Function apply_alpn_with_fallback

crates/stdlib/src/ssl/compat.rs:853–858

Apply ALPN protocols OpenSSL 1.1.0f+ allows ALPN negotiation to fail without aborting handshake. rustls follows RFC 7301 strictly and rejects connections with no matching protocol. To emulate OpenSSL behavior, we add a special fallback protocol (null byte).

(config_alpn: &mut Vec<Vec<u8>>, alpn_protocols: &[Vec<u8>])

/// rustls follows RFC 7301 strictly and rejects connections with no matching protocol.
/// To emulate OpenSSL behavior, we add a special fallback protocol (null byte).
fn apply_alpn_with_fallback(config_alpn: &mut Vec<Vec<u8>>, alpn_protocols: &[Vec<u8>]) {
    if !alpn_protocols.is_empty() {
        *config_alpn = alpn_protocols.to_vec();
        config_alpn.push(vec![0u8]); // Add null byte as fallback marker
    }
}

/// Create a client TLS configuration
///