A Usable, Secure Communications Protocol: Client-Side TLS - Implementing SSL/TLS Using Cryptography and PKI - page 323

Recall that CipherSuiteIdentifier was defi ned as part of the client hello.
parse_server_hello is something of the opposite of send_client_hello
and it even makes use of a function complementary to append_buffer , shown
in Listing 6-25.
Listing 6-25: “tls.c” read_buffer
static char *read_buffer( char *dest, char *src, size_t n )
{
memcpy( dest, src, n );
return src + n;
}
Reporting Server Alerts
What if the server doesn't happen to support TLS_RSA_WITH_3DES_EDE_CBC_
SHA (or any of the cipher suites on the list the client sends)? It doesn't return a
server_hello at all; instead it responds with an alert message. You need to be
prepared to deal with alerts at any time, so extend receive_tls_message to
handle alerts as shown in Listing 6-26.
Listing 6-26: “receive_tls_message” with alert support
static int receive_tls_msg( int connection,
TLSParameters *parameters )
{
…
if ( message.type == content_handshake )
{
…
}
else if ( message.type == content_alert )
{
while ( ( read_pos - decrypted_message ) < decrypted_length )
{
Alert alert;
read_pos = read_buffer( ( void * ) &alert.level,
( void * ) read_pos, 1 );
read_pos = read_buffer( ( void * ) &alert.description,
( void * ) read_pos, 1 );
report_alert( &alert );
if ( alert.level == fatal )
{
return -1;
}
}
}