ao, shairport: fix option parsing

- don't push unrecognised args to the audio driver
- get ao to parse from first argument
- ao checks for unrecognised options

audio_ao.c

@@ -47,7 +47,9 @@ static int init(int argc, char **argv) {
     int driver = ao_default_driver_id();
     ao_option *ao_opts = NULL;
 
-    optind = 0;
+    optind = 1; // optind=0 is equivalent to optind=1 plus special behaviour
+    argv--;     // so we shift the arguments to satisfy getopt()
+    argc++;
     // some platforms apparently require optreset = 1; - which?
     int opt;
     char *mid;
@@ -80,6 +82,9 @@ static int init(int argc, char **argv) {
         }
     }
 
+    if (optind < argc)
+        die("Invalid audio argument: %s", argv[optind]);
+
     ao_sample_format fmt;
     memset(&fmt, 0, sizeof(fmt));
 

shairport.c

@@ -88,6 +88,9 @@ void usage(char *progname) {
 }
 
 int parse_options(int argc, char **argv) {
+    // prevent unrecognised arguments from being shunted to the audio driver
+    setenv("POSIXLY_CORRECT", "", 1);
+
     int opt;
     while ((opt = getopt(argc, argv, "+hdvp:a:o:b:B:E:")) > 0) {
         switch (opt) {