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Filename : binding.py
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# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.

from __future__ import absolute_import, division, print_function

import collections
import threading
import types

from cryptography import utils
from cryptography.exceptions import InternalError
from cryptography.hazmat.bindings._openssl import ffi, lib
from cryptography.hazmat.bindings.openssl._conditional import CONDITIONAL_NAMES

_OpenSSLErrorWithText = collections.namedtuple(
    "_OpenSSLErrorWithText", ["code", "lib", "func", "reason", "reason_text"]
)


class _OpenSSLError(object):
    def __init__(self, code, lib, func, reason):
        self._code = code
        self._lib = lib
        self._func = func
        self._reason = reason

    def _lib_reason_match(self, lib, reason):
        return lib == self.lib and reason == self.reason

    code = utils.read_only_property("_code")
    lib = utils.read_only_property("_lib")
    func = utils.read_only_property("_func")
    reason = utils.read_only_property("_reason")


def _consume_errors(lib):
    errors = []
    while True:
        code = lib.ERR_get_error()
        if code == 0:
            break

        err_lib = lib.ERR_GET_LIB(code)
        err_func = lib.ERR_GET_FUNC(code)
        err_reason = lib.ERR_GET_REASON(code)

        errors.append(_OpenSSLError(code, err_lib, err_func, err_reason))

    return errors


def _openssl_assert(lib, ok):
    if not ok:
        errors = _consume_errors(lib)
        errors_with_text = []
        for err in errors:
            err_text_reason = ffi.string(
                lib.ERR_error_string(err.code, ffi.NULL)
            )
            errors_with_text.append(
                _OpenSSLErrorWithText(
                    err.code, err.lib, err.func, err.reason, err_text_reason
                )
            )

        raise InternalError(
            "Unknown OpenSSL error. This error is commonly encountered when "
            "another library is not cleaning up the OpenSSL error stack. If "
            "you are using cryptography with another library that uses "
            "OpenSSL try disabling it before reporting a bug. Otherwise "
            "please file an issue at https://github.com/pyca/cryptography/"
            "issues with information on how to reproduce "
            "this. ({0!r})".format(errors_with_text),
            errors_with_text
        )


def build_conditional_library(lib, conditional_names):
    conditional_lib = types.ModuleType("lib")
    conditional_lib._original_lib = lib
    excluded_names = set()
    for condition, names_cb in conditional_names.items():
        if not getattr(lib, condition):
            excluded_names.update(names_cb())

    for attr in dir(lib):
        if attr not in excluded_names:
            setattr(conditional_lib, attr, getattr(lib, attr))

    return conditional_lib


class Binding(object):
    """
    OpenSSL API wrapper.
    """
    lib = None
    ffi = ffi
    _lib_loaded = False
    _init_lock = threading.Lock()
    _lock_init_lock = threading.Lock()

    def __init__(self):
        self._ensure_ffi_initialized()

    @classmethod
    def _register_osrandom_engine(cls):
        # Clear any errors extant in the queue before we start. In many
        # scenarios other things may be interacting with OpenSSL in the same
        # process space and it has proven untenable to assume that they will
        # reliably clear the error queue. Once we clear it here we will
        # error on any subsequent unexpected item in the stack.
        cls.lib.ERR_clear_error()
        cls._osrandom_engine_id = cls.lib.Cryptography_osrandom_engine_id
        cls._osrandom_engine_name = cls.lib.Cryptography_osrandom_engine_name
        result = cls.lib.Cryptography_add_osrandom_engine()
        _openssl_assert(cls.lib, result in (1, 2))

    @classmethod
    def _ensure_ffi_initialized(cls):
        with cls._init_lock:
            if not cls._lib_loaded:
                cls.lib = build_conditional_library(lib, CONDITIONAL_NAMES)
                cls._lib_loaded = True
                # initialize the SSL library
                cls.lib.SSL_library_init()
                # adds all ciphers/digests for EVP
                cls.lib.OpenSSL_add_all_algorithms()
                # loads error strings for libcrypto and libssl functions
                cls.lib.SSL_load_error_strings()
                cls._register_osrandom_engine()

    @classmethod
    def init_static_locks(cls):
        with cls._lock_init_lock:
            cls._ensure_ffi_initialized()
            # Use Python's implementation if available, importing _ssl triggers
            # the setup for this.
            __import__("_ssl")

            if cls.lib.CRYPTO_get_locking_callback() != cls.ffi.NULL:
                return

            # If nothing else has setup a locking callback already, we set up
            # our own
            res = lib._setup_ssl_threads()
            _openssl_assert(cls.lib, res == 1)


# OpenSSL is not thread safe until the locks are initialized. We call this
# method in module scope so that it executes with the import lock. On
# Pythons < 3.4 this import lock is a global lock, which can prevent a race
# condition registering the OpenSSL locks. On Python 3.4+ the import lock
# is per module so this approach will not work.
Binding.init_static_locks()