mirror of
https://github.com/jkingsman/Remote-Terminal-for-MeshCore.git
synced 2026-03-28 17:43:05 +01:00
57 lines
1.9 KiB
Python
57 lines
1.9 KiB
Python
"""
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Centralized helpers for MeshCore multi-byte path encoding.
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The path_len wire byte is packed as [hash_mode:2][hop_count:6]:
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- hash_size = (hash_mode) + 1 → 1, 2, or 3 bytes per hop
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- hop_count = lower 6 bits → 0–63 hops
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- wire bytes = hop_count × hash_size
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Mode 3 (hash_size=4) is reserved and rejected.
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"""
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def decode_path_byte(path_byte: int) -> tuple[int, int]:
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"""Decode a packed path byte into (hop_count, hash_size).
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Returns:
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(hop_count, hash_size) where hash_size is 1, 2, or 3.
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Raises:
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ValueError: If hash_mode is 3 (reserved).
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"""
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hash_mode = (path_byte >> 6) & 0x03
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if hash_mode == 3:
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raise ValueError(f"Reserved path hash mode 3 (path_byte=0x{path_byte:02X})")
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hop_count = path_byte & 0x3F
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hash_size = hash_mode + 1
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return hop_count, hash_size
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def path_wire_len(hop_count: int, hash_size: int) -> int:
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"""Wire byte length of path data."""
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return hop_count * hash_size
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def split_path_hex(path_hex: str, hop_count: int) -> list[str]:
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"""Split a hex path string into per-hop chunks using the known hop count.
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If hop_count is 0 or the hex length doesn't divide evenly, falls back
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to 2-char (1-byte) chunks for backward compatibility.
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"""
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if not path_hex or hop_count <= 0:
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return []
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chars_per_hop = len(path_hex) // hop_count
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if chars_per_hop < 2 or chars_per_hop % 2 != 0 or chars_per_hop * hop_count != len(path_hex):
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# Inconsistent — fall back to legacy 2-char split
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return [path_hex[i : i + 2] for i in range(0, len(path_hex), 2)]
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return [path_hex[i : i + chars_per_hop] for i in range(0, len(path_hex), chars_per_hop)]
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def first_hop_hex(path_hex: str, hop_count: int) -> str | None:
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"""Extract the first hop identifier from a path hex string.
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Returns None for empty/direct paths.
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"""
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hops = split_path_hex(path_hex, hop_count)
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return hops[0] if hops else None
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