Get socket from i3 if I3SOCK not set

src/ipc.cpp

@@ -281,9 +281,31 @@ static std::shared_ptr<bar_config_t>  parse_bar_config_from_json(const Json::Val
 #undef i3IPC_TYPE_STR
 }
 
-
 std::string  get_socketpath() {
-	return std::getenv("I3SOCK");
+	const char*  envsock{std::getenv("I3SOCK")};
+	if (envsock) {
+		return envsock;
+	}
+
+	std::string  str;
+	{
+		auss_t  str_buf;
+		FILE*  in;
+		char  buf[512] = {0};
+		if (!(in = popen("i3 --get-socketpath", "r"))) {
+			throw errno_error("Failed to get socket path");
+		}
+
+		while (fgets(buf, sizeof(buf), in) != nullptr) {
+			str_buf << buf;
+		}
+		pclose(in);
+		str = str_buf;
+	}
+	if (str.back() == '\n') {
+		str.pop_back();
+	}
+	return str;
 }