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.cpp b/sys_file.cpp
new file mode 100644
index 0000000..2336af2
--- /dev/null
+++ b/sys_file.cpp
@@ -0,0 +1,124 @@
+#include "sys_file.hpp"
+
+#include <system_error>
+
+using namespace std::string_literals;
+
+static constexpr size_t rwBlockSize = 8192;
+
+namespace binstore
+{
+
+namespace
+{
+
+std::system_error errnoException(const std::string& message)
+{
+ return std::system_error(errno, std::generic_category(), message);
+}
+
+} // namespace
+
+SysFileImpl::SysFileImpl(const std::string& path, size_t offset,
+ const internal::Sys* sys) :
+ sys(sys)
+{
+ fd_ = sys->open(path.c_str(), O_RDWR);
+ offset_ = offset;
+
+ if (fd_ < 0)
+ {
+ throw errnoException("Error opening file "s + path);
+ }
+}
+
+SysFileImpl::~SysFileImpl()
+{
+ sys->close(fd_);
+}
+
+void SysFileImpl::lseek(size_t pos) const
+{
+ if (sys->lseek(fd_, offset_ + pos, SEEK_SET) < 0)
+ {
+ throw errnoException("Cannot lseek to pos "s + std::to_string(pos));
+ }
+}
+
+size_t SysFileImpl::readToBuf(size_t pos, size_t count, char* buf) const
+{
+
+ lseek(pos);
+
+ size_t bytesRead = 0;
+
+ do
+ {
+ auto ret = sys->read(fd_, &buf[bytesRead], count - bytesRead);
+ if (ret < 0)
+ {
+ if (errno == EINTR)
+ {
+ continue;
+ }
+
+ throw errnoException("Error reading from file"s);
+ }
+ else if (ret > 0)
+ {
+ bytesRead += ret;
+ }
+ else // ret == 0
+ {
+ break;
+ }
+ } while (bytesRead < count);
+
+ return bytesRead;
+}
+
+std::string SysFileImpl::readAsStr(size_t pos, size_t count) const
+{
+ std::string result;
+ result.resize(count);
+ size_t bytesRead = readToBuf(pos, count, result.data());
+ result.resize(bytesRead);
+ return result;
+}
+
+std::string SysFileImpl::readRemainingAsStr(size_t pos) const
+{
+ std::string result;
+ size_t bytesRead, size = 0;
+
+ /* Since we don't know how much to read, read 'rwBlockSize' at a time
+ * until there is nothing to read anymore. */
+ do
+ {
+ result.resize(size + rwBlockSize);
+ bytesRead = readToBuf(pos + size, rwBlockSize, result.data() + size);
+ size += bytesRead;
+ } while (bytesRead == rwBlockSize);
+
+ result.resize(size);
+ return result;
+}
+
+void SysFileImpl::writeStr(const std::string& data, size_t pos)
+{
+ lseek(pos);
+ ssize_t ret;
+ ret = sys->write(fd_, data.data(), data.size());
+ if (ret < 0)
+ {
+ throw errnoException("Error writing to file"s);
+ }
+ if (static_cast<size_t>(ret) != data.size())
+ {
+ throw std::runtime_error(
+ "Tried to send data size "s + std::to_string(data.size()) +
+ " but could only send "s + std::to_string(ret));
+ }
+}
+
+} // namespace binstore