extblock.go

package main

import (
	"crypto/md5"
	"encoding/base64"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"path"
	"strconv"
	"strings"

	"github.com/Workiva/go-datastructures/augmentedtree"
)

/*
ExtBlock is a simple container struct that implements the
augmentedtree.Interval interface, so it can be stored in the
range cache. It also defines how to map (url, offset, size)
ranges to local filenames.
*/
type ExtBlock struct {
	offset    uint64
	blockSize uint64
	realSize  uint64
	key       string
	path      string
	root      string
	hash      [16]byte
}

func (e ExtBlock) LowAtDimension(dim uint64) int64 {
	return int64(e.offset)
}

func (e ExtBlock) HighAtDimension(dim uint64) int64 {
	return int64(e.offset + e.blockSize - 1)
}

func (e ExtBlock) OverlapsAtDimension(other augmentedtree.Interval, dim uint64) bool {
	return (other.LowAtDimension(dim) >= e.LowAtDimension(dim) &&
		other.LowAtDimension(dim) <= e.HighAtDimension(dim))
}

func (e ExtBlock) ID() uint64 {
	return binary.LittleEndian.Uint64(e.hash[:8])
}

func (e *ExtBlock) GetKey() string {
	return hex.EncodeToString(e.hash[:])
}

func (e *ExtBlock) GetSize() uint64 {
	return e.blockSize
}

func (e *ExtBlock) GetPath() string {
	return e.path
}

func (e *ExtBlock) GetOffset() uint64 {
	return e.offset
}

func (e *ExtBlock) GetDir() string {
	return path.Join(e.root, hex.EncodeToString(e.hash[:1]))
}

func (e *ExtBlock) SetRealSize(size uint64) {
	e.realSize = size
}

func (e *ExtBlock) GetRealSize() uint64 {
	return e.realSize
}

func NewExtBlock(root string, path string, offset uint64, size uint64) *ExtBlock {
	keyStr := fmt.Sprintf("%s %d %d", path, offset, size)
	key := base64.URLEncoding.EncodeToString([]byte(keyStr))
	return &ExtBlock{key: key,
		offset:    offset,
		blockSize: size,
		path:      path,
		root:      root,
		hash:      md5.Sum([]byte(key))}
}

func ParseExtBlock(key string, realSize uint64) (*ExtBlock, error) {
	decoded, err := base64.URLEncoding.DecodeString(key)
	if err != nil {
		return nil, err
	}
	parts := strings.Split(string(decoded), " ")
	offset, err := strconv.ParseUint(parts[1], 10, 64)
	if err != nil {
		return nil, err
	}
	blockSize, err := strconv.ParseUint(parts[2], 10, 64)
	if err != nil {
		return nil, err
	}
	return &ExtBlock{key: key,
		offset:    offset,
		blockSize: blockSize,
		realSize:  realSize,
		path:      parts[0],
		hash:      md5.Sum([]byte(key))}, nil
}