How to use the pygit2.ffi.ffi.string function in pygit2

def maybe_string(ptr):
    if not ptr:
        return None

    return ffi.string(ptr).decode('utf8')

"""

        cvalue = ffi.new('char **')
        err = C.git_attr_get(cvalue, self._repo, flags, to_bytes(path), to_bytes(name))
        check_error(err)

        # Now let's see if we can figure out what the value is
        attr_kind = C.git_attr_value(cvalue[0])
        if attr_kind == C.GIT_ATTR_UNSPECIFIED_T:
            return None
        elif attr_kind == C.GIT_ATTR_TRUE_T:
            return True
        elif attr_kind == C.GIT_ATTR_FALSE_T:
            return False
        elif attr_kind == C.GIT_ATTR_VALUE_T:
            return ffi.string(cvalue[0]).decode('utf-8')

        assert False, "the attribute value from libgit2 is invalid"

def wrap_signature(csig):
    if not csig:
        return None

    return Signature(ffi.string(csig.name).decode('utf-8'),
                     ffi.string(csig.email).decode('utf-8'),
                     csig.when.time, csig.when.offset, 'utf-8')

def strarray_to_strings(arr):
    l = [None] * arr.count
    for i in range(arr.count):
        l[i] = ffi.string(arr.strings[i]).decode('utf-8')

    return l

def string(self):
        """String which was used to create this refspec"""
        return ffi.string(C.git_refspec_string(self._refspec)).decode('utf-8')

def _sideband_progress_cb(string, length, data):
        self = ffi.from_handle(data)

        progress = getattr(self, 'progress', None)
        if not progress:
            return 0

        try:
            s = ffi.string(string, length).decode('utf-8')
            progress(s)
        except Exception as e:
            self._stored_exception = e
            return C.GIT_EUSER

        return 0

def path(self):
        """Path of the submodule."""
        path = C.git_submodule_path(self._subm)
        return ffi.string(path).decode('utf-8')

def _certificate_cb(cert_i, valid, host, data):
        self = ffi.from_handle(data)

        # We want to simulate what should happen if libgit2 supported pass-through for
        # this callback. For SSH, 'valid' is always False, because it doesn't look
        # at known_hosts, but we do want to let it through in order to do what libgit2 would
        # if the callback were not set.
        try:
            is_ssh = cert_i.cert_type == C.GIT_CERT_HOSTKEY_LIBSSH2

            certificate_check = getattr(self, 'certificate_check', None)
            if not certificate_check:
                raise Passthrough

            # python's parsing is deep in the libraries and assumes an OpenSSL-owned cert
            val = certificate_check(None, bool(valid), ffi.string(host))
            if not val:
                return C.GIT_ECERTIFICATE
        except Passthrough:
            if is_ssh:
                return 0
            elif valid:
                return 0
            else:
                return C.GIT_ECERTIFICATE
        except Exception as e:
            self._stored_exception = e
            return C.GIT_EUSER

        return 0