I am trying to write a simple server program in Ocaml that communicates with other processes via a socket. I currently have a problem that the strings the server reads (with input_line ic) do not seem to compare with other strings properly. For example, I run the server program and use telnet to connect to it, if I send "end" as a line, the server program trys to match with "end", but this doesn't work as expected. The function that handles communication is service (below), which is called to handle a client as part of a forking server (something like the double fork treatment here).
let service ic oc
try while true do
let instr = input_line ic in
match instr with
| "end" -> print_endline "matching end" (* this never runs *)
| _ -> output_string oc ((String.uppercase instr) ^ "\n") ; flush oc
done
with End_of_file -> print_endline "Input stream ended."
;;
In fact, if I do print_endline (string_of_bool ("end" = instr)) I always get false (even when I send "end" via telnet). To try and get some sense of what is going I printed out the result of different comparison operations between the let-binding and the try block:
print_endline instr ;
print_endline "end" ;
print_endline (string_of_bool ("end" = instr)) ;
print_endline (string_of_bool ("end" == instr)) ;
print_endline (string_of_int (String.compare "end" instr)) ;
When I send "end" the server now prints out
end
end
false
false
-1
I'm really lost as to what could be going on - I presume it must be something about getting the instr via reading from a socket, as usually you can compare strings just fine.
I don't think I actually had a question in all that background so here are a few variants that could work:
- What am I doing wrong?
- Why can't I test the input in order to take different actions?
- Is this a bug in Ocaml?
- Do you need the complete source to figure this out?
