From 51b780f325f1c4fb7e891babb8bc0ebd99004e3f Mon Sep 17 00:00:00 2001
From: Ben Tovar <btovar@nd.edu>
Date: Tue, 13 Sep 2016 17:55:29 -0400
Subject: [PATCH] Adds IGNOREEMPTY=[0|1] to {P,C}BEACON cmd.

When using COMMENTCMD (PBEACON), or INFOCMD (CBEACON), direwolf reports
an error when the command does not produce any stdout, even when the
command exits with status 0.

This commit allows something like:

PBEACON IGNOREEMPTY=1 EVERY=00:30 COMMENTCMD='command_to_print_updates'

Say 'command_to_print_updates' only prints to stdout when its output
would be different from the last time it ran. With the above, direwolf
would run the command as before, but does not print an error when no new
updates are available. An error is still reported if the exit status is
not 0.
---
 beacon.c | 18 +++++++++++-------
 config.c |  3 +++
 config.h |  3 ++-
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/beacon.c b/beacon.c
index 1d0ca49..32e285f 100644
--- a/beacon.c
+++ b/beacon.c
@@ -761,12 +761,14 @@ static void beacon_send (int j, dwgps_info_t *gpsinfo)
 	          strlcat (super_comment, var_comment, sizeof(super_comment));
 	        }
 	        else {
-		  text_color_set(DW_COLOR_ERROR);
-	    	  dw_printf ("xBEACON, config file line %d, COMMENTCMD failure.\n", g_misc_config_p->beacon[j].lineno);
-	        }
+                if (k < 0 || !g_misc_config_p->beacon[j].ignore_empty_cmd_stdout) {
+                    text_color_set(DW_COLOR_ERROR);
+                    dw_printf ("xBEACON, config file line %d, COMMENTCMD failure.\n", g_misc_config_p->beacon[j].lineno);
+                }
+                strlcpy (super_comment, "", sizeof(super_comment)); /* abort */
+            }
 	      }
 
-
 /* 
  * Add the info part depending on beacon type. 
  */
@@ -882,9 +884,11 @@ static void beacon_send (int j, dwgps_info_t *gpsinfo)
 	              strlcat (beacon_text, info_part, sizeof(beacon_text));
 	            }
 	            else {
-		      text_color_set(DW_COLOR_ERROR);
-	    	      dw_printf ("CBEACON, config file line %d, INFOCMD failure.\n", g_misc_config_p->beacon[j].lineno);
-		      strlcpy (beacon_text, "", sizeof(beacon_text));  // abort!
+                    if(k < 0 || !g_misc_config_p->beacon[j].ignore_empty_cmd_stdout) {
+                        text_color_set(DW_COLOR_ERROR);
+                        dw_printf ("CBEACON, config file line %d, INFOCMD failure.\n", g_misc_config_p->beacon[j].lineno);
+                    }
+		            strlcpy (beacon_text, "", sizeof(beacon_text));  // abort!
 	            }
 		  }
 		  else {
diff --git a/config.c b/config.c
index e358b14..f608a61 100644
--- a/config.c
+++ b/config.c
@@ -4379,6 +4379,9 @@ static int beacon_options(char *cmd, struct beacon_s *b, int line, struct audio_
 	  else if (strcasecmp(keyword, "INFOCMD") == 0) {
 	    b->custom_infocmd = strdup(value);
 	  }
+	  else if (strcasecmp(keyword, "IGNOREEMPTY") == 0) {
+	    b->ignore_empty_cmd_stdout = atoi(value);
+	  }
 	  else if (strcasecmp(keyword, "OBJNAME") == 0) {
 	    strlcpy(b->objname, value, sizeof(b->objname));
 	  }
diff --git a/config.h b/config.h
index 1b3c602..8d2551d 100644
--- a/config.h
+++ b/config.h
@@ -145,7 +145,8 @@ struct misc_config_s {
 	  char *comment;	/* Comment or NULL. */
 	  char *commentcmd;	/* Command to append more to Comment or NULL. */
 
-
+      int ignore_empty_cmd_stdout; /* Do not print an error when infocmd exits
+                                      with status 0, and no output is generated. */
 	} beacon[MAX_BEACONS];
 
 };