支持SSL的封装类--CAsyncSslSocketLayer

Introduction

CAsyncSslSocketLayer is a layer class for CAsyncSocketEx which allows you to establish SSL secured connections to servers.

For information about CAsyncSocketEx and the layer system in general, please read my CAsyncSocketEx article.

How to use

Using this class is really simple. In the easiest case, just add an instance of CAsyncSslSocketLayer to your socket and call InitClientSsl after creation of the socket.

This class only has three new public functions:

• InitClientSsl();

  This functions establishes an SSL connection to the server. You can call it at any time once the socket has been created. Most likely you want to call this function right after calling Create for the socket. But sometimes, you'll need to call this function later. One example is for an FTP connection with explicit SSL: In this case you would have to call InitClientSsl after receiving the reply to an AUTH SSL command.

• UsingSSL();

  Returns true if you've previously called InitClientSsl()

• SetNotifyReply(int nID, int nCode, int result);

  You can call this function only after receiving a layer specific callback with the SSL_VERIFY_CERT ID. See below for details.

This layer sends some layer specific notifications to your socket instance, you can handle them in OnLayerCallback of your socket class. Valid notification IDs are:

• SSL_INFO 0

  There are two possible values for param2:

  • SSL_INFO_ESTABLISHED 0 - You'll get this notification if the SSL negotiation was successful.
  • SSL_INFO_SHUTDOWNCOMPLETE 1 - You'll get this notification if the SSL connection has been shut down successfully. See below for details.
• SSL_FAILURE 1

  This notification is sent if the SSL connection could not be established or if an existing connection failed. Valid values for param2 are:

  • SSL_FAILURE_UNKNOWN 0 - Details may have been sent with a SSL_VERBOSE_WARNING or SSL_VERBOSE_INFO notification.
  • SSL_FAILURE_ESTABLISH 1 - Problem during SSL negotiation
  • SSL_FAILURE_LOADDLLS 2
  • SSL_FAILURE_INITSSL 4
  • SSL_FAILURE_VERIFYCERT 8 - The remote SSL certificate was invalid
• SSL_VERBOSE_WARNING 3
• SSL_VERBOSE_INFO 4

  These two notifications contain some additional information. The value given by param2 is a pointer to a null-terminated character string (char *) with some useful information.

• SSL_VERIFY_CERT 2

  This notification is sent each time a remote certificate has to be verified. param2 is a pointer to a t_SslCertData structure which contains some information about the remote certificate. Return 1 if you trust the certificate and 0 if you don't trust it. If you're unsure so that the user has to choose to trust the certificate, return 2. In this case, you have to call SetNotifyReply later to resume the SSL connection. nID has to be the priv_data element of the t_SslCertData structure and nCode has to be SSL_VERIFY_CERT. Set nAction to 1 if you trust the certificate and 0 if you don't trust it.

Be careful with closing the connection after sending data, not all data may have been sent already. Before closing the connection, you should call Shutdown() and wait for the SSL_INFO_SHUTDOWNCOMPLETE notification. This assures that all encrypted data really has been sent.