Report an error if the config file is set to a directory.

Closes #1814. Thanks to Odysseus1710.

ChangeLog.txt

@@ -92,6 +92,7 @@ Broker:
 - Default for max_queued_messages has been changed to 1000.
 - Add `ciphers_tls1.3` option, to allow setting TLS v1.3 ciphersuites.
   Closes #1825.
+- Report an error if the config file is set to a directory. Closes #1814.
 
 Client library:
 - Client no longer generates random client ids for v3.1.1 clients, these are

src/conf.c

@@ -2174,6 +2174,18 @@ int config__read_file(struct mosquitto__config *config, bool reload, const char
 	FILE *fptr = NULL;
 	char *buf;
 	int buflen;
+#ifndef WIN32
+	DIR *dir;
+#endif
+
+#ifndef WIN32
+	dir = opendir(file);
+	if(dir){
+		closedir(dir);
+		log__printf(NULL, MOSQ_LOG_ERR, "Error: Config file %s is a directory.", file);
+		return 1;
+	}
+#endif
 
 	fptr = mosquitto__fopen(file, "rt", false);
 	if(!fptr){