Added functions to determine whether or not a .dbc file is valid or not.

The file extension is not a definitive answer to anything. Shoving a JPEG image with a modified extension would falsely identify that file as a valid DBC.

Author: SimonCahill

include/libdbc/dbc.hpp

@@ -8,6 +8,10 @@
 #include <string>
 #include <vector>
 
+#if __cplusplus >= 201703L
+	#include <filesystem>
+#endif // __cplusplus >= 201703L
+
 namespace Libdbc {
 
 class Parser {
@@ -35,6 +39,13 @@ class DbcParser : public Parser {
 
 	const std::vector<std::string>& unused_lines() const;
 
+	#if __cplusplus >= 201703L
+	static bool is_valid_dbc_file(const std::filesystem::path&);
+	#else
+	static bool is_valid_dbc_file(const std::string&);
+	#endif // __cplusplus >= 201703L
+	static bool is_valid_dbc_file(std::istream& stream);
+
 private:
 	std::string version{};
 	std::vector<std::string> nodes{};

src/dbc.cpp

@@ -70,6 +70,32 @@ DbcParser::DbcParser()
 			  + whiteSpace + receiverPattern) {
 }
 
+#if __cplusplus >= 201703L
+bool DbcParser::is_valid_dbc_file(const std::filesystem::path& file_path) {
+#else
+bool DbcParser::is_valid_dbc_file(const std::string& file_path) {
+#endif // __cplusplus >= 201703L
+
+	std::ifstream testStream{file_path};
+	if (!testStream.is_open()) { return false; }
+
+	return is_valid_dbc_file(testStream);
+}
+
+bool DbcParser::is_valid_dbc_file(std::istream& stream) {
+	stream.seekg(0, std::ios::beg);
+
+	try {
+		DbcParser parser{};
+		parser.parse_dbc_header(stream);
+	} catch (const Exception& e) {
+		// If the file is missing the version, it is not a valid DBC file
+		return false;
+	}
+
+	return true;
+}
+
 void DbcParser::parse_file(std::istream& stream) {
 	std::string line;
 	std::vector<std::string> lines;
@@ -88,9 +114,8 @@ void DbcParser::parse_file(std::istream& stream) {
 }
 
 void DbcParser::parse_file(const std::string& file_name) {
-	auto extension = get_extension(file_name);
-	if (extension != ".dbc") {
-		throw NonDbcFileFormatError(file_name, extension);
+	if (!is_valid_dbc_file(file_name)) {
+		throw NonDbcFileFormatError(file_name, get_extension(file_name));
 	}
 
 	std::ifstream stream(file_name);