CODEWITHSUNDEEP
socketsunixocaml
Seneca
Seneca

Reputation: 2412

ocaml simplistic http server with the Unix module

I'm trying to make a very simple http server with the low-level Unix module to get a better understanding of how a http server actually works. This is my current code:

let () =
   let socket_fd = Unix.socket Unix.PF_INET Unix.SOCK_STREAM 0 in
   let _ = Unix.bind socket_fd (Unix.ADDR_INET ((Unix.inet_addr_of_string "127.0.0.1"), 8888)) in
   let _ = Unix.listen socket_fd 1 in
   let (file_descr,sockaddr) = Unix.accept socket_fd in
   let b = Bytes.create 1024 in
   let _ = Unix.recv file_descr b 0 0 [Unix.MSG_PEEK] in
   print_endline b;

When I open a webbrowser & surf to localhost:8888 the program displays a newline and exits. Why isn't it printing out the request?

According to the Unix module documentation recv has the following signature:

val recv : file_descr -> bytes -> int -> int -> msg_flag list -> int
Receive data from a connected socket.

What is the meaning of the ... -> int -> int -> ... ? I have no idea what I should be passing in those two ints.

Also how do I know beforehand what size a should give to bytes ?

Upvotes: 3

Views: 458

Answers (1)

Pierre G.
Pierre G.

Reputation: 4425

Part of the answer lies in the C mapping of recv (sendrecv: .opam/version/build/ocaml/otherlibs/unix/sendrecv.c ).

CAMLprim value unix_recv(value sock, value buff, value ofs, value len,
                         value flags)
{
  int ret, cv_flags;
  long numbytes;
  char iobuf[UNIX_BUFFER_SIZE];

  cv_flags = convert_flag_list(flags, msg_flag_table);
  Begin_root (buff);
    numbytes = Long_val(len);
    if (numbytes > UNIX_BUFFER_SIZE) numbytes = UNIX_BUFFER_SIZE;
    enter_blocking_section();
    ret = recv(Int_val(sock), iobuf, (int) numbytes, cv_flags);
    leave_blocking_section();
    if (ret == -1) uerror("recv", Nothing);
    memmove (&Byte(buff, Long_val(ofs)), iobuf, ret);
  End_roots();
  return Val_int(ret);
}

So first int is an offset within the buffer, and second int is the length of the retrieval - that you shoud not set to 0.

Happy new year anyway ;)

Upvotes: 3

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