Carlos Florêncio
101 lines
3.2 KiB
Python
Executable File
101 lines
3.2 KiB
Python
Executable File
#!/usr/bin/env python3
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"""Read one bounded UTF-8 regular file from an immutable Git commit."""
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import argparse
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import os
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from pathlib import PurePosixPath
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import re
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import subprocess
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import sys
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MAX_BYTES = 512 * 1024
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SHA_RE = re.compile(r"^[0-9a-f]{40}$")
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REGULAR_MODES = {"100644", "100755"}
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class ReadError(Exception):
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pass
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def git(repo: str, *args: str, text: bool = False) -> subprocess.CompletedProcess:
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env = {"PATH": os.environ.get("PATH", "/usr/bin:/bin"), "LC_ALL": "C"}
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return subprocess.run(
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["git", *args],
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cwd=repo,
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env=env,
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capture_output=True,
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text=text,
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check=False,
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)
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def validate_path(value: str) -> str:
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path = PurePosixPath(value)
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parts = value.split("/")
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if (
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not value
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or value.startswith(("/", ":"))
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or "\\" in value
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or "\x00" in value
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or any(part in {"", ".", ".."} for part in parts)
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or path.is_absolute()
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):
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raise ReadError("invalid repository-relative path")
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return value
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def read_blob(repo: str, head_sha: str, path: str) -> str:
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if not SHA_RE.fullmatch(head_sha):
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raise ReadError("head SHA must be 40 lowercase hexadecimal characters")
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path = validate_path(path)
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commit = git(repo, "cat-file", "-e", f"{head_sha}^{{commit}}")
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if commit.returncode != 0:
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raise ReadError("head SHA is not an available commit")
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listing = git(repo, "--literal-pathspecs", "ls-tree", "-z", head_sha, "--", path)
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records = [record for record in listing.stdout.split(b"\0") if record]
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if listing.returncode != 0 or len(records) != 1:
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raise ReadError("path is not a regular file at the requested commit")
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metadata, separator, matched_path = records[0].partition(b"\t")
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fields = metadata.split()
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if not separator or len(fields) != 3 or matched_path != path.encode("utf-8"):
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raise ReadError("path is not a regular file at the requested commit")
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mode, object_type, object_id = (field.decode("ascii") for field in fields)
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if mode not in REGULAR_MODES or object_type != "blob":
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raise ReadError("path is not a regular file at the requested commit")
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size_result = git(repo, "cat-file", "-s", object_id, text=True)
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if size_result.returncode != 0:
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raise ReadError("could not inspect file object")
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size = int(size_result.stdout.strip())
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if size > MAX_BYTES:
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raise ReadError(f"file exceeds {MAX_BYTES} bytes")
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content = git(repo, "cat-file", "blob", object_id)
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if content.returncode != 0:
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raise ReadError("could not read file object")
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try:
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return content.stdout.decode("utf-8")
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except UnicodeDecodeError as exc:
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raise ReadError("file must be UTF-8 text") from exc
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def main() -> int:
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parser = argparse.ArgumentParser()
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parser.add_argument("--repo", required=True)
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parser.add_argument("--head-sha", required=True)
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parser.add_argument("--path", required=True)
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args = parser.parse_args()
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try:
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sys.stdout.write(read_blob(args.repo, args.head_sha, args.path))
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except (OSError, ReadError, ValueError) as exc:
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print(f"PR file read failed: {exc}", file=sys.stderr)
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return 1
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return 0
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if __name__ == "__main__":
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raise SystemExit(main())
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