Add support of server name extension to server side

Change-Id: Iccf5017e306ba6ead2e1026a29f397ead084cc4d
Signed-off-by: XiaokangQian <xiaokang.qian@arm.com>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 5331865..29a33f4 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -8210,4 +8210,55 @@
 }
 #endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
 
+#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
+int mbedtls_ssl_parse_servername_ext( mbedtls_ssl_context *ssl,
+                                             const unsigned char *buf,
+                                             const unsigned char *end )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    const unsigned char *p = buf;
+    size_t servername_list_size, hostname_len;
+    const unsigned char *servername_end;
+
+    if( ssl->conf->p_sni == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "No SNI callback configured. Skip SNI parsing." ) );
+        return( 0 );
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "Parse ServerName extension" ) );
+
+    MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, 2 );
+    servername_list_size = MBEDTLS_GET_UINT16_BE( p, 0 );
+    p += 2;
+
+    MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, servername_list_size );
+    servername_end = p + servername_list_size;
+    while ( p < servername_end )
+    {
+        MBEDTLS_SSL_CHK_BUF_READ_PTR( p, servername_end, 3 );
+        hostname_len = MBEDTLS_GET_UINT16_BE( p, 1 );
+        MBEDTLS_SSL_CHK_BUF_READ_PTR( p, servername_end, hostname_len + 3 );
+
+        if( p[0] == MBEDTLS_TLS_EXT_SERVERNAME_HOSTNAME )
+        {
+            ret = ssl->conf->f_sni( ssl->conf->p_sni,
+                                   ssl, p + 3, hostname_len );
+            if( ret != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_RET( 1, "sni_wrapper", ret );
+                mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                                               MBEDTLS_SSL_ALERT_MSG_UNRECOGNIZED_NAME );
+                return( MBEDTLS_ERR_SSL_UNRECOGNIZED_NAME );
+            }
+            return( 0 );
+        }
+
+        p += hostname_len + 3;
+    }
+
+    return( 0 );
+}
+#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
+
 #endif /* MBEDTLS_SSL_TLS_C */