[st][PATCH] externalpipe and externalpipein

This patch must be applied on the externalpipe patch. It adds the
function externalpipein to redirect the standard output of the external
command to the slave size of the pty, that is, as if the external
program had been manually executed on the terminal. It can be used to
send desired escape sequences to the terminal with a shortcut.

I created the patch to make use of the dynamic-colors program
(https://github.com/sos4nt/dynamic-colors) that uses the OSC escape
sequences to change the colors of the terminal. The program keeps the
last colorscheme selected in a file, so you can use it to select the
colorscheme for all newly opened terminals from that moment on. If you
want to change the color of the background and foreground independently
from the palette, you have to merge in the patch for the OSC escape
sequences 10, 11, and 12.

This patch includes the changes of the externalpipe sigaction patch to
prevent reseting the signal handler for SIGCHLD when the proces of the
external command exits.

patch/externalpipe.c

@@ -1,5 +1,9 @@
 void
+#if EXTERNALPIPEIN_PATCH
+extpipe(const Arg *arg, int in)
+#else
 externalpipe(const Arg *arg)
+#endif // EXTERNALPIPEIN_PATCH
 {
 	int to[2];
 	char buf[UTF_SIZ];
@@ -19,6 +23,11 @@ externalpipe(const Arg *arg)
 		dup2(to[0], STDIN_FILENO);
 		close(to[0]);
 		close(to[1]);
+		#if EXTERNALPIPEIN_PATCH
+		if (in)
+			dup2(csdfd, STDOUT_FILENO);
+		close(csdfd);
+		#endif // EXTERNALPIPEIN_PATCH
 		execvp(((char **)arg->v)[0], (char **)arg->v);
 		fprintf(stderr, "st: execvp %s\n", ((char **)arg->v)[0]);
 		perror("failed");
@@ -49,4 +58,16 @@ externalpipe(const Arg *arg)
 	close(to[1]);
 	/* restore */
 	signal(SIGPIPE, oldsigpipe);
-}
+}
+
+#if EXTERNALPIPEIN_PATCH
+void
+externalpipe(const Arg *arg) {
+	extpipe(arg, 0);
+}
+
+void
+externalpipein(const Arg *arg) {
+	extpipe(arg, 1);
+}
+#endif // EXTERNALPIPEIN_PATCH

patch/externalpipe.h

@@ -1 +1,4 @@
-void externalpipe(const Arg *);
+void externalpipe(const Arg *);
+#if EXTERNALPIPEIN_PATCH
+void externalpipein(const Arg *);
+#endif // EXTERNALPIPEIN_PATCH