How to Upgrade an Open TCP Connection to TLS in Go Safely and Efficiently?

Upgrading a Connection to TLS in Go

This discussion explores the issue of upgrading an open TCP connection to TLS when an error occurs during the TLS handshake.

Initial Issue Description

The original issue is described as encountering a segmentation fault when attempting to upgrade a TCP connection to TLS. The affected code involves using a textproto.Conn to read from the connection, which is then upgraded to TLS using tx.Conn = tls.Server(tx.Conn, tx.Server.Conf.TlsConf) and tx.Text = textproto.NewConn(tx.Conn).

Solution

The provided solution addresses the error by suggesting a different approach for upgrading the connection.

Steps for Upgrading Connection

1. Define TLS configuration and load certificates.
2. Accept a client connection (net.Conn type).
3. Upon receiving the STARTTLS command, initialize a TLS connection using the TLS configuration.
4. Perform the TLS handshake.
5. Convert the TLS connection back to a net.Conn type.

Explanations

• The tls.Server() function creates a new TLS connection that handles encryption and decryption.
• The TLS handshake establishes a secure channel between the client and server.
• Converting the TLS connection to a net.Conn type allows the server to continue using the upgraded connection as a regular network connection.

Additional Information

• When starting TLS from an insecure connection, the client does not establish a new connection on a different port. The existing connection is reused and upgraded to TLS.
• Go provides flexible type conversions, allowing for seamless integration of different types.

Tips for Testing

To test the upgraded TLS connection, the following command can be used:

openssl s_client -starttls smtp -crlf -connect example.com:25

This enables interaction with the TLS-protected server and allows commands to be issued.

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