+ \ Compute padding (if requested).
+ addr-min_clienthello_len get16 over - dup 0> if
+ \ We well add a Pad ClientHello extension, which has its
+ \ own header (4 bytes) and might be the only extension
+ \ (2 extra bytes for the extension list header).
+ total-ext-length ifnot swap 2+ swap 2- then
+ \ Account for the extension header.
+ 4 - dup 0< if drop 0 then
+ \ Adjust total extension length.
+ dup 4 + total-ext-length + >total-ext-length
+ \ Adjust ClientHello length.
+ swap 4 + over + swap
+ else
+ drop
+ -1
+ then
+ { ext-padding-amount }