libmill based pastebin clone

paste.c

// build: $ cc -o paste paste.c -lmill
// run:   $ ./paste &; disown
// use:   $ alias pastebin="nc localhost 6969"
//        $ echo wat up pimp | pastebin
//        $ pastebin < source_code.c

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include <libmill.h>

#define tcpstr(S, STR)  tcpsend(S, STR, sizeof(STR) - 1, -1)

static void rand_chars(char *buf, size_t size, size_t n)
{
    assert (n <= size);

    bzero(buf, size);

    int i, c, byte = 0;
    FILE *fp = fopen("/dev/urandom", "r");

    if (!fp)
        return;

    for (i = 1; i <= n; i++) {
        do {
            c = fgetc(fp);
        } while (!isalnum(c));

        buf[byte++] = c;
    }

    fclose(fp);
}

static coroutine void paste(tcpsock as)
{
    char filename[4096], chars[7];

    rand_chars(chars, sizeof(chars), 5);
    snprintf(filename, sizeof(filename),
             "/home/upload/p/%s.txt", chars);

    char buf[20480]; // 20 kib

    bzero(buf, sizeof(buf));
    tcprecv(as, buf, sizeof(buf), now() + 3000); // 3 secs

    if (strlen(buf) == 0) {
        tcpstr(as, "error: nothing to send\n");
        goto cleanup;
    }

    FILE *fp = fopen(filename, "w");

    if (!fp) {
        tcpstr(as, "error: couldn't upload file\n");
    } else {
        fprintf(fp, "%s", buf);
        fclose(fp);

        snprintf(filename, sizeof(filename),
                 "https://gandas.us.to/p/%s.txt\n", chars);

        tcpsend(as, filename, strlen(filename), -1);
    }

cleanup:
    tcpflush(as, -1);
    tcpclose(as);
}

int main(void)
{
    ipaddr addr = iplocal(NULL, 6969, 0);
    tcpsock ls  = tcplisten(addr, -1);

    if (!ls) {
        perror("fatal: failed to open listening socket");
        return 1;
    }

    while (1) {
        tcpsock as = tcpaccept(ls, -1);

        if (!as)
            continue;

        go (paste(as));
    }

    tcpclose(ls);

    return 0;
}