openssl.c

                     NULL);

  /* give application a chance to interfere with SSL set up. */
  if(data->set.ssl.fsslctx) {
    result = (*data->set.ssl.fsslctx)(data, connssl->ctx,
                                      data->set.ssl.fsslctxp);
    if(result) {
      failf(data, "error signaled by ssl ctx callback");
      return result;
    }
  }

  /* Lets make an SSL structure */
  if(connssl->handle)
    SSL_free(connssl->handle);
  connssl->handle = SSL_new(connssl->ctx);
  if(!connssl->handle) {
    failf(data, "SSL: couldn't create a context (handle)!");
    return CURLE_OUT_OF_MEMORY;
  }

#if (OPENSSL_VERSION_NUMBER >= 0x0090808fL) && !defined(OPENSSL_NO_TLSEXT) && \
    !defined(OPENSSL_IS_BORINGSSL)
  if(data->set.ssl.verifystatus)
    SSL_set_tlsext_status_type(connssl->handle, TLSEXT_STATUSTYPE_ocsp);
#endif

  SSL_set_connect_state(connssl->handle);

  connssl->server_cert = 0x0;

#ifdef SSL_CTRL_SET_TLSEXT_HOSTNAME
  if((0 == Curl_inet_pton(AF_INET, conn->host.name, &addr)) &&
#ifdef ENABLE_IPV6
     (0 == Curl_inet_pton(AF_INET6, conn->host.name, &addr)) &&
#endif
     sni &&
     !SSL_set_tlsext_host_name(connssl->handle, conn->host.name))
    infof(data, "WARNING: failed to configure server name indication (SNI) "
          "TLS extension\n");
#endif

  /* Check if there's a cached ID we can/should use here! */
  if(!Curl_ssl_getsessionid(conn, &ssl_sessionid, NULL)) {
    /* we got a session id, use it! */
    if(!SSL_set_session(connssl->handle, ssl_sessionid)) {
      failf(data, "SSL: SSL_set_session failed: %s",
            ERR_error_string(ERR_get_error(), NULL));
      return CURLE_SSL_CONNECT_ERROR;
    }
    /* Informational message */
    infof (data, "SSL re-using session ID\n");
  }

  /* pass the raw socket into the SSL layers */
  if(!SSL_set_fd(connssl->handle, (int)sockfd)) {
    failf(data, "SSL: SSL_set_fd failed: %s",
          ERR_error_string(ERR_get_error(), NULL));
    return CURLE_SSL_CONNECT_ERROR;
  }

  connssl->connecting_state = ssl_connect_2;

  return CURLE_OK;
}

static CURLcode ossl_connect_step2(struct connectdata *conn, int sockindex)
{
  struct SessionHandle *data = conn->data;
  int err;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  DEBUGASSERT(ssl_connect_2 == connssl->connecting_state
             || ssl_connect_2_reading == connssl->connecting_state
             || ssl_connect_2_writing == connssl->connecting_state);

  ERR_clear_error();

  err = SSL_connect(connssl->handle);

  /* 1  is fine
     0  is "not successful but was shut down controlled"
     <0 is "handshake was not successful, because a fatal error occurred" */
  if(1 != err) {
    int detail = SSL_get_error(connssl->handle, err);

    if(SSL_ERROR_WANT_READ == detail) {
      connssl->connecting_state = ssl_connect_2_reading;
      return CURLE_OK;
    }
    else if(SSL_ERROR_WANT_WRITE == detail) {
      connssl->connecting_state = ssl_connect_2_writing;
      return CURLE_OK;
    }
    else {
      /* untreated error */
      unsigned long errdetail;
      char error_buffer[256]=""; /* OpenSSL documents that this must be at
                                    least 256 bytes long. */
      CURLcode result;
      long lerr;

      connssl->connecting_state = ssl_connect_2; /* the connection failed,
                                                    we're not waiting for
                                                    anything else. */

      errdetail = ERR_get_error(); /* Gets the earliest error code from the
                                      thread's error queue and removes the
                                      entry. */

      switch(errdetail) {
      case 0x1407E086:
        /* 1407E086:
           SSL routines:
           SSL2_SET_CERTIFICATE:
           certificate verify failed */
        /* fall-through */
      case 0x14090086:
        /* 14090086:
           SSL routines:
           SSL3_GET_SERVER_CERTIFICATE:
           certificate verify failed */
        result = CURLE_SSL_CACERT;

        lerr = SSL_get_verify_result(connssl->handle);
        if(lerr != X509_V_OK) {
          snprintf(error_buffer, sizeof(error_buffer),
                   "SSL certificate problem: %s",
                   X509_verify_cert_error_string(lerr));
        }
        else
          /* strcpy() is fine here as long as the string fits within
             error_buffer */
          strcpy(error_buffer,
                 "SSL certificate problem, check your CA cert");
        break;
      default:
        result = CURLE_SSL_CONNECT_ERROR;
        SSL_strerror(errdetail, error_buffer, sizeof(error_buffer));
        break;
      }

      /* detail is already set to the SSL error above */

      /* If we e.g. use SSLv2 request-method and the server doesn't like us
       * (RST connection etc.), OpenSSL gives no explanation whatsoever and
       * the SO_ERROR is also lost.
       */
      if(CURLE_SSL_CONNECT_ERROR == result && errdetail == 0) {
        failf(data, "Unknown SSL protocol error in connection to %s:%ld ",
              conn->host.name, conn->remote_port);
        return result;
      }

      /* Could be a CERT problem */
      failf(data, "%s", error_buffer);

      return result;
    }
  }
  else {
    /* we have been connected fine, we're not waiting for anything else. */
    connssl->connecting_state = ssl_connect_3;

    /* Informational message */
    infof(data, "SSL connection using %s / %s\n",
          get_ssl_version_txt(connssl->handle),
          SSL_get_cipher(connssl->handle));

#ifdef HAS_ALPN
    /* Sets data and len to negotiated protocol, len is 0 if no protocol was
     * negotiated
     */
    if(data->set.ssl_enable_alpn) {
      const unsigned char* neg_protocol;
      unsigned int len;
      SSL_get0_alpn_selected(connssl->handle, &neg_protocol, &len);
      if(len != 0) {
        infof(data, "ALPN, server accepted to use %.*s\n", len, neg_protocol);

#ifdef USE_NGHTTP2
        if(len == NGHTTP2_PROTO_VERSION_ID_LEN &&
           !memcmp(NGHTTP2_PROTO_VERSION_ID, neg_protocol, len)) {
          conn->negnpn = CURL_HTTP_VERSION_2_0;
        }
        else
#endif
        if(len == ALPN_HTTP_1_1_LENGTH &&
           !memcmp(ALPN_HTTP_1_1, neg_protocol, ALPN_HTTP_1_1_LENGTH)) {
          conn->negnpn = CURL_HTTP_VERSION_1_1;
        }
      }
      else
        infof(data, "ALPN, server did not agree to a protocol\n");
    }
#endif

    return CURLE_OK;
  }
}

static int asn1_object_dump(ASN1_OBJECT *a, char *buf, size_t len)
{
  int i, ilen;

  if((ilen = (int)len) < 0)
    return 1; /* buffer too big */

  i = i2t_ASN1_OBJECT(buf, ilen, a);

  if(i >= ilen)
    return 1; /* buffer too small */

  return 0;
}

#define push_certinfo(_label, _num) \
do {                              \
  long info_len = BIO_get_mem_data(mem, &ptr); \
  Curl_ssl_push_certinfo_len(data, _num, _label, ptr, info_len); \
  BIO_reset(mem); \
} WHILE_FALSE

static void pubkey_show(struct SessionHandle *data,
                        BIO *mem,
                        int num,
                        const char *type,
                        const char *name,
                        BIGNUM *bn)
{
  char *ptr;
  char namebuf[32];

  snprintf(namebuf, sizeof(namebuf), "%s(%s)", type, name);

  BN_print(mem, bn);
  push_certinfo(namebuf, num);
}

#define print_pubkey_BN(_type, _name, _num)    \
do {                              \
  if(pubkey->pkey._type->_name) { \
    pubkey_show(data, mem, _num, #_type, #_name, pubkey->pkey._type->_name); \
  } \
} WHILE_FALSE

static int X509V3_ext(struct SessionHandle *data,
                      int certnum,
                      STACK_OF(X509_EXTENSION) *exts)
{
  int i;
  size_t j;

  if(sk_X509_EXTENSION_num(exts) <= 0)
    /* no extensions, bail out */
    return 1;

  for(i=0; i<sk_X509_EXTENSION_num(exts); i++) {
    ASN1_OBJECT *obj;
    X509_EXTENSION *ext = sk_X509_EXTENSION_value(exts, i);
    BUF_MEM *biomem;
    char buf[512];
    char *ptr=buf;
    char namebuf[128];
    BIO *bio_out = BIO_new(BIO_s_mem());

    if(!bio_out)
      return 1;

    obj = X509_EXTENSION_get_object(ext);

    asn1_object_dump(obj, namebuf, sizeof(namebuf));

    if(!X509V3_EXT_print(bio_out, ext, 0, 0))
      ASN1_STRING_print(bio_out, (ASN1_STRING *)X509_EXTENSION_get_data(ext));

    BIO_get_mem_ptr(bio_out, &biomem);

    for(j = 0; j < (size_t)biomem->length; j++) {
      const char *sep="";
      if(biomem->data[j] == '\n') {
        sep=", ";
        j++; /* skip the newline */
      };
      while((j<(size_t)biomem->length) && (biomem->data[j] == ' '))
        j++;
      if(j<(size_t)biomem->length)
        ptr+=snprintf(ptr, sizeof(buf)-(ptr-buf), "%s%c", sep,
                      biomem->data[j]);
    }

    Curl_ssl_push_certinfo(data, certnum, namebuf, buf);

    BIO_free(bio_out);

  }
  return 0; /* all is fine */
}

static CURLcode get_cert_chain(struct connectdata *conn,
                               struct ssl_connect_data *connssl)

{
  CURLcode result;
  STACK_OF(X509) *sk;
  int i;
  struct SessionHandle *data = conn->data;
  int numcerts;
  BIO *mem;

  sk = SSL_get_peer_cert_chain(connssl->handle);
  if(!sk) {
    return CURLE_OUT_OF_MEMORY;
  }

  numcerts = sk_X509_num(sk);

  result = Curl_ssl_init_certinfo(data, numcerts);
  if(result) {
    return result;
  }

  mem = BIO_new(BIO_s_mem());

  for(i = 0; i < numcerts; i++) {
    ASN1_INTEGER *num;

    X509 *x = sk_X509_value(sk, i);

    X509_CINF *cinf;
    EVP_PKEY *pubkey=NULL;
    int j;
    char *ptr;

    X509_NAME_print_ex(mem, X509_get_subject_name(x), 0, XN_FLAG_ONELINE);
    push_certinfo("Subject", i);

    X509_NAME_print_ex(mem, X509_get_issuer_name(x), 0, XN_FLAG_ONELINE);
    push_certinfo("Issuer", i);

    BIO_printf(mem, "%lx", X509_get_version(x));
    push_certinfo("Version", i);

    num = X509_get_serialNumber(x);
    if(num->type == V_ASN1_NEG_INTEGER)
      BIO_puts(mem, "-");
    for(j = 0; j < num->length; j++)
      BIO_printf(mem, "%02x", num->data[j]);
    push_certinfo("Serial Number", i);

    cinf = x->cert_info;

    i2a_ASN1_OBJECT(mem, cinf->signature->algorithm);
    push_certinfo("Signature Algorithm", i);

    ASN1_TIME_print(mem, X509_get_notBefore(x));
    push_certinfo("Start date", i);

    ASN1_TIME_print(mem, X509_get_notAfter(x));
    push_certinfo("Expire date", i);

    i2a_ASN1_OBJECT(mem, cinf->key->algor->algorithm);
    push_certinfo("Public Key Algorithm", i);

    pubkey = X509_get_pubkey(x);
    if(!pubkey)
      infof(data, "   Unable to load public key\n");
    else {
      switch(pubkey->type) {
      case EVP_PKEY_RSA:
        BIO_printf(mem, "%d", BN_num_bits(pubkey->pkey.rsa->n));
        push_certinfo("RSA Public Key", i);

        print_pubkey_BN(rsa, n, i);
        print_pubkey_BN(rsa, e, i);
        print_pubkey_BN(rsa, d, i);
        print_pubkey_BN(rsa, p, i);
        print_pubkey_BN(rsa, q, i);
        print_pubkey_BN(rsa, dmp1, i);
        print_pubkey_BN(rsa, dmq1, i);
        print_pubkey_BN(rsa, iqmp, i);
        break;
      case EVP_PKEY_DSA:
        print_pubkey_BN(dsa, p, i);
        print_pubkey_BN(dsa, q, i);
        print_pubkey_BN(dsa, g, i);
        print_pubkey_BN(dsa, priv_key, i);
        print_pubkey_BN(dsa, pub_key, i);
        break;
      case EVP_PKEY_DH:
        print_pubkey_BN(dh, p, i);
        print_pubkey_BN(dh, g, i);
        print_pubkey_BN(dh, priv_key, i);
        print_pubkey_BN(dh, pub_key, i);
        break;
#if 0
      case EVP_PKEY_EC: /* symbol not present in OpenSSL 0.9.6 */
        /* left TODO */
        break;
#endif
      }
      EVP_PKEY_free(pubkey);
    }

    X509V3_ext(data, i, cinf->extensions);

    for(j = 0; j < x->signature->length; j++)
      BIO_printf(mem, "%02x:", x->signature->data[j]);
    push_certinfo("Signature", i);

    PEM_write_bio_X509(mem, x);
    push_certinfo("Cert", i);
  }

  BIO_free(mem);

  return CURLE_OK;
}

/*
 * Heavily modified from:
 * https://www.owasp.org/index.php/Certificate_and_Public_Key_Pinning#OpenSSL
 */
static CURLcode pkp_pin_peer_pubkey(struct SessionHandle *data, X509* cert,
                                    const char *pinnedpubkey)
{
  /* Scratch */
  int len1 = 0, len2 = 0;
  unsigned char *buff1 = NULL, *temp = NULL;

  /* Result is returned to caller */
  CURLcode result = CURLE_SSL_PINNEDPUBKEYNOTMATCH;

  /* if a path wasn't specified, don't pin */
  if(!pinnedpubkey)
    return CURLE_OK;

  if(!cert)
    return result;

  do {
    /* Begin Gyrations to get the subjectPublicKeyInfo     */
    /* Thanks to Viktor Dukhovni on the OpenSSL mailing list */

    /* https://groups.google.com/group/mailing.openssl.users/browse_thread
     /thread/d61858dae102c6c7 */
    len1 = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), NULL);
    if(len1 < 1)
      break; /* failed */

    /* https://www.openssl.org/docs/crypto/buffer.html */
    buff1 = temp = OPENSSL_malloc(len1);
    if(!buff1)
      break; /* failed */

    /* https://www.openssl.org/docs/crypto/d2i_X509.html */
    len2 = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), &temp);

    /*
     * These checks are verifying we got back the same values as when we
     * sized the buffer. It's pretty weak since they should always be the
     * same. But it gives us something to test.
     */
    if((len1 != len2) || !temp || ((temp - buff1) != len1))
      break; /* failed */

    /* End Gyrations */

    /* The one good exit point */
    result = Curl_pin_peer_pubkey(data, pinnedpubkey, buff1, len1);
  } while(0);

  /* https://www.openssl.org/docs/crypto/buffer.html */
  if(buff1)
    OPENSSL_free(buff1);

  return result;
}

/*
 * Get the server cert, verify it and show it etc, only call failf() if the
 * 'strict' argument is TRUE as otherwise all this is for informational
 * purposes only!
 *
 * We check certificates to authenticate the server; otherwise we risk
 * man-in-the-middle attack.
 */
static CURLcode servercert(struct connectdata *conn,
                           struct ssl_connect_data *connssl,
                           bool strict)
{
  CURLcode result = CURLE_OK;
  int rc;
  long lerr, len;
  struct SessionHandle *data = conn->data;
  X509 *issuer;
  FILE *fp;
  char *buffer = data->state.buffer;
  const char *ptr;
  BIO *mem = BIO_new(BIO_s_mem());

  if(data->set.ssl.certinfo)
    /* we've been asked to gather certificate info! */
    (void)get_cert_chain(conn, connssl);

  connssl->server_cert = SSL_get_peer_certificate(connssl->handle);
  if(!connssl->server_cert) {
    if(!strict)
      return CURLE_OK;

    failf(data, "SSL: couldn't get peer certificate!");
    return CURLE_PEER_FAILED_VERIFICATION;
  }

  infof(data, "Server certificate:\n");

  rc = x509_name_oneline(X509_get_subject_name(connssl->server_cert),
                         buffer, BUFSIZE);
  infof(data, "\t subject: %s\n", rc?"[NONE]":buffer);

  ASN1_TIME_print(mem, X509_get_notBefore(connssl->server_cert));
  len = BIO_get_mem_data(mem, &ptr);
  infof(data, "\t start date: %.*s\n", len, ptr);
  BIO_reset(mem);

  ASN1_TIME_print(mem, X509_get_notAfter(connssl->server_cert));
  len = BIO_get_mem_data(mem, &ptr);
  infof(data, "\t expire date: %.*s\n", len, ptr);
  BIO_reset(mem);

  BIO_free(mem);

  if(data->set.ssl.verifyhost) {
    result = verifyhost(conn, connssl->server_cert);
    if(result) {
      X509_free(connssl->server_cert);
      connssl->server_cert = NULL;
      return result;
    }
  }

  rc = x509_name_oneline(X509_get_issuer_name(connssl->server_cert),
                         buffer, BUFSIZE);
  if(rc) {
    if(strict)
      failf(data, "SSL: couldn't get X509-issuer name!");
    result = CURLE_SSL_CONNECT_ERROR;
  }
  else {
    infof(data, "\t issuer: %s\n", buffer);

    /* We could do all sorts of certificate verification stuff here before
       deallocating the certificate. */

    /* e.g. match issuer name with provided issuer certificate */
    if(data->set.str[STRING_SSL_ISSUERCERT]) {
      fp = fopen(data->set.str[STRING_SSL_ISSUERCERT], FOPEN_READTEXT);
      if(!fp) {
        if(strict)
          failf(data, "SSL: Unable to open issuer cert (%s)",
                data->set.str[STRING_SSL_ISSUERCERT]);
        X509_free(connssl->server_cert);
        connssl->server_cert = NULL;
        return CURLE_SSL_ISSUER_ERROR;
      }

      issuer = PEM_read_X509(fp, NULL, ZERO_NULL, NULL);
      if(!issuer) {
        if(strict)
          failf(data, "SSL: Unable to read issuer cert (%s)",
                data->set.str[STRING_SSL_ISSUERCERT]);
        X509_free(connssl->server_cert);
        X509_free(issuer);
        fclose(fp);
        return CURLE_SSL_ISSUER_ERROR;
      }

      fclose(fp);

      if(X509_check_issued(issuer, connssl->server_cert) != X509_V_OK) {
        if(strict)
          failf(data, "SSL: Certificate issuer check failed (%s)",
                data->set.str[STRING_SSL_ISSUERCERT]);
        X509_free(connssl->server_cert);
        X509_free(issuer);
        connssl->server_cert = NULL;
        return CURLE_SSL_ISSUER_ERROR;
      }

      infof(data, "\t SSL certificate issuer check ok (%s)\n",
            data->set.str[STRING_SSL_ISSUERCERT]);
      X509_free(issuer);
    }

    lerr = data->set.ssl.certverifyresult =
      SSL_get_verify_result(connssl->handle);

    if(data->set.ssl.certverifyresult != X509_V_OK) {
      if(data->set.ssl.verifypeer) {
        /* We probably never reach this, because SSL_connect() will fail
           and we return earlier if verifypeer is set? */
        if(strict)
          failf(data, "SSL certificate verify result: %s (%ld)",
                X509_verify_cert_error_string(lerr), lerr);
        result = CURLE_PEER_FAILED_VERIFICATION;
      }
      else
        infof(data, "\t SSL certificate verify result: %s (%ld),"
              " continuing anyway.\n",
              X509_verify_cert_error_string(lerr), lerr);
    }
    else
      infof(data, "\t SSL certificate verify ok.\n");
  }

#if (OPENSSL_VERSION_NUMBER >= 0x0090808fL) && !defined(OPENSSL_NO_TLSEXT) && \
    !defined(OPENSSL_IS_BORINGSSL)
  if(data->set.ssl.verifystatus) {
    result = verifystatus(conn, connssl);
    if(result) {
      X509_free(connssl->server_cert);
      connssl->server_cert = NULL;
      return result;
    }
  }
#endif

  if(!strict)
    /* when not strict, we don't bother about the verify cert problems */
    result = CURLE_OK;

  ptr = data->set.str[STRING_SSL_PINNEDPUBLICKEY];
  if(!result && ptr) {
    result = pkp_pin_peer_pubkey(data, connssl->server_cert, ptr);
    if(result)
      failf(data, "SSL: public key does not match pinned public key!");
  }

  X509_free(connssl->server_cert);
  connssl->server_cert = NULL;
  connssl->connecting_state = ssl_connect_done;

  return result;
}

static CURLcode ossl_connect_step3(struct connectdata *conn, int sockindex)
{
  CURLcode result = CURLE_OK;
  void *old_ssl_sessionid = NULL;
  struct SessionHandle *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  bool incache;
  SSL_SESSION *our_ssl_sessionid;

  DEBUGASSERT(ssl_connect_3 == connssl->connecting_state);

  our_ssl_sessionid = SSL_get1_session(connssl->handle);

  /* SSL_get1_session() will increment the reference count and the session
     will stay in memory until explicitly freed with SSL_SESSION_free(3),
     regardless of its state. */

  incache = !(Curl_ssl_getsessionid(conn, &old_ssl_sessionid, NULL));
  if(incache) {
    if(old_ssl_sessionid != our_ssl_sessionid) {
      infof(data, "old SSL session ID is stale, removing\n");
      Curl_ssl_delsessionid(conn, old_ssl_sessionid);
      incache = FALSE;
    }
  }

  if(!incache) {
    result = Curl_ssl_addsessionid(conn, our_ssl_sessionid,
                                   0 /* unknown size */);
    if(result) {
      failf(data, "failed to store ssl session");
      return result;
    }
  }
  else {
    /* Session was incache, so refcount already incremented earlier.
     * Avoid further increments with each SSL_get1_session() call.
     * This does not free the session as refcount remains > 0
     */
    SSL_SESSION_free(our_ssl_sessionid);
  }

  /*
   * We check certificates to authenticate the server; otherwise we risk
   * man-in-the-middle attack; NEVERTHELESS, if we're told explicitly not to
   * verify the peer ignore faults and failures from the server cert
   * operations.
   */

  result = servercert(conn, connssl,
                      (data->set.ssl.verifypeer || data->set.ssl.verifyhost));

  if(!result)
    connssl->connecting_state = ssl_connect_done;

  return result;
}

static Curl_recv ossl_recv;
static Curl_send ossl_send;

static CURLcode ossl_connect_common(struct connectdata *conn,
                                    int sockindex,
                                    bool nonblocking,
                                    bool *done)
{
  CURLcode result;
  struct SessionHandle *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  curl_socket_t sockfd = conn->sock[sockindex];
  long timeout_ms;
  int what;

  /* check if the connection has already been established */
  if(ssl_connection_complete == connssl->state) {
    *done = TRUE;
    return CURLE_OK;
  }

  if(ssl_connect_1 == connssl->connecting_state) {
    /* Find out how much more time we're allowed */
    timeout_ms = Curl_timeleft(data, NULL, TRUE);

    if(timeout_ms < 0) {
      /* no need to continue if time already is up */
      failf(data, "SSL connection timeout");
      return CURLE_OPERATION_TIMEDOUT;
    }

    result = ossl_connect_step1(conn, sockindex);
    if(result)
      return result;
  }

  while(ssl_connect_2 == connssl->connecting_state ||
        ssl_connect_2_reading == connssl->connecting_state ||
        ssl_connect_2_writing == connssl->connecting_state) {

    /* check allowed time left */
    timeout_ms = Curl_timeleft(data, NULL, TRUE);

    if(timeout_ms < 0) {
      /* no need to continue if time already is up */
      failf(data, "SSL connection timeout");
      return CURLE_OPERATION_TIMEDOUT;
    }

    /* if ssl is expecting something, check if it's available. */
    if(connssl->connecting_state == ssl_connect_2_reading ||
       connssl->connecting_state == ssl_connect_2_writing) {

      curl_socket_t writefd = ssl_connect_2_writing==
        connssl->connecting_state?sockfd:CURL_SOCKET_BAD;
      curl_socket_t readfd = ssl_connect_2_reading==
        connssl->connecting_state?sockfd:CURL_SOCKET_BAD;

      what = Curl_socket_ready(readfd, writefd, nonblocking?0:timeout_ms);
      if(what < 0) {
        /* fatal error */
        failf(data, "select/poll on SSL socket, errno: %d", SOCKERRNO);
        return CURLE_SSL_CONNECT_ERROR;
      }
      else if(0 == what) {
        if(nonblocking) {
          *done = FALSE;
          return CURLE_OK;
        }
        else {
          /* timeout */
          failf(data, "SSL connection timeout");
          return CURLE_OPERATION_TIMEDOUT;
        }
      }
      /* socket is readable or writable */
    }

    /* Run transaction, and return to the caller if it failed or if this
     * connection is done nonblocking and this loop would execute again. This
     * permits the owner of a multi handle to abort a connection attempt
     * before step2 has completed while ensuring that a client using select()
     * or epoll() will always have a valid fdset to wait on.
     */
    result = ossl_connect_step2(conn, sockindex);
    if(result || (nonblocking &&
                  (ssl_connect_2 == connssl->connecting_state ||
                   ssl_connect_2_reading == connssl->connecting_state ||
                   ssl_connect_2_writing == connssl->connecting_state)))
      return result;

  } /* repeat step2 until all transactions are done. */

  if(ssl_connect_3 == connssl->connecting_state) {
    result = ossl_connect_step3(conn, sockindex);
    if(result)
      return result;
  }

  if(ssl_connect_done == connssl->connecting_state) {
    connssl->state = ssl_connection_complete;
    conn->recv[sockindex] = ossl_recv;
    conn->send[sockindex] = ossl_send;
    *done = TRUE;
  }
  else
    *done = FALSE;

  /* Reset our connect state machine */
  connssl->connecting_state = ssl_connect_1;

  return CURLE_OK;
}

CURLcode Curl_ossl_connect_nonblocking(struct connectdata *conn,
                                       int sockindex,
                                       bool *done)
{
  return ossl_connect_common(conn, sockindex, TRUE, done);
}

CURLcode Curl_ossl_connect(struct connectdata *conn, int sockindex)
{
  CURLcode result;
  bool done = FALSE;

  result = ossl_connect_common(conn, sockindex, FALSE, &done);
  if(result)
    return result;

  DEBUGASSERT(done);

  return CURLE_OK;
}

bool Curl_ossl_data_pending(const struct connectdata *conn, int connindex)
{
  if(conn->ssl[connindex].handle)
    /* SSL is in use */
    return (0 != SSL_pending(conn->ssl[connindex].handle)) ? TRUE : FALSE;
  else
    return FALSE;
}

static ssize_t ossl_send(struct connectdata *conn,
                         int sockindex,
                         const void *mem,
                         size_t len,
                         CURLcode *curlcode)
{
  /* SSL_write() is said to return 'int' while write() and send() returns
     'size_t' */
  int err;
  char error_buffer[120]; /* OpenSSL documents that this must be at least 120
                             bytes long. */
  unsigned long sslerror;
  int memlen;
  int rc;

  ERR_clear_error();

  memlen = (len > (size_t)INT_MAX) ? INT_MAX : (int)len;
  rc = SSL_write(conn->ssl[sockindex].handle, mem, memlen);

  if(rc <= 0) {
    err = SSL_get_error(conn->ssl[sockindex].handle, rc);

    switch(err) {
    case SSL_ERROR_WANT_READ:
    case SSL_ERROR_WANT_WRITE:
      /* The operation did not complete; the same TLS/SSL I/O function
         should be called again later. This is basically an EWOULDBLOCK
         equivalent. */
      *curlcode = CURLE_AGAIN;
      return -1;
    case SSL_ERROR_SYSCALL:
      failf(conn->data, "SSL_write() returned SYSCALL, errno = %d",
            SOCKERRNO);
      *curlcode = CURLE_SEND_ERROR;
      return -1;
    case SSL_ERROR_SSL:
      /*  A failure in the SSL library occurred, usually a protocol error.
          The OpenSSL error queue contains more information on the error. */
      sslerror = ERR_get_error();
      failf(conn->data, "SSL_write() error: %s",
            ERR_error_string(sslerror, error_buffer));
      *curlcode = CURLE_SEND_ERROR;
      return -1;
    }
    /* a true error */
    failf(conn->data, "SSL_write() return error %d", err);
    *curlcode = CURLE_SEND_ERROR;
    return -1;
  }
  *curlcode = CURLE_OK;
  return (ssize_t)rc; /* number of bytes */
}

static ssize_t ossl_recv(struct connectdata *conn, /* connection data */
                         int num,                  /* socketindex */
                         char *buf,                /* store read data here */
                         size_t buffersize,        /* max amount to read */
                         CURLcode *curlcode)
{
  char error_buffer[120]; /* OpenSSL documents that this must be at
                             least 120 bytes long. */
  unsigned long sslerror;
  ssize_t nread;
  int buffsize;

  ERR_clear_error();

  buffsize = (buffersize > (size_t)INT_MAX) ? INT_MAX : (int)buffersize;
  nread = (ssize_t)SSL_read(conn->ssl[num].handle, buf, buffsize);
  if(nread <= 0) {
    /* failed SSL_read */
    int err = SSL_get_error(conn->ssl[num].handle, (int)nread);

    switch(err) {
    case SSL_ERROR_NONE: /* this is not an error */
    case SSL_ERROR_ZERO_RETURN: /* no more data */
      break;
    case SSL_ERROR_WANT_READ:
    case SSL_ERROR_WANT_WRITE:
      /* there's data pending, re-invoke SSL_read() */
      *curlcode = CURLE_AGAIN;
      return -1;
    default:
      /* openssl/ssl.h for SSL_ERROR_SYSCALL says "look at error stack/return
         value/errno" */
      /* https://www.openssl.org/docs/crypto/ERR_get_error.html */
      sslerror = ERR_get_error();
      if((nread < 0) || sslerror) {
        /* If the return code was negative or there actually is an error in the
           queue */
        failf(conn->data, "SSL read: %s, errno %d",
              ERR_error_string(sslerror, error_buffer),
              SOCKERRNO);
        *curlcode = CURLE_RECV_ERROR;
        return -1;
      }
    }
  }
  return nread;
}

size_t Curl_ossl_version(char *buffer, size_t size)
{
#ifdef YASSL_VERSION
  /* yassl provides an OpenSSL API compatibility layer so it looks identical
     to OpenSSL in all other aspects */
  return snprintf(buffer, size, "yassl/%s", YASSL_VERSION);
#else /* YASSL_VERSION */
#ifdef OPENSSL_IS_BORINGSSL
  return snprintf(buffer, size, "BoringSSL");
#else /* OPENSSL_IS_BORINGSSL */

#if(OPENSSL_VERSION_NUMBER >= 0x905000)
  {
    char sub[3];
    unsigned long ssleay_value;
    sub[2]='\0';
    sub[1]='\0';
    ssleay_value=SSLeay();
    if(ssleay_value < 0x906000) {
      ssleay_value=SSLEAY_VERSION_NUMBER;
      sub[0]='\0';
    }
    else {
      if(ssleay_value&0xff0) {
        int minor_ver = (ssleay_value >> 4) & 0xff;
        if(minor_ver > 26) {
          /* handle extended version introduced for 0.9.8za */
          sub[1] = (char) ((minor_ver - 1) % 26 + 'a' + 1);
          sub[0] = 'z';
        }
        else {
          sub[0]=(char)(((ssleay_value>>4)&0xff) + 'a' -1);
        }
      }
      else
        sub[0]='\0';
    }

    return snprintf(buffer, size, "%s/%lx.%lx.%lx%s",
#ifdef LIBRESSL_VERSION_NUMBER
                    "LibreSSL"
#else
                    "OpenSSL"
#endif
                    , (ssleay_value>>28)&0xf,
                    (ssleay_value>>20)&0xff,
                    (ssleay_value>>12)&0xff,
                    sub);
  }

#else /* OPENSSL_VERSION_NUMBER is less than 0.9.5 */