import shutil
import tempfile

from twisted.internet.utils import getProcessOutputAndValue


class InvalidGPGSignature(Exception):
"""Raised when the gpg signature for a given file is invalid."""


def gpg_verify(filename, signature, gpg="/usr/bin/gpg"):
"""Verify the GPG signature of a file.

@param filename: Path to the file to verify the signature against.
@param signature: Path to signature to use.
@param gpg: Optionally, path to the GPG binary to use.
@return: a C{Deferred} resulting in C{True} if the signature is
valid, C{False} otherwise.
"""

def remove_gpg_home(ignored):
shutil.rmtree(gpg_home)
return ignored

def check_gpg_exit_code((out, err, code)):
if code != 0:
raise InvalidGPGSignature("%s failed (out='%s', err='%s', "
"code='%d')" % (gpg, out, err, code))

gpg_home = tempfile.mkdtemp()
args = ("--no-options", "--homedir", gpg_home, "--no-default-keyring",
"--ignore-time-conflict", "--keyring", "/etc/apt/trusted.gpg",
"--verify", signature, filename)

result = getProcessOutputAndValue(gpg, args=args)
result.addBoth(remove_gpg_home)
result.addCallback(check_gpg_exit_code)
return result