/* GnuTLS glue for GNU Emacs.
   Copyright (C) 2010-2014 Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>
#include <errno.h>
#include <stdio.h>

#include "lisp.h"
#include "process.h"
#include "coding.h"

#ifdef HAVE_GNUTLS
#include <gnutls/gnutls.h>

#ifdef WINDOWSNT
#include <windows.h>
#include "w32.h"
#endif

static bool emacs_gnutls_handle_error (gnutls_session_t, int);

static Lisp_Object Qgnutls_dll;
static Lisp_Object Qgnutls_code;
static Lisp_Object Qgnutls_anon, Qgnutls_x509pki;
static Lisp_Object Qgnutls_e_interrupted, Qgnutls_e_again,
  Qgnutls_e_invalid_session, Qgnutls_e_not_ready_for_handshake;
static bool gnutls_global_initialized;

/* The following are for the property list of `gnutls-boot'.  */
static Lisp_Object QCgnutls_bootprop_priority;
static Lisp_Object QCgnutls_bootprop_trustfiles;
static Lisp_Object QCgnutls_bootprop_keylist;
static Lisp_Object QCgnutls_bootprop_crlfiles;
static Lisp_Object QCgnutls_bootprop_callbacks;
static Lisp_Object QCgnutls_bootprop_loglevel;
static Lisp_Object QCgnutls_bootprop_hostname;
static Lisp_Object QCgnutls_bootprop_min_prime_bits;
static Lisp_Object QCgnutls_bootprop_verify_flags;
static Lisp_Object QCgnutls_bootprop_verify_error;

/* Callback keys for `gnutls-boot'.  Unused currently.  */
static Lisp_Object QCgnutls_bootprop_callbacks_verify;

static void gnutls_log_function (int, const char *);
static void gnutls_log_function2 (int, const char *, const char *);
#ifdef HAVE_GNUTLS3
static void gnutls_audit_log_function (gnutls_session_t, const char *);
#endif

static enum
  {
    CERTIFICATE_NOT_MATCHING = 2,
  } extra_peer_verification_t;


#ifdef WINDOWSNT

/* Macro for defining functions that will be loaded from the GnuTLS DLL.  */
#define DEF_GNUTLS_FN(rettype,func,args) static rettype (FAR CDECL *fn_##func)args

/* Macro for loading GnuTLS functions from the library.  */
#define LOAD_GNUTLS_FN(lib,func) {					\
    fn_##func = (void *) GetProcAddress (lib, #func);			\
    if (!fn_##func) return 0;						\
  }

DEF_GNUTLS_FN (gnutls_alert_description_t, gnutls_alert_get,
	       (gnutls_session_t));
DEF_GNUTLS_FN (const char *, gnutls_alert_get_name,
	       (gnutls_alert_description_t));
DEF_GNUTLS_FN (int, gnutls_alert_send_appropriate, (gnutls_session_t, int));
DEF_GNUTLS_FN (int, gnutls_anon_allocate_client_credentials,
	       (gnutls_anon_client_credentials_t *));
DEF_GNUTLS_FN (void, gnutls_anon_free_client_credentials,
	       (gnutls_anon_client_credentials_t));
DEF_GNUTLS_FN (int, gnutls_bye, (gnutls_session_t, gnutls_close_request_t));
DEF_GNUTLS_FN (int, gnutls_certificate_allocate_credentials,
	       (gnutls_certificate_credentials_t *));
DEF_GNUTLS_FN (void, gnutls_certificate_free_credentials,
	       (gnutls_certificate_credentials_t));
DEF_GNUTLS_FN (const gnutls_datum_t *, gnutls_certificate_get_peers,
	       (gnutls_session_t, unsigned int *));
DEF_GNUTLS_FN (void, gnutls_certificate_set_verify_flags,
	       (gnutls_certificate_credentials_t, unsigned int));
DEF_GNUTLS_FN (int, gnutls_certificate_set_x509_crl_file,
	       (gnutls_certificate_credentials_t, const char *,
		gnutls_x509_crt_fmt_t));
DEF_GNUTLS_FN (int, gnutls_certificate_set_x509_key_file,
	       (gnutls_certificate_credentials_t, const char *, const char *,
		gnutls_x509_crt_fmt_t));
DEF_GNUTLS_FN (int, gnutls_certificate_set_x509_trust_file,
	       (gnutls_certificate_credentials_t, const char *,
		gnutls_x509_crt_fmt_t));
DEF_GNUTLS_FN (gnutls_certificate_type_t, gnutls_certificate_type_get,
	       (gnutls_session_t));
DEF_GNUTLS_FN (int, gnutls_certificate_verify_peers2,
	       (gnutls_session_t, unsigned int *));
DEF_GNUTLS_FN (int, gnutls_credentials_set,
	       (gnutls_session_t, gnutls_credentials_type_t, void *));
DEF_GNUTLS_FN (void, gnutls_deinit, (gnutls_session_t));
DEF_GNUTLS_FN (void, gnutls_dh_set_prime_bits,
	       (gnutls_session_t, unsigned int));
DEF_GNUTLS_FN (int, gnutls_error_is_fatal, (int));
DEF_GNUTLS_FN (int, gnutls_global_init, (void));
DEF_GNUTLS_FN (void, gnutls_global_set_log_function, (gnutls_log_func));
#ifdef HAVE_GNUTLS3
DEF_GNUTLS_FN (void, gnutls_global_set_audit_log_function, (gnutls_audit_log_func));
#endif
DEF_GNUTLS_FN (void, gnutls_global_set_log_level, (int));
DEF_GNUTLS_FN (void, gnutls_global_set_mem_functions,
	       (gnutls_alloc_function, gnutls_alloc_function,
		gnutls_is_secure_function, gnutls_realloc_function,
		gnutls_free_function));
DEF_GNUTLS_FN (int, gnutls_handshake, (gnutls_session_t));
DEF_GNUTLS_FN (int, gnutls_init, (gnutls_session_t *, gnutls_connection_end_t));
DEF_GNUTLS_FN (int, gnutls_priority_set_direct,
	       (gnutls_session_t, const char *, const char **));
DEF_GNUTLS_FN (size_t, gnutls_record_check_pending, (gnutls_session_t));
DEF_GNUTLS_FN (ssize_t, gnutls_record_recv, (gnutls_session_t, void *, size_t));
DEF_GNUTLS_FN (ssize_t, gnutls_record_send,
	       (gnutls_session_t, const void *, size_t));
DEF_GNUTLS_FN (const char *, gnutls_strerror, (int));
DEF_GNUTLS_FN (void, gnutls_transport_set_errno, (gnutls_session_t, int));
DEF_GNUTLS_FN (const char *, gnutls_check_version, (const char *));
DEF_GNUTLS_FN (void, gnutls_transport_set_lowat, (gnutls_session_t, int));
DEF_GNUTLS_FN (void, gnutls_transport_set_ptr2,
	       (gnutls_session_t, gnutls_transport_ptr_t,
		gnutls_transport_ptr_t));
DEF_GNUTLS_FN (void, gnutls_transport_set_pull_function,
	       (gnutls_session_t, gnutls_pull_func));
DEF_GNUTLS_FN (void, gnutls_transport_set_push_function,
	       (gnutls_session_t, gnutls_push_func));
DEF_GNUTLS_FN (int, gnutls_x509_crt_check_hostname,
	       (gnutls_x509_crt_t, const char *));
DEF_GNUTLS_FN (void, gnutls_x509_crt_deinit, (gnutls_x509_crt_t));
DEF_GNUTLS_FN (int, gnutls_x509_crt_import,
	       (gnutls_x509_crt_t, const gnutls_datum_t *,
		gnutls_x509_crt_fmt_t));
DEF_GNUTLS_FN (int, gnutls_x509_crt_init, (gnutls_x509_crt_t *));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_fingerprint,
	       (gnutls_x509_crt_t,
		gnutls_digest_algorithm_t, void *, size_t *));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_version,
	       (gnutls_x509_crt_t));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_serial,
	       (gnutls_x509_crt_t, void *, size_t *));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_issuer_dn,
	       (gnutls_x509_crt_t, char *, size_t *));
DEF_GNUTLS_FN (time_t, gnutls_x509_crt_get_activation_time,
	       (gnutls_x509_crt_t));
DEF_GNUTLS_FN (time_t, gnutls_x509_crt_get_expiration_time,
	       (gnutls_x509_crt_t));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_dn,
	       (gnutls_x509_crt_t, char *, size_t *));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_pk_algorithm,
	       (gnutls_x509_crt_t, unsigned int *));
DEF_GNUTLS_FN (const char*, gnutls_pk_algorithm_get_name,
	       (gnutls_pk_algorithm_t));
DEF_GNUTLS_FN (int, gnutls_pk_bits_to_sec_param,
	       (gnutls_pk_algorithm_t, unsigned int));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_issuer_unique_id,
	       (gnutls_x509_crt_t, char *, size_t *));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_subject_unique_id,
	       (gnutls_x509_crt_t, char *, size_t *));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_signature_algorithm,
	       (gnutls_x509_crt_t));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_signature,
	       (gnutls_x509_crt_t, char *, size_t *));
DEF_GNUTLS_FN (int, gnutls_x509_crt_get_key_id,
	       (gnutls_x509_crt_t, unsigned int,
		unsigned char *, size_t *_size));
DEF_GNUTLS_FN (const char*, gnutls_sec_param_get_name, (gnutls_sec_param_t));
DEF_GNUTLS_FN (const char*, gnutls_sign_algorithm_get_name,
	       (gnutls_sign_algorithm_t));

static bool
init_gnutls_functions (void)
{
  HMODULE library;
  int max_log_level = 1;

  if (!(library = w32_delayed_load (Qgnutls_dll)))
    {
      GNUTLS_LOG (1, max_log_level, "GnuTLS library not found");
      return 0;
    }

  LOAD_GNUTLS_FN (library, gnutls_alert_get);
  LOAD_GNUTLS_FN (library, gnutls_alert_get_name);
  LOAD_GNUTLS_FN (library, gnutls_alert_send_appropriate);
  LOAD_GNUTLS_FN (library, gnutls_anon_allocate_client_credentials);
  LOAD_GNUTLS_FN (library, gnutls_anon_free_client_credentials);
  LOAD_GNUTLS_FN (library, gnutls_bye);
  LOAD_GNUTLS_FN (library, gnutls_certificate_allocate_credentials);
  LOAD_GNUTLS_FN (library, gnutls_certificate_free_credentials);
  LOAD_GNUTLS_FN (library, gnutls_certificate_get_peers);
  LOAD_GNUTLS_FN (library, gnutls_certificate_set_verify_flags);
  LOAD_GNUTLS_FN (library, gnutls_certificate_set_x509_crl_file);
  LOAD_GNUTLS_FN (library, gnutls_certificate_set_x509_key_file);
  LOAD_GNUTLS_FN (library, gnutls_certificate_set_x509_trust_file);
  LOAD_GNUTLS_FN (library, gnutls_certificate_type_get);
  LOAD_GNUTLS_FN (library, gnutls_certificate_verify_peers2);
  LOAD_GNUTLS_FN (library, gnutls_credentials_set);
  LOAD_GNUTLS_FN (library, gnutls_deinit);
  LOAD_GNUTLS_FN (library, gnutls_dh_set_prime_bits);
  LOAD_GNUTLS_FN (library, gnutls_error_is_fatal);
  LOAD_GNUTLS_FN (library, gnutls_global_init);
  LOAD_GNUTLS_FN (library, gnutls_global_set_log_function);
#ifdef HAVE_GNUTLS3
  LOAD_GNUTLS_FN (library, gnutls_global_set_audit_log_function);
#endif
  LOAD_GNUTLS_FN (library, gnutls_global_set_log_level);
  LOAD_GNUTLS_FN (library, gnutls_global_set_mem_functions);
  LOAD_GNUTLS_FN (library, gnutls_handshake);
  LOAD_GNUTLS_FN (library, gnutls_init);
  LOAD_GNUTLS_FN (library, gnutls_priority_set_direct);
  LOAD_GNUTLS_FN (library, gnutls_record_check_pending);
  LOAD_GNUTLS_FN (library, gnutls_record_recv);
  LOAD_GNUTLS_FN (library, gnutls_record_send);
  LOAD_GNUTLS_FN (library, gnutls_strerror);
  LOAD_GNUTLS_FN (library, gnutls_transport_set_errno);
  LOAD_GNUTLS_FN (library, gnutls_check_version);
  /* We don't need to call gnutls_transport_set_lowat in GnuTLS 2.11.1
     and later, and the function was removed entirely in 3.0.0.  */
  if (!fn_gnutls_check_version ("2.11.1"))
    LOAD_GNUTLS_FN (library, gnutls_transport_set_lowat);
  LOAD_GNUTLS_FN (library, gnutls_transport_set_ptr2);
  LOAD_GNUTLS_FN (library, gnutls_transport_set_pull_function);
  LOAD_GNUTLS_FN (library, gnutls_transport_set_push_function);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_check_hostname);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_deinit);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_import);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_init);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_fingerprint);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_version);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_serial);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_issuer_dn);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_activation_time);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_expiration_time);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_dn);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_pk_algorithm);
  LOAD_GNUTLS_FN (library, gnutls_pk_algorithm_get_name);
  LOAD_GNUTLS_FN (library, gnutls_pk_bits_to_sec_param);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_issuer_unique_id);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_subject_unique_id);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_signature_algorithm);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_signature);
  LOAD_GNUTLS_FN (library, gnutls_x509_crt_get_key_id);
  LOAD_GNUTLS_FN (library, gnutls_sec_param_get_name);
  LOAD_GNUTLS_FN (library, gnutls_sign_algorithm_get_name);

  max_log_level = global_gnutls_log_level;

  {
    Lisp_Object name = CAR_SAFE (Fget (Qgnutls_dll, QCloaded_from));
    GNUTLS_LOG2 (1, max_log_level, "GnuTLS library loaded:",
                 STRINGP (name) ? (const char *) SDATA (name) : "unknown");
  }

  return 1;
}

#else /* !WINDOWSNT */

#define fn_gnutls_alert_get			gnutls_alert_get
#define fn_gnutls_alert_get_name		gnutls_alert_get_name
#define fn_gnutls_alert_send_appropriate	gnutls_alert_send_appropriate
#define fn_gnutls_anon_allocate_client_credentials gnutls_anon_allocate_client_credentials
#define fn_gnutls_anon_free_client_credentials	gnutls_anon_free_client_credentials
#define fn_gnutls_bye				gnutls_bye
#define fn_gnutls_certificate_allocate_credentials gnutls_certificate_allocate_credentials
#define fn_gnutls_certificate_free_credentials	gnutls_certificate_free_credentials
#define fn_gnutls_certificate_get_peers		gnutls_certificate_get_peers
#define fn_gnutls_certificate_set_verify_flags	gnutls_certificate_set_verify_flags
#define fn_gnutls_certificate_set_x509_crl_file	gnutls_certificate_set_x509_crl_file
#define fn_gnutls_certificate_set_x509_key_file gnutls_certificate_set_x509_key_file
#define fn_gnutls_certificate_set_x509_trust_file gnutls_certificate_set_x509_trust_file
#define fn_gnutls_certificate_type_get		gnutls_certificate_type_get
#define fn_gnutls_certificate_verify_peers2	gnutls_certificate_verify_peers2
#define fn_gnutls_credentials_set		gnutls_credentials_set
#define fn_gnutls_deinit			gnutls_deinit
#define fn_gnutls_dh_set_prime_bits		gnutls_dh_set_prime_bits
#define fn_gnutls_error_is_fatal		gnutls_error_is_fatal
#define fn_gnutls_global_init			gnutls_global_init
#define fn_gnutls_global_set_log_function	gnutls_global_set_log_function
#ifdef HAVE_GNUTLS3
#define fn_gnutls_global_set_audit_log_function	gnutls_global_set_audit_log_function
#endif
#define fn_gnutls_global_set_log_level		gnutls_global_set_log_level
#define fn_gnutls_global_set_mem_functions	gnutls_global_set_mem_functions
#define fn_gnutls_handshake			gnutls_handshake
#define fn_gnutls_init				gnutls_init
#define fn_gnutls_priority_set_direct		gnutls_priority_set_direct
#define fn_gnutls_record_check_pending		gnutls_record_check_pending
#define fn_gnutls_record_recv			gnutls_record_recv
#define fn_gnutls_record_send			gnutls_record_send
#define fn_gnutls_strerror			gnutls_strerror
#ifdef WINDOWSNT
#define fn_gnutls_transport_set_errno		gnutls_transport_set_errno
#endif
#define fn_gnutls_transport_set_ptr2		gnutls_transport_set_ptr2
#define fn_gnutls_x509_crt_check_hostname	gnutls_x509_crt_check_hostname
#define fn_gnutls_x509_crt_deinit		gnutls_x509_crt_deinit
#define fn_gnutls_x509_crt_import		gnutls_x509_crt_import
#define fn_gnutls_x509_crt_init			gnutls_x509_crt_init
#define fn_gnutls_x509_crt_get_fingerprint	gnutls_x509_crt_get_fingerprint	
#define fn_gnutls_x509_crt_get_version          gnutls_x509_crt_get_version
#define fn_gnutls_x509_crt_get_serial           gnutls_x509_crt_get_serial
#define fn_gnutls_x509_crt_get_issuer_dn        gnutls_x509_crt_get_issuer_dn
#define fn_gnutls_x509_crt_get_activation_time  gnutls_x509_crt_get_activation_time
#define fn_gnutls_x509_crt_get_expiration_time  gnutls_x509_crt_get_expiration_time
#define fn_gnutls_x509_crt_get_dn               gnutls_x509_crt_get_dn
#define fn_gnutls_x509_crt_get_pk_algorithm     gnutls_x509_crt_get_pk_algorithm
#define fn_gnutls_pk_algorithm_get_name         gnutls_pk_algorithm_get_name
#define fn_gnutls_pk_bits_to_sec_param          gnutls_pk_bits_to_sec_param
#define fn_gnutls_x509_crt_get_issuer_unique_id gnutls_x509_crt_get_issuer_unique_id
#define fn_gnutls_x509_crt_get_subject_unique_id gnutls_x509_crt_get_subject_unique_id
#define fn_gnutls_x509_crt_get_signature_algorithm gnutls_x509_crt_get_signature_algorithm
#define fn_gnutls_x509_crt_get_signature        gnutls_x509_crt_get_signature
#define fn_gnutls_x509_crt_get_key_id           gnutls_x509_crt_get_key_id
#define fn_gnutls_sec_param_get_name            gnutls_sec_param_get_name
#define fn_gnutls_sign_algorithm_get_name       gnutls_sign_algorithm_get_name

#endif /* !WINDOWSNT */


#ifdef HAVE_GNUTLS3
/* Function to log a simple audit message.  */
static void
gnutls_audit_log_function (gnutls_session_t session, const char *string)
{
  if (global_gnutls_log_level >= 1)
    {
      message ("gnutls.c: [audit] %s", string);
    }
}
#endif

/* Function to log a simple message.  */
static void
gnutls_log_function (int level, const char *string)
{
  message ("gnutls.c: [%d] %s", level, string);
}

/* Function to log a message and a string.  */
static void
gnutls_log_function2 (int level, const char *string, const char *extra)
{
  message ("gnutls.c: [%d] %s %s", level, string, extra);
}

/* Function to log a message and an integer.  */
static void
gnutls_log_function2i (int level, const char *string, int extra)
{
  message ("gnutls.c: [%d] %s %d", level, string, extra);
}

static int
emacs_gnutls_handshake (struct Lisp_Process *proc)
{
  gnutls_session_t state = proc->gnutls_state;
  int ret;

  if (proc->gnutls_initstage < GNUTLS_STAGE_HANDSHAKE_CANDO)
    return -1;

  if (proc->gnutls_initstage < GNUTLS_STAGE_TRANSPORT_POINTERS_SET)
    {
#ifdef WINDOWSNT
      /* On W32 we cannot transfer socket handles between different runtime
	 libraries, so we tell GnuTLS to use our special push/pull
	 functions.  */
      fn_gnutls_transport_set_ptr2 (state,
				    (gnutls_transport_ptr_t) proc,
				    (gnutls_transport_ptr_t) proc);
      fn_gnutls_transport_set_push_function (state, &emacs_gnutls_push);
      fn_gnutls_transport_set_pull_function (state, &emacs_gnutls_pull);

      /* For non blocking sockets or other custom made pull/push
	 functions the gnutls_transport_set_lowat must be called, with
	 a zero low water mark value. (GnuTLS 2.10.4 documentation)

	 (Note: this is probably not strictly necessary as the lowat
	  value is only used when no custom pull/push functions are
	  set.)  */
      /* According to GnuTLS NEWS file, lowat level has been set to
	 zero by default in version 2.11.1, and the function
	 gnutls_transport_set_lowat was removed from the library in
	 version 2.99.0.  */
      if (!fn_gnutls_check_version ("2.11.1"))
	fn_gnutls_transport_set_lowat (state, 0);
#else
      /* This is how GnuTLS takes sockets: as file descriptors passed
	 in.  For an Emacs process socket, infd and outfd are the
	 same but we use this two-argument version for clarity.  */
      fn_gnutls_transport_set_ptr2 (state,
				    (void *) (intptr_t) proc->infd,
				    (void *) (intptr_t) proc->outfd);
#endif

      proc->gnutls_initstage = GNUTLS_STAGE_TRANSPORT_POINTERS_SET;
    }

  do
    {
      ret = fn_gnutls_handshake (state);
      emacs_gnutls_handle_error (state, ret);
      QUIT;
    }
  while (ret < 0 && fn_gnutls_error_is_fatal (ret) == 0);

  proc->gnutls_initstage = GNUTLS_STAGE_HANDSHAKE_TRIED;

  if (ret == GNUTLS_E_SUCCESS)
    {
      /* Here we're finally done.  */
      proc->gnutls_initstage = GNUTLS_STAGE_READY;
    }
  else
    {
      fn_gnutls_alert_send_appropriate (state, ret);
    }
  return ret;
}

ptrdiff_t
emacs_gnutls_record_check_pending (gnutls_session_t state)
{
  return fn_gnutls_record_check_pending (state);
}

#ifdef WINDOWSNT
void
emacs_gnutls_transport_set_errno (gnutls_session_t state, int err)
{
  fn_gnutls_transport_set_errno (state, err);
}
#endif

ptrdiff_t
emacs_gnutls_write (struct Lisp_Process *proc, const char *buf, ptrdiff_t nbyte)
{
  ssize_t rtnval = 0;
  ptrdiff_t bytes_written;
  gnutls_session_t state = proc->gnutls_state;

  if (proc->gnutls_initstage != GNUTLS_STAGE_READY)
    {
      errno = EAGAIN;
      return 0;
    }

  bytes_written = 0;

  while (nbyte > 0)
    {
      rtnval = fn_gnutls_record_send (state, buf, nbyte);

      if (rtnval < 0)
	{
	  if (rtnval == GNUTLS_E_INTERRUPTED)
	    continue;
	  else
	    {
	      /* If we get GNUTLS_E_AGAIN, then set errno
		 appropriately so that send_process retries the
		 correct way instead of erroring out. */
	      if (rtnval == GNUTLS_E_AGAIN)
		errno = EAGAIN;
	      break;
	    }
	}

      buf += rtnval;
      nbyte -= rtnval;
      bytes_written += rtnval;
    }

  emacs_gnutls_handle_error (state, rtnval);
  return (bytes_written);
}

ptrdiff_t
emacs_gnutls_read (struct Lisp_Process *proc, char *buf, ptrdiff_t nbyte)
{
  ssize_t rtnval;
  gnutls_session_t state = proc->gnutls_state;

  int log_level = proc->gnutls_log_level;

  if (proc->gnutls_initstage != GNUTLS_STAGE_READY)
    {
      /* If the handshake count is under the limit, try the handshake
         again and increment the handshake count.  This count is kept
         per process (connection), not globally.  */
      if (proc->gnutls_handshakes_tried < GNUTLS_EMACS_HANDSHAKES_LIMIT)
        {
          proc->gnutls_handshakes_tried++;
          emacs_gnutls_handshake (proc);
          GNUTLS_LOG2i (5, log_level, "Retried handshake",
                        proc->gnutls_handshakes_tried);
          return -1;
        }

      GNUTLS_LOG (2, log_level, "Giving up on handshake; resetting retries");
      proc->gnutls_handshakes_tried = 0;
      return 0;
    }
  rtnval = fn_gnutls_record_recv (state, buf, nbyte);
  if (rtnval >= 0)
    return rtnval;
  else if (rtnval == GNUTLS_E_UNEXPECTED_PACKET_LENGTH)
    /* The peer closed the connection. */
    return 0;
  else if (emacs_gnutls_handle_error (state, rtnval))
    /* non-fatal error */
    return -1;
  else {
    /* a fatal error occurred */
    return 0;
  }
}

/* Report a GnuTLS error to the user.
   Return true if the error code was successfully handled.  */
static bool
emacs_gnutls_handle_error (gnutls_session_t session, int err)
{
  int max_log_level = 0;

  bool ret;
  const char *str;

  /* TODO: use a Lisp_Object generated by gnutls_make_error?  */
  if (err >= 0)
    return 1;

  max_log_level = global_gnutls_log_level;

  /* TODO: use gnutls-error-fatalp and gnutls-error-string.  */

  str = fn_gnutls_strerror (err);
  if (!str)
    str = "unknown";

  if (fn_gnutls_error_is_fatal (err))
    {
      ret = 0;
      GNUTLS_LOG2 (0, max_log_level, "fatal error:", str);
    }
  else
    {
      ret = 1;

      switch (err)
        {
        case GNUTLS_E_AGAIN:
          GNUTLS_LOG2 (3,
                       max_log_level,
                       "retry:",
                       str);
        default:
          GNUTLS_LOG2 (1,
                       max_log_level,
                       "non-fatal error:",
                       str);
        }
    }

  if (err == GNUTLS_E_WARNING_ALERT_RECEIVED
      || err == GNUTLS_E_FATAL_ALERT_RECEIVED)
    {
      int alert = fn_gnutls_alert_get (session);
      int level = (err == GNUTLS_E_FATAL_ALERT_RECEIVED) ? 0 : 1;
      str = fn_gnutls_alert_get_name (alert);
      if (!str)
	str = "unknown";

      GNUTLS_LOG2 (level, max_log_level, "Received alert: ", str);
    }
  return ret;
}

/* convert an integer error to a Lisp_Object; it will be either a
   known symbol like `gnutls_e_interrupted' and `gnutls_e_again' or
   simply the integer value of the error.  GNUTLS_E_SUCCESS is mapped
   to Qt.  */
static Lisp_Object
gnutls_make_error (int err)
{
  switch (err)
    {
    case GNUTLS_E_SUCCESS:
      return Qt;
    case GNUTLS_E_AGAIN:
      return Qgnutls_e_again;
    case GNUTLS_E_INTERRUPTED:
      return Qgnutls_e_interrupted;
    case GNUTLS_E_INVALID_SESSION:
      return Qgnutls_e_invalid_session;
    }

  return make_number (err);
}

Lisp_Object
emacs_gnutls_deinit (Lisp_Object proc)
{
  int log_level;

  CHECK_PROCESS (proc);

  if (XPROCESS (proc)->gnutls_p == 0)
    return Qnil;

  log_level = XPROCESS (proc)->gnutls_log_level;

  if (XPROCESS (proc)->gnutls_x509_cred)
    {
      GNUTLS_LOG (2, log_level, "Deallocating x509 credentials");
      fn_gnutls_certificate_free_credentials (XPROCESS (proc)->gnutls_x509_cred);
      XPROCESS (proc)->gnutls_x509_cred = NULL;
    }

  if (XPROCESS (proc)->gnutls_anon_cred)
    {
      GNUTLS_LOG (2, log_level, "Deallocating anon credentials");
      fn_gnutls_anon_free_client_credentials (XPROCESS (proc)->gnutls_anon_cred);
      XPROCESS (proc)->gnutls_anon_cred = NULL;
    }

  if (XPROCESS (proc)->gnutls_state)
    {
      fn_gnutls_deinit (XPROCESS (proc)->gnutls_state);
      XPROCESS (proc)->gnutls_state = NULL;
      if (GNUTLS_INITSTAGE (proc) >= GNUTLS_STAGE_INIT)
	GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_INIT - 1;
    }

  XPROCESS (proc)->gnutls_p = 0;
  return Qt;
}

DEFUN ("gnutls-get-initstage", Fgnutls_get_initstage, Sgnutls_get_initstage, 1, 1, 0,
       doc: /* Return the GnuTLS init stage of process PROC.
See also `gnutls-boot'.  */)
  (Lisp_Object proc)
{
  CHECK_PROCESS (proc);

  return make_number (GNUTLS_INITSTAGE (proc));
}

DEFUN ("gnutls-errorp", Fgnutls_errorp, Sgnutls_errorp, 1, 1, 0,
       doc: /* Return t if ERROR indicates a GnuTLS problem.
ERROR is an integer or a symbol with an integer `gnutls-code' property.
usage: (gnutls-errorp ERROR)  */)
  (Lisp_Object err)
{
  if (EQ (err, Qt)) return Qnil;

  return Qt;
}

DEFUN ("gnutls-error-fatalp", Fgnutls_error_fatalp, Sgnutls_error_fatalp, 1, 1, 0,
       doc: /* Check if ERROR is fatal.
ERROR is an integer or a symbol with an integer `gnutls-code' property.
usage: (gnutls-error-fatalp ERROR)  */)
  (Lisp_Object err)
{
  Lisp_Object code;

  if (EQ (err, Qt)) return Qnil;

  if (SYMBOLP (err))
    {
      code = Fget (err, Qgnutls_code);
      if (NUMBERP (code))
	{
	  err = code;
	}
      else
	{
	  error ("Symbol has no numeric gnutls-code property");
	}
    }

  if (! TYPE_RANGED_INTEGERP (int, err))
    error ("Not an error symbol or code");

  if (0 == fn_gnutls_error_is_fatal (XINT (err)))
    return Qnil;

  return Qt;
}

DEFUN ("gnutls-error-string", Fgnutls_error_string, Sgnutls_error_string, 1, 1, 0,
       doc: /* Return a description of ERROR.
ERROR is an integer or a symbol with an integer `gnutls-code' property.
usage: (gnutls-error-string ERROR)  */)
  (Lisp_Object err)
{
  Lisp_Object code;

  if (EQ (err, Qt)) return build_string ("Not an error");

  if (SYMBOLP (err))
    {
      code = Fget (err, Qgnutls_code);
      if (NUMBERP (code))
	{
	  err = code;
	}
      else
	{
	  return build_string ("Symbol has no numeric gnutls-code property");
	}
    }

  if (! TYPE_RANGED_INTEGERP (int, err))
    return build_string ("Not an error symbol or code");

  return build_string (fn_gnutls_strerror (XINT (err)));
}

DEFUN ("gnutls-deinit", Fgnutls_deinit, Sgnutls_deinit, 1, 1, 0,
       doc: /* Deallocate GnuTLS resources associated with process PROC.
See also `gnutls-init'.  */)
  (Lisp_Object proc)
{
  return emacs_gnutls_deinit (proc);
}

DEFUN ("gnutls-available-p", Fgnutls_available_p, Sgnutls_available_p, 0, 0, 0,
       doc: /* Return t if GnuTLS is available in this instance of Emacs.  */)
     (void)
{
#ifdef WINDOWSNT
  Lisp_Object found = Fassq (Qgnutls_dll, Vlibrary_cache);
  if (CONSP (found))
    return XCDR (found);
  else
    {
      Lisp_Object status;
      status = init_gnutls_functions () ? Qt : Qnil;
      Vlibrary_cache = Fcons (Fcons (Qgnutls_dll, status), Vlibrary_cache);
      return status;
    }
#else
  return Qt;
#endif
}

Lisp_Object
gnutls_hex_string (char *buf, size_t buf_size, char *prefix) {
  size_t prefix_length = strlen (prefix);
  char *string = malloc (buf_size * 3 + prefix_length);
  Lisp_Object ret;

  strcpy (string, prefix);

  for (int i = 0; i < buf_size; i++)
    sprintf (string + i * 3 + prefix_length,
	     i == buf_size - 1? "%02x": "%02x:",
	     ((unsigned char*)buf)[i]);

  ret = build_string (string);
  free (string);
  return ret;
}

Lisp_Object
gnutls_certificate_details (gnutls_x509_crt_t cert)
{
  Lisp_Object res = Qnil;
  int err;

  /* Version. */
  {
    int version = fn_gnutls_x509_crt_get_version (cert);
    if (version >= GNUTLS_E_SUCCESS)
      res = nconc2 (res, list2 (intern (":version"),
				make_number (version)));
  }

  /* Serial. */
  {
    size_t serial_size = 0;

    err = fn_gnutls_x509_crt_get_serial (cert, NULL, &serial_size);
    if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
      char *serial = malloc (serial_size);
      err = fn_gnutls_x509_crt_get_serial (cert, serial, &serial_size);
      if (err >= GNUTLS_E_SUCCESS) {
	res = nconc2 (res, list2 (intern (":serial-number"),
				  gnutls_hex_string (serial, serial_size, "")));
      }
      free (serial);
    }
  }

  /* Issuer. */
  {
    size_t dn_size = 0;

    err = fn_gnutls_x509_crt_get_issuer_dn (cert, NULL, &dn_size);
    if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
      char *dn = malloc (dn_size);
      err = fn_gnutls_x509_crt_get_issuer_dn (cert, dn, &dn_size);
      if (err >= GNUTLS_E_SUCCESS)
	res = nconc2 (res, list2 (intern (":issuer"),
				  make_string (dn, dn_size)));
      free (dn);
    }
  }

  /* Validity. */
  {
    char buf[11];
    size_t buf_size = sizeof (buf);
    struct tm t;
    time_t tim = fn_gnutls_x509_crt_get_activation_time (cert);

    if (gmtime_r (&tim, &t) != NULL &&
	strftime (buf, buf_size, "%Y-%m-%d", &t) != 0)
      res = nconc2 (res, list2 (intern (":valid-from"), build_string (buf)));

    tim = fn_gnutls_x509_crt_get_expiration_time (cert);
    if (gmtime_r (&tim, &t) != NULL &&
	strftime (buf, buf_size, "%Y-%m-%d", &t) != 0)
      res = nconc2 (res, list2 (intern (":valid-to"), build_string (buf)));
  }

  /* Subject. */
  {
    size_t dn_size = 0;

    err = fn_gnutls_x509_crt_get_dn (cert, NULL, &dn_size);
    if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
      char *dn = malloc (dn_size);
      err = fn_gnutls_x509_crt_get_dn (cert, dn, &dn_size);
      if (err >= GNUTLS_E_SUCCESS)
	res = nconc2 (res, list2 (intern (":subject"),
				  make_string (dn, dn_size)));
      free (dn);
    }
  }

  /* SubjectPublicKeyInfo. */
  {
    unsigned int bits;

    err = fn_gnutls_x509_crt_get_pk_algorithm (cert, &bits);
    if (err >= GNUTLS_E_SUCCESS) {
      const char *name = fn_gnutls_pk_algorithm_get_name (err);
      if (name)
	res = nconc2 (res, list2 (intern (":public-key-algorithm"),
				  build_string (name)));

      name = fn_gnutls_sec_param_get_name (fn_gnutls_pk_bits_to_sec_param
					   (err, bits));
      res = nconc2 (res, list2 (intern (":certificate-security-level"),
				build_string (name)));
    }
  }

  /* Unique IDs. */
  {
    size_t buf_size = 0;

    err = fn_gnutls_x509_crt_get_issuer_unique_id (cert, NULL, &buf_size);
    if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
      char *buf = malloc (buf_size);
      err = fn_gnutls_x509_crt_get_issuer_unique_id (cert, buf, &buf_size);
      if (err >= GNUTLS_E_SUCCESS)
	res = nconc2 (res, list2 (intern (":issuer-unique-id"),
				  make_string (buf, buf_size)));
      free (buf);
    }

    buf_size = 0;
    err = fn_gnutls_x509_crt_get_subject_unique_id (cert, NULL, &buf_size);
    if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
      char *buf = malloc (buf_size);
      err = fn_gnutls_x509_crt_get_subject_unique_id (cert, buf, &buf_size);
      if (err >= GNUTLS_E_SUCCESS)
	res = nconc2 (res, list2 (intern (":subject-unique-id"),
				  make_string (buf, buf_size)));
      free (buf);
    }
  }

  /* Signature. */
  {
    size_t buf_size = 0;

    err = fn_gnutls_x509_crt_get_signature_algorithm (cert);
    if (err >= GNUTLS_E_SUCCESS) {
      const char *name = fn_gnutls_sign_algorithm_get_name (err);
      if (name)
	res = nconc2 (res, list2 (intern (":signature-algorithm"),
				  build_string (name)));

      err = fn_gnutls_x509_crt_get_signature (cert, NULL, &buf_size);
      if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
	char *buf = malloc (buf_size);
	err = fn_gnutls_x509_crt_get_signature (cert, buf, &buf_size);
	if (err >= GNUTLS_E_SUCCESS) {
	  res = nconc2 (res, list2 (intern (":signature"),
				    gnutls_hex_string (buf, buf_size, "")));
	}
	free (buf);
      }
    }
  }

  /* Public key ID. */
  {
    size_t buf_size = 0;

    err = fn_gnutls_x509_crt_get_key_id (cert, 0, NULL, &buf_size);
    if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
      unsigned char *buf = malloc (buf_size);
      err = fn_gnutls_x509_crt_get_key_id (cert, 0, buf, &buf_size);
      if (err >= GNUTLS_E_SUCCESS)
	  res = nconc2 (res, list2 (intern (":public-key-id"),
				    gnutls_hex_string ((char *)buf,
						       buf_size, "sha1:")));
      free (buf);
    }
  }

  /* Certificate fingerprint. */
  {
    size_t buf_size = 0;

    err = fn_gnutls_x509_crt_get_fingerprint (cert, GNUTLS_DIG_SHA1,
					      NULL, &buf_size);
    if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
      unsigned char *buf = malloc (buf_size);
      err = fn_gnutls_x509_crt_get_fingerprint (cert, GNUTLS_DIG_SHA1,
						buf, &buf_size);
      if (err >= GNUTLS_E_SUCCESS)
	  res = nconc2 (res, list2 (intern (":certificate-id"),
				    gnutls_hex_string ((char *)buf,
						       buf_size, "sha1:")));
      free (buf);
    }
  }

  return res;
}

DEFUN ("gnutls-peer-status", Fgnutls_peer_status, Sgnutls_peer_status, 1, 1, 0,
       doc: /* Return the status of the gnutls PROC peer certificate.
The return value is a property list.  */)
  (Lisp_Object proc)
{
  Lisp_Object warnings = Qnil, result = Qnil;
  unsigned int verification;

  CHECK_PROCESS (proc);

  if (XPROCESS (proc)->gnutls_p == 0)
    return Qnil;

  /* Then collect any warnings already computed by the handshake. */
  verification = XPROCESS (proc)->gnutls_peer_verification;

  if (verification & GNUTLS_CERT_INVALID)
    warnings = Fcons (list2 (intern (":invalid"),
			     build_string("certificate could not be verified")),
		      warnings);

  if (verification & GNUTLS_CERT_REVOKED)
    warnings = Fcons (list2 (intern (":revoked"),
			     build_string("certificate was revoked (CRL)")),
		      warnings);

  if (verification & GNUTLS_CERT_SIGNER_NOT_FOUND)
    warnings = Fcons (list2 (intern (":self-signed"),
			     build_string("certificate signer was not found (self-signed)")),
		      warnings);

  if (verification & GNUTLS_CERT_SIGNER_NOT_CA)
    warnings = Fcons (list2 (intern (":not-ca"),
			     build_string("certificate signer is not a CA")),
		      warnings);

  if (verification & GNUTLS_CERT_INSECURE_ALGORITHM)
    warnings = Fcons (list2 (intern (":insecure"),
			     build_string("certificate was signed with an insecure algorithm")),
		      warnings);

  if (verification & GNUTLS_CERT_NOT_ACTIVATED)
    warnings = Fcons (list2 (intern (":not-activated"),
			     build_string("certificate is not yet activated")),
		      warnings);

  if (verification & GNUTLS_CERT_EXPIRED)
    warnings = Fcons (list2 (intern (":expired"),
			     build_string("certificate has expired")),
		      warnings);

  if (XPROCESS (proc)->gnutls_extra_peer_verification &
      CERTIFICATE_NOT_MATCHING)
    warnings = Fcons (list2 (intern (":no-host-match"),
			     build_string("certificate host does not match hostname")),
		      warnings);

  if (!NILP (warnings))
    result = list2 (intern (":warnings"), warnings);

  result = nconc2 (result, list2
		   (intern (":certificate"),
		    gnutls_certificate_details(XPROCESS (proc)->gnutls_certificate)));

  return result;
}


/* Initializes global GnuTLS state to defaults.
Call `gnutls-global-deinit' when GnuTLS usage is no longer needed.
Returns zero on success.  */
static Lisp_Object
emacs_gnutls_global_init (void)
{
  int ret = GNUTLS_E_SUCCESS;

  if (!gnutls_global_initialized)
    {
      fn_gnutls_global_set_mem_functions (xmalloc, xmalloc, NULL,
					  xrealloc, xfree);
      ret = fn_gnutls_global_init ();
    }
  gnutls_global_initialized = 1;

  return gnutls_make_error (ret);
}

#if 0
/* Deinitializes global GnuTLS state.
See also `gnutls-global-init'.  */
static Lisp_Object
emacs_gnutls_global_deinit (void)
{
  if (gnutls_global_initialized)
    gnutls_global_deinit ();

  gnutls_global_initialized = 0;

  return gnutls_make_error (GNUTLS_E_SUCCESS);
}
#endif

DEFUN ("gnutls-boot", Fgnutls_boot, Sgnutls_boot, 3, 3, 0,
       doc: /* Initialize GnuTLS client for process PROC with TYPE+PROPLIST.
Currently only client mode is supported.  Return a success/failure
value you can check with `gnutls-errorp'.

TYPE is a symbol, either `gnutls-anon' or `gnutls-x509pki'.
PROPLIST is a property list with the following keys:

:hostname is a string naming the remote host.

:priority is a GnuTLS priority string, defaults to "NORMAL".

:trustfiles is a list of PEM-encoded trust files for `gnutls-x509pki'.

:crlfiles is a list of PEM-encoded CRL lists for `gnutls-x509pki'.

:keylist is an alist of PEM-encoded key files and PEM-encoded
certificates for `gnutls-x509pki'.

:callbacks is an alist of callback functions, see below.

:loglevel is the debug level requested from GnuTLS, try 4.

:verify-flags is a bitset as per GnuTLS'
gnutls_certificate_set_verify_flags.

:verify-hostname-error is ignored.  Pass :hostname in :verify-error
instead.

:verify-error is a list of symbols to express verification checks or
`t' to do all checks.  Currently it can contain `:trustfiles' and
`:hostname' to verify the certificate or the hostname respectively.

:min-prime-bits is the minimum accepted number of bits the client will
accept in Diffie-Hellman key exchange.

The debug level will be set for this process AND globally for GnuTLS.
So if you set it higher or lower at any point, it affects global
debugging.

Note that the priority is set on the client.  The server does not use
the protocols's priority except for disabling protocols that were not
specified.

Processes must be initialized with this function before other GnuTLS
functions are used.  This function allocates resources which can only
be deallocated by calling `gnutls-deinit' or by calling it again.

The callbacks alist can have a `verify' key, associated with a
verification function (UNUSED).

Each authentication type may need additional information in order to
work.  For X.509 PKI (`gnutls-x509pki'), you probably need at least
one trustfile (usually a CA bundle).  */)
  (Lisp_Object proc, Lisp_Object type, Lisp_Object proplist)
{
  int ret = GNUTLS_E_SUCCESS;
  int max_log_level = 0;
  bool verify_error_all = 0;

  gnutls_session_t state;
  gnutls_certificate_credentials_t x509_cred = NULL;
  gnutls_anon_client_credentials_t anon_cred = NULL;
  Lisp_Object global_init;
  char const *priority_string_ptr = "NORMAL"; /* default priority string.  */
  unsigned int peer_verification;
  char *c_hostname;

  /* Placeholders for the property list elements.  */
  Lisp_Object priority_string;
  Lisp_Object trustfiles;
  Lisp_Object crlfiles;
  Lisp_Object keylist;
  /* Lisp_Object callbacks; */
  Lisp_Object loglevel;
  Lisp_Object hostname;
  Lisp_Object verify_error;
  Lisp_Object prime_bits;

  CHECK_PROCESS (proc);
  CHECK_SYMBOL (type);
  CHECK_LIST (proplist);

  if (NILP (Fgnutls_available_p ()))
    error ("GnuTLS not available");

  if (!EQ (type, Qgnutls_x509pki) && !EQ (type, Qgnutls_anon))
    error ("Invalid GnuTLS credential type");

  hostname              = Fplist_get (proplist, QCgnutls_bootprop_hostname);
  priority_string       = Fplist_get (proplist, QCgnutls_bootprop_priority);
  trustfiles            = Fplist_get (proplist, QCgnutls_bootprop_trustfiles);
  keylist               = Fplist_get (proplist, QCgnutls_bootprop_keylist);
  crlfiles              = Fplist_get (proplist, QCgnutls_bootprop_crlfiles);
  loglevel              = Fplist_get (proplist, QCgnutls_bootprop_loglevel);
  verify_error          = Fplist_get (proplist, QCgnutls_bootprop_verify_error);
  prime_bits            = Fplist_get (proplist, QCgnutls_bootprop_min_prime_bits);

  if (EQ (verify_error, Qt))
    {
      verify_error_all = 1;
    }
  else if (NILP (Flistp (verify_error)))
    {
      error ("gnutls-boot: invalid :verify_error parameter (not a list)");
    }

  if (!STRINGP (hostname))
    error ("gnutls-boot: invalid :hostname parameter (not a string)");
  c_hostname = SSDATA (hostname);

  state = XPROCESS (proc)->gnutls_state;

  if (TYPE_RANGED_INTEGERP (int, loglevel))
    {
      fn_gnutls_global_set_log_function (gnutls_log_function);
#ifdef HAVE_GNUTLS3
      fn_gnutls_global_set_audit_log_function (gnutls_audit_log_function);
#endif
      fn_gnutls_global_set_log_level (XINT (loglevel));
      max_log_level = XINT (loglevel);
      XPROCESS (proc)->gnutls_log_level = max_log_level;
    }

  /* always initialize globals.  */
  global_init = emacs_gnutls_global_init ();
  if (! NILP (Fgnutls_errorp (global_init)))
    return global_init;

  /* Before allocating new credentials, deallocate any credentials
     that PROC might already have.  */
  emacs_gnutls_deinit (proc);

  /* Mark PROC as a GnuTLS process.  */
  XPROCESS (proc)->gnutls_state = NULL;
  XPROCESS (proc)->gnutls_x509_cred = NULL;
  XPROCESS (proc)->gnutls_anon_cred = NULL;
  pset_gnutls_cred_type (XPROCESS (proc), type);
  GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_EMPTY;

  GNUTLS_LOG (1, max_log_level, "allocating credentials");
  if (EQ (type, Qgnutls_x509pki))
    {
      Lisp_Object verify_flags;
      unsigned int gnutls_verify_flags = GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT;

      GNUTLS_LOG (2, max_log_level, "allocating x509 credentials");
      fn_gnutls_certificate_allocate_credentials (&x509_cred);
      XPROCESS (proc)->gnutls_x509_cred = x509_cred;

      verify_flags = Fplist_get (proplist, QCgnutls_bootprop_verify_flags);
      if (NUMBERP (verify_flags))
	{
	  gnutls_verify_flags = XINT (verify_flags);
	  GNUTLS_LOG (2, max_log_level, "setting verification flags");
	}
      else if (NILP (verify_flags))
	GNUTLS_LOG (2, max_log_level, "using default verification flags");
      else
	GNUTLS_LOG (2, max_log_level, "ignoring invalid verify-flags");

      fn_gnutls_certificate_set_verify_flags (x509_cred, gnutls_verify_flags);
    }
  else /* Qgnutls_anon: */
    {
      GNUTLS_LOG (2, max_log_level, "allocating anon credentials");
      fn_gnutls_anon_allocate_client_credentials (&anon_cred);
      XPROCESS (proc)->gnutls_anon_cred = anon_cred;
    }

  GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_CRED_ALLOC;

  if (EQ (type, Qgnutls_x509pki))
    {
      /* TODO: GNUTLS_X509_FMT_DER is also an option.  */
      int file_format = GNUTLS_X509_FMT_PEM;
      Lisp_Object tail;

      for (tail = trustfiles; CONSP (tail); tail = XCDR (tail))
	{
	  Lisp_Object trustfile = XCAR (tail);
	  if (STRINGP (trustfile))
	    {
	      GNUTLS_LOG2 (1, max_log_level, "setting the trustfile: ",
			   SSDATA (trustfile));
	      trustfile = ENCODE_FILE (trustfile);
#ifdef WINDOWSNT
	      /* Since GnuTLS doesn't support UTF-8 or UTF-16 encoded
		 file names on Windows, we need to re-encode the file
		 name using the current ANSI codepage.  */
	      trustfile = ansi_encode_filename (trustfile);
#endif
	      ret = fn_gnutls_certificate_set_x509_trust_file
		(x509_cred,
		 SSDATA (trustfile),
		 file_format);

	      if (ret < GNUTLS_E_SUCCESS)
		return gnutls_make_error (ret);
	    }
	  else
	    {
	      emacs_gnutls_deinit (proc);
	      error ("Invalid trustfile");
	    }
	}

      for (tail = crlfiles; CONSP (tail); tail = XCDR (tail))
	{
	  Lisp_Object crlfile = XCAR (tail);
	  if (STRINGP (crlfile))
	    {
	      GNUTLS_LOG2 (1, max_log_level, "setting the CRL file: ",
			   SSDATA (crlfile));
	      crlfile = ENCODE_FILE (crlfile);
#ifdef WINDOWSNT
	      crlfile = ansi_encode_filename (crlfile);
#endif
	      ret = fn_gnutls_certificate_set_x509_crl_file
		(x509_cred, SSDATA (crlfile), file_format);

	      if (ret < GNUTLS_E_SUCCESS)
		return gnutls_make_error (ret);
	    }
	  else
	    {
	      emacs_gnutls_deinit (proc);
	      error ("Invalid CRL file");
	    }
	}

      for (tail = keylist; CONSP (tail); tail = XCDR (tail))
	{
	  Lisp_Object keyfile = Fcar (XCAR (tail));
	  Lisp_Object certfile = Fcar (Fcdr (XCAR (tail)));
	  if (STRINGP (keyfile) && STRINGP (certfile))
	    {
	      GNUTLS_LOG2 (1, max_log_level, "setting the client key file: ",
			   SSDATA (keyfile));
	      GNUTLS_LOG2 (1, max_log_level, "setting the client cert file: ",
			   SSDATA (certfile));
	      keyfile = ENCODE_FILE (keyfile);
	      certfile = ENCODE_FILE (certfile);
#ifdef WINDOWSNT
	      keyfile = ansi_encode_filename (keyfile);
	      certfile = ansi_encode_filename (certfile);
#endif
	      ret = fn_gnutls_certificate_set_x509_key_file
		(x509_cred, SSDATA (certfile), SSDATA (keyfile), file_format);

	      if (ret < GNUTLS_E_SUCCESS)
		return gnutls_make_error (ret);
	    }
	  else
	    {
	      emacs_gnutls_deinit (proc);
	      error (STRINGP (keyfile) ? "Invalid client cert file"
		     : "Invalid client key file");
	    }
	}
    }

  GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_FILES;
  GNUTLS_LOG (1, max_log_level, "gnutls callbacks");
  GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_CALLBACKS;

  /* Call gnutls_init here: */

  GNUTLS_LOG (1, max_log_level, "gnutls_init");
  ret = fn_gnutls_init (&state, GNUTLS_CLIENT);
  XPROCESS (proc)->gnutls_state = state;
  if (ret < GNUTLS_E_SUCCESS)
    return gnutls_make_error (ret);
  GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_INIT;

  if (STRINGP (priority_string))
    {
      priority_string_ptr = SSDATA (priority_string);
      GNUTLS_LOG2 (1, max_log_level, "got non-default priority string:",
		   priority_string_ptr);
    }
  else
    {
      GNUTLS_LOG2 (1, max_log_level, "using default priority string:",
		   priority_string_ptr);
    }

  GNUTLS_LOG (1, max_log_level, "setting the priority string");
  ret = fn_gnutls_priority_set_direct (state,
				       priority_string_ptr,
				       NULL);
  if (ret < GNUTLS_E_SUCCESS)
    return gnutls_make_error (ret);

  GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_PRIORITY;

  if (INTEGERP (prime_bits))
    fn_gnutls_dh_set_prime_bits (state, XUINT (prime_bits));

  ret = EQ (type, Qgnutls_x509pki)
    ? fn_gnutls_credentials_set (state, GNUTLS_CRD_CERTIFICATE, x509_cred)
    : fn_gnutls_credentials_set (state, GNUTLS_CRD_ANON, anon_cred);
  if (ret < GNUTLS_E_SUCCESS)
    return gnutls_make_error (ret);

  GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_CRED_SET;
  ret = emacs_gnutls_handshake (XPROCESS (proc));
  if (ret < GNUTLS_E_SUCCESS)
    return gnutls_make_error (ret);

  /* Now verify the peer, following
     http://www.gnu.org/software/gnutls/manual/html_node/Verifying-peer_0027s-certificate.html.
     The peer should present at least one certificate in the chain; do a
     check of the certificate's hostname with
     gnutls_x509_crt_check_hostname() against :hostname.  */

  ret = fn_gnutls_certificate_verify_peers2 (state, &peer_verification);
  if (ret < GNUTLS_E_SUCCESS)
    return gnutls_make_error (ret);

  XPROCESS (proc)->gnutls_peer_verification = peer_verification;

  if (XINT (loglevel) > 0 && peer_verification & GNUTLS_CERT_INVALID)
    message ("%s certificate could not be verified.", c_hostname);

  if (peer_verification & GNUTLS_CERT_REVOKED)
    GNUTLS_LOG2 (1, max_log_level, "certificate was revoked (CRL):",
		 c_hostname);

  if (peer_verification & GNUTLS_CERT_SIGNER_NOT_FOUND)
    GNUTLS_LOG2 (1, max_log_level, "certificate signer was not found:",
		 c_hostname);

  if (peer_verification & GNUTLS_CERT_SIGNER_NOT_CA)
    GNUTLS_LOG2 (1, max_log_level, "certificate signer is not a CA:",
		 c_hostname);

  if (peer_verification & GNUTLS_CERT_INSECURE_ALGORITHM)
    GNUTLS_LOG2 (1, max_log_level,
		 "certificate was signed with an insecure algorithm:",
		 c_hostname);

  if (peer_verification & GNUTLS_CERT_NOT_ACTIVATED)
    GNUTLS_LOG2 (1, max_log_level, "certificate is not yet activated:",
		 c_hostname);

  if (peer_verification & GNUTLS_CERT_EXPIRED)
    GNUTLS_LOG2 (1, max_log_level, "certificate has expired:",
		 c_hostname);

  if (peer_verification != 0)
    {
      if (verify_error_all
          || !NILP (Fmember (QCgnutls_bootprop_trustfiles, verify_error)))
        {
	  emacs_gnutls_deinit (proc);
	  error ("Certificate validation failed %s, verification code %d",
		 c_hostname, peer_verification);
        }
      else
	{
          GNUTLS_LOG2 (1, max_log_level, "certificate validation failed:",
                       c_hostname);
	}
    }

  /* Up to here the process is the same for X.509 certificates and
     OpenPGP keys.  From now on X.509 certificates are assumed.  This
     can be easily extended to work with openpgp keys as well.  */
  if (fn_gnutls_certificate_type_get (state) == GNUTLS_CRT_X509)
    {
      gnutls_x509_crt_t gnutls_verify_cert;
      const gnutls_datum_t *gnutls_verify_cert_list;
      unsigned int gnutls_verify_cert_list_size;

      ret = fn_gnutls_x509_crt_init (&gnutls_verify_cert);
      if (ret < GNUTLS_E_SUCCESS)
	return gnutls_make_error (ret);

      gnutls_verify_cert_list =
	fn_gnutls_certificate_get_peers (state, &gnutls_verify_cert_list_size);

      if (gnutls_verify_cert_list == NULL)
	{
	  fn_gnutls_x509_crt_deinit (gnutls_verify_cert);
	  emacs_gnutls_deinit (proc);
	  error ("No x509 certificate was found\n");
	}

      /* We only check the first certificate in the given chain.  */
      ret = fn_gnutls_x509_crt_import (gnutls_verify_cert,
				       &gnutls_verify_cert_list[0],
				       GNUTLS_X509_FMT_DER);

      if (ret < GNUTLS_E_SUCCESS)
	{
	  fn_gnutls_x509_crt_deinit (gnutls_verify_cert);
	  return gnutls_make_error (ret);
	}

      XPROCESS (proc)->gnutls_certificate = gnutls_verify_cert;

      if (!fn_gnutls_x509_crt_check_hostname (gnutls_verify_cert, c_hostname))
	{
	  XPROCESS (proc)->gnutls_extra_peer_verification |=
	    CERTIFICATE_NOT_MATCHING;
          if (verify_error_all
              || !NILP (Fmember (QCgnutls_bootprop_hostname, verify_error)))
            {
	      fn_gnutls_x509_crt_deinit (gnutls_verify_cert);
	      emacs_gnutls_deinit (proc);
	      error ("The x509 certificate does not match \"%s\"", c_hostname);
            }
	  else
	    {
              GNUTLS_LOG2 (1, max_log_level, "x509 certificate does not match:",
                           c_hostname);
	    }
	}
    }

  /* Set this flag only if the whole initialization succeeded.  */
  XPROCESS (proc)->gnutls_p = 1;

  return gnutls_make_error (ret);
}

DEFUN ("gnutls-bye", Fgnutls_bye,
       Sgnutls_bye, 2, 2, 0,
       doc: /* Terminate current GnuTLS connection for process PROC.
The connection should have been initiated using `gnutls-handshake'.

If CONT is not nil the TLS connection gets terminated and further
receives and sends will be disallowed.  If the return value is zero you
may continue using the connection.  If CONT is nil, GnuTLS actually
sends an alert containing a close request and waits for the peer to
reply with the same message.  In order to reuse the connection you
should wait for an EOF from the peer.

This function may also return `gnutls-e-again', or
`gnutls-e-interrupted'.  */)
    (Lisp_Object proc, Lisp_Object cont)
{
  gnutls_session_t state;
  int ret;

  CHECK_PROCESS (proc);

  state = XPROCESS (proc)->gnutls_state;

  fn_gnutls_x509_crt_deinit (XPROCESS (proc)->gnutls_certificate);

  ret = fn_gnutls_bye (state,
		       NILP (cont) ? GNUTLS_SHUT_RDWR : GNUTLS_SHUT_WR);

  return gnutls_make_error (ret);
}

void
syms_of_gnutls (void)
{
  gnutls_global_initialized = 0;

  DEFSYM (Qgnutls_dll, "gnutls");
  DEFSYM (Qgnutls_code, "gnutls-code");
  DEFSYM (Qgnutls_anon, "gnutls-anon");
  DEFSYM (Qgnutls_x509pki, "gnutls-x509pki");
  DEFSYM (QCgnutls_bootprop_hostname, ":hostname");
  DEFSYM (QCgnutls_bootprop_priority, ":priority");
  DEFSYM (QCgnutls_bootprop_trustfiles, ":trustfiles");
  DEFSYM (QCgnutls_bootprop_keylist, ":keylist");
  DEFSYM (QCgnutls_bootprop_crlfiles, ":crlfiles");
  DEFSYM (QCgnutls_bootprop_callbacks, ":callbacks");
  DEFSYM (QCgnutls_bootprop_callbacks_verify, "verify");
  DEFSYM (QCgnutls_bootprop_min_prime_bits, ":min-prime-bits");
  DEFSYM (QCgnutls_bootprop_loglevel, ":loglevel");
  DEFSYM (QCgnutls_bootprop_verify_flags, ":verify-flags");
  DEFSYM (QCgnutls_bootprop_verify_error, ":verify-error");

  DEFSYM (Qgnutls_e_interrupted, "gnutls-e-interrupted");
  Fput (Qgnutls_e_interrupted, Qgnutls_code,
	make_number (GNUTLS_E_INTERRUPTED));

  DEFSYM (Qgnutls_e_again, "gnutls-e-again");
  Fput (Qgnutls_e_again, Qgnutls_code,
	make_number (GNUTLS_E_AGAIN));

  DEFSYM (Qgnutls_e_invalid_session, "gnutls-e-invalid-session");
  Fput (Qgnutls_e_invalid_session, Qgnutls_code,
	make_number (GNUTLS_E_INVALID_SESSION));

  DEFSYM (Qgnutls_e_not_ready_for_handshake, "gnutls-e-not-ready-for-handshake");
  Fput (Qgnutls_e_not_ready_for_handshake, Qgnutls_code,
	make_number (GNUTLS_E_APPLICATION_ERROR_MIN));

  defsubr (&Sgnutls_get_initstage);
  defsubr (&Sgnutls_errorp);
  defsubr (&Sgnutls_error_fatalp);
  defsubr (&Sgnutls_error_string);
  defsubr (&Sgnutls_boot);
  defsubr (&Sgnutls_deinit);
  defsubr (&Sgnutls_bye);
  defsubr (&Sgnutls_available_p);
  defsubr (&Sgnutls_peer_status);

  DEFVAR_INT ("gnutls-log-level", global_gnutls_log_level,
	      doc: /* Logging level used by the GnuTLS functions.
Set this larger than 0 to get debug output in the *Messages* buffer.
1 is for important messages, 2 is for debug data, and higher numbers
are as per the GnuTLS logging conventions.  */);
  global_gnutls_log_level = 0;
}

#endif /* HAVE_GNUTLS */