From 707b2f7979d456160eac03289eb6558610385636 Mon Sep 17 00:00:00 2001
From: Siraaj Khandkar <siraaj@khandkar.net>
Date: Sat, 21 Mar 2020 17:45:12 -0400
Subject: [PATCH] Write to pipe form the sensor directly

shell redirection isn't sufficient because the writer process is killed
upon closing of the pipe by the reader.
---
 x5/khatus_sensor_time.c | 80 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 68 insertions(+), 12 deletions(-)

diff --git a/x5/khatus_sensor_time.c b/x5/khatus_sensor_time.c
index f156f45..983ebdf 100644
--- a/x5/khatus_sensor_time.c
+++ b/x5/khatus_sensor_time.c
@@ -1,5 +1,8 @@
+#include <assert.h>
+#include <ctype.h>
 #include <errno.h>
-#include <stdarg.h>
+#include <fcntl.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -9,19 +12,24 @@
 #include "khatus_lib_log.h"
 #include "khatus_lib_time.h"
 
+#define usage(...) {print_usage(); fprintf(stderr, "Error:\n    " __VA_ARGS__); exit(EXIT_FAILURE);}
+
+#define MAX_LEN 20
+#define END_OF_MESSAGE '\n'
+
 char *argv0;
 
 void
-usage()
+print_usage()
 {
 	printf(
-	    "%s: [OPT ...]\n"
+	    "%s: [OPT ...] FIFO\n"
 	    "\n"
+	    "FIFO = string    # path to fifo file\n"
 	    "OPT = -i int     # interval\n"
 	    "    | -f string  # format string\n"
 	    "    | -h         # help message (i.e. what you're reading now :) )\n",
 	    argv0);
-	fatal("usage\n");
 }
 
 int
@@ -34,10 +42,19 @@ main(int argc, char **argv)
 
 	time_t t;
 	struct timespec ti;
-	char buf[128];
+	char buf[MAX_LEN];
 	char c;
 
-	memset(buf, '\0', 128);
+	char *fifo_name;
+	int   fifo_fd = -1;
+
+	int n = 0;  /* written */
+	int r = 0;  /* remaining */
+	int i = 0;  /* buffer position */
+
+	signal(SIGPIPE, SIG_IGN);  /* Handling manually */
+
+	memset(buf, '\0', MAX_LEN);
 	while ((c = getopt(argc, argv, "f:i:h")) != -1)
 		switch (c) {
 		case 'f':
@@ -48,17 +65,56 @@ main(int argc, char **argv)
 			opt_interval = atof(optarg);
 			break;
 		case 'h':
-			usage();
-			break;
+			print_usage();
+			return 0;
+		case '?':
+			if (optopt == 'f' || optopt == 'i')
+				fprintf(stderr,
+					"Option -%c requires an argument.\n",
+					optopt);
+			else if (isprint(optopt))
+				fprintf (stderr,
+					"Unknown option `-%c'.\n",
+					optopt);
+			else
+				fprintf(stderr,
+					"Unknown option character `\\x%x'.\n",
+					optopt);
+			return 1;
 		default:
-			usage();
+			assert(0);
 		}
+	fifo_name = argv[optind];
+	debug("fifo_name: %s\n", fifo_name);
+	if (!fifo_name)
+		usage("No filename was provided\n");
 	ti = timespec_of_float(opt_interval);
 	for (;;) {
+		debug("openning \"%s\"\n", fifo_name);
+		fifo_fd = open(fifo_name, O_WRONLY);
+		if (fifo_fd < 0)
+			fatal("Failed to open FIFO file: \"%s\". Error: %s\n",
+			    fifo_name,
+			    strerror(errno));
+		debug("openned. fd: %d\n", fifo_fd);
 		t = time(NULL);
-		strftime(buf, sizeof(buf), opt_fmt, localtime(&t));
-		puts(buf);
-		fflush(stdout);
+		strftime(buf, MAX_LEN, opt_fmt, localtime(&t));
+		r = strlen(buf);
+		buf[r] = END_OF_MESSAGE;
+		for (i = 0; (n = write(fifo_fd, buf + i++, 1)) && r; r--)
+			;
+		if (n < 0)
+			fatal("Failed to write to %s. Err num: %d, Err msg: %s\n",
+			    fifo_name,
+			    errno,
+			    strerror(errno));
+		if (close(fifo_fd) < 0)
+			fatal("Failed to close %s. Err num: %d, Err msg: %s\n",
+			    fifo_name,
+			    errno,
+			    strerror(errno));
+		fifo_fd = -1;
+		debug("closed. fd: %d\n", fifo_fd);
 		snooze(&ti);
 	}
 	return EXIT_SUCCESS;
-- 
2.20.1