dagmodifier.go 5.19 KB
Newer Older
1 2 3 4 5 6
package io

import (
	"bytes"
	"errors"

7
	proto "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/goprotobuf/proto"
8

9
	chunk "github.com/jbenet/go-ipfs/importer/chunk"
10 11
	mdag "github.com/jbenet/go-ipfs/merkledag"
	ft "github.com/jbenet/go-ipfs/unixfs"
12
	ftpb "github.com/jbenet/go-ipfs/unixfs/pb"
13 14 15
	u "github.com/jbenet/go-ipfs/util"
)

16 17
var log = u.Logger("dagio")

18 19 20 21
// DagModifier is the only struct licensed and able to correctly
// perform surgery on a DAG 'file'
// Dear god, please rename this to something more pleasant
type DagModifier struct {
22
	dagserv mdag.DAGService
23 24
	curNode *mdag.Node

25
	pbdata   *ftpb.Data
26 27 28
	splitter chunk.BlockSplitter
}

29
func NewDagModifier(from *mdag.Node, serv mdag.DAGService, spl chunk.BlockSplitter) (*DagModifier, error) {
30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63
	pbd, err := ft.FromBytes(from.Data)
	if err != nil {
		return nil, err
	}

	return &DagModifier{
		curNode:  from.Copy(),
		dagserv:  serv,
		pbdata:   pbd,
		splitter: spl,
	}, nil
}

// WriteAt will modify a dag file in place
// NOTE: it currently assumes only a single level of indirection
func (dm *DagModifier) WriteAt(b []byte, offset uint64) (int, error) {

	// Check bounds
	if dm.pbdata.GetFilesize() < offset {
		return 0, errors.New("Attempted to perform write starting past end of file")
	}

	// First need to find where we are writing at
	end := uint64(len(b)) + offset

	// This shouldnt be necessary if we do subblocks sizes properly
	newsize := dm.pbdata.GetFilesize()
	if end > dm.pbdata.GetFilesize() {
		newsize = end
	}
	zeroblocklen := uint64(len(dm.pbdata.Data))
	origlen := len(b)

	if end <= zeroblocklen {
Juan Batiz-Benet's avatar
Juan Batiz-Benet committed
64
		log.Debug("Writing into zero block")
65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80
		// Replacing zeroeth data block (embedded in the root node)
		//TODO: check chunking here
		copy(dm.pbdata.Data[offset:], b)
		return len(b), nil
	}

	// Find where write should start
	var traversed uint64
	startsubblk := len(dm.pbdata.Blocksizes)
	if offset < zeroblocklen {
		dm.pbdata.Data = dm.pbdata.Data[:offset]
		startsubblk = 0
	} else {
		traversed = uint64(zeroblocklen)
		for i, size := range dm.pbdata.Blocksizes {
			if uint64(offset) < traversed+size {
Juan Batiz-Benet's avatar
Juan Batiz-Benet committed
81
				log.Debugf("Starting mod at block %d. [%d < %d + %d]", i, offset, traversed, size)
82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
				// Here is where we start
				startsubblk = i
				lnk := dm.curNode.Links[i]
				node, err := dm.dagserv.Get(u.Key(lnk.Hash))
				if err != nil {
					return 0, err
				}
				data, err := ft.UnwrapData(node.Data)
				if err != nil {
					return 0, err
				}

				// We have to rewrite the data before our write in this block.
				b = append(data[:offset-traversed], b...)
				break
			}
			traversed += size
		}
		if startsubblk == len(dm.pbdata.Blocksizes) {
			// TODO: Im not sure if theres any case that isnt being handled here.
			// leaving this note here as a future reference in case something breaks
		}
	}

	// Find blocks that need to be overwritten
	var changed []int
	mid := -1
	var midoff uint64
	for i, size := range dm.pbdata.Blocksizes[startsubblk:] {
		if end > traversed {
			changed = append(changed, i+startsubblk)
		} else {
			break
		}
		traversed += size
		if end < traversed {
			mid = i + startsubblk
			midoff = end - (traversed - size)
			break
		}
	}

	// If our write starts in the middle of a block...
	var midlnk *mdag.Link
	if mid >= 0 {
		midlnk = dm.curNode.Links[mid]
		midnode, err := dm.dagserv.Get(u.Key(midlnk.Hash))
		if err != nil {
			return 0, err
		}

		// NOTE: this may have to be changed later when we have multiple
		// layers of indirection
		data, err := ft.UnwrapData(midnode.Data)
		if err != nil {
			return 0, err
		}
		b = append(b, data[midoff:]...)
	}

	// Generate new sub-blocks, and sizes
	subblocks := splitBytes(b, dm.splitter)
	var links []*mdag.Link
	var sizes []uint64
	for _, sb := range subblocks {
		n := &mdag.Node{Data: ft.WrapData(sb)}
		_, err := dm.dagserv.Add(n)
		if err != nil {
Juan Batiz-Benet's avatar
Juan Batiz-Benet committed
150
			log.Errorf("Failed adding node to DAG service: %s", err)
151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175
			return 0, err
		}
		lnk, err := mdag.MakeLink(n)
		if err != nil {
			return 0, err
		}
		links = append(links, lnk)
		sizes = append(sizes, uint64(len(sb)))
	}

	// This is disgusting (and can be rewritten if performance demands)
	if len(changed) > 0 {
		sechalflink := append(links, dm.curNode.Links[changed[len(changed)-1]+1:]...)
		dm.curNode.Links = append(dm.curNode.Links[:changed[0]], sechalflink...)
		sechalfblks := append(sizes, dm.pbdata.Blocksizes[changed[len(changed)-1]+1:]...)
		dm.pbdata.Blocksizes = append(dm.pbdata.Blocksizes[:changed[0]], sechalfblks...)
	} else {
		dm.curNode.Links = append(dm.curNode.Links, links...)
		dm.pbdata.Blocksizes = append(dm.pbdata.Blocksizes, sizes...)
	}
	dm.pbdata.Filesize = proto.Uint64(newsize)

	return origlen, nil
}

Jeromy's avatar
Jeromy committed
176 177 178 179 180 181 182
func (dm *DagModifier) Size() uint64 {
	if dm == nil {
		return 0
	}
	return dm.pbdata.GetFilesize()
}

183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202
// splitBytes uses a splitterFunc to turn a large array of bytes
// into many smaller arrays of bytes
func splitBytes(b []byte, spl chunk.BlockSplitter) [][]byte {
	out := spl.Split(bytes.NewReader(b))
	var arr [][]byte
	for blk := range out {
		arr = append(arr, blk)
	}
	return arr
}

// GetNode gets the modified DAG Node
func (dm *DagModifier) GetNode() (*mdag.Node, error) {
	b, err := proto.Marshal(dm.pbdata)
	if err != nil {
		return nil, err
	}
	dm.curNode.Data = b
	return dm.curNode.Copy(), nil
}