action.py

#!/usr/bin/env python

# Copyright 2022 The Sigstore Authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# action.py: run sigstore-python
#
# most state is passed in as environment variables; the only argument
# is a whitespace-separated list of inputs

import os
import shlex
import string
import subprocess
import sys
from glob import glob
from pathlib import Path

import requests

_HERE = Path(__file__).parent.resolve()
_TEMPLATES = _HERE / "templates"

_summary_path = os.getenv("GITHUB_STEP_SUMMARY")
assert _summary_path is not None
_SUMMARY = Path(_summary_path).open("a")

_RENDER_SUMMARY = os.getenv("GHA_SIGSTORE_PYTHON_SUMMARY", "true") == "true"
_DEBUG = (
    os.getenv("GHA_SIGSTORE_PYTHON_INTERNAL_BE_CAREFUL_DEBUG", "false") != "false"
    or os.getenv("ACTIONS_STEP_DEBUG", "false") == "true"
)

_RELEASE_SIGNING_ARTIFACTS = (
    os.getenv("GHA_SIGSTORE_PYTHON_RELEASE_SIGNING_ARTIFACTS", "true") == "true"
    and os.getenv("GITHUB_EVENT_NAME") == "release"
)


def _template(name):
    path = _TEMPLATES / f"{name}.md"
    return string.Template(path.read_text())


def _summary(msg):
    if _RENDER_SUMMARY:
        print(msg, file=_SUMMARY)


def _debug(msg):
    if _DEBUG:
        print(f"\033[93mDEBUG: {msg}\033[0m", file=sys.stderr)


def _log(msg):
    print(msg, file=sys.stderr)


def _download_ref_asset(ext):
    repo = os.getenv("GITHUB_REPOSITORY")
    ref = os.getenv("GITHUB_REF")

    # NOTE: Branch names often have `/` in them (e.g. `feat/some-name`),
    # which would break the artifact path we construct below.
    # We "fix" these by lossily replacing all `/` with `-`.
    ref_name_normalized = os.getenv("GITHUB_REF_NAME").replace("/", "-")

    artifact = Path(f"/tmp/{ref_name_normalized}.{ext}")

    # GitHub supports /:org/:repo/archive/:ref<.tar.gz|.zip>.
    r = requests.get(f"https://github.com/{repo}/archive/{ref}.{ext}", stream=True)
    r.raise_for_status()
    with artifact.open("wb") as io:
        for chunk in r.iter_content(chunk_size=None):
            io.write(chunk)

    return str(artifact)


def _sigstore_sign(global_args, sign_args):
    return [sys.executable, "-m", "sigstore", *global_args, "sign", *sign_args]


def _sigstore_verify(global_args, verify_args):
    return [
        sys.executable,
        "-m",
        "sigstore",
        *global_args,
        "verify",
        "identity",
        *verify_args,
    ]


def _fatal_help(msg):
    print(f"::error::❌ {msg}")
    sys.exit(1)


# Allow inputs to be empty if the event type is release and release-signing-artifacts is
# set to true. This allows projects without artifacts to still sign the source
# archives in their releases.
inputs = shlex.split(sys.argv[1]) if len(sys.argv) == 2 else []
if not inputs and not _RELEASE_SIGNING_ARTIFACTS:
    _fatal_help(
        "inputs must be specified when release-signing-artifacts is disabled "
        "and the event type is not release"
    )

# The arguments we pass into `sigstore-python` get built up in these lists.
sigstore_global_args = []
sigstore_sign_args = []
sigstore_verify_args = []

# The environment variables that we apply to `sigstore-python`.
sigstore_python_env = {}

# Flag to check whether we want enable the verify step.
enable_verify = bool(os.getenv("GHA_SIGSTORE_PYTHON_VERIFY", "false").lower() == "true")

# A list of paths to signing artifacts generated by `sigstore-python`. We want
# to upload these as workflow artifacts after signing.
signing_artifact_paths = []

if _DEBUG:
    sigstore_python_env["SIGSTORE_LOGLEVEL"] = "DEBUG"

identity_token = os.getenv("GHA_SIGSTORE_PYTHON_IDENTITY_TOKEN")
if identity_token:
    sigstore_sign_args.extend(["--identity-token", identity_token])

client_id = os.getenv("GHA_SIGSTORE_PYTHON_OIDC_CLIENT_ID")
if client_id:
    sigstore_sign_args.extend(["--oidc-client-id", client_id])

client_secret = os.getenv("GHA_SIGSTORE_PYTHON_OIDC_CLIENT_SECRET")
if client_secret:
    sigstore_sign_args.extend(["--oidc-client-secret", client_secret])

if os.getenv("GHA_SIGSTORE_PYTHON_STAGING", "false") != "false":
    sigstore_global_args.append("--staging")

verify_cert_identity = os.getenv("GHA_SIGSTORE_PYTHON_VERIFY_CERT_IDENTITY")
if enable_verify and not verify_cert_identity:
    _fatal_help("verify-cert-identity must be specified when verify is enabled")
elif not enable_verify and verify_cert_identity:
    _fatal_help("verify-cert-identity cannot be specified without verify: true")
elif verify_cert_identity:
    sigstore_verify_args.extend(["--cert-identity", verify_cert_identity])

verify_oidc_issuer = os.getenv("GHA_SIGSTORE_PYTHON_VERIFY_OIDC_ISSUER")
if enable_verify and not verify_oidc_issuer:
    _fatal_help("verify-oidc-issuer must be specified when verify is enabled")
elif not enable_verify and verify_oidc_issuer:
    _fatal_help("verify-oidc-issuer cannot be specified without verify: true")
elif verify_oidc_issuer:
    sigstore_verify_args.extend(["--cert-oidc-issuer", verify_oidc_issuer])

if _RELEASE_SIGNING_ARTIFACTS:
    for filetype in ["zip", "tar.gz"]:
        artifact = _download_ref_asset(filetype)
        if artifact is not None:
            inputs.append(artifact)

for input_ in inputs:
    # Forbid things that look like flags. This isn't a security boundary; just
    # a way to prevent (less motivated) users from breaking the action on themselves.
    if input_.startswith("-"):
        _fatal_help(f"input {input_} looks like a flag")

    # NOTE: We use a set here to deduplicate inputs, in case a glob expands
    # to the same input multiple times.
    files = {Path(f).resolve() for f in glob(input_, recursive=True)}

    # Prevent empty glob expansions, rather than silently allowing them.
    # Either behavior is technically correct but an empty glob indicates
    # user confusion, so we fail for them.
    if not files:
        _fatal_help(f"input {input_} doesn't expand to one or more filenames")

    for file_ in files:
        if not file_.is_file():
            _fatal_help(f"input {file_} does not look like a file")

        # Also upload artifact being signed for.
        signing_artifact_paths.append(str(file_))

        if "--bundle" not in sigstore_sign_args:
            signing_artifact_paths.append(f"{file_}.sigstore.json")

    sigstore_sign_args.extend([str(f) for f in files])
    sigstore_verify_args.extend([str(f) for f in files])

_debug(f"signing: sigstore-python {[str(a) for a in sigstore_sign_args]}")

sign_status = subprocess.run(
    _sigstore_sign(sigstore_global_args, sigstore_sign_args),
    text=True,
    stdout=subprocess.PIPE,
    stderr=subprocess.STDOUT,
    env={**os.environ, **sigstore_python_env},
)

_debug(sign_status.stdout)

if sign_status.returncode == 0:
    _summary("🎉 sigstore-python signing exited successfully")
else:
    _summary("❌ sigstore-python failed to sign package")

verify_status = None
if sign_status.returncode == 0 and enable_verify:
    _debug(f"verifying: sigstore-python {[str(a) for a in sigstore_verify_args]}")

    verify_status = subprocess.run(
        _sigstore_verify(sigstore_global_args, sigstore_verify_args),
        text=True,
        stdout=subprocess.PIPE,
        stderr=subprocess.STDOUT,
        env={**os.environ, **sigstore_python_env},
    )

    _debug(verify_status.stdout)

if verify_status is None:
    # Don't add anything to the summary if verification is disabled.
    if enable_verify:
        _summary("❌ sigstore-python verification skipped due to failed signing")
elif verify_status.returncode == 0:
    _summary("🎉 sigstore-python verification exited successfully")
else:
    _summary("❌ sigstore-python failed to verify package")


_log(sign_status.stdout)
_summary(_template("sigstore-python-sign").substitute(output=sign_status.stdout))

if verify_status is not None:
    _log(verify_status.stdout)
    _summary(
        _template("sigstore-python-verify").substitute(output=verify_status.stdout)
    )

if sign_status.returncode != 0:
    assert verify_status is None
    sys.exit(sign_status.returncode)

# Now populate the `GHA_SIGSTORE_PYTHON_INTERNAL_SIGNING_ARTIFACTS` environment
# variable so that later steps know which files to upload as workflow artifacts.
#
# In GitHub Actions, environment variables can be made to persist across
# workflow steps by appending to the file at `GITHUB_ENV`.
_github_env = os.getenv("GITHUB_ENV")
assert _github_env is not None
with Path(_github_env).open("a") as gh_env:
    # Multiline values must match the following syntax:
    #
    #  {name}<<{delimiter}
    #  {value}
    #  {delimiter}
    #
    # We use a random delimiter to avoid potential conflicts with our input;
    # see: https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions
    delim = os.urandom(16).hex()
    print(f"GHA_SIGSTORE_PYTHON_INTERNAL_SIGNING_ARTIFACTS<<{delim}", file=gh_env)
    print("\n".join(signing_artifact_paths), file=gh_env)
    print(delim, file=gh_env)


# If signing didn't fail, then we check the verification status, if present.
if verify_status is not None:
    sys.exit(verify_status.returncode)