Add implementation of a system file interface
Implement simple read/write file operation semantics for the commit
operation. Add unit tests using the mock sys interface to verify the
behaviors.
Signed-off-by: Kun Yi <kunyi@google.com>
Change-Id: I75f8005561ab342138375bccb46c21e2841aa5e1
diff --git a/sys_file.hpp b/sys_file.hpp
new file mode 100644
index 0000000..5a2bb85
--- /dev/null
+++ b/sys_file.hpp
@@ -0,0 +1,90 @@
+#pragma once
+
+#include "sys.hpp"
+
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <string>
+
+namespace binstore
+{
+
+/**
+ * @brief Represents a file that supports read/write semantics
+ * TODO: leverage stdplus's support for smart file descriptors when it's ready.
+ */
+class SysFile
+{
+ public:
+ virtual ~SysFile() = default;
+
+ /**
+ * @brief Reads content at pos to char* buffer
+ * @param pos The byte pos into the file to read from
+ * @param count How many bytes to read
+ * @param buf Output data
+ * @returns The size of data read
+ * @throws std::system_error if read operation cannot be completed
+ */
+ virtual size_t readToBuf(size_t pos, size_t count, char* buf) const = 0;
+
+ /**
+ * @brief Reads content at pos
+ * @param pos The byte pos into the file to read from
+ * @param count How many bytes to read
+ * @returns The data read in a vector, whose size might be smaller than
+ * count if there is not enough to read.
+ * @throws std::system_error if read operation cannot be completed
+ */
+ virtual std::string readAsStr(size_t pos, size_t count) const = 0;
+
+ /**
+ * @brief Reads all the content in file after pos
+ * @param pos The byte pos to read from
+ * @returns The data read in a vector, whose size might be smaller than
+ * count if there is not enough to read.
+ * @throws std::system_error if read operation cannot be completed
+ */
+ virtual std::string readRemainingAsStr(size_t pos) const = 0;
+
+ /**
+ * @brief Writes all of data into file at pos
+ * @param pos The byte pos to write
+ * @returns void
+ * @throws std::system_error if write operation cannot be completed or
+ * not all of the bytes can be written
+ */
+ virtual void writeStr(const std::string& data, size_t pos) = 0;
+};
+
+class SysFileImpl : public SysFile
+{
+ public:
+ /**
+ * @brief Constructs sysFile specified by path and offset
+ * @param path The file path
+ * @param offset The byte offset relatively. Reading a sysfile at position 0
+ * actually reads underlying file at 'offset'
+ * @param sys Syscall operation interface
+ */
+ explicit SysFileImpl(const std::string& path, size_t offset = 0,
+ const internal::Sys* sys = &internal::sys_impl);
+ ~SysFileImpl();
+ SysFileImpl() = delete;
+ SysFileImpl(const SysFileImpl&) = delete;
+ SysFileImpl& operator=(SysFileImpl) = delete;
+
+ size_t readToBuf(size_t pos, size_t count, char* buf) const override;
+ std::string readAsStr(size_t pos, size_t count) const override;
+ std::string readRemainingAsStr(size_t pos) const override;
+ void writeStr(const std::string& data, size_t pos) override;
+
+ private:
+ int fd_;
+ size_t offset_;
+ void lseek(size_t pos) const;
+ const internal::Sys* sys;
+};
+
+} // namespace binstore