NCurses chat misbehaving, blocking in select - c

Question

I wrote a C application for a socialization network and also a simple room-based chat. I used ncurses, sockets and basic networking stuff.
The problem is that my function uses select() to read from server socket AND stdin so when I start to write a message, the output window freezes and only shows messages from other clients after I hit enter.
I tried everything possible .. Is there a way to fix this ?
I also tried to force nocbreak().It works okay but if I do that, when I write the message, the echoing is disabled and nothing shows up in the input window as I type, even though the message is there but like "invisible".
Here is the code :
ssize_t safePrefRead(int sock, void *buffer)
{
size_t length = strlen(buffer);
ssize_t nbytesR = read(sock, &length, sizeof(size_t));
if (nbytesR == -1)
{
perror("read() error for length ! Exiting !\n");
exit(EXIT_FAILURE);
}
nbytesR = read(sock, buffer, length);
if (nbytesR == -1)
{
perror("read() error for data ! Exiting !\n");
exit(EXIT_FAILURE);
}
return nbytesR;
}
ssize_t safePrefWrite(int sock, const void *buffer)
{
size_t length = strlen(buffer);
ssize_t nbytesW = write(sock, &length, sizeof(size_t));
if (nbytesW == -1)
{
perror("write() error for length ! Exiting !\n");
exit(EXIT_FAILURE);
}
nbytesW = write(sock, buffer, length);
if (nbytesW == -1)
{
perror("write() error for data ! Exiting !\n");
exit(EXIT_FAILURE);
}
return nbytesW;
}
void activeChat(int sC, const char *currentUser, const char *room)
{
char inMesg[513], outMesg[513];
char user[33];
int winrows, wincols;
WINDOW *winput, *woutput;
initscr();
nocbreak();
getmaxyx(stdscr, winrows, wincols);
winput = newwin(1, wincols, winrows - 1, 0);
woutput = newwin(winrows - 1, wincols, 0, 0);
keypad(winput, true);
scrollok(woutput, true);
wrefresh(woutput);
wrefresh(winput);
fd_set all;
fd_set read_fds;
FD_ZERO(&all);
FD_ZERO(&read_fds);
FD_SET(0, &all);
FD_SET(sC, &all);
wprintw(woutput, "Welcome to room '%s' \n Use /quitChat to exit !\n!", room);
wrefresh(woutput);
while (true)
{
memcpy( &read_fds, &all, sizeof read_fds );
if (select(sC + 1, &read_fds, NULL, NULL, NULL) == -1)
{
perror("select() error or forced exit !\n");
break;
}
if (FD_ISSET(sC, &read_fds))
{
memset(inMesg, 0, 513);
safePrefRead(sC, user);
safePrefRead(sC, inMesg);
wprintw(woutput, "%s : %s\n", user, inMesg);
wrefresh(woutput);
wrefresh(winput);
}
if (FD_ISSET(0, &read_fds))
{
//wgetnstr(winput, "%s", outMesg);
int a, i = 0;
while ( i < MAX_BUF_LEN && (a = wgetch(winput)) != '\n')
{
outMesg[i] = (char)a;
i++;
}
outMesg[i] = 0;
if (outMesg[0] == 0)
continue;
if (strcmp(outMesg, "/quitChat") == 0)
{
safePrefWrite(sC, outMesg);
break;
}
safePrefWrite(sC, outMesg);
delwin(winput);
winput = newwin(1, wincols, winrows - 1, 0);
keypad(winput, true);
wrefresh(winput);
}
}
delwin(winput);
delwin(woutput);
endwin();
}
-safePrefWrite and safePrefRead are wrappers for prexied read / write and error treating
-sC is the server socket.
LE: I tried using fork and threads. Using fork was behaving the same and threads were a disaster, the terminal was messed up.
Thank you.

Answer 1

modify the while(true) loop to only handle one char at a time for the stdin.
Which mostly means for stdin, read a single char:
if char is '\n' then handle as currently,
otherwise, just append char to the buffer to write.
Always, before appending a char to buffer to write, check that buffer is not full.
add code to handle the case where the buffer to write is full
end the function with this sequence:
delwin(winput);
delwin(woutput);
endwin();
endwin();
to end both windows.
Do not call endwin() during processing of the socket input.
Do not call endwin() when select() returns an error condition
the fd_set is not an intrinsic size in C, so use memcpy() to set
read_fds from all. suggest:
memcpy( &read_fds, &all, sizeof read_fds );
the parameter: currentUser is not used, suggest inserting the line:
(void)currentUser;
to eliminate a compiler warning message.
for readability, and ease of understandability, suggest #define the magic numbers 513 and 33 with meaningful names, then use those meaningful names throughout the code.
#define MAX_BUF_LEN (513)
#define MAX_USER_LEN (33)
this line: outMesg[i] = a; raises a compiler warning, suggest:
outMesg[i] = (char)a;
This line: while ( (a = wgetch(winput)) != '\n') can allow the buffer outMesg[] to be overrun, resulting in undefined behaviour and can lead to a seg fault event. suggest:
while ( i < MAX_BUF_LEN && (a = wgetch(winput)) != '\n')
Suggest posting the prototypes for the safePrefWrite() and safePrefRead() functions, similar to:
void safePrefRead( int, char * );
void safePrefWrite( int, char * );

Answer 2

As noted by #user3629249, there are several criticisms which can be applied to the sample code. However, OP's question is not addressed by those improvements.
OP seems to have overlooked these functions:
cbreak or raw, to make wgetch read unbuffered data, i.e., not waiting for '\n'.
nodelay or timeout, to control the amount of time wgetch spends waiting for input.
By the way, making select work with a curses program will make assumptions about the curses library internal behavior: getting that to work reliably can be troublesome.

Answer 3

Fixed it finally by using only the big loop.
Here is the code if anyone has the same problem in the future :
if (FD_ISSET(0, &read_fds))
{
inChar = wgetch(winput);
if (inChar == 27)
{
safePrefWrite(sC, "/quit");
break;
}
if (inChar == KEY_UP || inChar == KEY_DOWN || inChar == KEY_LEFT || inChar == KEY_RIGHT)
continue;
if (inChar == KEY_BACKSPACE || inChar == KEY_DC || inChar == 127)
{
wdelch(winput);
wrefresh(winput);
if (i != 0)
{
outMesg[i - 1] = 0;
i--;
}
}
else
{
outMesg[i] = (char)inChar;
i++;
}
if (outMesg[i - 1] == '\n')
{
outMesg[i - 1] = 0;
i = 0;
if (outMesg[0] == 0)
continue;
if (strcmp(outMesg, "/quit") == 0)
{
safePrefWrite(sC, outMesg);
break;
}
safePrefWrite(sC, outMesg);
delwin(winput);
winput = newwin(1, wincols, winrows - 1, 0);
keypad(winput, true);
wrefresh(winput);
memset(outMesg, 0, 513);
}
}
I also use raw() to disable signals and to treat the codes how I want.
Anything else above and below this "if" is just like in the 1st post.