miniserver.c

/*
 * miniserver - a simple server using the messaging module
 *
 * This simple server receives and prints (to stdout) a message and
 * expects the user to enter one line of stdin, which it sends back;
 * each printed message is surrounded by 'quotes'.
 *
 * This program is an atypical use of the message module because it
 * blocks on input from stdin during a call to handleMessage, rather
 * than using handleInput; this approach allows it to respond to each
 * message from each correspondent, one by one.
 *
 * David Kotz - June 2021
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include "message.h"

/**************** file-local functions ****************/

static bool handleMessage(void* arg, const addr_t from, const char* message);

/***************** main *******************************/
int
main(const int argc, char* argv[])
{
    // initialize the message module (without logging)
    int myPort = message_init(NULL);
    if (myPort == 0) {
        return 2; // failure to initialize message module
    } else {
        printf("serverPort=%d\n", myPort);
    }

    // check arguments (there should be none)
    const char* program = argv[0];
    if (argc != 1) {
        fprintf(stderr, "usage: %s\n", program);
        return 3; // bad commandline
    }

    // Loop, waiting for input or for messages; provide callback functions.
    // We use the 'arg' parameter to carry a pointer to 'server'.
    bool ok = message_loop(NULL, 0, NULL, NULL, handleMessage);

    // shut down the message module
    message_done();

    return ok? 0 : 1; // status code depends on result of message_loop
}

/**************** handleMessage ****************/
/* Datagram received; print it, read a line from stdin, and use it as reply.
* We ignore 'arg' here.
* Return true if EOF on stdin or any fatal error.
*/
static bool
handleMessage(void* arg, const addr_t from, const char* message)
{
    // print the message and a prompt
    printf("'%s'\n", message);
    printf("> ");
    fflush(stdout);

    // allocate a buffer into which we can read a line of input
    // (it can't be any longer than a message)!
    char line[message_MaxBytes];

    // read a line from stdin: this is VERY unusual for a handleMessage()
    if (fgets(line, message_MaxBytes, stdin) == NULL) {
        // EOF case: stop looping
        putchar('\n');
        return true;
    } else {
        // strip trailing newline
        const int len = strlen(line);
        if (len > 0 && line[len-1] == '\n') {
            line[len-1] = '\0';
        }

        // send as message back to client
        message_send(from, line);

        // normal case: keep looping
        return false;
    }
}