Function read

cmd/cql-fuse/block.go:193–222

read returns the data [from, to). Requires: to > from and [to, from) is contained in the file.

(e sqlExecutor, inodeID, from, to uint64)

// read returns the data [from, to).
// Requires: to > from and [to, from) is contained in the file.
func read(e sqlExecutor, inodeID, from, to uint64) ([]byte, error) {
	readRange := newBlockRange(from, to-from)
	end := readRange.last
	if readRange.lastLength == 0 {
		end--
	}

	blockInfos, err := getBlocksBetween(e, inodeID, readRange.start, end)
	if err != nil {
		return nil, err
	}
	if len(blockInfos) != end-readRange.start+1 {
		return nil, fmt.Errorf("wrong number of blocks, asked for [%d-%d], got %d back",
			readRange.start, end, len(blockInfos))
	}

	if readRange.lastLength != 0 {
		// We have a last partial block, truncate it.
		last := len(blockInfos) - 1
		blockInfos[last].data = blockInfos[last].data[:readRange.lastLength]
	}
	blockInfos[0].data = blockInfos[0].data[readRange.startOffset:]

	var data []byte
	for _, b := range blockInfos {
		data = append(data, b.data...)
	}

	return data, nil
}

// write commits data to the blocks starting at 'offset'
// Amount of data to write must be non-zero.