fs/io/FileReader: add method Skip()

src/fs/io/FileReader.cxx

@@ -66,6 +66,16 @@ FileReader::Seek(off_t offset)
 }
 
 void
+FileReader::Skip(off_t offset)
+{
+	assert(IsDefined());
+
+	auto result = SetFilePointer(handle, offset, nullptr, FILE_CURRENT);
+	if (result == INVALID_SET_FILE_POINTER)
+		throw MakeLastError("Failed to seek");
+}
+
+void
 FileReader::Close()
 {
 	assert(IsDefined());
@@ -121,6 +131,17 @@ FileReader::Seek(off_t offset)
 }
 
 void
+FileReader::Skip(off_t offset)
+{
+	assert(IsDefined());
+
+	auto result = fd.Skip(offset);
+	const bool success = result >= 0;
+	if (!success)
+		throw MakeErrno("Failed to seek");
+}
+
+void
 FileReader::Close()
 {
 	assert(IsDefined());

src/fs/io/FileReader.hxx

@@ -92,6 +92,7 @@ public:
 	FileInfo GetFileInfo() const;
 
 	void Seek(off_t offset);
+	void Skip(off_t offset);
 
 	/* virtual methods from class Reader */
 	size_t Read(void *data, size_t size) override;