handle error in ProtoBufFile::load

[CkTD]

braft/src/braft/protobuf_file.cpp

Lines 87 to 120 in e32b78a

	int ProtoBufFile::load(google::protobuf::Message* message) {
	butil::File::Error e;
	FileAdaptor* file = _fs->open(_path, O_RDONLY, NULL, &e);
	if (!file) {
	LOG(WARNING) << "open file failed, path: " << _path
	<< ": " << butil::File::ErrorToString(e);
	return -1;
	}
	std::unique_ptr<FileAdaptor, DestroyObj<FileAdaptor> > guard(file);
	// len
	butil::IOPortal header_buf;
	if (sizeof(int32_t) != file->read(&header_buf, 0, sizeof(int32_t))) {
	LOG(WARNING) << "read len failed, path: " << _path;
	return -1;
	}
	int32_t len = 0;
	header_buf.copy_to(&len, sizeof(int32_t));
	int32_t left_len = butil::NetToHost32(len);
	// read protobuf data
	butil::IOPortal msg_buf;
	if (left_len != file->read(&msg_buf, sizeof(int32_t), left_len)) {
	LOG(WARNING) << "read body failed, path: " << _path;
	return -1;
	}
	// parse msg
	butil::IOBufAsZeroCopyInputStream msg_wrapper(msg_buf);
	message->ParseFromZeroCopyStream(&msg_wrapper);
	return 0;
	}

1. 117 行没有检查返回值
2. 如果执行到了112行， 且原因是实际文件长度比预期的短，返回了 -1。但读文件是成功的，errno 不会被更新。加载 log_meta时，如果发生了上述问题，且原来的 errno 正好是 ENOENT，后续逻辑会认为日志是空的，直接把 log 删光。

braft/src/braft/log.cpp

Lines 1155 to 1175 in e32b78a

	int SegmentLogStorage::load_meta() {
	butil::Timer timer;
	timer.start();
	std::string meta_path(_path);
	meta_path.append("/" BRAFT_SEGMENT_META_FILE);
	ProtoBufFile pb_file(meta_path);
	LogPBMeta meta;
	if (0 != pb_file.load(&meta)) {
	PLOG_IF(ERROR, errno != ENOENT) << "Fail to load meta from " << meta_path;
	return -1;
	}
	_first_log_index.store(meta.first_log_index());
	timer.stop();
	LOG(INFO) << "log load_meta " << meta_path << " first_log_index: " << meta.first_log_index()
	<< " time: " << timer.u_elapsed();
	return 0;
	}