conf: handle array of arguments in context.exec

We handeled "arg1 arg2 ... " before and used to split between spaces to
get the arguments for execvp but that doesn't work so well when there
are arguments with spaces.

Instead use JSON parsing to get the array of arguments. This make it
possible to use [ arg1 arg2 .. ] and quote each arg separately. You
can still use the old method and even double escape:

"\"arg1\" \"arg2 with spaces\"" or
 [ "arg1" "arg2 with spaces" ]

doc/dox/config/pipewire.conf.5.md

@@ -413,7 +413,7 @@ part of the initialization of the PipeWire program.
 ```json
 context.exec = [
     #{   path = <program-name>
-    #    ( args = "<arguments>" )
+    #    ( args = "<arguments>" | [ <arg1> <arg2> ... ] )
     #    ( condition = [ { <key> = <value> ... } ... ] )
     #}
 ]

src/daemon/minimal.conf.in

@@ -426,7 +426,7 @@ context.objects = [
 
 context.exec = [
     #{   path = <program-name>
-    #    ( args = "<arguments>" )
+    #    ( args = "<arguments>" | [ <arg1> <arg2> ... ] )
     #    ( condition = [ { <key> = <value> ... } ... ] )
     #}
     #

src/daemon/pipewire.conf.in

@@ -319,7 +319,7 @@ context.objects = [
 
 context.exec = [
     #{   path = <program-name>
-    #    ( args = "<arguments>" )
+    #    ( args = "<arguments>" | [ <arg1> <arg2> ... ] )
     #    ( condition = [ { <key> = <value> ... } ... ] )
     #}
     #
@@ -339,6 +339,6 @@ context.exec = [
     # It can be interesting to start another daemon here that listens
     # on another address with the -a option (eg. -a tcp:4713).
     #
-    @pulse_comment@{ path = "@pipewire_path@" args = "-c pipewire-pulse.conf"
+    @pulse_comment@{ path = "@pipewire_path@" args = [ "-c" "pipewire-pulse.conf" ]
     @pulse_comment@  condition = [ { exec.pipewire-pulse = null } { exec.pipewire-pulse = true } ] }
 ]

src/pipewire/conf.c

@@ -927,38 +927,69 @@ static int parse_objects(void *user_data, const char *location,
 	return res;
 }
 
-static int do_exec(struct pw_context *context, const char *key, const char *args)
+static char **pw_strv_insert_at(char **strv, int len, int pos, const char *str)
 {
-	int pid, res, n_args;
+	char **n;
+
+	if (len < 0) {
+		len = 0;
+		while (strv != NULL && strv[len] != NULL)
+			len++;
+	}
+	if (pos < 0 || pos > len)
+		pos = len+1;
+
+	n = realloc(strv, sizeof(char*) * (len + 2));
+	if (n == NULL) {
+		free(strv);
+		return NULL;
+	}
+	strv = n;
+
+	memmove(strv+pos+1, strv+pos, sizeof(char*) * (len+1-pos));
+	strv[pos] = strdup(str);
+	return strv;
+}
+
+static int do_exec(struct pw_context *context, const char *path, const char *args)
+{
+	int pid, res;
 
 	pid = fork();
 
 	if (pid == 0) {
-		char *cmd, **argv;
+		char **arg;
+		int n_args;
 
 		/* Double fork to avoid zombies; we don't want to set SIGCHLD handler */
 		pid = fork();
 
 		if (pid < 0) {
 			pw_log_error("fork error: %m");
-			exit(1);
+			goto done;
 		} else if (pid != 0) {
 			exit(0);
 		}
 
-		cmd = spa_aprintf("%s %s", key, args ? args : "");
-		argv = pw_split_strv(cmd, " \t", INT_MAX, &n_args);
-		free(cmd);
-
-		pw_log_info("exec %s '%s'", key, args);
-		res = execvp(key, argv);
-		pw_free_strv(argv);
+		arg = pw_strv_parse(args, strlen(args), INT_MAX, &n_args);
+		if (arg == NULL) {
+			pw_log_error("error parsing arguments: %m");
+			goto done;
+		}
+		arg = pw_strv_insert_at(arg, n_args, 0, path);
+		if (arg == NULL) {
+			pw_log_error("error constructing arguments: %m");
+			goto done;
+		}
+		pw_log_info("exec %s '%s'", path, args);
+		res = execvp(path, arg);
+		pw_free_strv(arg);
 
 		if (res == -1) {
 			res = -errno;
-			pw_log_error("execvp error '%s': %m", key);
+			pw_log_error("execvp error '%s': %m", path);
 		}
-
+done:
 		exit(1);
 	} else if (pid < 0) {
 		pw_log_error("fork error: %m");
@@ -976,7 +1007,7 @@ static int do_exec(struct pw_context *context, const char *key, const char *args
 /*
  * context.exec = [
  *   {   path = <program-name>
- *       ( args = "<arguments>" )
+ *       ( args = "<arguments>" | [ <arg1> <arg2> ... ] )
  *       ( condition = [ { key = value, .. } .. ] )
  *   }
  * ]
@@ -1016,6 +1047,8 @@ static int parse_exec(void *user_data, const char *location,
 				path = (char*)val;
 				spa_json_parse_stringn(val, l, path, l+1);
 			} else if (spa_streq(key, "args")) {
+				if (spa_json_is_container(val, l))
+					l = spa_json_container_len(&it[2], val, l);
 				args = (char*)val;
 				spa_json_parse_stringn(val, l, args, l+1);
 			} else if (spa_streq(key, "condition")) {