provide -B/-E for running shell commands on begin/end of playing

Implements functionality described by MaZderMind <github@mazdermind.de>
in issue #201.

common.h

@@ -26,6 +26,7 @@ typedef struct {
     int buffer_start_fill;
     int daemonise;
     int mdns_internal;
+    char *cmd_start, *cmd_stop;
 } shairport_cfg;
 
 extern int debuglev;

player.c

@@ -36,6 +36,7 @@
 #include <sys/signal.h>
 #include <assert.h>
 #include <fcntl.h>
+#include <stdlib.h>
 
 #include "common.h"
 #include "player.h"
@@ -515,6 +516,11 @@ int player_play(stream_cfg *stream) {
 #endif
 
     please_stop = 0;
+    if (config.cmd_start && !fork()) {
+        if (system(config.cmd_start))
+            warn("exec of external start command failed\n");
+        exit(0);
+    }
     config.output->start(sampling_rate);
     pthread_create(&player_thread, NULL, player_thread_func, NULL);
 
@@ -525,6 +531,11 @@ void player_stop(void) {
     please_stop = 1;
     pthread_join(player_thread, NULL);
     config.output->stop();
+    if (config.cmd_stop && !fork()) {
+        if (system(config.cmd_stop))
+            warn("exec of external stop command failed\n");
+        exit(0);
+    }
     free_buffer();
     free_decoder();
 #ifdef FANCY_RESAMPLING

shairport.c

@@ -71,6 +71,9 @@ void usage(char *progname) {
            "                    This value is in frames; default %d\n"
            "    -d          fork (daemonise)\n"
            "                    The PID of the child process is written to stdout\n"
+           "    -B command  run a shell command when playback begins\n"
+           "    -E command  run a shell command when playback ends\n"
+           "\n"
            "Run %s -o <output> -h to find the available options for a specific output\n"
            "\n", config.buffer_start_fill, progname);
 
@@ -86,7 +89,7 @@ void usage(char *progname) {
 
 int parse_options(int argc, char **argv) {
     int opt;
-    while ((opt = getopt(argc, argv, "+hdvp:a:o:b:")) > 0) {
+    while ((opt = getopt(argc, argv, "+hdvp:a:o:b:B:E:")) > 0) {
         switch (opt) {
             default:
                 printf("Unknown argument -%c\n", optopt);
@@ -111,6 +114,12 @@ int parse_options(int argc, char **argv) {
             case 'b':
                 config.buffer_start_fill = atoi(optarg);
                 break;
+            case 'B':
+                config.cmd_start = optarg;
+                break;
+            case 'E':
+                config.cmd_stop = optarg;
+                break;
         }
     }
     return optind;