Force SNI to be the --xmpphost if passed

XMPP can be used with SNI in two contexts:

- Standard RFC 6120 STARTTLS-based connections; in that case, SNI
  is most likely to be ignored, as XMPP uses another way to signal
  the target domain name (via the @to attribute on the stream
  header, which is already set correctly by testssl.sh). However,
  setting SNI to a different value than the @to attribute may
  lead to confusion.

- XEP-0368 (XMPP-over-TLS) connections which omit the STARTTLS
  phase and go right for TLS (and inside that, XMPP). In that case,
  SNI is obviously required to be correct. XEP-0368 specifies that
  the SNI name MUST be the domain name of the service (not
  necessarily the host name of the endpoint, thanks to SRV
  records).

Hence, this patch forces the SNI name to be the --xmpphost value,
if --xmpphost is given. Note that it blatantly ignores whether
XMPP is used otherwise.

Author: horazont

testssl.sh

@@ -4522,10 +4522,11 @@ modify_clienthello() {
                # the SNI extension or replace it with the correct server name.
                sni_extension_found=true
                if [[ -n "$SNI" ]]; then
+                    servername=${XMPP_HOST:-${NODE}}
                     # Create a server name extension that corresponds to $SNI
-                    len_servername=${#NODE}
+                    len_servername=${#servername}
                     hexdump_format_str="$len_servername/1 \"%02x\""
-                    servername_hexstr=$(printf $NODE | hexdump -v -e "${hexdump_format_str}")
+                    servername_hexstr=$(printf $servername | hexdump -v -e "${hexdump_format_str}")
                     # convert lengths we need to fill in from dec to hex:
                     len_servername_hex=$(printf "%02x\n" $len_servername)
                     len_sni_listlen=$(printf "%02x\n" $((len_servername+3)))
@@ -14514,9 +14515,10 @@ prepare_tls_clienthello() {
                #00       # server_name type (hostname)
                #00 15    # server_name length
                #66 66 66 66 66 66 2e 66 66 66 66 66 66 66 66 66 66 2e 66 66 66  target.mydomain1.tld # server_name target
-               len_servername=${#NODE}
+               servername=${XMPP_HOST:-${NODE}}
+               len_servername=${#servername}
                hexdump_format_str="$len_servername/1 \"%02x,\""
-               servername_hexstr=$(printf $NODE | hexdump -v -e "${hexdump_format_str}" | sed 's/,$//')
+               servername_hexstr=$(printf $servername | hexdump -v -e "${hexdump_format_str}" | sed 's/,$//')
                # convert lengths we need to fill in from dec to hex:
                len_servername_hex=$(printf "%02x\n" $len_servername)
                len_sni_listlen=$(printf "%02x\n" $((len_servername+3)))
@@ -19710,7 +19712,12 @@ parse_hn_port() {
      fi
 
      debugme echo $NODE:$PORT
-     SNI="-servername $NODE"
+     if [[ -n "$XMPP_HOST" ]]; then
+          # XMPP host is set, force SNI to be that
+          SNI="-servername $XMPP_HOST"
+     else
+          SNI="-servername $NODE"
+     fi
      URL_PATH=$(sed 's/https:\/\///' <<< "$1" | sed 's/'"${NODE}"'//' | sed 's/.*'"${PORT}"'//')      # remove protocol and node part and port
      URL_PATH=$(sed 's/\/\//\//g' <<< "$URL_PATH")          # we rather want // -> /
      URL_PATH=${URL_PATH%%.}                                # strip trailing "." so that it is not interpreted as URL