path: root/ptyim.c

//required for posix_openpt to work
#define _XOPEN_SOURCE 600
#define _DEFAULT_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#include <fcntl.h>
#include <sys/ioctl.h>
#include <termios.h>

#include <signal.h>
#include <pthread.h>
#include <semaphore.h>

#include "im.h"
#include "escape.h"
#define WRITE_BUFFER_LEN 128
//determines if the master process is running
int running = 1;
//pty master and slave fd
int pty_slave = -1;
int pty_master = -1;
//freopen requires fn and not fd since its a unix function
char * pty_slave_fn;
//termios of stdin before we condition it, restored on process exit
struct termios stdin_termio_bk;
//terminal rows and cols
int trows = 0;
int tcols = 0;
//hook for SIGWINCH
void winchhook(int a) {
	struct winsize sz;
	ioctl(STDIN_FILENO, TIOCGWINSZ, &sz);
	trows = sz.ws_row;
	tcols = sz.ws_col;
	//trick programs into thinking the terminal is smaller than it is
	if (sz.ws_row >= 1) {
		sz.ws_row--;
	}
	ioctl(pty_slave, TIOCSWINSZ, &sz);

}
//child process pids
pid_t shell_pid;
pthread_t om_thread;
pthread_t im_disp_thread;
//stdout semaphore
sem_t out_sem;


//return 0 on success, -1 on error
//sets the global vars pty_master and pty_slave
int make_pty() {
	//creates the pty master
	pty_master = posix_openpt(O_RDWR);
	if (pty_master < 0) {
		fprintf(stderr, "errno: %d, failed to create pty master", errno);
		return errno;
	}
	//unlock the slave pty
	if ( unlockpt(pty_master) <0) {
		fprintf(stderr, "errno: %d, failed to unlock pty slave", errno);
		return errno;
	}

	//gets slave path
	pty_slave_fn = ptsname(pty_master);
	//tries to open pty slave
	pty_slave = open(pty_slave_fn, O_RDWR);
	if (pty_slave < 0) {
		fprintf(stderr, "errno: %d, failed to open pty slave '%s'",\
			errno, pty_slave_fn);
		return errno;
	}

	//make the pty slave the same line discipline stdin was
	tcsetattr(pty_slave,TCSANOW,&stdin_termio_bk);
	return 0;
}
//makes stdin raw  previous state stored in global var
//stdin_termio_bk
void condition_stdin() {
	struct termios stdin_termio;
	//save existing termios settings
	tcgetattr(STDIN_FILENO,&stdin_termio);
	tcgetattr(STDIN_FILENO,&stdin_termio_bk);
	//make it raw
	cfmakeraw(&stdin_termio);
	tcsetattr(STDIN_FILENO,TCSANOW,&stdin_termio);
	//move cursor to top left and clear screen
	write(STDIN_FILENO,"\033[0;0f",6);
	write(STDIN_FILENO,"\033[2J", 4);
}
void restore_stdin() {
	tcsetattr(STDIN_FILENO,TCSANOW,&stdin_termio_bk);
}
void * om_routine( void *arg) {
	//thread handling pty -> stdout
	while (running) {
		//output manager child process
		//buffer for reading from pty_master and writing to stdout
		char write_buffer[WRITE_BUFFER_LEN] = {0};
		//only read/write syscalls work well for this, printfs
		//etcs do not work, this is blocking which is why its its own
		//thread
		// pty_master -> STDOUT
		int wchars_read = read(pty_master,write_buffer, WRITE_BUFFER_LEN);
		if (wchars_read >0) {
			sem_wait(&out_sem);
			out_state = update_esc_state(write_buffer, wchars_read, out_state,
				&out_c_parity, &out_clr);
			write(STDOUT_FILENO,write_buffer,wchars_read);
			sem_post(&out_sem);
		}
	}
}
void * im_disp_routine (void *args) {
	while (running) {
		// Every run of this loop, it checks to see if im_buffer has
		// updated, or if the screen has been cleared

		//then checks if the cursor save parity is right, and if the
		//last output tot the terminal is safe to append to
		if (im_updated | out_clr) {
			if (out_c_parity != 0) {
				continue;
			}
			if (safe_state(out_state)) {
				sem_wait(&out_sem);
				disp_im(STDIN_FILENO, trows, tcols);
				sem_post(&out_sem);
				im_updated = 0;
				out_clr = 0;
			}
		}
	}
}
//main thread exit
void exit_main() {
	//kill shell , can not be blocked
	kill(shell_pid, SIGKILL);
	pthread_cancel(om_thread);
	pthread_cancel(im_disp_thread);
	//exit, only the master process should reach this point
	close(pty_master);
	close(pty_slave);
	restore_stdin();
	//clears the screen so the im statusline goes away
	write(STDIN_FILENO,"\033[2J", 4);
	//resets scroll region
	unrestrict_scroll(STDIN_FILENO);
	_exit(0);
}
//hook for when the pty child process dies
void childhook(int a) {
	running = 0;
	//this way it exists even if the loop is waiting for 1 last read char
	exit_main();
}
int main (int argc, char * argv[], char * envp[]) {
	condition_stdin();
	if (make_pty() != 0) {
		restore_stdin();
		return errno;
	}
	//syncs the window sizes for the first time by manually running the
	//resize interrupt handler
	winchhook(0);
	//forks for running bash
	shell_pid = fork();
	if (shell_pid == 0) {
		//shell child process
		//set self to be session leader
		if (setsid() <0) {
			fprintf(stderr, "failed to make new session\n");
		}
		//all the stand streams
		freopen(pty_slave_fn, "r", stdin);
		freopen(pty_slave_fn, "w", stdout);
		freopen(pty_slave_fn, "w", stderr);
		//must be a session leader to set the controlling terminal
		if (ioctl(pty_slave, TIOCSCTTY, 0)) {
			fprintf(stderr, "errno: %d, failed to set controlling tty\n", errno);
		}
		/*
		 *  Opens up the Shell now
		 */
		// First checks argument, then env, then default /bin/sh
		char * shellpath = "/bin/sh";
		if (argc >1) {
			shellpath = argv[1];
		} else if (getenv("SHELL") != NULL) {
			shellpath = getenv("SHELL");
		}
		//by convention we should set the first arg to the path to the
		//shell, also should be null terminated
		char * shell_args[2] = {shellpath, NULL};
		//the process is now replaced with bash
		if (execve(shellpath,shell_args, envp) == -1) {
			fprintf(stderr, "errno: %d, Failed to start shell '%s'\n", errno, shellpath);
			return errno;
		}
		//code should never reach this point since we ran execve
		//should automatically close any file descriptors
		_exit(0);
	} else {
		//creates stdout semaphire
		if (sem_init(&out_sem, 0, 1)) {
			fprintf(stderr, "errno: %d, Error creating output sempahore\n", errno);
			exit_main();
		}
		//creates a thread that just handles pty -> stdout transfers
		if (pthread_create(&om_thread, NULL, &om_routine, NULL) ) {
			fprintf(stderr, "errno: %d, Error creating om thread\n", errno);
			exit_main();
		}
		if (pthread_create(&im_disp_thread, NULL, &im_disp_routine, NULL) ) {
			fprintf(stderr, "errno: %d, Error creating im display thread\n", errno);
			exit_main();
		}
		//master process
		//registers interrupts
		signal(SIGCHLD, childhook);
		signal(SIGWINCH, winchhook);

		//1 char buffer for reading from stdin and writing to pty_master
		char read_buffer[1] = {0};

		//open
		while (running) {
			int rchars_read = read(STDIN_FILENO, read_buffer, 1);
			if (rchars_read > 0) {
				//feeds input char into the escape state
				//machine
				in_state = update_esc_state(read_buffer, 1, in_state, NULL, NULL);
				//skips if the char was anything but
				//normal
				if (in_state == NORMAL || in_state ==DOUBLE_ESC) {
					//feeds the input char into the im state machine
					char input_buffer[IM_TABLE_ENTRY_LEN+1] = {0};
					int im_chars = update_im_state(read_buffer[0],
							input_buffer);
					//just in case it wasn't null terminated right
					input_buffer[im_chars] = 0;
					if (im_chars >0) {
						//writes the input into pty_master if
						//there was an output from the state
						//machine
						write(pty_master,input_buffer,im_chars);
					}
				} else {
					write(pty_master,read_buffer,1);
				}
			}
		}
	}
	exit_main();
	return 0;
}