vtls: add a MesaLink vtls backend

Closes #2984

5 files changed, 666 insertions, 1 deletions

diff --git a/lib/curl_setup.h b/lib/curl_setup.h
index 24989874e..6513d30f1 100644
--- a/lib/curl_setup.h
+++ b/lib/curl_setup.h
@@ -645,7 +645,7 @@ int netware_init(void);
 #if defined(USE_GNUTLS) || defined(USE_OPENSSL) || defined(USE_NSS) || \
     defined(USE_POLARSSL) || defined(USE_AXTLS) || defined(USE_MBEDTLS) || \
     defined(USE_CYASSL) || defined(USE_SCHANNEL) || \
-    defined(USE_DARWINSSL) || defined(USE_GSKIT)
+    defined(USE_DARWINSSL) || defined(USE_GSKIT) || defined(USE_MESALINK)
 #define USE_SSL    /* SSL support has been enabled */
 #endif
 
diff --git a/lib/vtls/mesalink.c b/lib/vtls/mesalink.c
new file mode 100644
index 000000000..8198fa1c8
--- /dev/null
+++ b/lib/vtls/mesalink.c
@@ -0,0 +1,627 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2017-2018, Yiming Jing, <jingyiming@baidu.com>
+ * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+/*
+ * Source file for all MesaLink-specific code for the TLS/SSL layer. No code
+ * but vtls.c should ever call or use these functions.
+ *
+ */
+
+/*
+ * Based upon the CyaSSL implementation in cyassl.c and cyassl.h:
+ *   Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * Thanks for code and inspiration!
+ */
+
+#include "curl_setup.h"
+
+#ifdef USE_MESALINK
+
+#include <mesalink/options.h>
+#include <mesalink/version.h>
+
+#include "urldata.h"
+#include "sendf.h"
+#include "inet_pton.h"
+#include "vtls.h"
+#include "parsedate.h"
+#include "connect.h" /* for the connect timeout */
+#include "select.h"
+#include "strcase.h"
+#include "x509asn1.h"
+#include "curl_printf.h"
+
+#include "mesalink.h"
+#include <mesalink/openssl/ssl.h>
+#include <mesalink/openssl/err.h>
+
+/* The last #include files should be: */
+#include "curl_memory.h"
+#include "memdebug.h"
+
+#define MESALINK_MAX_ERROR_SZ 80
+
+struct ssl_backend_data
+{
+  SSL_CTX *ctx;
+  SSL *handle;
+};
+
+#define BACKEND connssl->backend
+
+static Curl_recv mesalink_recv;
+static Curl_send mesalink_send;
+
+/*
+ * This function loads all the client/CA certificates and CRLs. Setup the TLS
+ * layer and do all necessary magic.
+ */
+static CURLcode
+mesalink_connect_step1(struct connectdata *conn, int sockindex)
+{
+  char *ciphers;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  const bool verifypeer = SSL_CONN_CONFIG(verifypeer);
+  const char *const ssl_cafile = SSL_CONN_CONFIG(CAfile);
+  const char *const ssl_capath = SSL_CONN_CONFIG(CApath);
+  struct in_addr addr4;
+#ifdef ENABLE_IPV6
+  struct in6_addr addr6;
+#endif
+  const char *const hostname =
+    SSL_IS_PROXY() ? conn->http_proxy.host.name : conn->host.name;
+  size_t hostname_len = strlen(hostname);
+
+  SSL_METHOD *req_method = NULL;
+  curl_socket_t sockfd = conn->sock[sockindex];
+
+  if(connssl->state == ssl_connection_complete)
+    return CURLE_OK;
+
+  if(SSL_CONN_CONFIG(version_max) != CURL_SSLVERSION_MAX_NONE) {
+    failf(data, "MesaLink does not support to set maximum SSL/TLS version");
+    return CURLE_SSL_CONNECT_ERROR;
+  }
+
+  switch(SSL_CONN_CONFIG(version)) {
+  case CURL_SSLVERSION_SSLv3:
+  case CURL_SSLVERSION_TLSv1:
+  case CURL_SSLVERSION_TLSv1_0:
+  case CURL_SSLVERSION_TLSv1_1:
+    failf(data, "MesaLink does not support SSL 3.0, TLS 1.0, or TLS 1.1");
+    return CURLE_NOT_BUILT_IN;
+  case CURL_SSLVERSION_DEFAULT:
+  case CURL_SSLVERSION_TLSv1_2:
+    req_method = TLSv1_2_client_method();
+    break;
+  case CURL_SSLVERSION_TLSv1_3:
+    req_method = TLSv1_3_client_method();
+    break;
+  case CURL_SSLVERSION_SSLv2:
+    failf(data, "MesaLink does not support SSLv2");
+    return CURLE_SSL_CONNECT_ERROR;
+  default:
+    failf(data, "Unrecognized parameter passed via CURLOPT_SSLVERSION");
+    return CURLE_SSL_CONNECT_ERROR;
+  }
+
+  if(!req_method) {
+    failf(data, "SSL: couldn't create a method!");
+    return CURLE_OUT_OF_MEMORY;
+  }
+
+  if(BACKEND->ctx)
+    SSL_CTX_free(BACKEND->ctx);
+  BACKEND->ctx = SSL_CTX_new(req_method);
+
+  if(!BACKEND->ctx) {
+    failf(data, "SSL: couldn't create a context!");
+    return CURLE_OUT_OF_MEMORY;
+  }
+
+  SSL_CTX_set_verify(
+    BACKEND->ctx, verifypeer ? SSL_VERIFY_PEER : SSL_VERIFY_NONE, NULL);
+
+  if(ssl_cafile || ssl_capath) {
+    if(!SSL_CTX_load_verify_locations(BACKEND->ctx, ssl_cafile, ssl_capath)) {
+      if(verifypeer) {
+        failf(data,
+              "error setting certificate verify locations:\n"
+              "  CAfile: %s\n  CApath: %s",
+              ssl_cafile ? ssl_cafile : "none",
+              ssl_capath ? ssl_capath : "none");
+        return CURLE_SSL_CACERT_BADFILE;
+      }
+      infof(data,
+            "error setting certificate verify locations,"
+            " continuing anyway:\n");
+    }
+    else {
+      infof(data, "successfully set certificate verify locations:\n");
+    }
+    infof(data,
+          "  CAfile: %s\n"
+          "  CApath: %s\n",
+          ssl_cafile ? ssl_cafile : "none",
+          ssl_capath ? ssl_capath : "none");
+  }
+
+  ciphers = SSL_CONN_CONFIG(cipher_list);
+  if(ciphers) {
+#ifdef MESALINK_HAVE_CIPHER
+    if(!SSL_CTX_set_cipher_list(BACKEND->ctx, ciphers)) {
+      failf(data, "failed setting cipher list: %s", ciphers);
+      return CURLE_SSL_CIPHER;
+    }
+#endif
+    infof(data, "Cipher selection: %s\n", ciphers);
+  }
+
+  if(BACKEND->handle)
+    SSL_free(BACKEND->handle);
+  BACKEND->handle = SSL_new(BACKEND->ctx);
+  if(!BACKEND->handle) {
+    failf(data, "SSL: couldn't create a context (handle)!");
+    return CURLE_OUT_OF_MEMORY;
+  }
+
+  if((hostname_len < USHRT_MAX) &&
+     (0 == Curl_inet_pton(AF_INET, hostname, &addr4))
+#ifdef ENABLE_IPV6
+     && (0 == Curl_inet_pton(AF_INET6, hostname, &addr6))
+#endif
+  ) {
+    /* hostname is not a valid IP address */
+    if(SSL_set_tlsext_host_name(BACKEND->handle, hostname) != SSL_SUCCESS) {
+      failf(data,
+            "WARNING: failed to configure server name indication (SNI) "
+            "TLS extension\n");
+      return CURLE_SSL_CONNECT_ERROR;
+    }
+  }
+  else {
+#ifdef CURLDEBUG
+    /* Check if the hostname is 127.0.0.1 or [::1];
+     * otherwise reject because MesaLink always wants a valid DNS Name
+     * specified in RFC 5280 Section 7.2 */
+    if(strncmp(hostname, "127.0.0.1", 9) == 0
+#ifdef ENABLE_IPV6
+       || strncmp(hostname, "[::1]", 5) == 0
+#endif
+    ) {
+      SSL_set_tlsext_host_name(BACKEND->handle, "localhost");
+    }
+    else
+#endif
+    {
+      failf(data,
+            "ERROR: MesaLink does not accept an IP address as a hostname\n");
+      return CURLE_SSL_CONNECT_ERROR;
+    }
+  }
+
+#ifdef MESALINK_HAVE_SESSION
+  if(SSL_SET_OPTION(primary.sessionid)) {
+    void *ssl_sessionid = NULL;
+
+    Curl_ssl_sessionid_lock(conn);
+    if(!Curl_ssl_getsessionid(conn, &ssl_sessionid, NULL, sockindex)) {
+      /* we got a session id, use it! */
+      if(!SSL_set_session(BACKEND->handle, ssl_sessionid)) {
+        Curl_ssl_sessionid_unlock(conn);
+        failf(
+          data,
+          "SSL: SSL_set_session failed: %s",
+          ERR_error_string(SSL_get_error(BACKEND->handle, 0), error_buffer));
+        return CURLE_SSL_CONNECT_ERROR;
+      }
+      /* Informational message */
+      infof(data, "SSL re-using session ID\n");
+    }
+    Curl_ssl_sessionid_unlock(conn);
+  }
+#endif /* MESALINK_HAVE_SESSION */
+
+  if(SSL_set_fd(BACKEND->handle, (int)sockfd) != SSL_SUCCESS) {
+    failf(data, "SSL: SSL_set_fd failed");
+    return CURLE_SSL_CONNECT_ERROR;
+  }
+
+  connssl->connecting_state = ssl_connect_2;
+  return CURLE_OK;
+}
+
+static CURLcode
+mesalink_connect_step2(struct connectdata *conn, int sockindex)
+{
+  int ret = -1;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+
+  conn->recv[sockindex] = mesalink_recv;
+  conn->send[sockindex] = mesalink_send;
+
+  ret = SSL_connect(BACKEND->handle);
+  if(ret != SSL_SUCCESS) {
+    char error_buffer[MESALINK_MAX_ERROR_SZ];
+    int detail = SSL_get_error(BACKEND->handle, ret);
+
+    if(SSL_ERROR_WANT_CONNECT == detail) {
+      connssl->connecting_state = ssl_connect_2_reading;
+      return CURLE_OK;
+    }
+    else {
+      failf(data,
+            "SSL_connect failed with error %d: %s",
+            detail,
+            ERR_error_string_n(detail, error_buffer, sizeof(error_buffer)));
+      ERR_print_errors_fp(stderr);
+      if(detail && SSL_CONN_CONFIG(verifypeer)) {
+        detail &= ~0xFF;
+        if(detail == TLS_ERROR_WEBPKI_ERRORS) {
+          failf(data, "Cert verify failed");
+          return CURLE_PEER_FAILED_VERIFICATION;
+        }
+      }
+      return CURLE_SSL_CONNECT_ERROR;
+    }
+  }
+
+  connssl->connecting_state = ssl_connect_3;
+  infof(data,
+        "SSL connection using %s / %s\n",
+        SSL_get_version(BACKEND->handle),
+        SSL_get_cipher_name(BACKEND->handle));
+
+  return CURLE_OK;
+}
+
+static CURLcode
+mesalink_connect_step3(struct connectdata *conn, int sockindex)
+{
+  CURLcode result = CURLE_OK;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+
+  DEBUGASSERT(ssl_connect_3 == connssl->connecting_state);
+
+#ifdef MESALINK_HAVE_SESSION
+  if(SSL_SET_OPTION(primary.sessionid)) {
+    bool incache;
+    SSL_SESSION *our_ssl_sessionid;
+    void *old_ssl_sessionid = NULL;
+
+    our_ssl_sessionid = SSL_get_session(BACKEND->handle);
+
+    Curl_ssl_sessionid_lock(conn);
+    incache =
+      !(Curl_ssl_getsessionid(conn, &old_ssl_sessionid, NULL, sockindex));
+    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 */, sockindex);
+      if(result) {
+        Curl_ssl_sessionid_unlock(conn);
+        failf(data, "failed to store ssl session");
+        return result;
+      }
+    }
+    Curl_ssl_sessionid_unlock(conn);
+  }
+#endif /* MESALINK_HAVE_SESSION */
+
+  connssl->connecting_state = ssl_connect_done;
+
+  return result;
+}
+
+static ssize_t
+mesalink_send(struct connectdata *conn, int sockindex, const void *mem,
+              size_t len, CURLcode *curlcode)
+{
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  char error_buffer[MESALINK_MAX_ERROR_SZ];
+  int memlen = (len > (size_t)INT_MAX) ? INT_MAX : (int)len;
+  int rc = SSL_write(BACKEND->handle, mem, memlen);
+
+  if(rc < 0) {
+    int err = SSL_get_error(BACKEND->handle, rc);
+    switch(err) {
+    case SSL_ERROR_WANT_READ:
+    case SSL_ERROR_WANT_WRITE:
+      /* there's data pending, re-invoke SSL_write() */
+      *curlcode = CURLE_AGAIN;
+      return -1;
+    default:
+      failf(conn->data,
+            "SSL write: %s, errno %d",
+            ERR_error_string_n(err, error_buffer, sizeof(error_buffer)),
+            SOCKERRNO);
+      *curlcode = CURLE_SEND_ERROR;
+      return -1;
+    }
+  }
+  return rc;
+}
+
+static void
+Curl_mesalink_close(struct connectdata *conn, int sockindex)
+{
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+
+  if(BACKEND->handle) {
+    (void)SSL_shutdown(BACKEND->handle);
+    SSL_free(BACKEND->handle);
+    BACKEND->handle = NULL;
+  }
+  if(BACKEND->ctx) {
+    SSL_CTX_free(BACKEND->ctx);
+    BACKEND->ctx = NULL;
+  }
+}
+
+static ssize_t
+mesalink_recv(struct connectdata *conn, int num, char *buf, size_t buffersize,
+              CURLcode *curlcode)
+{
+  struct ssl_connect_data *connssl = &conn->ssl[num];
+  char error_buffer[MESALINK_MAX_ERROR_SZ];
+  int buffsize = (buffersize > (size_t)INT_MAX) ? INT_MAX : (int)buffersize;
+  int nread = SSL_read(BACKEND->handle, buf, buffsize);
+
+  if(nread <= 0) {
+    int err = SSL_get_error(BACKEND->handle, nread);
+
+    switch(err) {
+    case SSL_ERROR_ZERO_RETURN: /* no more data */
+    case IO_ERROR_CONNECTION_ABORTED:
+      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:
+      failf(conn->data,
+            "SSL read: %s, errno %d",
+            ERR_error_string_n(err, error_buffer, sizeof(error_buffer)),
+            SOCKERRNO);
+      *curlcode = CURLE_RECV_ERROR;
+      return -1;
+    }
+  }
+  return nread;
+}
+
+static size_t
+Curl_mesalink_version(char *buffer, size_t size)
+{
+  return snprintf(buffer, size, "MesaLink/%s", MESALINK_VERSION_STRING);
+}
+
+static int
+Curl_mesalink_init(void)
+{
+  return (SSL_library_init() == SSL_SUCCESS);
+}
+
+/*
+ * This function is called to shut down the SSL layer but keep the
+ * socket open (CCC - Clear Command Channel)
+ */
+static int
+Curl_mesalink_shutdown(struct connectdata *conn, int sockindex)
+{
+  int retval = 0;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+
+  if(BACKEND->handle) {
+    SSL_free(BACKEND->handle);
+    BACKEND->handle = NULL;
+  }
+  return retval;
+}
+
+static CURLcode
+mesalink_connect_common(struct connectdata *conn, int sockindex,
+                        bool nonblocking, bool *done)
+{
+  CURLcode result;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  curl_socket_t sockfd = conn->sock[sockindex];
+  time_t 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 = mesalink_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_check(
+        readfd, CURL_SOCKET_BAD, 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 part of a multi handle 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 = mesalink_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 = mesalink_connect_step3(conn, sockindex);
+    if(result)
+      return result;
+  }
+
+  if(ssl_connect_done == connssl->connecting_state) {
+    connssl->state = ssl_connection_complete;
+    conn->recv[sockindex] = mesalink_recv;
+    conn->send[sockindex] = mesalink_send;
+    *done = TRUE;
+  }
+  else
+    *done = FALSE;
+
+  /* Reset our connect state machine */
+  connssl->connecting_state = ssl_connect_1;
+
+  return CURLE_OK;
+}
+
+static CURLcode
+Curl_mesalink_connect_nonblocking(struct connectdata *conn, int sockindex,
+                                  bool *done)
+{
+  return mesalink_connect_common(conn, sockindex, TRUE, done);
+}
+
+static CURLcode
+Curl_mesalink_connect(struct connectdata *conn, int sockindex)
+{
+  CURLcode result;
+  bool done = FALSE;
+
+  result = mesalink_connect_common(conn, sockindex, FALSE, &done);
+  if(result)
+    return result;
+
+  DEBUGASSERT(done);
+
+  return CURLE_OK;
+}
+
+static void *
+Curl_mesalink_get_internals(struct ssl_connect_data *connssl,
+                            CURLINFO info UNUSED_PARAM)
+{
+  (void)info;
+  return BACKEND->handle;
+}
+
+const struct Curl_ssl Curl_ssl_mesalink = {
+  { CURLSSLBACKEND_WOLFSSL, "MesaLink" }, /* info */
+
+  SSLSUPP_SSL_CTX,
+
+  sizeof(struct ssl_backend_data),
+
+  Curl_mesalink_init, /* init */
+  Curl_none_cleanup, /* cleanup */
+  Curl_mesalink_version, /* version */
+  Curl_none_check_cxn, /* check_cxn */
+  Curl_mesalink_shutdown, /* shutdown */
+  Curl_none_data_pending, /* data_pending */
+  Curl_none_random, /* random */
+  Curl_none_cert_status_request, /* cert_status_request */
+  Curl_mesalink_connect, /* connect */
+  Curl_mesalink_connect_nonblocking, /* connect_nonblocking */
+  Curl_mesalink_get_internals, /* get_internals */
+  Curl_mesalink_close, /* close_one */
+  Curl_none_close_all, /* close_all */
+  Curl_none_session_free, /* session_free */
+  Curl_none_set_engine, /* set_engine */
+  Curl_none_set_engine_default, /* set_engine_default */
+  Curl_none_engines_list, /* engines_list */
+  Curl_none_false_start, /* false_start */
+  Curl_none_md5sum, /* md5sum */
+  NULL /* sha256sum */
+};
+
+#endif
diff --git a/lib/vtls/mesalink.h b/lib/vtls/mesalink.h
new file mode 100644
index 000000000..54cb94ad3
--- /dev/null
+++ b/lib/vtls/mesalink.h
@@ -0,0 +1,32 @@
+#ifndef HEADER_CURL_MESALINK_H
+#define HEADER_CURL_MESALINK_H
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2017-2018, Yiming Jing, <jingyiming@baidu.com>
+ * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+#include "curl_setup.h"
+
+#ifdef USE_MESALINK
+
+extern const struct Curl_ssl Curl_ssl_mesalink;
+
+#endif /* USE_MESALINK */
+#endif /* HEADER_CURL_MESALINK_H */
diff --git a/lib/vtls/vtls.c b/lib/vtls/vtls.c
index b61c64034..6af39feab 100644
--- a/lib/vtls/vtls.c
+++ b/lib/vtls/vtls.c
@@ -1190,6 +1190,8 @@ const struct Curl_ssl *Curl_ssl =
   &Curl_ssl_polarssl;
 #elif defined(USE_SCHANNEL)
   &Curl_ssl_schannel;
+#elif defined(USE_MESALINK)
+  &Curl_ssl_mesalink;
 #else
 #error "Missing struct Curl_ssl for selected SSL backend"
 #endif
@@ -1225,6 +1227,9 @@ static const struct Curl_ssl *available_backends[] = {
 #if defined(USE_SCHANNEL)
   &Curl_ssl_schannel,
 #endif
+#if defined(USE_MESALINK)
+  &Curl_ssl_mesalink,
+#endif
   NULL
 };
 
diff --git a/lib/vtls/vtls.h b/lib/vtls/vtls.h
index 40f9d7479..5cd11602e 100644
--- a/lib/vtls/vtls.h
+++ b/lib/vtls/vtls.h
@@ -108,6 +108,7 @@ CURLcode Curl_none_md5sum(unsigned char *input, size_t inputlen,
 #include "schannel.h"       /* Schannel SSPI version */
 #include "darwinssl.h"      /* SecureTransport (Darwin) version */
 #include "mbedtls.h"        /* mbedTLS versions */
+#include "mesalink.h"       /* MesaLink versions */
 
 #ifndef MAX_PINNED_PUBKEY_SIZE
 #define MAX_PINNED_PUBKEY_SIZE 1048576 /* 1MB */