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ttyaccess.c
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/* File: ttyaccess.c
Author: Mats Engstrom, April 2020
Language: C (UNIX)
Purpose: Handle character-by-character input from stdin and udp using pthreads
*/
#define _XOPEN_SOURCE 500 // Enable timestruct definitions in C99
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/select.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sgtty.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/errno.h>
#include <time.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include "ttyaccess.h"
struct threaddata_struct {
int termpipe;
int udp_socket;
};
static pthread_t thread;
static int pipes[2];
static struct threaddata_struct td;
#define RBLEN 1024
static volatile int rbhead = 0; // head pointer for ring buffer queue
static volatile int rbtail = 0; // tail pointer for ring buffer queue
static volatile char rbqueue[RBLEN];
static pthread_mutex_t rblock; // Mutex for locking the ring buffer
static char breakcnt;
//
// Store character into ringbuffer
//
static void queue_to_rb(char ch) {
int newtail = (rbtail + 1) % RBLEN;
if (newtail != rbhead) {
rbqueue[rbtail] = ch;
rbtail = newtail;
}
if (ch==3) breakcnt++;
else breakcnt=0;
}
//
// Get a character from ringbuffer
// returns -1 if empty, else the character
//
int get_from_rb(void) {
int ch=-1;
pthread_mutex_lock(&rblock);
if (rbhead != rbtail) {
ch = rbqueue[rbhead];
rbhead = (rbhead + 1) % RBLEN;
}
pthread_mutex_unlock(&rblock);
return ch;
}
//
// Return number of characters available in the ring buffer
//
int count_rb(void) {
int cnt;
pthread_mutex_lock(&rblock);
cnt=abs(rbhead-rbtail);
pthread_mutex_unlock(&rblock);
return cnt;
}
//
// Set stdin to either "raw" or normal mode
// mode=true for raw, false=normal
//
static void set_stdin_raw(int mode) {
static struct termios oldtio;
static int lastMode=0;
struct termios newtio;
if (mode) {
tcgetattr(STDIN_FILENO, &oldtio); // save current port settings
bzero(&newtio, sizeof(newtio));
newtio.c_lflag=0; // set input mode (non-canonical, no echo
newtio.c_cc[VTIME]=0; // inter-character timer unused
newtio.c_cc[VMIN]=1; // blocking read
tcflush(STDIN_FILENO, TCIFLUSH);
tcsetattr(STDIN_FILENO, TCSANOW, &newtio);
} else {
if (lastMode) tcsetattr(STDIN_FILENO, TCSANOW, &oldtio);
}
lastMode=mode;
}
//
// Create and bind to a listening UDP socket
//
static int create_udp_socket(int port) {
struct sockaddr_in server_address;
int sock;
int r;
memset(&server_address, 0, sizeof(server_address));
server_address.sin_family = AF_INET;
server_address.sin_port = htons(port);
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
sock = socket(PF_INET, SOCK_DGRAM, 0);
for (int i=0; i<5; i++) {
r=bind(sock, (struct sockaddr *)&server_address, sizeof(server_address));
if (r==0) break;
sleep(1);
}
if (r < 0) {
printf("Could not bind socket to UDP port %d\n",port);
exit(1);
}
return sock;
}
//
// Thread that waits for keypresses or udp messages and puts them into the ring buffer
//
void *keyin_thread(void *td) {
char buffer[256];
int len;
fd_se
A41A
t rfds;
int termpipe = ((struct threaddata_struct *)td)->termpipe;
int udp_socket = ((struct threaddata_struct *)td)->udp_socket;
for (;;) {
FD_ZERO(&rfds);
FD_SET(STDIN_FILENO, &rfds);
FD_SET(termpipe, &rfds);
FD_SET(udp_socket, &rfds);
while (select(udp_socket+1, &rfds, NULL, NULL, NULL) == 0);
if (FD_ISSET(termpipe, &rfds)) {
close(termpipe);
break;
}
if (FD_ISSET(STDIN_FILENO, &rfds)) {
len=read(STDIN_FILENO, buffer, sizeof(buffer));
pthread_mutex_lock(&rblock);
for (int i=0; i<len; i++) queue_to_rb(buffer[i]);
pthread_mutex_unlock(&rblock);
}
if (FD_ISSET(udp_socket, &rfds)) {
len=recv(udp_socket, buffer, sizeof(buffer),0);
pthread_mutex_lock(&rblock);
for (int i=0; i<len; i++) queue_to_rb(buffer[i]);
pthread_mutex_unlock(&rblock);
}
}
pthread_exit(NULL);
}
//
// Traps ctrl-c and send it to the ring buffer for normal processing
//
static void mykill(int arg) {
queue_to_rb(3);
}
//
//
//
void comms_init(void) {
pthread_mutex_init(&rblock, NULL);
pipe(pipes);
td.termpipe=pipes[0];
td.udp_socket=create_udp_socket(2288);
set_stdin_raw(1);
breakcnt=0;
signal(SIGINT, mykill);
pthread_create(&thread, NULL, keyin_thread, &td);
}
//
//
//
void comms_cleanup(void) {
set_stdin_raw(0);
close(pipes[1]);
printf("Closing socket %d\r\n",td.udp_socket);
close(td.udp_socket);
pthread_mutex_destroy(&rblock);
// pthread_exit(NULL);
}
//
// blocking 7 bit read from console
//
int ttygetc(void) {
int ch;
struct timespec ts100us = { .tv_sec = 0, .tv_nsec = 1000000 };
do {
ch=get_from_rb();
if (ch<0) {
if (breakcnt>4) ttybreak();
nanosleep(&ts100us,NULL);
}
} while (ch<0);
return ch;
}
//
// poll for a character from the console
//
int ttypoll(void) {
if (breakcnt>4) ttybreak();
return get_from_rb();
}
//
//
//
void ttygets(char * buf, int len) {
int i = 0;
int ch;
char c;
do {
ch = ttygetc();
if (ch == '\b' || ch==127) {
if (i > 0) {
write(STDOUT_FILENO, "\b \b", 3);
i--;
}
} else if (ch >= ' ') {
if (i < (len - 1)) {
c=ch;
write(STDOUT_FILENO, &c, 1);
buf[i] = ch;
i++;
}
}
} while ((ch != '\r') && (ch != '\n'));
write(STDOUT_FILENO, "\r\n", 2);
if (i < len) {
buf[i] = '\0';
} else {
buf[len - 1] = '\0';
}
}