How can I determine whether an incoming connection

问题:

I want to use 1 port for both unencrypted TCP and SSL.

The goal is to make 1 port the entrance to the machine. That mean to mux all protocols and transports into the port. For example, i peek at the first 4 bytes of the stream. If it begins with 'GET', 'POST', 'HEAD', etc. I know that it is the HTTP protocol so I pass off the connection to the HTTP server. If it is 'HELO' or 'EHLO' i know to pass it off to the SMTP server.

The problem is, what do I look for if it is an SSL connection (in order to pass it off to OpenSSL)?

回答1:

SSL 2 will have 8x yz (hex) as first two bytes (x yz can be anything, eg. 8F 13), and SSL 3 and later have 16 03 hex as first two bytes.

Update: as pointed in the comments, some protocols require the server to send something first (FTP and POP3 to name a few, and SMTP has been mentioned in the comment) so your approach will work only for limited number of protocols.