109 lines
3.8 KiB
Python
109 lines
3.8 KiB
Python
import shlex
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import subprocess
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from typing import Callable, Dict, List, NamedTuple, Optional, Sequence
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import bashlex # type: ignore
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# a function that takes a shell command and the environment, and returns the result
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EnvironmentExecutor = Callable[[str, Dict[str, str]], str]
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def local_environment_executor(command: str, env: Dict[str, str]) -> str:
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return subprocess.check_output(shlex.split(command), env=env, universal_newlines=True)
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class NodeExecutionContext(NamedTuple):
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environment: Dict[str, str]
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input: str
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executor: EnvironmentExecutor
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def evaluate(value: str, environment: Dict[str, str], executor: Optional[EnvironmentExecutor] = None) -> str:
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if not value:
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# empty string evaluates to empty string
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# (but trips up bashlex)
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return ''
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command_node = bashlex.parsesingle(value)
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if len(command_node.parts) != 1:
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raise ValueError(f'"{value}" has too many parts')
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value_word_node = command_node.parts[0]
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return evaluate_node(
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value_word_node,
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context=NodeExecutionContext(environment=environment, input=value, executor=executor or local_environment_executor)
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)
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def evaluate_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
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if node.kind == 'word':
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return evaluate_word_node(node, context=context)
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elif node.kind == 'commandsubstitution':
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return evaluate_command_node(node.command, context=context)
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elif node.kind == 'parameter':
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return evaluate_parameter_node(node, context=context)
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else:
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raise ValueError(f'Unsupported bash construct: "{node.kind}"')
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def evaluate_word_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
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word_start = node.pos[0]
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word_end = node.pos[1]
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word_string = context.input[word_start:word_end]
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letters = list(word_string)
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for part in node.parts:
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part_start = part.pos[0] - word_start
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part_end = part.pos[1] - word_start
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# Set all the characters in the part to None
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for i in range(part_start, part_end):
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letters[i] = ''
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letters[part_start] = evaluate_node(part, context=context)
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# remove the None letters and concat
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value = ''.join(letters)
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# apply bash-like quotes/whitespace treatment
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return ' '.join(word.strip() for word in shlex.split(value))
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def evaluate_command_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
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if any(n.kind == 'operator' for n in node.parts):
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return evaluate_nodes_as_compound_command(node.parts, context=context)
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else:
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return evaluate_nodes_as_simple_command(node.parts, context=context)
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def evaluate_nodes_as_compound_command(nodes: Sequence[bashlex.ast.node], context: NodeExecutionContext) -> str:
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# bashlex doesn't support any operators besides ';' inside command
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# substitutions, so we only need to handle that case. We do so assuming
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# that `set -o errexit` is on, because it's easier to code!
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result = ''
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for node in nodes:
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if node.kind == 'command':
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result += evaluate_command_node(node, context=context)
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elif node.kind == 'operator':
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if node.op == ';':
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pass
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else:
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raise ValueError(f'Unsupported bash operator: "{node.op}"')
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else:
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raise ValueError(f'Unsupported bash node in compound command: "{node.kind}"')
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return result
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def evaluate_nodes_as_simple_command(nodes: List[bashlex.ast.node], context: NodeExecutionContext):
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words = [evaluate_node(part, context=context) for part in nodes]
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command = ' '.join(words)
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return context.executor(command, context.environment)
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def evaluate_parameter_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
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return context.environment.get(node.value, '')
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