438 lines
15 KiB
Python
Executable File
438 lines
15 KiB
Python
Executable File
#!/usr/bin/env python3
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"""Use the private Atlas Forgejo API through a least-authority PR boundary."""
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from __future__ import annotations
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import argparse
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import json
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import os
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import re
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import sys
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import urllib.error
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import urllib.parse
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import urllib.request
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from collections.abc import Callable
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from pathlib import Path
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from gitea_api_policy import (
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PolicyError,
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_draft_title,
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_validate_body,
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_validate_pr_number,
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_validate_pr_number_segment,
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_validate_query,
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_validate_ref,
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_validate_repo,
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_validate_sha,
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)
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CANONICAL_BASE_URL = "https://scm.bstein.dev"
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ALLOWED_OWNER = "atlas"
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DEFAULT_TOKEN_FILE = Path("/runtime-access/gitea-token")
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CREATE_PATH_RE = re.compile(r"/api/v1/repos/atlas/([^/]+)/pulls\Z")
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MAX_ERROR_BYTES = 8192
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MAX_RESPONSE_BYTES = 2 * 1024 * 1024
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MAX_API_TARGET_LENGTH = 768
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MAX_API_PATH_LENGTH = 512
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RAW_API_TARGET_RE = re.compile(r"[A-Za-z0-9/_.?&=-]+\Z")
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class RejectRedirectHandler(urllib.request.HTTPRedirectHandler):
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"""Reject every redirect before urllib can copy authentication headers."""
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def redirect_request(self, req, fp, code, msg, headers, newurl):
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raise PolicyError("Forgejo redirects are not allowed")
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_SAFE_OPENER = urllib.request.build_opener(RejectRedirectHandler())
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def _safe_urlopen(request: urllib.request.Request, timeout: int):
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"""Open one request using a handler that never follows redirects."""
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return _SAFE_OPENER.open(request, timeout=timeout)
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def read_token(path: Path = DEFAULT_TOKEN_FILE) -> str:
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"""Read the token from the pod-lifetime Vault projection."""
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token = path.read_text(encoding="utf-8").strip()
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if not token:
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raise ValueError(f"runtime credential is empty: {path}")
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return token
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def configured_base_url() -> str:
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"""Reject attempts to redirect credentials away from the canonical origin."""
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configured = os.environ.get("GITEA_BASE_URL", CANONICAL_BASE_URL)
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if configured != CANONICAL_BASE_URL:
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raise PolicyError("Forgejo origin is fixed to the private Atlas SCM service")
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return configured
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def _split_api_path(path: str) -> urllib.parse.SplitResult:
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if not isinstance(path, str) or len(path) > MAX_API_TARGET_LENGTH:
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raise PolicyError("API target exceeds the safe size limit")
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if (
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not path.isascii()
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or any(ord(character) < 32 or ord(character) == 127 for character in path)
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or "\\" in path
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or not RAW_API_TARGET_RE.fullmatch(path)
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):
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raise PolicyError("API target contains non-canonical raw characters")
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target = urllib.parse.urlsplit(path)
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canonical = urllib.parse.urlunsplit(("", "", target.path, target.query, ""))
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if canonical != path:
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raise PolicyError("API target is not in exact canonical form")
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if target.scheme or target.netloc or target.fragment:
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raise PolicyError("API path must be relative to the Atlas SCM origin")
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if not target.path.startswith("/api/v1/"):
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raise PolicyError("API path must start with /api/v1/")
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if len(target.path) > MAX_API_PATH_LENGTH:
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raise PolicyError("API path exceeds the safe size limit")
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segments = target.path.split("/")
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if "//" in target.path or any(segment in {".", ".."} for segment in segments):
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raise PolicyError("encoded or non-canonical API paths are not allowed")
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return target
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def _authorize_read(target: urllib.parse.SplitResult) -> str:
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"""Allow only repository, PR, branch, commit, and status metadata reads."""
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prefix = "/api/v1/repos/atlas/"
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remainder = target.path.removeprefix(prefix)
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if remainder == target.path:
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raise PolicyError("reads are limited to explicit Atlas repository metadata")
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repo, separator, suffix = remainder.partition("/")
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_validate_repo(repo)
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if not separator:
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_validate_query(target, set())
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return "repository"
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if suffix == "pulls":
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_validate_query(target, {"page", "limit", "state"})
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return "pull-list"
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content_match = re.fullmatch(r"pulls/([^/]+)\.(?:patch|diff)", suffix)
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if content_match:
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_validate_pr_number_segment(content_match.group(1))
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raise PolicyError("repository API route is outside the metadata read allowlist")
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pull_match = re.fullmatch(r"pulls/([^/]+)", suffix)
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if pull_match:
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_validate_pr_number_segment(pull_match.group(1))
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_validate_query(target, set())
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return "pull"
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evidence_match = re.fullmatch(r"pulls/([^/]+)/(?:commits|files)", suffix)
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if evidence_match:
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_validate_pr_number_segment(evidence_match.group(1))
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_validate_query(target, {"page", "limit"})
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return "pull-evidence"
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if suffix == "branches":
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_validate_query(target, {"page", "limit"})
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return "branch-list"
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branch_match = re.fullmatch(r"branches/([^/]+)", suffix)
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if branch_match:
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_validate_ref(branch_match.group(1), "branch")
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_validate_query(target, set())
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return "branch"
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if suffix == "commits":
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_validate_query(target, {"page", "limit"})
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return "commit-list"
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if re.fullmatch(r"git/commits/[0-9a-fA-F]{40}", suffix):
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_validate_query(target, set())
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return "commit"
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if re.fullmatch(
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r"(?:commits/[0-9a-fA-F]{40}/status|commits/[0-9a-fA-F]{40}/statuses|statuses/[0-9a-fA-F]{40})",
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suffix,
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):
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_validate_query(target, {"page", "limit"})
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return "status"
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raise PolicyError("repository API route is outside the metadata read allowlist")
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def api_url(base_url: str, path: str) -> str:
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"""Return a canonical same-origin URL without forwarding credentials."""
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if base_url != CANONICAL_BASE_URL:
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raise PolicyError("Forgejo origin is fixed to the private Atlas SCM service")
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target = _split_api_path(path)
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return urllib.parse.urlunsplit(
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("https", "scm.bstein.dev", target.path, target.query, "")
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)
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def authorize_request(method: str, path: str, data: object | None) -> str:
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"""Validate one request and return its bounded operation name."""
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normalized_method = method.upper()
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target = _split_api_path(path)
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if normalized_method == "GET":
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if data is not None:
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raise PolicyError("read operations cannot include a request body")
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return _authorize_read(target)
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if target.query:
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raise PolicyError("mutating operations cannot include query parameters")
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if normalized_method != "POST":
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raise PolicyError("only read and create-draft operations are available")
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match = CREATE_PATH_RE.fullmatch(target.path)
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if not match:
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raise PolicyError("POST is limited to creating an Atlas draft pull request")
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_validate_repo(match.group(1))
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if not isinstance(data, dict) or set(data) != {"base", "body", "head", "title"}:
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raise PolicyError("draft creation accepts only base, body, head, and title")
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_validate_ref(data["base"], "base")
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_validate_ref(data["head"], "head")
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if data["title"] != _draft_title(data["title"]):
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raise PolicyError("new pull requests must use the Gitea draft-title prefix")
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_validate_body(data["body"])
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return "create-draft"
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def build_request(
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method: str,
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path: str,
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*,
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base_url: str,
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token: str,
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data: object | None = None,
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) -> urllib.request.Request:
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"""Build an authorized request without putting the token in its URL or body."""
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authorize_request(method, path, data)
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if method.upper() == "POST":
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assert isinstance(data, dict)
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_draft_title(data["title"], forbidden=(token,))
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_validate_body(data["body"], forbidden=(token,))
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payload = None
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if data is not None:
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payload = json.dumps(data, separators=(",", ":")).encode("utf-8")
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return urllib.request.Request(
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api_url(base_url, path),
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data=payload,
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method=method.upper(),
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headers={
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"Accept": "application/json",
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"Authorization": f"token {token}",
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"Content-Type": "application/json",
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"User-Agent": "hermes-atlas-pr-client/2",
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},
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)
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def redact_bytes(value: bytes, token: str) -> bytes:
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"""Remove exact runtime-token and authorization-header values from output."""
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redacted = value.replace(token.encode("utf-8"), b"[REDACTED]")
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return re.sub(
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rb"(?i)(authorization\s*[:=]\s*)(?:token|bearer)?\s*[^\s,;\"}]+",
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rb"\1[REDACTED]",
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redacted,
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)
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def _request(
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method: str,
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path: str,
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data: object | None,
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*,
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token: str,
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opener: Callable[..., object] = _safe_urlopen,
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) -> bytes:
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request = build_request(
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method, path, base_url=configured_base_url(), token=token, data=data
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)
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with opener(request, timeout=30) as response: # type: ignore[attr-defined]
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body = response.read(MAX_RESPONSE_BYTES + 1) # type: ignore[attr-defined]
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if len(body) > MAX_RESPONSE_BYTES:
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raise PolicyError("Forgejo response exceeds the safe size limit")
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return redact_bytes(body, token)
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def read(
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path: str, *, token: str, opener: Callable[..., object] = _safe_urlopen
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) -> bytes:
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"""Read one explicitly allowed Atlas repository metadata resource."""
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return _request("GET", path, None, token=token, opener=opener)
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def _nested(document: dict[str, object], *keys: str) -> object:
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value: object = document
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for key in keys:
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if not isinstance(value, dict) or key not in value:
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raise PolicyError("Forgejo omitted required pull-request evidence")
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value = value[key]
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return value
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def _require_create_response(
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value: bytes,
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*,
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repo: str,
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base: str,
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head: str,
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head_sha: str,
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title: str,
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body: str,
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) -> dict[str, object]:
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"""Require exact server evidence for the intended open draft handoff."""
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try:
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document = json.loads(value)
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except json.JSONDecodeError as exc:
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raise PolicyError("Forgejo returned invalid pull-request metadata") from exc
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if not isinstance(document, dict):
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raise PolicyError("Forgejo returned invalid pull-request metadata")
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number = _validate_pr_number(document.get("number"))
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full_name = f"{ALLOWED_OWNER}/{repo}"
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expected_html = f"{CANONICAL_BASE_URL}/{full_name}/pulls/{number}"
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checks = (
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document.get("state") == "open",
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document.get("draft") is True,
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document.get("merged") is False,
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document.get("html_url") == expected_html,
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document.get("url") == expected_html,
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document.get("title") == title,
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document.get("body") == body,
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_nested(document, "base", "ref") == base,
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_nested(document, "base", "repo", "full_name") == full_name,
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_nested(document, "head", "ref") == head,
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_nested(document, "head", "sha") == head_sha,
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_nested(document, "head", "repo", "full_name") == full_name,
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)
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if not all(checks):
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raise PolicyError("Forgejo did not confirm the exact draft pull-request state")
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return document
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def create_draft(
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repo: str,
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*,
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base: str,
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head: str,
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head_sha: str,
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title: str,
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body: str,
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token: str,
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opener: Callable[..., object] = _safe_urlopen,
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) -> bytes:
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"""Create and verify a same-repository draft pull request for human review."""
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repo = _validate_repo(repo)
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base = _validate_ref(base, "base")
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head = _validate_ref(head, "head")
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head_sha = _validate_sha(head_sha)
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title = _draft_title(title, forbidden=(token,))
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body = _validate_body(body, forbidden=(token,))
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data = {"base": base, "body": body, "head": head, "title": title}
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result = _request(
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"POST",
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f"/api/v1/repos/{ALLOWED_OWNER}/{repo}/pulls",
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data,
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token=token,
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opener=opener,
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)
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_require_create_response(
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result,
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repo=repo,
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base=base,
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head=head,
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head_sha=head_sha,
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title=title,
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body=body,
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)
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return result
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def parse_args(argv: list[str] | None = None) -> argparse.Namespace:
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"""Parse the intentionally narrow read and create-draft operations."""
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parser = argparse.ArgumentParser(description=__doc__)
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parser.add_argument(
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"--dry-run",
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action="store_true",
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help="validate and describe the request without reading a token or using the network",
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)
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subparsers = parser.add_subparsers(dest="operation", required=True)
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read_parser = subparsers.add_parser("read", help="read allowed Atlas metadata")
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read_parser.add_argument("path")
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create_parser = subparsers.add_parser(
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"create-draft", help="create a same-repository draft pull request"
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)
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create_parser.add_argument("repo")
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create_parser.add_argument("--base", required=True)
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create_parser.add_argument("--head", required=True)
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create_parser.add_argument("--head-sha", required=True)
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create_parser.add_argument("--title", required=True)
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create_parser.add_argument("--body", default="")
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return parser.parse_args(argv)
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def _operation(args: argparse.Namespace) -> tuple[str, str, object | None]:
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if args.operation == "read":
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return "GET", args.path, None
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repo = _validate_repo(args.repo)
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_validate_sha(args.head_sha)
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data = {
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"base": _validate_ref(args.base, "base"),
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"body": _validate_body(args.body),
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"head": _validate_ref(args.head, "head"),
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"title": _draft_title(args.title),
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}
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return "POST", f"/api/v1/repos/{ALLOWED_OWNER}/{repo}/pulls", data
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def _write_body(body: bytes) -> None:
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if body:
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sys.stdout.buffer.write(body)
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if not body.endswith(b"\n"):
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sys.stdout.buffer.write(b"\n")
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def main(argv: list[str] | None = None) -> int:
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"""Validate, optionally describe, and execute one safe Forgejo operation."""
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token = ""
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try:
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args = parse_args(argv)
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method, path, data = _operation(args)
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operation = authorize_request(method, path, data)
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if args.dry_run:
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print(
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json.dumps(
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{
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"dry_run": True,
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"host": "scm.bstein.dev",
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"operation": operation,
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"owner": ALLOWED_OWNER,
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"path": path,
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"request_fields": sorted(data)
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if isinstance(data, dict)
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else [],
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},
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sort_keys=True,
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)
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)
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return 0
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token = read_token()
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if args.operation == "read":
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body = read(path, token=token)
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else:
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assert isinstance(data, dict)
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body = create_draft(
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args.repo,
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base=str(data["base"]),
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head=str(data["head"]),
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head_sha=args.head_sha,
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title=str(data["title"]),
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body=str(data["body"]),
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token=token,
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)
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_write_body(body)
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return 0
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except urllib.error.HTTPError as exc:
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body = redact_bytes(exc.read(MAX_ERROR_BYTES), token) if token else b""
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print(f"Forgejo request failed with HTTP {exc.code}", file=sys.stderr)
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if body:
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sys.stderr.buffer.write(body)
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if not body.endswith(b"\n"):
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sys.stderr.buffer.write(b"\n")
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return 1
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except (OSError, PolicyError, ValueError, json.JSONDecodeError):
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print(
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"Forgejo request rejected or unavailable; no credential was disclosed",
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file=sys.stderr,
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)
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return 1
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if __name__ == "__main__":
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raise SystemExit(main())
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