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// Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_FILE_DESCRIPTOR_H__
#define CHROMEOS_PLATFORM_UPDATE_ENGINE_FILE_DESCRIPTOR_H__
#include <errno.h>
#include <sys/types.h>
#include "base/logging.h"
#include "update_engine/utils.h"
// Abstraction for managing opening, reading, writing and closing of file
// descriptors. This includes an abstract class and one standard implementation
// based on POSIX system calls.
//
// TODO(garnold) this class is modeled after (and augments the functionality of)
// the FileWriter class; ultimately, the latter should be replaced by the former
// throughout the codebase. A few deviations from the original FileWriter:
//
// * Providing two flavors of Open()
//
// * A FileDescriptor is reusable and can be used to read/write multiple files
// as long as open/close preconditions are respected.
//
// * Write() returns the number of bytes written: this appears to be more useful
// for clients, who may wish to retry or otherwise do something useful with
// the remaining data that was not written.
//
// * Provides a Reset() method, which will force to abandon a currently open
// file descriptor and allow opening another file, without necessarily
// properly closing the old one. This may be useful in cases where a "closer"
// class does not care whether Close() was successful, but may need to reuse
// the same file descriptor again.
namespace chromeos_update_engine {
// An abstract class defining the file descriptor API.
class FileDescriptor {
public:
FileDescriptor() {}
virtual ~FileDescriptor() {}
// Opens a file descriptor. The descriptor must be in the closed state prior
// to this call. Returns true on success, false otherwise. Specific
// implementations may set errno accordingly.
virtual bool Open(const char* path, int flags, mode_t mode) = 0;
virtual bool Open(const char* path, int flags) = 0;
// Reads from a file descriptor up to a given count. The descriptor must be
// open prior to this call. Returns the number of bytes read, or -1 on error.
// Specific implementations may set errno accordingly.
virtual ssize_t Read(void* buf, size_t count) = 0;
// Writes to a file descriptor. The descriptor must be open prior to this
// call. Returns the number of bytes written, or -1 if an error occurred and
// no bytes were written. Specific implementations may set errno accordingly.
virtual ssize_t Write(const void* buf, size_t count) = 0;
// Closes a file descriptor. The descriptor must be open prior to this call.
// Returns true on success, false otherwise. Specific implementations may set
// errno accordingly.
virtual bool Close() = 0;
// Resets the file descriptor, abandoning a currently open file and returning
// the descriptor to the closed state.
virtual void Reset() = 0;
// Indicates whether or not an implementation sets meaningful errno.
virtual bool IsSettingErrno() = 0;
// Indicates whether the descriptor is currently open.
virtual bool IsOpen() = 0;
private:
DISALLOW_COPY_AND_ASSIGN(FileDescriptor);
};
// A simple EINTR-immune wrapper implementation around standard system calls.
class EintrSafeFileDescriptor : public FileDescriptor {
public:
EintrSafeFileDescriptor() : fd_(-1) {}
virtual ~EintrSafeFileDescriptor() {};
// Interface methods.
virtual bool Open(const char* path, int flags, mode_t mode);
virtual bool Open(const char* path, int flags);
virtual ssize_t Read(void* buf, size_t count);
virtual ssize_t Write(const void* buf, size_t count);
virtual bool Close();
virtual void Reset();
virtual bool IsSettingErrno() {
return true;
}
virtual bool IsOpen() {
return (fd_ >= 0);
}
private:
int fd_;
};
// A scoped closer for a FileDescriptor object. The destructor of this class
// invokes the Close() method of the given file descriptor, if it's not in the
// closed state already. Note, however, that if Close() fails, this class will
// force a Reset() invocation, which will abandon the current file descriptor.
class ScopedFileDescriptorCloser {
public:
explicit ScopedFileDescriptorCloser(FileDescriptor* descriptor)
: descriptor_(descriptor) {}
~ScopedFileDescriptorCloser();
private:
FileDescriptor* descriptor_;
DISALLOW_COPY_AND_ASSIGN(ScopedFileDescriptorCloser);
};
} // namespace chromeos_update_engine
#endif // CHROMEOS_PLATFORM_UPDATE_ENGINE_FILE_DESCRIPTOR_H__