On Fri, May 10, 2019 at 11:45:46AM -0300, Jeronimo Pellegrini wrote:
> Or I can try to make the shell code that is sent to the remote
> end do the verification itself (I'd test using dash, which I
> hope will work on most systems of interest). Something like
> 
> { hexdump < /dev/null && HD=hexdump; } || \
> { busybox hexdump < /dev/null && HD="busybox hexdump"; } &&  \
> $HD ...

I actually implemented the shell scripting solution.
Only tramp-hexdump-awk-encode is in the email body, but the
full patch is attached.

This seems to work, and requires no extra coding in tramp
(only the constant strings are changed).

I can also do the templating in elisp, if you think it would be 
better.

J.

(defconst tramp-hexdump-awk-encode
  "{ { awk '{}' </dev/null && BA=\"\"  ; } || \
     { busybox awk '{}' </dev/null &&  BA=busybox ; } } && \
   { { hexdump -v -e '16/1 \" %%02x\" \"\\n\"' < /dev/null && BH=\"\" ; } || \
     { busybox hexdump -v -e '16/1 \" %%02x\" \"\\n\"' < /dev/null && BH=busybox ; } } && \
$BH hexdump -v -e '16/1 \" %%02x\" \"\\n\"'| $BA awk '\\
BEGIN {
  b64 = \"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/\"
  b16 = \"0123456789abcdef\"
}
{
  for (c=1; c<=length($0); c++) {
    d=index(b16, substr($0,c,1))
    if (d--) {
      for (b=1; b<=4; b++) {
        o=o*2+int(d/8); d=(d*2)%%16
        if (++obc==6) {
          printf substr(b64,o+1,1)
          if (++rc>75) { printf \"\\n\"; rc=0 }
          obc=0; o=0
        }
      }
    }
  }
}
END {
  if (obc) {
    tail=(obc==2) ? \"==\\n\" : \"=\\n\"
    while (obc++<6) { o=o*2 }
    printf \"%%c\", substr(b64,o+1,1)
  } else {
    tail=\"\\n\"
  }
  printf tail
}'"
  "Awk/hexdump program to use for encoding a file.
This string is passed to `format', so percent characters need to be doubled.")