Merge pull request #7610 from gasbytes/sni-wrappers

CSharp Wrapper SNI Support

src/ssl.c

@@ -20181,16 +20181,9 @@ VerifyCallback wolfSSL_CTX_get_verify_callback(WOLFSSL_CTX* ctx)
     return NULL;
 }
 
-
 #ifdef HAVE_SNI
-
+/* this is a compatibily function, consider using
-void wolfSSL_CTX_set_servername_callback(WOLFSSL_CTX* ctx, CallbackSniRecv cb)
+ * wolfSSL_CTX_set_servername_callback */
-{
-    WOLFSSL_ENTER("wolfSSL_CTX_set_servername_callback");
-    if (ctx)
-        ctx->sniRecvCb = cb;
-}
-
 int wolfSSL_CTX_set_tlsext_servername_callback(WOLFSSL_CTX* ctx,
                                                CallbackSniRecv cb)
 {
@@ -20202,19 +20195,8 @@ int wolfSSL_CTX_set_tlsext_servername_callback(WOLFSSL_CTX* ctx,
     return WOLFSSL_FAILURE;
 }
 
-int wolfSSL_CTX_set_servername_arg(WOLFSSL_CTX* ctx, void* arg)
-{
-    WOLFSSL_ENTER("wolfSSL_CTX_set_servername_arg");
-    if (ctx) {
-        ctx->sniRecvCbArg = arg;
-        return WOLFSSL_SUCCESS;
-    }
-    return WOLFSSL_FAILURE;
-}
-
 #endif /* HAVE_SNI */
 
-
 #ifndef NO_BIO
 void wolfSSL_ERR_load_BIO_strings(void) {
     WOLFSSL_ENTER("wolfSSL_ERR_load_BIO_strings");
@@ -20249,6 +20231,27 @@ void wolfSSL_THREADID_set_numeric(void* id, unsigned long val)
         * HAVE_LIGHTY || WOLFSSL_HAPROXY || WOLFSSL_OPENSSH ||
         * HAVE_SBLIM_SFCB)) */
 
+#ifdef HAVE_SNI
+
+void wolfSSL_CTX_set_servername_callback(WOLFSSL_CTX* ctx, CallbackSniRecv cb)
+{
+    WOLFSSL_ENTER("wolfSSL_CTX_set_servername_callback");
+    if (ctx)
+        ctx->sniRecvCb = cb;
+}
+
+
+int wolfSSL_CTX_set_servername_arg(WOLFSSL_CTX* ctx, void* arg)
+{
+    WOLFSSL_ENTER("wolfSSL_CTX_set_servername_arg");
+    if (ctx) {
+        ctx->sniRecvCbArg = arg;
+        return WOLFSSL_SUCCESS;
+    }
+    return WOLFSSL_FAILURE;
+}
+
+#endif /* HAVE_SNI */
 
 #if defined(OPENSSL_EXTRA)
 

wolfssl/ssl.h

@@ -3813,7 +3813,6 @@ WOLFSSL_API void* wolfSSL_CTX_GetHeap(WOLFSSL_CTX* ctx, WOLFSSL* ssl);
 /* SNI types */
 enum {
     WOLFSSL_SNI_HOST_NAME = 0,
-    WOLFSSL_SNI_HOST_NAME_OUTER = 0,
 };
 
 WOLFSSL_ABI WOLFSSL_API int wolfSSL_UseSNI(WOLFSSL* ssl, unsigned char type,
@@ -4875,14 +4874,17 @@ typedef int (*CallbackSniRecv)(WOLFSSL *ssl, int *ret, void* exArg);
 
 WOLFSSL_API void wolfSSL_CTX_set_servername_callback(WOLFSSL_CTX* ctx,
         CallbackSniRecv cb);
-WOLFSSL_API int wolfSSL_CTX_set_tlsext_servername_callback(WOLFSSL_CTX* ctx,
-        CallbackSniRecv cb);
 
 WOLFSSL_API int  wolfSSL_CTX_set_servername_arg(WOLFSSL_CTX* ctx, void* arg);
 #endif
 
-#if defined(OPENSSL_ALL) || defined(HAVE_STUNNEL) || defined(WOLFSSL_NGINX) \
+#if defined(OPENSSL_ALL) || defined(HAVE_STUNNEL) || defined(WOLFSSL_NGINX) || \
-    || defined(WOLFSSL_HAPROXY) || defined(OPENSSL_EXTRA) || defined(HAVE_LIGHTY)
+    defined(WOLFSSL_HAPROXY) || defined(OPENSSL_EXTRA) || defined(HAVE_LIGHTY)
+
+#ifdef HAVE_SNI
+WOLFSSL_API int wolfSSL_CTX_set_tlsext_servername_callback(WOLFSSL_CTX* ctx,
+        CallbackSniRecv cb);
+#endif
 
 WOLFSSL_API void wolfSSL_ERR_remove_thread_state(void* pid);
 

wrapper/CSharp/README.md

@@ -20,15 +20,17 @@ A Visual Studio solution `wolfSSL_CSharp.sln` is provided. This will allow you
 to build the wrapper library and examples. It includes the wolfSSL Visual Studio
 project directly.
 
-## Linux (using Mono)
+## Linux (Ubuntu) using mono
 
 Prerequisites for linux:
 
 ```
-apt install mono-tools-devel
+apt-get update
+apt-get upgrade
+apt-get install mono-complete
 ```
 
-Build wolfSSL and install:
+### Build wolfSSL and install
 
 ```
 ./autogen.sh
@@ -38,24 +40,52 @@ make check
 sudo make install
 ```
 
-Build and run the wrapper:
+### Build and run the wrapper
+
+From the wolfssl root directory:
 
 ```
 cd wrapper/CSharp
+```
 
-csc wolfSSL_CSharp/wolfSSL.cs wolfSSL_CSharp/X509.cs \
+Compile server:
-    wolfSSL-TLS-Server/wolfSSL-TLS-Server.cs
-
-Run the example:
 
 ```
-cp wolfSSL-TLS-Server.exe ../../certs
+mcs wolfSSL_CSharp/wolfSSL.cs wolfSSL_CSharp/X509.cs \
-cd ../../certs
+wolfSSL-TLS-Server/wolfSSL-TLS-Server.cs -OUT:server.exe
-
+```
-mono wolfSSL-TLS-Server.exe
+
-
+Compile client:
-Calling ctx Init from wolfSSL
+
-Finished init of ctx .... now load in cert and key
+```
-Ciphers : TLS13-AES128-GCM-SHA256:TLS13-AES256-GCM-SHA384:TLS13-CHACHA20-POLY1305-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA:ECDHE-RSA-AES128-SHA:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-CHACHA20-POLY1305:DHE-RSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305-OLD:ECDHE-ECDSA-CHACHA20-POLY1305-OLD:DHE-RSA-CHACHA20-POLY1305-OLD
+mcs wolfSSL_CSharp/wolfSSL.cs wolfSSL_CSharp/X509.cs \
-Started TCP and waiting for a connection
+wolfSSL-TLS-Client/wolfSSL-TLS-Client.cs -OUT:client.exe
+```
+
+### Run the example
+
+In one terminal instance run the server:
+
+```
+mono server.exe
+```
+
+And in another terminal instance run the client:
+
+```
+mono client.exe
+```
+
+### Enabling SNI
+
+To enable SNI, just pass the `-S` argument with the specified hostname to the client:
+
+```
+mono client.exe -S hostname 
+```
+
+And run the server with the `-S` flag:
+
+```
+mono server.exe -S
 ```

wrapper/CSharp/wolfSSL-DTLS-PSK-Server/wolfSSL-DTLS-PSK-Server.cs

@@ -78,9 +78,14 @@ public class wolfSSL_DTLS_PSK_Server
         IntPtr ssl;
 
         /* These paths should be changed according to use */
-        string fileCert = @"server-cert.pem";
+        string fileCert = wolfssl.setPath("server-cert.pem");
-        string fileKey = @"server-key.pem";
+        string fileKey = wolfssl.setPath("server-key.pem");
-        StringBuilder dhparam = new StringBuilder("dh2048.pem");
+        StringBuilder dhparam = new StringBuilder(wolfssl.setPath("dh2048.pem"));
+
+        if (fileCert == "" || fileKey == "" || dhparam.Length == 0) {
+            Console.WriteLine("Platform not supported");
+            return;
+        }
 
         wolfssl.psk_delegate psk_cb = new wolfssl.psk_delegate(my_psk_server_cb);
 
@@ -106,6 +111,12 @@ public class wolfSSL_DTLS_PSK_Server
             return;
         }
 
+        if (!File.Exists(dhparam.ToString())) {
+            Console.WriteLine("Could not find dh file");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
+
 
         if (wolfssl.CTX_use_certificate_file(ctx, fileCert, wolfssl.SSL_FILETYPE_PEM) != wolfssl.SUCCESS)
         {

wrapper/CSharp/wolfSSL-DTLS-Server/wolfSSL-DTLS-Server.cs

@@ -58,9 +58,14 @@ public class wolfSSL_DTLS_Server
         IntPtr ssl;
 
         /* These paths should be changed for use */
-        string fileCert = @"server-cert.pem";
+        string fileCert = wolfssl.setPath("server-cert.pem");
-        string fileKey = @"server-key.pem";
+        string fileKey = wolfssl.setPath(@"server-key.pem");
-        StringBuilder dhparam = new StringBuilder("dh2048.pem");
+        StringBuilder dhparam = new StringBuilder(wolfssl.setPath("dh2048.pem"));
+
+        if (fileCert == "" || fileKey == "" || dhparam.Length == 0) {
+            Console.WriteLine("Platform not supported");
+            return;
+        }
 
         StringBuilder buff = new StringBuilder(1024);
         StringBuilder reply = new StringBuilder("Hello, this is the wolfSSL C# wrapper");
@@ -87,6 +92,12 @@ public class wolfSSL_DTLS_Server
             return;
         }
 
+        if (!File.Exists(dhparam.ToString())) {
+            Console.WriteLine("Could not find dh file");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
+
 
         if (wolfssl.CTX_use_certificate_file(ctx, fileCert, wolfssl.SSL_FILETYPE_PEM) != wolfssl.SUCCESS)
         {

wrapper/CSharp/wolfSSL-Example-IOCallbacks/wolfSSL-Example-IOCallbacks.cs

@@ -214,12 +214,17 @@ class wolfSSL_Example_IOCallbacks
         IntPtr ssl;
         Socket fd;
 
-        wolfssl.psk_delegate psk_cb = new wolfssl.psk_delegate(my_psk_server_cb);
         wolfssl.CallbackVerify_delegate verify_cb = new wolfssl.CallbackVerify_delegate(my_verify_cb);
 
         /* These paths should be changed according to use */
-        string fileCert = @"server-cert.pem";
+        string fileCert = wolfssl.setPath("server-cert.pem");
-        string fileKey = @"server-key.pem";
+        string fileKey = wolfssl.setPath("server-key.pem");
+        StringBuilder dhparam = new StringBuilder(wolfssl.setPath("dh2048.pem"));
+
+        if (fileCert == "" || fileKey == "" || dhparam.Length == 0) {
+            Console.WriteLine("Platform not supported");
+            return;
+        }
 
         StringBuilder buff = new StringBuilder(1024);
         StringBuilder reply = new StringBuilder("Hello, this is the wolfSSL C# wrapper");
@@ -242,6 +247,12 @@ class wolfSSL_Example_IOCallbacks
             return;
         }
 
+        if (!File.Exists(dhparam.ToString())) {
+            Console.WriteLine("Could not find dh file");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
+
         if (wolfssl.CTX_use_certificate_file(ctx, fileCert, wolfssl.SSL_FILETYPE_PEM) != wolfssl.SUCCESS)
         {
             Console.WriteLine("Error in setting cert file");

wrapper/CSharp/wolfSSL-TLS-Client/wolfSSL-TLS-Client.cs

@@ -19,7 +19,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
  */
 
-
 using System;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -60,15 +59,39 @@ public class wolfSSL_TLS_Client
         return preverify;
     }
 
+    /// <summary>
+    /// Checks if the SNI option was enabled via command line.
+    /// Must be enabled with ./configure --enable-sni when configuring
+    /// wolfSSL.
+    /// <param name="args">Parameters passed via command line</param>
+    /// </summary>
+    private static int haveSNI(string[] args)
+    {
+        for (int i = 0; i < args.Length; i++) {
+            if (args[i] == "-S") {
+                Console.WriteLine("SNI IS ON");
+                return i+1;
+            }
+        }
+        Console.WriteLine("SNI IS OFF");
+        return -1;
+    }
+
     public static void Main(string[] args)
     {
         IntPtr ctx;
         IntPtr ssl;
         Socket tcp;
+        IntPtr sniHostName;
 
         /* These paths should be changed for use */
-        string caCert = @"ca-cert.pem";
+        string caCert = wolfssl.setPath("ca-cert.pem");
-        StringBuilder dhparam = new StringBuilder("dh2048.pem");
+        StringBuilder dhparam = new StringBuilder(wolfssl.setPath("dh2048.pem"));
+
+        if (caCert == "" || dhparam.Length == 0) {
+            Console.WriteLine("Platform not supported.");
+            return; 
+        }
 
         StringBuilder buff = new StringBuilder(1024);
         StringBuilder reply = new StringBuilder("Hello, this is the wolfSSL C# wrapper");
@@ -78,7 +101,6 @@ public class wolfSSL_TLS_Client
 
         wolfssl.Init();
 
-
         Console.WriteLine("Calling ctx Init from wolfSSL");
         ctx = wolfssl.CTX_new(wolfssl.usev23_client());
         if (ctx == IntPtr.Zero)
@@ -96,11 +118,34 @@ public class wolfSSL_TLS_Client
             return;
         }
 
+        if (!File.Exists(dhparam.ToString())) {
+            Console.WriteLine("Could not find dh file");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
 
         if (wolfssl.CTX_load_verify_locations(ctx, caCert, null)
             != wolfssl.SUCCESS)
         {
             Console.WriteLine("Error loading CA cert");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
+
+        int sniArg = haveSNI(args);
+        if (sniArg >= 0) 
+        {
+            string sniHostNameString = args[sniArg].Trim();
+            sniHostName = Marshal.StringToHGlobalAnsi(sniHostNameString);
+
+            ushort size = (ushort)sniHostNameString.Length;
+
+           if (wolfssl.CTX_UseSNI(ctx, (byte)wolfssl.WOLFSSL_SNI_HOST_NAME, sniHostName, size) != wolfssl.SUCCESS) 
+           {
+               Console.WriteLine("UseSNI failed");
+               wolfssl.CTX_free(ctx);
+               return;
+           }
         }
 
         StringBuilder ciphers = new StringBuilder(new String(' ', 4096));

wrapper/CSharp/wolfSSL-TLS-PSK-Client/wolfSSL-TLS-PSK-Client.cs

@@ -82,7 +82,11 @@ public class wolfSSL_TLS_PSK_Client
 
         wolfssl.psk_client_delegate psk_cb = new wolfssl.psk_client_delegate(my_psk_client_cb);
 
-        StringBuilder dhparam = new StringBuilder("dh2048.pem");
+        StringBuilder dhparam = new StringBuilder(wolfssl.setPath("dh2048.pem"));
+        if (dhparam.Length == 0) {
+            Console.WriteLine("Platform not supported");
+            return;
+        }
 
         StringBuilder buff = new StringBuilder(1024);
         StringBuilder reply = new StringBuilder("Hello, this is the wolfSSL C# client psk wrapper");
@@ -157,6 +161,12 @@ public class wolfSSL_TLS_PSK_Client
             return;
         }
 
+        if (!File.Exists(dhparam.ToString())) {
+            Console.WriteLine("Could not find dh file");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
+
         wolfssl.SetTmpDH_file(ssl, dhparam, wolfssl.SSL_FILETYPE_PEM);
 
         if (wolfssl.connect(ssl) != wolfssl.SUCCESS)

wrapper/CSharp/wolfSSL-TLS-PSK-Server/wolfSSL-TLS-PSK-Server.cs

@@ -80,9 +80,14 @@ public class wolfSSL_TLS_PSK_Server
         wolfssl.psk_delegate psk_cb = new wolfssl.psk_delegate(my_psk_server_cb);
 
         /* These paths should be changed according to use */
-        string fileCert = @"server-cert.pem";
+        string fileCert = wolfssl.setPath("server-cert.pem");
-        string fileKey = @"server-key.pem";
+        string fileKey = wolfssl.setPath("server-key.pem");
-        StringBuilder dhparam = new StringBuilder("dh2048.pem");
+        StringBuilder dhparam = new StringBuilder(wolfssl.setPath("dh2048.pem"));
+
+        if (fileCert == "" || fileKey == "" || dhparam.Length == 0) {
+            Console.WriteLine("Platform not supported");
+            return;
+        }
 
         StringBuilder buff = new StringBuilder(1024);
         StringBuilder reply = new StringBuilder("Hello, this is the wolfSSL C# wrapper");
@@ -105,6 +110,12 @@ public class wolfSSL_TLS_PSK_Server
             return;
         }
 
+        if (!File.Exists(dhparam.ToString())) {
+            Console.WriteLine("Could not find dh file");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
+
         if (wolfssl.CTX_use_certificate_file(ctx, fileCert, wolfssl.SSL_FILETYPE_PEM) != wolfssl.SUCCESS)
         {
             Console.WriteLine("Error in setting cert file");

wrapper/CSharp/wolfSSL-TLS-Server/wolfSSL-TLS-Server.cs

@@ -19,9 +19,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
  */
 
-
-
-
 using System;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -50,17 +47,55 @@ public class wolfSSL_TLS_CSHarp
         wolfssl.Cleanup();
     }
 
+    /// <summary>
+    /// Checks if the SNI option was enabled via command line.
+    /// Must be enabled with ./configure --enable-sni when configuring
+    /// wolfSSL.
+    /// <param name="args">Parameters passed via command line</param>
+    /// </summary>
+    private static bool haveSNI(string[] args)
+    {
+        bool sniON = false;
+        for (int i = 0; i < args.Length; i++) {
+            if (args[i] == "-S") {
+                sniON = true;
+                break;
+            }
+        }
+        Console.WriteLine("SNI IS: " + sniON);
+        return sniON;
+    }
+
+    /// <summary>
+    /// Example of a SNI function call back
+    /// </summary>
+    /// <param name="ssl">pointer to ssl structure</param>
+    /// <param name="ret">alert code</param>
+    /// <param name="exArg">context arg, can be set with the function wolfssl.CTX_set_servername_arg</param>
+    /// <returns></returns>
+    public static int my_sni_server_cb(IntPtr ssl, IntPtr ret, IntPtr exArg) {
+        /* Trivial callback just for testing */
+        Console.WriteLine("my sni server callback");
+
+        return 0;
+    }
 
     public static void Main(string[] args)
     {
         IntPtr ctx;
         IntPtr ssl;
         Socket fd;
+        IntPtr arg_sni;
 
         /* These paths should be changed for use */
-        string fileCert = @"server-cert.pem";
+        string fileCert = wolfssl.setPath("server-cert.pem");
-        string fileKey = @"server-key.pem";
+        string fileKey = wolfssl.setPath("server-key.pem");
-        StringBuilder dhparam = new StringBuilder("dh2048.pem");
+        StringBuilder dhparam = new StringBuilder(wolfssl.setPath("dh2048.pem"));
+
+        if (fileCert == "" || fileKey == "" || dhparam.Length == 0) {
+            Console.WriteLine("Platform not supported.");
+            return;
+        }
 
         StringBuilder buff = new StringBuilder(1024);
         StringBuilder reply = new StringBuilder("Hello, this is the wolfSSL C# wrapper");
@@ -70,7 +105,6 @@ public class wolfSSL_TLS_CSHarp
 
         wolfssl.Init();
 
-
         Console.WriteLine("Calling ctx Init from wolfSSL");
         ctx = wolfssl.CTX_new(wolfssl.usev23_server());
         if (ctx == IntPtr.Zero)
@@ -87,6 +121,12 @@ public class wolfSSL_TLS_CSHarp
             return;
         }
 
+        if (!File.Exists(dhparam.ToString())) {
+            Console.WriteLine("Could not find dh file");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
+
         if (wolfssl.CTX_use_certificate_file(ctx, fileCert, wolfssl.SSL_FILETYPE_PEM) != wolfssl.SUCCESS)
         {
             Console.WriteLine("Error in setting cert file");
@@ -101,7 +141,6 @@ public class wolfSSL_TLS_CSHarp
             return;
         }
 
-
         StringBuilder ciphers = new StringBuilder(new String(' ', 4096));
         wolfssl.get_ciphers(ciphers, 4096);
         Console.WriteLine("Ciphers : " + ciphers.ToString());
@@ -124,6 +163,23 @@ public class wolfSSL_TLS_CSHarp
             return;
         }
 
+        if (haveSNI(args)) 
+        {
+           // Allocating memory and setting SNI arg
+           int test_value = 32;
+           arg_sni = Marshal.AllocHGlobal(sizeof(int));
+           Marshal.WriteInt32(arg_sni, test_value);
+           if (wolfssl.CTX_set_servername_arg(ctx, arg_sni) == wolfssl.FAILURE) {
+               Console.WriteLine("wolfssl.CTX_set_servername_arg failed");
+               wolfssl.CTX_free(ctx);
+               return;
+           }
+
+           // Setting SNI delegate
+           wolfssl.sni_delegate sni_cb  = new wolfssl.sni_delegate(my_sni_server_cb);
+           wolfssl.CTX_set_servername_callback(ctx, sni_cb);
+        }
+
         Console.WriteLine("Connection made wolfSSL_accept ");
         if (wolfssl.set_fd(ssl, fd) != wolfssl.SUCCESS)
         {
@@ -134,7 +190,14 @@ public class wolfSSL_TLS_CSHarp
             return;
         }
 
-        wolfssl.SetTmpDH_file(ssl, dhparam, wolfssl.SSL_FILETYPE_PEM);
+        if (wolfssl.SetTmpDH_file(ssl, dhparam, wolfssl.SSL_FILETYPE_PEM) != wolfssl.SUCCESS)
+        {
+            Console.WriteLine("Error in setting dh2048Pem");
+            Console.WriteLine(wolfssl.get_error(ssl));
+            tcp.Stop();
+            clean(ssl, ctx);
+            return;
+        }
 
         if (wolfssl.accept(ssl) != wolfssl.SUCCESS)
         {
@@ -170,6 +233,7 @@ public class wolfSSL_TLS_CSHarp
         wolfssl.shutdown(ssl);
         fd.Close();
         tcp.Stop();
+
         clean(ssl, ctx);
     }
 }

wrapper/CSharp/wolfSSL-TLS-ServerThreaded/wolfSSL-TLS-ServerThreaded.cs

@@ -116,9 +116,14 @@ public class wolfSSL_TLS_ServerThreaded
         IntPtr ctx;
 
         /* These paths should be changed for use */
-        string fileCert = @"server-cert.pem";
+        string fileCert = wolfssl.setPath("server-cert.pem");
-        string fileKey = @"server-key.pem";
+        string fileKey = wolfssl.setPath("server-key.pem");
-        StringBuilder dhparam = new StringBuilder("dh2048.pem");
+        StringBuilder dhparam = new StringBuilder(wolfssl.setPath("dh2048.pem"));
+
+        if (fileCert == "" || fileKey == "" || dhparam.Length == 0) {
+            Console.WriteLine("Platform not supported");
+            return;
+        }
 
         /* example of function used for setting logging */
         wolfssl.SetLogging(standard_log);
@@ -140,6 +145,12 @@ public class wolfSSL_TLS_ServerThreaded
             return;
         }
 
+        if (!File.Exists(dhparam.ToString())) {
+            Console.WriteLine("Could not find dh file");
+            wolfssl.CTX_free(ctx);
+            return;
+        }
+
         if (wolfssl.CTX_use_certificate_file(ctx, fileCert, wolfssl.SSL_FILETYPE_PEM) != wolfssl.SUCCESS)
         {
             Console.WriteLine("Error in setting cert file");

wrapper/CSharp/wolfSSL_CSharp/wolfSSL.cs

@@ -59,6 +59,8 @@ namespace wolfSSL.CSharp {
             private GCHandle rec_cb;
             private GCHandle snd_cb;
             private GCHandle psk_cb;
+            private GCHandle sni_cb;
+            private GCHandle sni_arg;
             private GCHandle vrf_cb;
             private IntPtr ctx;
 
@@ -89,6 +91,22 @@ namespace wolfSSL.CSharp {
                 return this.psk_cb;
             }
 
+            public void set_sni(GCHandle input) {
+                this.sni_cb = input;
+            }
+
+            public GCHandle get_sni(GCHandle input) {
+                return this.sni_cb;
+            }
+
+            public void set_arg(GCHandle input) {
+                this.sni_arg= input;
+            }
+
+            public GCHandle get_arg(GCHandle input) {
+                return this.sni_arg;
+            }
+
             public void set_vrf(GCHandle input)
             {
                 if (!Object.Equals(this.vrf_cb, default(GCHandle)))
@@ -129,6 +147,10 @@ namespace wolfSSL.CSharp {
                 {
                     this.psk_cb.Free();
                 }
+                if (!Object.Equals(this.sni_cb, default(GCHandle)))
+                {
+                    this.sni_cb.Free();
+                }
                 if (!Object.Equals(this.vrf_cb, default(GCHandle)))
                 {
                     this.vrf_cb.Free();
@@ -144,6 +166,7 @@ namespace wolfSSL.CSharp {
         {
             private GCHandle fd_pin;
             private GCHandle psk_cb;
+            private GCHandle sni_cb;
             private GCHandle vrf_cb;
             private IntPtr ssl;
 
@@ -198,6 +221,10 @@ namespace wolfSSL.CSharp {
                 {
                     this.psk_cb.Free();
                 }
+                if (!Object.Equals(this.sni_cb, default(GCHandle)))
+                {
+                    this.sni_cb.Free();
+                }
                 if (!Object.Equals(this.vrf_cb, default(GCHandle)))
                 {
                     this.vrf_cb.Free();
@@ -290,6 +317,19 @@ namespace wolfSSL.CSharp {
         [DllImport(wolfssl_dll, CallingConvention = CallingConvention.Cdecl)]
         private extern static int wolfSSL_CTX_use_psk_identity_hint(IntPtr ctx, StringBuilder identity);
 
+        /********************************
+         * SNI
+         */
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+        public delegate int sni_delegate(IntPtr ssl, IntPtr ret, IntPtr exArg);
+        [DllImport(wolfssl_dll, CallingConvention = CallingConvention.Cdecl)]
+        private extern static void wolfSSL_CTX_set_servername_callback(IntPtr ctx, sni_delegate sni_cb);
+        [DllImport(wolfssl_dll, CallingConvention = CallingConvention.Cdecl)]
+        private extern static int wolfSSL_CTX_set_servername_arg(IntPtr ctx, IntPtr arg);
+        [DllImport(wolfssl_dll, CallingConvention = CallingConvention.Cdecl)]
+        private extern static int wolfSSL_CTX_UseSNI(IntPtr ctx, byte type, IntPtr data, ushort size);
+        [DllImport(wolfssl_dll, CallingConvention = CallingConvention.Cdecl)]
+        private extern static int wolfSSL_UseSNI(IntPtr ssl, byte type, IntPtr data, ushort size);
 
         /********************************
          * SSL Structure
@@ -417,6 +457,7 @@ namespace wolfSSL.CSharp {
 
         public static readonly int SUCCESS = 1;
         public static readonly int FAILURE = 0;
+        public static readonly int WOLFSSL_SNI_HOST_NAME = 0;
 
 
         private static IntPtr unwrap_ctx(IntPtr ctx)
@@ -444,6 +485,26 @@ namespace wolfSSL.CSharp {
             }
         }
 
+        /// <summary>
+        /// Utility function used to access the certificates
+        /// based on the platform.
+        /// <returns>return the platform specific path to the certificate</returns>
+        /// </summary>
+        public static string setPath(string file) {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            {
+                Console.WriteLine("Linux - " + file);
+                return @"../../certs/" + file;
+            } else if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                Console.WriteLine("Windows - " + file);
+                return @"../../../../certs/" + file;
+            } else
+            {
+                return "";
+            }
+        }
+
 
         /// <summary>
         /// Call back to allow receiving TLS information
@@ -1084,6 +1145,60 @@ namespace wolfSSL.CSharp {
             }
         }
 
+        public static void CTX_set_servername_callback(IntPtr ctx, sni_delegate sni_cb) 
+        {
+            try {
+                GCHandle gch = GCHandle.FromIntPtr(ctx);
+                ctx_handle handles = (ctx_handle)gch.Target;
+
+                handles.set_sni(GCHandle.Alloc(sni_cb));
+
+                wolfSSL_CTX_set_servername_callback(handles.get_ctx(), sni_cb);
+            } catch (Exception e) {
+                log(ERROR_LOG, "wolfssl servername callback error: " + e.ToString());
+            }
+        }
+
+        public static int CTX_set_servername_arg(IntPtr ctx, IntPtr arg) 
+        {
+            try {
+                GCHandle gch = GCHandle.FromIntPtr(ctx);
+                ctx_handle handles = (ctx_handle)gch.Target;
+
+                handles.set_arg(GCHandle.Alloc(arg));
+
+                return wolfSSL_CTX_set_servername_arg(handles.get_ctx(), arg);
+            } catch (Exception e) {
+                log(ERROR_LOG, "wolfssl arg servername callback error: " + e.ToString());
+                return FAILURE;
+            }
+        }
+
+        public static int CTX_UseSNI(IntPtr ctx, byte type, IntPtr data, ushort size) 
+        {
+            try {
+                GCHandle gch = GCHandle.FromIntPtr(ctx);
+                ctx_handle handles = (ctx_handle)gch.Target;
+
+                return  wolfSSL_CTX_UseSNI(handles.get_ctx(), type, data, size);
+            } catch (Exception e) {
+                log(ERROR_LOG, "wolfssl ctx use sni error: " + e.ToString());
+                return FAILURE;
+            }
+        }
+
+        public static int UseSNI(IntPtr ssl, byte type, IntPtr data, ushort size) 
+        {
+            try {
+                GCHandle gch = GCHandle.FromIntPtr(ssl);
+                ssl_handle handles = (ssl_handle)gch.Target;
+
+                return  wolfSSL_UseSNI(handles.get_ssl(), type, data, size);
+            } catch (Exception e) {
+                log(ERROR_LOG, "wolfssl use sni error: " + e.ToString());
+                return FAILURE;
+            }
+        }
 
         /// <summary>
         /// Set identity hint to use