clean up code, make it have a nicer interface

importer/importer.go

@@ -20,11 +20,11 @@ var ErrSizeLimitExceeded = fmt.Errorf("object size limit exceeded")
 // NewDagFromReader constructs a Merkle DAG from the given io.Reader.
 // size required for block construction.
 func NewDagFromReader(r io.Reader) (*dag.Node, error) {
-	return NewDagFromReaderWithSplitter(r, SplitterBySize(1024*512))
+	return NewDagFromReaderWithSplitter(r, &SizeSplitter{1024 * 512})
 }
 
 func NewDagFromReaderWithSplitter(r io.Reader, spl BlockSplitter) (*dag.Node, error) {
-	blkChan := spl(r)
+	blkChan := spl.Split(r)
 	root := &dag.Node{Data: dag.FilePBData()}
 
 	for blk := range blkChan {

importer/importer_test.go

@@ -34,30 +34,15 @@ func TestBuildDag(t *testing.T) {
 
 //Test where calls to read are smaller than the chunk size
 func TestSizeBasedSplit(t *testing.T) {
-	bs := SplitterBySize(512)
+	bs := &SizeSplitter{512}
 	testFileConsistency(t, bs, 32*512)
-	bs = SplitterBySize(4096)
+	bs = &SizeSplitter{4096}
 	testFileConsistency(t, bs, 32*4096)
 
 	// Uneven offset
 	testFileConsistency(t, bs, 31*4095)
 }
 
-func TestOtherSplit(t *testing.T) {
-	//split := WhyrusleepingCantImplementRabin
-	//testFileConsistency(t, split, 4096*64)
-}
-
-type testData struct{ n uint64 }
-
-func (t *testData) Read(b []byte) (int, error) {
-	for i, _ := range b {
-		b[i] = byte(t.n % 256)
-		t.n++
-	}
-	return len(b), nil
-}
-
 func testFileConsistency(t *testing.T, bs BlockSplitter, nbytes int) {
 	buf := new(bytes.Buffer)
 	io.CopyN(buf, rand.Reader, int64(nbytes))
@@ -95,27 +80,5 @@ func arrComp(a, b []byte) error {
 }
 
 func TestMaybeRabinConsistency(t *testing.T) {
-	testFileConsistency(t, ThisMightBeRabin, 256*4096)
-}
-
-func TestRabinSplit(t *testing.T) {
-
-	//Generate some random data
-	nbytes := 256 * 4096
-	buf := new(bytes.Buffer)
-	io.CopyN(buf, rand.Reader, int64(nbytes))
-	good := buf.Bytes()
-
-	// Get block generator for random data
-	ch := ThisMightBeRabin(buf)
-
-	i := 0
-	var blocks [][]byte
-	for blk := range ch {
-		if !bytes.Equal(blk, good[i:len(blk)+i]) {
-			t.Fatalf("bad block! %v", blk[:32])
-		}
-		i += len(blk)
-		blocks = append(blocks, blk)
-	}
+	testFileConsistency(t, NewMaybeRabin(4096), 256*4096)
 }

importer/rabin.go

@@ -5,93 +5,79 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"math"
 )
 
-//pseudocode stolen from the internet
-func rollhash(S []byte) {
-	a := 10
-	mask := 0xfff
-	MOD := 33554383 //randomly chosen
-	windowSize := 16
-	an := 1
-	rollingHash := 0
-	for i := 0; i < windowSize; i++ {
-		rollingHash = (rollingHash*a + int(S[i])) % MOD
-		an = (an * a) % MOD
-	}
-	if rollingHash&mask == mask {
-		// "match"
-		fmt.Println("match")
-	}
-	for i := 1; i < len(S)-windowSize; i++ {
-		rollingHash = (rollingHash*a + int(S[i+windowSize-1]) - an*int(S[i-1])) % MOD
-		if rollingHash&mask == mask {
-			//print "match"
-			fmt.Println("match")
-		}
-	}
+type MaybeRabin struct {
+	mask       int
+	windowSize int
 }
 
-func ThisMightBeRabin(r io.Reader) chan []byte {
-	out := make(chan []byte)
+func NewMaybeRabin(avgBlkSize int) *MaybeRabin {
+	blkbits := uint(math.Log2(float64(avgBlkSize)))
+	rb := new(MaybeRabin)
+	rb.mask = (1 << blkbits) - 1
+	rb.windowSize = 16 // probably a good number...
+	return rb
+}
+
+func (mr *MaybeRabin) Split(r io.Reader) chan []byte {
+	out := make(chan []byte, 16)
 	go func() {
 		inbuf := bufio.NewReader(r)
 		blkbuf := new(bytes.Buffer)
 
-		// some bullshit numbers
-		a := 10
-		mask := 0xfff   //make this smaller for smaller blocks
-		MOD := 33554383 //randomly chosen
-		windowSize := 16
+		// some bullshit numbers i made up
+		a := 10         // honestly, no idea what this is
+		MOD := 33554383 // randomly chosen (seriously)
 		an := 1
 		rollingHash := 0
 
-		window := make([]byte, windowSize)
-		get := func(i int) int { return int(window[i%len(window)]) }
-		set := func(i int, val byte) { window[i%len(window)] = val }
+		// Window is a circular buffer
+		window := make([]byte, mr.windowSize)
+		push := func(i int, val byte) (outval int) {
+			outval = int(window[i%len(window)])
+			window[i%len(window)] = val
+			return
+		}
+
+		// Duplicate byte slice
 		dup := func(b []byte) []byte {
 			d := make([]byte, len(b))
 			copy(d, b)
 			return d
 		}
 
+		// Fill up the window
 		i := 0
-		for ; i < windowSize; i++ {
+		for ; i < mr.windowSize; i++ {
 			b, err := inbuf.ReadByte()
 			if err != nil {
 				fmt.Println(err)
 				return
 			}
 			blkbuf.WriteByte(b)
-			window[i] = b
+			push(i, b)
 			rollingHash = (rollingHash*a + int(b)) % MOD
 			an = (an * a) % MOD
 		}
-		/* This is too short for a block
-		if rollingHash&mask == mask {
-			// "match"
-			fmt.Println("match")
-		}
-		*/
+
 		for ; true; i++ {
 			b, err := inbuf.ReadByte()
 			if err != nil {
 				break
 			}
-			outval := get(i)
-			set(i, b)
+			outval := push(i, b)
 			blkbuf.WriteByte(b)
-			rollingHash = (rollingHash*a + get(i) - an*outval) % MOD
-			if rollingHash&mask == mask {
-				//print "match"
+			rollingHash = (rollingHash*a + int(b) - an*outval) % MOD
+			if rollingHash&mr.mask == mr.mask {
 				out <- dup(blkbuf.Bytes())
 				blkbuf.Reset()
 			}
-			peek, err := inbuf.Peek(windowSize)
-			if err != nil {
-				break
-			}
-			if len(peek) != windowSize {
+
+			// Check if there are enough remaining
+			peek, err := inbuf.Peek(mr.windowSize)
+			if err != nil || len(peek) != mr.windowSize {
 				break
 			}
 		}

importer/splitting.go

@@ -6,29 +6,33 @@ import (
 	u "github.com/jbenet/go-ipfs/util"
 )
 
-type BlockSplitter func(io.Reader) chan []byte
+type BlockSplitter interface {
+	Split(io.Reader) chan []byte
+}
 
-func SplitterBySize(n int) BlockSplitter {
-	return func(r io.Reader) chan []byte {
-		out := make(chan []byte)
-		go func(n int) {
-			defer close(out)
-			for {
-				chunk := make([]byte, n)
-				nread, err := r.Read(chunk)
-				if err != nil {
-					if err == io.EOF {
-						return
-					}
-					u.PErr("block split error: %v\n", err)
+type SizeSplitter struct {
+	Size int
+}
+
+func (ss *SizeSplitter) Split(r io.Reader) chan []byte {
+	out := make(chan []byte)
+	go func() {
+		defer close(out)
+		for {
+			chunk := make([]byte, ss.Size)
+			nread, err := r.Read(chunk)
+			if err != nil {
+				if err == io.EOF {
 					return
 				}
-				if nread < n {
-					chunk = chunk[:nread]
-				}
-				out <- chunk
+				u.PErr("block split error: %v\n", err)
+				return
 			}
-		}(n)
-		return out
-	}
+			if nread < ss.Size {
+				chunk = chunk[:nread]
+			}
+			out <- chunk
+		}
+	}()
+	return out
 }