Allow setting custom config file path, for platforms that do not support ENV VARS.

Author: zeyus

include/lsl/common.h

@@ -227,3 +227,12 @@ extern LIBLSL_C_API double lsl_local_clock();
  * no free() method is available (e.g., in some scripting languages).
  */
 extern LIBLSL_C_API void lsl_destroy_string(char *s);
+
+/**
+ * Set the name of the configuration file to be used.
+ *
+ * This is a global setting that will be used by all LSL
+ * after this function is called. If, and only if, this function
+ * is called before the first call to any other LSL function.
+ */
+extern LIBLSL_C_API void lsl_set_config_filename(const char *filename);

src/api_config.cpp

@@ -55,6 +55,16 @@ api_config::api_config() {
 	// for each config file location under consideration...
 	std::vector<std::string> filenames;
 
+	// NOLINTNEXTLINE(concurrency-mt-unsafe)
+	if (api_config_filename_ != "") {
+		// if a config file name was set, use it if it is readable
+		if (file_is_readable(api_config_filename_)) {
+			filenames.insert(filenames.begin(), api_config_filename_);
+		} else {
+			LOG_F(ERROR, "Config file %s not found", api_config_filename_.c_str());
+		}
+	}
+
 	// NOLINTNEXTLINE(concurrency-mt-unsafe)
 	if (auto *cfgpath = getenv("LSLAPICFG")) {
 		std::string envcfg(cfgpath);

src/api_config.h

@@ -76,6 +76,21 @@ class api_config {
 	bool allow_ipv6() const { return allow_ipv6_; }
 	bool allow_ipv4() const { return allow_ipv4_; }
 
+	/**
+	 * @brief An additional settings path to load configuration from.
+	 */
+	const std::string &api_config_filename() const { return api_config_filename_; }
+
+	/**
+	 * @brief Set the config file name used to load the settings.
+	 * 
+	 * This MUST be called before the first call to get_instance() to have any effect.
+	 */
+	static void set_api_config_filename(const std::string &filename) {
+		api_config_filename_ = filename;
+	}
+
+
 	/**
 	 * @brief The range or scope of stream lookup when using multicast-based discovery
 	 *
@@ -221,6 +236,8 @@ class api_config {
 	 */
 	void load_from_file(const std::string &filename = std::string());
 
+	static std::string api_config_filename_ = "";
+
 	// core parameters
 	bool allow_ipv6_, allow_ipv4_;
 	uint16_t base_port_;

src/common.cpp

@@ -26,6 +26,12 @@ LIBLSL_C_API int32_t lsl_protocol_version() {
 	return lsl::api_config::get_instance()->use_protocol_version();
 }
 
+LIBLSL_C_API void lsl_set_config_filename(const char *filename) {
+	if (filename) {
+		lsl::api_config::set_api_config_filename(filename);
+	}
+}
+
 LIBLSL_C_API int32_t lsl_library_version() { return LSL_LIBRARY_VERSION; }
 
 LIBLSL_C_API double lsl_local_clock() {