#include <stdio.h>  
#include <stdlib.h> 
#include <string.h>  
#include <unistd.h> 
#include <fcntl.h>  
#include <termios.h>
#include <unistd.h>
#include <stdlib.h>      
#include <fcntl.h>
#include <signal.h>
#include <errno.h>
#include <sys/time.h>
#include <sys/resource.h>

struct termios saved_termios;
int saved_flags = 0, odd_keyboard = 0, done_atexit = 0;

#define kbb_sz 256
char kbbuff[kbb_sz];
int kbb_b = 0, kbb_e = 0, kbb_n = 0, kbb_l = 0;

const char * signame[] =
   { "", "HUP", "INT", "QUIT", "ILL", "TRAP", "ABRT", "EMT", "FPE", "KILL",
     "BUS", "SEGV", "SYS", "PIPE", "ALRM", "TERM", "URG", "STOP", "TSTP", "CONT",
     "CHLD", "TTIN", "TTOU", "IO", "XCPU", "XFSZ", "VTALRM", "PROF", "WINCH", "INFO",
     "USR1", "USR2", "THR", "LIBRT" };
const int numsigs = sizeof(signame) / sizeof(signame[0]);

void saysignal(int n)
{ printf("signal %d: ", n);
  if (n > 0 && n < numsigs)
    printf("SIG%s\n", signame[n]);
  else
    printf("incorrect\n"); }

void ignore_signals()
{ signal(SIGHUP, saysignal);
  signal(SIGILL, saysignal);
  signal(SIGTRAP, saysignal);
  signal(SIGABRT, saysignal);
  signal(SIGEMT, saysignal);
  signal(SIGFPE, saysignal);
  signal(SIGSYS, saysignal);
  signal(SIGPIPE, saysignal);
  signal(SIGALRM, saysignal);
  signal(SIGURG, saysignal);
  signal(SIGSTOP, saysignal);
  signal(SIGTSTP, saysignal);
  signal(SIGCONT, saysignal);
  signal(SIGCHLD, saysignal);
  signal(SIGTTIN, saysignal);
  signal(SIGTTOU, saysignal);
  signal(SIGXCPU, saysignal);
  signal(SIGXFSZ, saysignal);
  signal(SIGVTALRM, saysignal);
  signal(SIGPROF, saysignal);
  signal(SIGWINCH, saysignal);
  signal(SIGINFO, saysignal);
  signal(SIGUSR1, saysignal);
  signal(SIGUSR2, saysignal);
  signal(SIGTHR, saysignal);
  signal(SIGLIBRT, saysignal); }

int enqueue(char c)
{ if (kbb_n == kbb_sz)
    return 0;
  kbbuff[kbb_e] = c;
  kbb_e += 1;
  if (kbb_e == kbb_sz)
    kbb_e = 0;
  kbb_n += 1;
  if (c == '\n')
    kbb_l += 1;
  return 1; }

int kb_line_ready(void)
{ return kbb_l > 0; }

int kb_char_ready(void)
{ return kbb_n > 0; }

char read_kb_char(void)
{ if (kbb_n == 0)
    return '\0';
  char c = kbbuff[kbb_b];
  kbb_b += 1;
  if (kbb_b == kbb_sz)
    kbb_b = 0;
  kbb_n -= 1;
  if (c == '\n')
    kbb_l -= 1;
  return c; }

char * read_kb_line(char * s, int n)
{ int len = 0;
  if (kbb_l == 0)
    return NULL;
  while (1)
  { if (kbb_n == 0)
      break;
    if (len == n - 1)
      break;
    char c = read_kb_char();
    if (c == '\n')
      break;
    s[len] = c;
    len += 1; }
  s[len] = '\0';
  return s; }

static void sigio(int x)
{ char c;
  int n = read(0, & c, 1);
  if (n > 0)
  { int ok = enqueue(c); } }

int keyboard_back_to_normal(void)
{ if (! odd_keyboard)
    return 0;
  int r = tcsetattr(0, TCSAFLUSH, & saved_termios);
  if (r < 0)
    return r;
  odd_keyboard = 0;
  signal(SIGIO, SIG_IGN);
  fcntl(0, F_SETFL, saved_flags);
  return 0; }

int keyboard_immediate(void)
{ struct termios temp;
  int r = tcgetattr(0, & saved_termios);
  if (r < 0)
    return r;
  temp = saved_termios;
  temp.c_lflag &= ~ ICANON;
  temp.c_lflag &= ~ ECHO;
  temp.c_cc[VMIN] = 1;
  temp.c_cc[VTIME] = 0;
  r = tcsetattr(0, TCSAFLUSH, & temp);
  if (r < 0)
    return r;
  odd_keyboard = 1;
  signal(SIGIO, sigio);
  int pid = getpid();
  saved_flags = fcntl(0, F_GETFL, 0);
  fcntl(0, F_SETFL, saved_flags | O_ASYNC | O_NONBLOCK);
  fcntl(0, F_SETOWN, pid);
  if (! done_atexit)
  { atexit((void (*)(void)) keyboard_back_to_normal);
    ignore_signals();
    done_atexit = 1; }
  return 0; }

void safeprint(const char * s)
{ int i = 0;
  while (1)
  { char c = s[i];
    if (c == '\0')
      break;
    else if (c == '\\')
      printf("\\\\");
    else if (c >= ' ' && c <= '~')
      putchar(c);
    else
      printf("\\%03o", c);
    i += 1; } }

int main()
{ int r = keyboard_immediate();
  if (r < 0)
  { perror("keyboard_immediate");
    exit(1); }
  const int linelen = 100;
  char line[linelen], * s;
  while (1)
  { printf("> ");
    fflush(stdout);
    while (1)
    { s = read_kb_line(line, linelen);
      if (s != NULL)
        break;
      putchar('.');
      fflush(stdout);
      while (1)
      { int r = usleep(1000000);
        if (r < 0)
        { if (kb_line_ready())
            break;
          else if (errno = EINTR)
            continue;
          else
            perror("usleep"); }
        else
          break; } }
    printf("received \"");
    safeprint(line);
    printf("\"\n"); } }