Complex getchar() operation in omxplayer - c++

Question

Recently I have been trying to redirect the output of a named pipe into a running instance of omxplayer (see here for a minimum working example that doesn't control omxplayer even though it should). I suspected that it had something to do with reading and writing to pipes --perhaps a new line got appended-- so I got some help and wrote a C program which writes to a pipe and reads from it (see here) but turns out that it is not a read/write error either. So I went and traced omxplayer's code thinking that no matter how complicated it was, eventually there has to be a place which has standard C++ code which reads user input, and thank god I found it. Here is the method which, to the best of my understanding, is responsible for getting user input and preparing it for the Dbus to do all its heavenly goodness:
void Keyboard::Process()
{
while(!m_bStop && conn && dbus_connection_read_write_dispatch(conn, 0))
{
int ch[8];
int chnum = 0;
while ((ch[chnum] = getchar()) != EOF) chnum++;
if (chnum > 1) ch[0] = ch[chnum - 1] | (ch[chnum - 2] << 8);
if (m_keymap[ch[0]] != 0)
send_action(m_keymap[ch[0]]);
else
Sleep(20);
}
}
As far as I can glean, the while(!m_bStop... is a conditional just to make sure things are still working, m_keymap is a cypher which matches integers such as 'p' or 'q' to enum values such as ACTION_PAUSE and ACTION_QUIT, and I presume send_action() just gets the ball rolling.
Questions:
Here is what I do not understand:
How is EOF detected when I am not even pressing Enter --> while ((ch[chnum] = getchar()) != EOF) (in case you are confused by this, when a movie is playing I press p to pause the film, not p and then Enter or Ctrl+D). I have attached a small script below labeled getchar.c which illustrates how it is looping forever.
Why are we looping for potentially more than 8 iterations in the while loop while ((ch[chnum] = getchar()) != EOF) chnum++ when the array ch is only of length 8?
This might be implementation specific, but why an array of size 8 when all inputs are guaranteed to be 1 character long (I can both see it here in the map, and by the fact that keys are processed instantly). Is this in any way related to the arrow keys and the escape key?
Assuming it is possible to have more than 1 character, somehow, what is this line supposed to do if (chnum > 1) ch[0] = ch[chnum - 1] | (ch[chnum - 2] << 8)?
Knowing, finally, how omxplayer reads user generated input, can anyone tell me why my simple script, labelled omxplayer_test.c, does not succeed in controlling the player?
getchar.c:
#include <stdio.h>
int main( int argc, char *argv[] ) {
int ch [ 8 ];
int chnum = 0;
while ( ( ch [ chnum ] = getchar() ) != EOF ) chnum++;
printf ( "You will never make it here!\n" );
return 0;
}
omxplayer_test.c:
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <stdbool.h>
#define PIPE_PATH "testpipe"
#define VIDEO_PATH "Matrix.mkv"
#define P_MESSAGE "p"
#define Q_MESSAGE "q"
#define I_MESSAGE "."
#define VIDEO_PLAYER "omxplayer"
#define SLEEP_PERIOD 2L
int main()
{
int fd;
pid_t pid;
pid_t wpid;
int status;
char shellCmd [ 1000 ];
struct timespec time1, time2; //used for sleeping
bool parent;
char c;
parent = false;
//Make pipe BEFORE forking
mkfifo ( PIPE_PATH, 0666 );
if ( ( pid = fork () ) < 0 )
{
perror ( "Fork Failed\n" );
return -1;
}
else if ( pid == 0 )
{ //first child launches the movie
sprintf ( shellCmd, "%s %s < %s >/dev/null 2>&1", VIDEO_PLAYER, VIDEO_PATH, PIPE_PATH );
if ( system ( shellCmd ) == -1 )
{
printf ( "Error: %s\n", shellCmd );
fflush(stdout);
}
printf ("First child finished\n");
fflush (stdout);
}
else
{
if ( ( pid = fork () ) < 0 )
{
perror ( "Fork Failed\n" );
return -1;
}
else if ( pid == 0 )
{ //second child waits x seconds then pauses/unpauses/quits movie
time1.tv_sec = SLEEP_PERIOD; //sleep for x seconds
time1.tv_nsec = 0L; //Dont worry about milli seconds
nanosleep ( &time1, &time2 );
//Suprisingly, this signal which gets ball rolling works
fd = open ( PIPE_PATH, O_WRONLY );
write ( fd, I_MESSAGE, sizeof ( I_MESSAGE ) );
nanosleep ( &time1, &time2 );
printf ( "Sleep over, pausing movie\n");
fflush(stdout);
write ( fd, I_MESSAGE, sizeof ( P_MESSAGE ) );
nanosleep ( &time1, &time2 );
printf ( "Sleep over, unpausing movie\n");
fflush(stdout);
write ( fd, P_MESSAGE, sizeof ( P_MESSAGE ) );
nanosleep ( &time1, &time2 );
printf ( "Sleep over, quiting movie\n");
fflush(stdout);
write ( fd, Q_MESSAGE, sizeof ( Q_MESSAGE ) );
close ( fd );
printf ("Second child finished\n");
fflush (stdout);
}
else
{
parent = true;
}
}
while ( ( wpid = wait ( &status ) ) > 0 )
{
printf ( "Exit status of %d was %d (%s)\n", ( int ) wpid, status, ( status == 0 ) ? "accept" : "reject" );
fflush(stdout);
}
if ( parent == true )
{
printf ("deleting pipe\n");
fflush(stdout);
unlink ( PIPE_PATH );
}
return 0;
}

Answer 1

#puk I stumbled upon your 'old´ question but in case you didn't have it answered by yourself.
Look at something similar on https://github.com/popcornmix/omxplayer/issues/131. As omxplayer releases 0.3.x comes from this 'popcornmix' repository, I will answer these questions there because it is a better place for your omxplayer questions ;)
But I will answer the question why your omxplayer_test.c isn't working here, as it is your code that let omxplayer fail :) Strictly not true, as it is a current issue in omxplayer :(
The sending of I_MESSAGE surprises me the most, as I don't know of any keyboard input handling on a '.' character. On the other hand, 'i' commands omxplayer to go to the previous chapter. So if you didn't key-mapped anything on the '.' input key or meant the real 'i' actions, just leave that out; it isn't (and shouldn't be) needed to start omxplayer.
To pause omxplayer, your typo'd it with the I_MESSAGE in stead of P_MESSAGE.
But sending commands to omxplayer with the write() and the sizeof() of the message causes the same effect as mentioned in forementioned issue. The sizeof() of an x_MESSAGE gives 2 as result back, and not 1 (one)! The sizeof() counts in the '\0'-character of a (c-coded) string; e.g. "p" is stored as 'p''\0', so at least 2 characters. So use strlen() (which needs #include <string.h>) in stead, as it will sent only the x_MESSAGE character.