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dagmodifier.go
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dagmodifier.go
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package mod
import (
"bytes"
"errors"
"io"
"os"
"time"
proto "github.com/ipfs/go-ipfs/Godeps/_workspace/src/github.com/gogo/protobuf/proto"
mh "github.com/ipfs/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multihash"
context "github.com/ipfs/go-ipfs/Godeps/_workspace/src/golang.org/x/net/context"
key "github.com/ipfs/go-ipfs/blocks/key"
imp "github.com/ipfs/go-ipfs/importer"
chunk "github.com/ipfs/go-ipfs/importer/chunk"
help "github.com/ipfs/go-ipfs/importer/helpers"
trickle "github.com/ipfs/go-ipfs/importer/trickle"
mdag "github.com/ipfs/go-ipfs/merkledag"
pin "github.com/ipfs/go-ipfs/pin"
ft "github.com/ipfs/go-ipfs/unixfs"
uio "github.com/ipfs/go-ipfs/unixfs/io"
u "github.com/ipfs/go-ipfs/util"
)
var ErrSeekFail = errors.New("failed to seek properly")
var ErrSeekEndNotImpl = errors.New("SEEK_END currently not implemented")
var ErrUnrecognizedWhence = errors.New("unrecognized whence")
// 2MB
var writebufferSize = 1 << 21
var log = u.Logger("dagio")
// 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 {
dagserv mdag.DAGService
curNode *mdag.Node
mp pin.ManualPinner
splitter chunk.BlockSplitter
ctx context.Context
readCancel func()
writeStart uint64
curWrOff uint64
wrBuf *bytes.Buffer
read *uio.DagReader
}
func NewDagModifier(ctx context.Context, from *mdag.Node, serv mdag.DAGService, mp pin.ManualPinner, spl chunk.BlockSplitter) (*DagModifier, error) {
return &DagModifier{
curNode: from.Copy(),
dagserv: serv,
splitter: spl,
ctx: ctx,
mp: mp,
}, nil
}
// WriteAt will modify a dag file in place
func (dm *DagModifier) WriteAt(b []byte, offset int64) (int, error) {
// TODO: this is currently VERY inneficient
// each write that happens at an offset other than the current one causes a
// flush to disk, and dag rewrite
if offset == int64(dm.writeStart) && dm.wrBuf != nil {
// If we would overwrite the previous write
if len(b) >= dm.wrBuf.Len() {
dm.wrBuf.Reset()
}
} else if uint64(offset) != dm.curWrOff {
size, err := dm.Size()
if err != nil {
return 0, err
}
if offset > size {
err := dm.expandSparse(offset - size)
if err != nil {
return 0, err
}
}
err = dm.Sync()
if err != nil {
return 0, err
}
dm.writeStart = uint64(offset)
}
return dm.Write(b)
}
// A reader that just returns zeros
type zeroReader struct{}
func (zr zeroReader) Read(b []byte) (int, error) {
for i := range b {
b[i] = 0
}
return len(b), nil
}
// expandSparse grows the file with zero blocks of 4096
// A small blocksize is chosen to aid in deduplication
func (dm *DagModifier) expandSparse(size int64) error {
spl := chunk.SizeSplitter{4096}
r := io.LimitReader(zeroReader{}, size)
blks := spl.Split(r)
nnode, err := dm.appendData(dm.curNode, blks)
if err != nil {
return err
}
_, err = dm.dagserv.Add(nnode)
if err != nil {
return err
}
dm.curNode = nnode
return nil
}
// Write continues writing to the dag at the current offset
func (dm *DagModifier) Write(b []byte) (int, error) {
if dm.read != nil {
dm.read = nil
}
if dm.wrBuf == nil {
dm.wrBuf = new(bytes.Buffer)
}
n, err := dm.wrBuf.Write(b)
if err != nil {
return n, err
}
dm.curWrOff += uint64(n)
if dm.wrBuf.Len() > writebufferSize {
err := dm.Sync()
if err != nil {
return n, err
}
}
return n, nil
}
func (dm *DagModifier) Size() (int64, error) {
pbn, err := ft.FromBytes(dm.curNode.Data)
if err != nil {
return 0, err
}
if dm.wrBuf != nil {
if uint64(dm.wrBuf.Len())+dm.writeStart > pbn.GetFilesize() {
return int64(dm.wrBuf.Len()) + int64(dm.writeStart), nil
}
}
return int64(pbn.GetFilesize()), nil
}
// Sync writes changes to this dag to disk
func (dm *DagModifier) Sync() error {
// No buffer? Nothing to do
if dm.wrBuf == nil {
return nil
}
// If we have an active reader, kill it
if dm.read != nil {
dm.read = nil
dm.readCancel()
}
// Number of bytes we're going to write
buflen := dm.wrBuf.Len()
// Grab key for unpinning after mod operation
curk, err := dm.curNode.Key()
if err != nil {
return err
}
// overwrite existing dag nodes
thisk, done, err := dm.modifyDag(dm.curNode, dm.writeStart, dm.wrBuf)
if err != nil {
return err
}
nd, err := dm.dagserv.Get(dm.ctx, thisk)
if err != nil {
return err
}
dm.curNode = nd
// need to write past end of current dag
if !done {
blks := dm.splitter.Split(dm.wrBuf)
nd, err = dm.appendData(dm.curNode, blks)
if err != nil {
return err
}
thisk, err = dm.dagserv.Add(nd)
if err != nil {
return err
}
dm.curNode = nd
}
// Finalize correct pinning, and flush pinner
dm.mp.PinWithMode(thisk, pin.Recursive)
dm.mp.RemovePinWithMode(curk, pin.Recursive)
err = dm.mp.Flush()
if err != nil {
return err
}
dm.writeStart += uint64(buflen)
dm.wrBuf = nil
return nil
}
// modifyDag writes the data in 'data' over the data in 'node' starting at 'offset'
// returns the new key of the passed in node and whether or not all the data in the reader
// has been consumed.
func (dm *DagModifier) modifyDag(node *mdag.Node, offset uint64, data io.Reader) (key.Key, bool, error) {
f, err := ft.FromBytes(node.Data)
if err != nil {
return "", false, err
}
// If we've reached a leaf node.
if len(node.Links) == 0 {
n, err := data.Read(f.Data[offset:])
if err != nil && err != io.EOF {
return "", false, err
}
// Update newly written node..
b, err := proto.Marshal(f)
if err != nil {
return "", false, err
}
nd := &mdag.Node{Data: b}
k, err := dm.dagserv.Add(nd)
if err != nil {
return "", false, err
}
// Hey look! we're done!
var done bool
if n < len(f.Data[offset:]) {
done = true
}
return k, done, nil
}
var cur uint64
var done bool
for i, bs := range f.GetBlocksizes() {
// We found the correct child to write into
if cur+bs > offset {
// Unpin block
ckey := key.Key(node.Links[i].Hash)
dm.mp.RemovePinWithMode(ckey, pin.Indirect)
child, err := node.Links[i].GetNode(dm.ctx, dm.dagserv)
if err != nil {
return "", false, err
}
k, sdone, err := dm.modifyDag(child, offset-cur, data)
if err != nil {
return "", false, err
}
// pin the new node
dm.mp.PinWithMode(k, pin.Indirect)
offset += bs
node.Links[i].Hash = mh.Multihash(k)
// Recache serialized node
_, err = node.Encoded(true)
if err != nil {
return "", false, err
}
if sdone {
// No more bytes to write!
done = true
break
}
offset = cur + bs
}
cur += bs
}
k, err := dm.dagserv.Add(node)
return k, done, err
}
// appendData appends the blocks from the given chan to the end of this dag
func (dm *DagModifier) appendData(node *mdag.Node, blks <-chan []byte) (*mdag.Node, error) {
dbp := &help.DagBuilderParams{
Dagserv: dm.dagserv,
Maxlinks: help.DefaultLinksPerBlock,
NodeCB: imp.BasicPinnerCB(dm.mp),
}
return trickle.TrickleAppend(node, dbp.New(blks))
}
// Read data from this dag starting at the current offset
func (dm *DagModifier) Read(b []byte) (int, error) {
err := dm.readPrep()
if err != nil {
return 0, err
}
n, err := dm.read.Read(b)
dm.curWrOff += uint64(n)
return n, err
}
func (dm *DagModifier) readPrep() error {
err := dm.Sync()
if err != nil {
return err
}
if dm.read == nil {
ctx, cancel := context.WithCancel(dm.ctx)
dr, err := uio.NewDagReader(ctx, dm.curNode, dm.dagserv)
if err != nil {
return err
}
i, err := dr.Seek(int64(dm.curWrOff), os.SEEK_SET)
if err != nil {
return err
}
if i != int64(dm.curWrOff) {
return ErrSeekFail
}
dm.readCancel = cancel
dm.read = dr
}
return nil
}
// Read data from this dag starting at the current offset
func (dm *DagModifier) CtxReadFull(ctx context.Context, b []byte) (int, error) {
err := dm.readPrep()
if err != nil {
return 0, err
}
n, err := dm.read.CtxReadFull(ctx, b)
dm.curWrOff += uint64(n)
return n, err
}
// GetNode gets the modified DAG Node
func (dm *DagModifier) GetNode() (*mdag.Node, error) {
err := dm.Sync()
if err != nil {
return nil, err
}
return dm.curNode.Copy(), nil
}
// HasChanges returned whether or not there are unflushed changes to this dag
func (dm *DagModifier) HasChanges() bool {
return dm.wrBuf != nil
}
func (dm *DagModifier) Seek(offset int64, whence int) (int64, error) {
err := dm.Sync()
if err != nil {
return 0, err
}
switch whence {
case os.SEEK_CUR:
dm.curWrOff += uint64(offset)
dm.writeStart = dm.curWrOff
case os.SEEK_SET:
dm.curWrOff = uint64(offset)
dm.writeStart = uint64(offset)
case os.SEEK_END:
return 0, ErrSeekEndNotImpl
default:
return 0, ErrUnrecognizedWhence
}
if dm.read != nil {
_, err = dm.read.Seek(offset, whence)
if err != nil {
return 0, err
}
}
return int64(dm.curWrOff), nil
}
func (dm *DagModifier) Truncate(size int64) error {
err := dm.Sync()
if err != nil {
return err
}
realSize, err := dm.Size()
if err != nil {
return err
}
// Truncate can also be used to expand the file
if size > int64(realSize) {
return dm.expandSparse(int64(size) - realSize)
}
nnode, err := dagTruncate(dm.curNode, uint64(size), dm.dagserv)
if err != nil {
return err
}
_, err = dm.dagserv.Add(nnode)
if err != nil {
return err
}
dm.curNode = nnode
return nil
}
// dagTruncate truncates the given node to 'size' and returns the modified Node
func dagTruncate(nd *mdag.Node, size uint64, ds mdag.DAGService) (*mdag.Node, error) {
if len(nd.Links) == 0 {
// TODO: this can likely be done without marshaling and remarshaling
pbn, err := ft.FromBytes(nd.Data)
if err != nil {
return nil, err
}
nd.Data = ft.WrapData(pbn.Data[:size])
return nd, nil
}
var cur uint64
end := 0
var modified *mdag.Node
ndata := new(ft.FSNode)
for i, lnk := range nd.Links {
ctx, cancel := context.WithTimeout(context.TODO(), time.Minute)
defer cancel()
child, err := lnk.GetNode(ctx, ds)
if err != nil {
return nil, err
}
childsize, err := ft.DataSize(child.Data)
if err != nil {
return nil, err
}
// found the child we want to cut
if size < cur+childsize {
nchild, err := dagTruncate(child, size-cur, ds)
if err != nil {
return nil, err
}
ndata.AddBlockSize(size - cur)
modified = nchild
end = i
break
}
cur += childsize
ndata.AddBlockSize(childsize)
}
_, err := ds.Add(modified)
if err != nil {
return nil, err
}
nd.Links = nd.Links[:end]
err = nd.AddNodeLinkClean("", modified)
if err != nil {
return nil, err
}
d, err := ndata.GetBytes()
if err != nil {
return nil, err
}
nd.Data = d
// invalidate cache and recompute serialized data
_, err = nd.Encoded(true)
if err != nil {
return nil, err
}
return nd, nil
}