ssl.py

# Wrapper module for _ssl, providing some additional facilities
# implemented in Python.  Written by Bill Janssen.

"""\
This module provides some more Pythonic support for SSL.

Object types:

  SSLSocket -- subtype of socket.socket which does SSL over the socket

Exceptions:

  SSLError -- exception raised for I/O errors

Functions:

  cert_time_to_seconds -- convert time string used for certificate
                          notBefore and notAfter functions to integer
                          seconds past the Epoch (the time values
                          returned from time.time())

  fetch_server_certificate (HOST, PORT) -- fetch the certificate provided
                          by the server running on HOST at port PORT.  No
                          validation of the certificate is performed.

Integer constants:

SSL_ERROR_ZERO_RETURN
SSL_ERROR_WANT_READ
SSL_ERROR_WANT_WRITE
SSL_ERROR_WANT_X509_LOOKUP
SSL_ERROR_SYSCALL
SSL_ERROR_SSL
SSL_ERROR_WANT_CONNECT

SSL_ERROR_EOF
SSL_ERROR_INVALID_ERROR_CODE

The following group define certificate requirements that one side is
allowing/requiring from the other side:

CERT_NONE - no certificates from the other side are required (or will
            be looked at if provided)
CERT_OPTIONAL - certificates are not required, but if provided will be
                validated, and if validation fails, the connection will
                also fail
CERT_REQUIRED - certificates are required, and will be validated, and
                if validation fails, the connection will also fail

The following constants identify various SSL protocol variants:

PROTOCOL_SSLv2
PROTOCOL_SSLv3
PROTOCOL_SSLv23
PROTOCOL_TLSv1
"""

import os, sys, textwrap

import _ssl             # if we can't import it, let the error propagate

from _ssl import SSLError
from _ssl import CERT_NONE, CERT_OPTIONAL, CERT_REQUIRED
from _ssl import PROTOCOL_SSLv2, PROTOCOL_SSLv3, PROTOCOL_SSLv23, PROTOCOL_TLSv1
from _ssl import RAND_status, RAND_egd, RAND_add
from _ssl import \
     SSL_ERROR_ZERO_RETURN, \
     SSL_ERROR_WANT_READ, \
     SSL_ERROR_WANT_WRITE, \
     SSL_ERROR_WANT_X509_LOOKUP, \
     SSL_ERROR_SYSCALL, \
     SSL_ERROR_SSL, \
     SSL_ERROR_WANT_CONNECT, \
     SSL_ERROR_EOF, \
     SSL_ERROR_INVALID_ERROR_CODE

from socket import socket
from socket import getnameinfo as _getnameinfo
import base64        # for DER-to-PEM translation

class SSLSocket (socket):

    """This class implements a subtype of socket.socket that wraps
    the underlying OS socket in an SSL context when necessary, and
    provides read and write methods over that channel."""

    def __init__(self, sock, keyfile=None, certfile=None,
                 server_side=False, cert_reqs=CERT_NONE,
                 ssl_version=PROTOCOL_SSLv23, ca_certs=None):
        socket.__init__(self, _sock=sock._sock)
        if certfile and not keyfile:
            keyfile = certfile
        # see if it's connected
        try:
            socket.getpeername(self)
        except:
            # no, no connection yet
            self._sslobj = None
        else:
            # yes, create the SSL object
            self._sslobj = _ssl.sslwrap(self._sock, server_side,
                                        keyfile, certfile,
                                        cert_reqs, ssl_version, ca_certs)
        self.keyfile = keyfile
        self.certfile = certfile
        self.cert_reqs = cert_reqs
        self.ssl_version = ssl_version
        self.ca_certs = ca_certs

    def read(self, len=1024):

        """Read up to LEN bytes and return them.
        Return zero-length string on EOF."""

        return self._sslobj.read(len)

    def write(self, data):

        """Write DATA to the underlying SSL channel.  Returns
        number of bytes of DATA actually transmitted."""

        return self._sslobj.write(data)

    def getpeercert(self, binary_form=False):

        """Returns a formatted version of the data in the
        certificate provided by the other end of the SSL channel.
        Return None if no certificate was provided, {} if a
        certificate was provided, but not validated."""

        return self._sslobj.peer_certificate(binary_form)

    def cipher (self):

        if not self._sslobj:
            return None
        else:
            return self._sslobj.cipher()

    def send (self, data, flags=0):
        if self._sslobj:
            if flags != 0:
                raise ValueError(
                    "non-zero flags not allowed in calls to send() on %s" %
                    self.__class__)
            return self._sslobj.write(data)
        else:
            return socket.send(self, data, flags)

    def send_to (self, data, addr, flags=0):
        if self._sslobj:
            raise ValueError("send_to not allowed on instances of %s" %
                             self.__class__)
        else:
            return socket.send_to(self, data, addr, flags)

    def sendall (self, data, flags=0):
        if self._sslobj:
            if flags != 0:
                raise ValueError(
                    "non-zero flags not allowed in calls to sendall() on %s" %
                    self.__class__)
            return self._sslobj.write(data)
        else:
            return socket.sendall(self, data, flags)

    def recv (self, buflen=1024, flags=0):
        if self._sslobj:
            if flags != 0:
                raise ValueError(
                    "non-zero flags not allowed in calls to sendall() on %s" %
                    self.__class__)
            return self._sslobj.read(data, buflen)
        else:
            return socket.recv(self, buflen, flags)

    def recv_from (self, addr, buflen=1024, flags=0):
        if self._sslobj:
            raise ValueError("recv_from not allowed on instances of %s" %
                             self.__class__)
        else:
            return socket.recv_from(self, addr, buflen, flags)

    def shutdown(self, how):
        self._sslobj = None
        socket.shutdown(self, how)

    def close(self):
        self._sslobj = None
        socket.close(self)

    def connect(self, addr):

        """Connects to remote ADDR, and then wraps the connection in
        an SSL channel."""

        # Here we assume that the socket is client-side, and not
        # connected at the time of the call.  We connect it, then wrap it.
        if self._sslobj:
            raise ValueError("attempt to connect already-connected SSLSocket!")
        socket.connect(self, addr)
        self._sslobj = _ssl.sslwrap(self._sock, False, self.keyfile, self.certfile,
                                    self.cert_reqs, self.ssl_version,
                                    self.ca_certs)

    def accept(self):

        """Accepts a new connection from a remote client, and returns
        a tuple containing that new connection wrapped with a server-side
        SSL channel, and the address of the remote client."""

        newsock, addr = socket.accept(self)
        return (SSLSocket(newsock, True, self.keyfile, self.certfile,
                          self.cert_reqs, self.ssl_version,
                          self.ca_certs), addr)


    def makefile(self, mode='r', bufsize=-1):

        """Ouch.  Need to make and return a file-like object that
        works with the SSL connection."""

        if self._sslobj:
            return SSLFileStream(self._sslobj, mode, bufsize)
        else:
            return socket.makefile(self, mode, bufsize)


class SSLFileStream:

    """A class to simulate a file stream on top of a socket.
    Most of this is just lifted from the socket module, and
    adjusted to work with an SSL stream instead of a socket."""


    default_bufsize = 8192
    name = "<SSL stream>"

    __slots__ = ["mode", "bufsize", "softspace",
                 # "closed" is a property, see below
                 "_sslobj", "_rbufsize", "_wbufsize", "_rbuf", "_wbuf",
                 "_close", "_fileno"]

    def __init__(self, sslobj, mode='rb', bufsize=-1, close=False):
        self._sslobj = sslobj
        self.mode = mode # Not actually used in this version
        if bufsize < 0:
            bufsize = self.default_bufsize
        self.bufsize = bufsize
        self.softspace = False
        if bufsize == 0:
            self._rbufsize = 1
        elif bufsize == 1:
            self._rbufsize = self.default_bufsize
        else:
            self._rbufsize = bufsize
        self._wbufsize = bufsize
        self._rbuf = "" # A string
        self._wbuf = [] # A list of strings
        self._close = close
        self._fileno = -1

    def _getclosed(self):
        return self._sslobj is None
    closed = property(_getclosed, doc="True if the file is closed")

    def fileno(self):
        return self._fileno

    def close(self):
        try:
            if self._sslobj:
                self.flush()
        finally:
            if self._close and self._sslobj:
                self._sslobj.close()
            self._sslobj = None

    def __del__(self):
        try:
            self.close()
        except:
            # close() may fail if __init__ didn't complete
            pass

    def flush(self):
        if self._wbuf:
            buffer = "".join(self._wbuf)
            self._wbuf = []
            count = 0
            while (count < len(buffer)):
                written = self._sslobj.write(buffer)
                count += written
                buffer = buffer[written:]

    def write(self, data):
        data = str(data) # XXX Should really reject non-string non-buffers
        if not data:
            return
        self._wbuf.append(data)
        if (self._wbufsize == 0 or
            self._wbufsize == 1 and '\n' in data or
            self._get_wbuf_len() >= self._wbufsize):
            self.flush()

    def writelines(self, list):
        # XXX We could do better here for very long lists
        # XXX Should really reject non-string non-buffers
        self._wbuf.extend(filter(None, map(str, list)))
        if (self._wbufsize <= 1 or
            self._get_wbuf_len() >= self._wbufsize):
            self.flush()

    def _get_wbuf_len(self):
        buf_len = 0
        for x in self._wbuf:
            buf_len += len(x)
        return buf_len

    def read(self, size=-1):
        data = self._rbuf
        if size < 0:
            # Read until EOF
            buffers = []
            if data:
                buffers.append(data)
            self._rbuf = ""
            if self._rbufsize <= 1:
                recv_size = self.default_bufsize
            else:
                recv_size = self._rbufsize
            while True:
                data = self._sslobj.read(recv_size)
                if not data:
                    break
                buffers.append(data)
            return "".join(buffers)
        else:
            # Read until size bytes or EOF seen, whichever comes first
            buf_len = len(data)
            if buf_len >= size:
                self._rbuf = data[size:]
                return data[:size]
            buffers = []
            if data:
                buffers.append(data)
            self._rbuf = ""
            while True:
                left = size - buf_len
                recv_size = max(self._rbufsize, left)
                data = self._sslobj.read(recv_size)
                if not data:
                    break
                buffers.append(data)
                n = len(data)
                if n >= left:
                    self._rbuf = data[left:]
                    buffers[-1] = data[:left]
                    break
                buf_len += n
            return "".join(buffers)

    def readline(self, size=-1):
        data = self._rbuf
        if size < 0:
            # Read until \n or EOF, whichever comes first
            if self._rbufsize <= 1:
                # Speed up unbuffered case
                assert data == ""
                buffers = []
                while data != "\n":
                    data = self._sslobj.read(1)
                    if not data:
                        break
                    buffers.append(data)
                return "".join(buffers)
            nl = data.find('\n')
            if nl >= 0:
                nl += 1
                self._rbuf = data[nl:]
                return data[:nl]
            buffers = []
            if data:
                buffers.append(data)
            self._rbuf = ""
            while True:
                data = self._sslobj.read(self._rbufsize)
                if not data:
                    break
                buffers.append(data)
                nl = data.find('\n')
                if nl >= 0:
                    nl += 1
                    self._rbuf = data[nl:]
                    buffers[-1] = data[:nl]
                    break
            return "".join(buffers)
        else:
            # Read until size bytes or \n or EOF seen, whichever comes first
            nl = data.find('\n', 0, size)
            if nl >= 0:
                nl += 1
                self._rbuf = data[nl:]
                return data[:nl]
            buf_len = len(data)
            if buf_len >= size:
                self._rbuf = data[size:]
                return data[:size]
            buffers = []
            if data:
                buffers.append(data)
            self._rbuf = ""
            while True:
                data = self._sslobj.read(self._rbufsize)
                if not data:
                    break
                buffers.append(data)
                left = size - buf_len
                nl = data.find('\n', 0, left)
                if nl >= 0:
                    nl += 1
                    self._rbuf = data[nl:]
                    buffers[-1] = data[:nl]
                    break
                n = len(data)
                if n >= left:
                    self._rbuf = data[left:]
                    buffers[-1] = data[:left]
                    break
                buf_len += n
            return "".join(buffers)

    def readlines(self, sizehint=0):
        total = 0
        list = []
        while True:
            line = self.readline()
            if not line:
                break
            list.append(line)
            total += len(line)
            if sizehint and total >= sizehint:
                break
        return list

    # Iterator protocols

    def __iter__(self):
        return self

    def next(self):
        line = self.readline()
        if not line:
            raise StopIteration
        return line




def wrap_socket(sock, keyfile=None, certfile=None,
                server_side=False, cert_reqs=CERT_NONE,
                ssl_version=PROTOCOL_SSLv23, ca_certs=None):

    return SSLSocket(sock, keyfile=keyfile, certfile=certfile,
                     server_side=server_side, cert_reqs=cert_reqs,
                     ssl_version=ssl_version, ca_certs=ca_certs)

# some utility functions

def cert_time_to_seconds(cert_time):

    """Takes a date-time string in standard ASN1_print form
    ("MON DAY 24HOUR:MINUTE:SEC YEAR TIMEZONE") and return
    a Python time value in seconds past the epoch."""

    import time
    return time.mktime(time.strptime(cert_time, "%b %d %H:%M:%S %Y GMT"))

PEM_HEADER = "-----BEGIN CERTIFICATE-----"
PEM_FOOTER = "-----END CERTIFICATE-----"

def DER_cert_to_PEM_cert(der_cert_bytes):

    """Takes a certificate in binary DER format and returns the
    PEM version of it as a string."""

    if hasattr(base64, 'standard_b64encode'):
        # preferred because older API gets line-length wrong
        f = base64.standard_b64encode(der_cert_bytes)
        return (PEM_HEADER + '\n' +
                textwrap.fill(f, 64) +
                PEM_FOOTER + '\n')
    else:
        return (PEM_HEADER + '\n' +
                base64.encodestring(der_cert_bytes) +
                PEM_FOOTER + '\n')

def PEM_cert_to_DER_cert(pem_cert_string):

    """Takes a certificate in ASCII PEM format and returns the
    DER-encoded version of it as a byte sequence"""

    if not pem_cert_string.startswith(PEM_HEADER):
        raise ValueError("Invalid PEM encoding; must start with %s"
                         % PEM_HEADER)
    if not pem_cert_string.strip().endswith(PEM_FOOTER):
        raise ValueError("Invalid PEM encoding; must end with %s"
                         % PEM_FOOTER)
    d = pem_cert_string.strip()[len(PEM_HEADER):-len(PEM_FOOTER)]
    return base64.decodestring(d)

def get_server_certificate (addr, ssl_version=PROTOCOL_SSLv3, ca_certs=None):

    """Retrieve the certificate from the server at the specified address,
    and return it as a PEM-encoded string.
    If 'ca_certs' is specified, validate the server cert against it.
    If 'ssl_version' is specified, use it in the connection attempt."""

    host, port = addr
    if (ca_certs is not None):
        cert_reqs = CERT_REQUIRED
    else:
        cert_reqs = CERT_NONE
    s = wrap_socket(socket(), ssl_version=ssl_version,
                    cert_reqs=cert_reqs, ca_certs=ca_certs)
    s.connect(addr)
    dercert = s.getpeercert(True)
    s.close()
    return DER_cert_to_PEM_cert(dercert)

def get_protocol_name (protocol_code):
    if protocol_code == PROTOCOL_TLSv1:
        return "TLSv1"
    elif protocol_code == PROTOCOL_SSLv23:
        return "SSLv23"
    elif protocol_code == PROTOCOL_SSLv2:
        return "SSLv2"
    elif protocol_code == PROTOCOL_SSLv3:
        return "SSLv3"
    else:
        return "<unknown>"


# a replacement for the old socket.ssl function

def sslwrap_simple (sock, keyfile=None, certfile=None):

    """A replacement for the old socket.ssl function.  Designed
    for compability with Python 2.5 and earlier.  Will disappear in
    Python 3.0."""

    return _ssl.sslwrap(sock._sock, 0, keyfile, certfile, CERT_NONE,
                        PROTOCOL_SSLv23, None)