Allow caller to provide extra extensions to tls_sockets()

This PR allows the caller to provide additional extensions to `tls_sockets()` to be included in the ClientHello. If the caller provides an extension that would have already been included in the ClientHello, then the caller's value for the extension is used rather than the default value.

testssl.sh

@@ -6196,6 +6196,7 @@ sslv2_sockets() {
 
 # ARG1: TLS version low byte (00: SSLv3,  01: TLS 1.0,  02: TLS 1.1,  03: TLS 1.2)
 # ARG2: CIPHER_SUITES string
+# ARG3: (optional) additional request extensions
 socksend_tls_clienthello() {
      local tls_low_byte="$1"
      local tls_word_reclayer="03, 01"      # the first TLS version number is the record layer and always 0301 -- except: SSLv3
@@ -6208,9 +6209,11 @@ socksend_tls_clienthello() {
      local len_client_hello_word len_all_word
      local ecc_cipher_suite_found=false
      local extension_signature_algorithms extension_heartbeat
-     local extension_session_ticket extension_next_protocol extensions_ecc extension_padding
+     local extension_session_ticket extension_next_protocol extension_padding
+     local extension_supported_groups="" extension_supported_point_formats=""
+     local extra_extensions extra_extensions_list=""
 
-     code2network "$2"             # convert CIPHER_SUITES
+     code2network "$(echo "$2" | tr 'A-Z' 'a-z')"   # convert CIPHER_SUITES
      cipher_suites="$NW_STR"                      # we don't have the leading \x here so string length is two byte less, see next
 
      len_ciph_suites_byte=$(echo ${#cipher_suites})
@@ -6287,43 +6290,79 @@ socksend_tls_clienthello() {
           extension_next_protocol="
           33, 74, 00, 00"
 
-          # Supported Elliptic Curves Extension and Supported Point Formats Extension.
+          if "$ecc_cipher_suite_found"; then
-          extensions_ecc="
+               # Supported Groups Extension
+               extension_supported_groups="
                00, 0a,                    # Type: Supported Elliptic Curves , see RFC 4492
                00, 3e, 00, 3c,            # lengths
                00, 0e, 00, 0d, 00, 19, 00, 1c, 00, 1e, 00, 0b, 00, 0c, 00, 1b,
                00, 18, 00, 09, 00, 0a, 00, 1a, 00, 16, 00, 17, 00, 1d, 00, 08,
                00, 06, 00, 07, 00, 14, 00, 15, 00, 04, 00, 05, 00, 12, 00, 13,
-          00, 01, 00, 02, 00, 03, 00, 0f, 00, 10, 00, 11,
+               00, 01, 00, 02, 00, 03, 00, 0f, 00, 10, 00, 11"
+               # Supported Point Formats Extension
+               extension_supported_point_formats="
                00, 0b,                    # Type: Supported Point Formats , see RFC 4492 
                00, 02,                    # len
                01, 00"
+          fi
 
+          # Each extension should appear in the ClientHello at most once. So,
+          # find out what extensions were provided as an argument and only use
+          # the provided values for those extensions.
+          extra_extensions="$(echo "$3" | tr 'A-Z' 'a-z')"
+          code2network "$extra_extensions"
+          len_all=${#extra_extensions}
+          for (( i=0; i < len_all; i=i+16+4*0x$len_extension_hex )); do
+               part2=$i+4
+               extra_extensions_list+=" ${NW_STR:i:2}${NW_STR:part2:2} "
+               j=$i+8
+               part2=$j+4
+               len_extension_hex="${NW_STR:j:2}${NW_STR:part2:2}"
+          done
+
+          if [[ -n "$SNI" ]] && [[ ! "$extra_extensions_list" =~ " 0000 " ]]; then
                all_extensions="
-           $extension_heartbeat
+                00, 00                  # extension server_name
-          ,$extension_session_ticket
-          ,$extension_next_protocol"
-
-          if [[ -n "$SNI" ]]; then
-               all_extensions="$all_extensions
-               ,00, 00                  # extension server_name
                ,00, $len_sni_ext        # length SNI EXT
                ,00, $len_sni_listlen    # server_name list_length
                ,00                      # server_name type (hostname)
                ,00, $len_servername_hex # server_name length. We assume len(hostname) < FF - 9
                ,$servername_hexstr"     # server_name target
           fi
+          if [[ ! "$extra_extensions_list" =~ " 000f " ]]; then
+               [[ -n "$all_extensions" ]] && all_extensions+=","
+               all_extensions+="$extension_heartbeat"
+          fi
+          if [[ ! "$extra_extensions_list" =~ " 0023 " ]]; then
+               [[ -n "$all_extensions" ]] && all_extensions+=","
+               all_extensions+="$extension_session_ticket"
+          fi
+
+          # If the ClientHello will include the ALPN extension, then don't include the NPN extension.
+          if [[ ! "$extra_extensions_list" =~ " 3374 " ]] && [[ ! "$extra_extensions_list" =~ " 0010 " ]]; then
+               [[ -n "$all_extensions" ]] && all_extensions+=","
+               all_extensions+="$extension_next_protocol"
+          fi
 
           # RFC 5246 says that clients MUST NOT offer the signature algorithms
           # extension if they are offering TLS versions prior to 1.2.
-          if [[ "0x$tls_low_byte" -ge "0x03" ]]; then
+          if [[ "0x$tls_low_byte" -ge "0x03" ]] && [[ ! "$extra_extensions_list" =~ " 000d " ]]; then
-               all_extensions="$all_extensions
+               [[ -n "$all_extensions" ]] && all_extensions+=","
-               ,$extension_signature_algorithms"
+               all_extensions+="$extension_signature_algorithms"
           fi
 
-          if $ecc_cipher_suite_found; then
+          if [[ -n "$extension_supported_groups" ]] && [[ ! "$extra_extensions_list" =~ " 000a " ]]; then
-               all_extensions="$all_extensions
+               [[ -n "$all_extensions" ]] && all_extensions+=","
-               ,$extensions_ecc"
+               all_extensions+="$extension_supported_groups"
+          fi
+          if [[ -n "$extension_supported_point_formats" ]] && [[ ! "$extra_extensions_list" =~ " 000b " ]]; then
+               [[ -n "$all_extensions" ]] && all_extensions+=","
+               all_extensions+="$extension_supported_point_formats"
+          fi
+
+          if [[ -n "$extra_extensions" ]]; then
+               [[ -n "$all_extensions" ]] && all_extensions+=","
+               all_extensions+="$extra_extensions"
           fi
 
           code2network "$all_extensions" # convert extensions
@@ -6336,7 +6375,7 @@ socksend_tls_clienthello() {
           # If the length of the Client Hello would be between 256 and 511 bytes,
           # then add a padding extension (see RFC 7685)
           len_all=$((0x$len_ciph_suites + 0x2b + 0x$len_extension_hex + 0x2))
-          if [[ $len_all -ge 256 ]] && [[ $len_all -le 511 ]]; then
+          if [[ $len_all -ge 256 ]] && [[ $len_all -le 511 ]] && [[ ! "$extra_extensions_list" =~ " 0015 " ]]; then
                if [[ $len_all -gt 508 ]]; then
                     len_padding_extension=0
                else
@@ -6413,6 +6452,7 @@ socksend_tls_clienthello() {
 # arg2: (optional) list of cipher suites
 # arg3: (optional): "all" - process full response (including Certificate and certificate_status handshake messages)
 #                   "ephemeralkey" - extract the server's ephemeral key (if any)
+# arg4: (optional) additional request extensions
 tls_sockets() {
      local -i ret=0
      local -i save=0
@@ -6435,7 +6475,7 @@ tls_sockets() {
      fi
 
      debugme echo "sending client hello..."
-     socksend_tls_clienthello "$tls_low_byte" "$cipher_list_2send"
+     socksend_tls_clienthello "$tls_low_byte" "$cipher_list_2send" "$4"
      ret=$?                             # 6 means opening socket didn't succeed, e.g. timeout
 
      # if sending didn't succeed we don't bother