139 lines
4.7 KiB
Python
139 lines
4.7 KiB
Python
import struct
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from string import printable
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from collections import defaultdict
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from typing import Tuple, Iterable, Callable, Optional
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from lbry.wallet.server.db import DB_PREFIXES
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_OP_STRUCT = struct.Struct('>BLL')
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class RevertableOp:
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__slots__ = [
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'key',
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'value',
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]
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is_put = 0
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def __init__(self, key: bytes, value: bytes):
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self.key = key
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self.value = value
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@property
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def is_delete(self) -> bool:
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return not self.is_put
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def invert(self) -> 'RevertableOp':
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raise NotImplementedError()
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def pack(self) -> bytes:
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"""
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Serialize to bytes
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"""
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return struct.pack(
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f'>BLL{len(self.key)}s{len(self.value)}s', int(self.is_put), len(self.key), len(self.value), self.key,
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self.value
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)
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@classmethod
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def unpack(cls, packed: bytes) -> Tuple['RevertableOp', bytes]:
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"""
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Deserialize from bytes
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:param packed: bytes containing at least one packed revertable op
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:return: tuple of the deserialized op (a put or a delete) and the remaining serialized bytes
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"""
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is_put, key_len, val_len = _OP_STRUCT.unpack(packed[:9])
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key = packed[9:9 + key_len]
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value = packed[9 + key_len:9 + key_len + val_len]
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if is_put == 1:
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return RevertablePut(key, value), packed[9 + key_len + val_len:]
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return RevertableDelete(key, value), packed[9 + key_len + val_len:]
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def __eq__(self, other: 'RevertableOp') -> bool:
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return (self.is_put, self.key, self.value) == (other.is_put, other.key, other.value)
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def __repr__(self) -> str:
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return str(self)
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def __str__(self) -> str:
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from lbry.wallet.server.db.prefixes import auto_decode_item
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k, v = auto_decode_item(self.key, self.value)
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key = ''.join(c if c in printable else '.' for c in str(k))
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val = ''.join(c if c in printable else '.' for c in str(v))
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return f"{'PUT' if self.is_put else 'DELETE'} {DB_PREFIXES(self.key[:1]).name}: {key} | {val}"
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class RevertableDelete(RevertableOp):
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def invert(self):
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return RevertablePut(self.key, self.value)
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class RevertablePut(RevertableOp):
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is_put = True
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def invert(self):
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return RevertableDelete(self.key, self.value)
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class OpStackIntegrity(Exception):
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pass
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class RevertableOpStack:
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def __init__(self, get_fn: Callable[[bytes], Optional[bytes]]):
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self._get = get_fn
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self._items = defaultdict(list)
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def append(self, op: RevertableOp):
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inverted = op.invert()
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if self._items[op.key] and inverted == self._items[op.key][-1]:
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self._items[op.key].pop() # if the new op is the inverse of the last op, we can safely null both
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return
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elif self._items[op.key] and self._items[op.key][-1] == op: # duplicate of last op
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return # raise an error?
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stored_val = self._get(op.key)
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has_stored_val = stored_val is not None
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delete_stored_op = None if not has_stored_val else RevertableDelete(op.key, stored_val)
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will_delete_existing_stored = False if delete_stored_op is None else (delete_stored_op in self._items[op.key])
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if op.is_put and has_stored_val and not will_delete_existing_stored:
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raise OpStackIntegrity(
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f"db op tries to add on top of existing key without deleting first: {op}"
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)
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elif op.is_delete and has_stored_val and stored_val != op.value and not will_delete_existing_stored:
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# there is a value and we're not deleting it in this op
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# check that a delete for the stored value is in the stack
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raise OpStackIntegrity(f"delete {op}")
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elif op.is_delete and not has_stored_val:
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raise OpStackIntegrity(f"db op tries to delete nonexistent key: {op}")
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elif op.is_delete and stored_val != op.value:
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raise OpStackIntegrity(f"db op tries to delete with incorrect value: {op}")
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self._items[op.key].append(op)
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def extend(self, ops: Iterable[RevertableOp]):
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for op in ops:
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self.append(op)
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def clear(self):
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self._items.clear()
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def __len__(self):
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return sum(map(len, self._items.values()))
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def __iter__(self):
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for key, ops in self._items.items():
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for op in ops:
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yield op
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def __reversed__(self):
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for key, ops in self._items.items():
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for op in reversed(ops):
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yield op
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def get_undo_ops(self) -> bytes:
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return b''.join(op.invert().pack() for op in reversed(self))
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def apply_packed_undo_ops(self, packed: bytes):
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while packed:
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op, packed = RevertableOp.unpack(packed)
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self.append(op)
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