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res += (value & LOW_MASK) << shift
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if not value & HIGH_MASK:
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break
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return res
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def encode_varint_prefixed(msg_bytes: bytes) -> bytes:
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varint_len = encode_uvarint(len(msg_bytes))
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return varint_len + msg_bytes
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async def read_varint_prefixed_bytes(reader: Reader) -> bytes:
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len_msg = await decode_uvarint_from_stream(reader)
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data = await reader.read(len_msg)
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if len(data) != len_msg:
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raise ValueError(
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f"failed to read enough bytes: len_msg={len_msg}, data={data!r}"
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)
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return data
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# Delimited read/write, used by multistream-select.
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# Reference: https://github.com/gogo/protobuf/blob/07eab6a8298cf32fac45cceaac59424f98421bbc/io/varint.go#L109-L126 # noqa: E501
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def encode_delim(msg: bytes) -> bytes:
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delimited_msg = msg + b"\n"
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return encode_varint_prefixed(delimited_msg)
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async def read_delim(reader: Reader) -> bytes:
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msg_bytes = await read_varint_prefixed_bytes(reader)
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# TODO: Investigate if it is possible to have empty `msg_bytes`
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if len(msg_bytes) != 0 and msg_bytes[-1:] != b"\n":
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raise ValueError(f'msg_bytes is not delimited by b"\\n": msg_bytes={msg_bytes}')
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return msg_bytes[:-1]
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SIZE_LEN_BYTES = 4
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# Fixed-prefixed read/write, used by "/plaintext/2.0.0".
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# Reference: https://github.com/libp2p/go-msgio/blob/d5bbf59d3c4240266b1d2e5df9dc993454c42011/num.go#L11-L33 # noqa: E501 # noqa: E501
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def encode_fixedint_prefixed(msg_bytes: bytes) -> bytes:
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len_prefix = len(msg_bytes).to_bytes(SIZE_LEN_BYTES, "big")
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return len_prefix + msg_bytes
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async def read_fixedint_prefixed(reader: Reader) -> bytes:
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len_bytes = await reader.read(SIZE_LEN_BYTES)
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len_int = int.from_bytes(len_bytes, "big")
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return await reader.read(len_int)
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