fix: object_store: stop throwing errors when checking generation file

A new routine is added to File class, to check whether a file exists or
not. It will allow file existence check, without trying to open the file
and thus throw an error when the use case is valid.

This new routine is added to Generation wasUpdated routine: if the
generation file does not exist, the routine will exit without error,
instead of trying to open the file and report an error.

Fixes #753

Signed-off-by: Alexandre Besnard <alexandre.besnard@softathome.com>

Author: amananas

src/lib/object_store/File.cpp

@@ -143,6 +143,28 @@ File::~File()
 	}
 }
 
+// Check if a file exists without trying to open it
+// May be used when a routine just wants to check file existence,
+// and does not want to throw an error by trying to open it.
+bool File::exists(std::string path)
+{
+#ifndef _WIN32
+	struct stat buf;
+	return stat(path.c_str(), &buf) == 0;
+#else
+	int fd;
+	// Try opening the file directly
+	fd = _open(path.c_str(), _O_BINARY | _O_RDONLY, _S_IREAD | _S_IWRITE);
+	if (fd != -1)
+	{
+		_close(fd);
+		return true;
+	}
+	return false;
+#endif
+}
+
+
 // Check if the file is valid
 bool File::isValid()
 {

src/lib/object_store/File.h

@@ -47,6 +47,11 @@ class File
 	// Destructor
 	virtual ~File();
 
+	// Check if a file exists without trying to open it
+	// May be used when a routine just wants to check file existence,
+	// and does not want to throw an error by trying to open it.
+	static bool exists(std::string path);
+
 	// Check if the file is valid
 	bool isValid();
 

src/lib/object_store/Generation.cpp

@@ -88,6 +88,13 @@ bool Generation::sync(File &objectFile)
 // Check if the target was updated
 bool Generation::wasUpdated()
 {
+
+	// Check if path file exists before anything
+	if (!File::exists(path))
+	{
+		return true;
+	}
+
 	if (isToken)
 	{
 		MutexLocker lock(genMutex);