Make chunker resettable

chunker/chunker.go

@@ -77,14 +77,17 @@ func New(rd io.Reader, bufsize int, hashfn func() hash.Hash) *Chunker {
 	c := &Chunker{
 		buf: make([]byte, bufsize),
 		hfn: hashfn,
-		rd:  rd,
 	}
-	c.reset()
+	c.Reset(rd)
 
 	return c
 }
 
-func (c *Chunker) reset() {
+// Reset restarts a chunker so that it can be reused with a different reader as
+// the source.
+func (c *Chunker) Reset(rd io.Reader) {
+	c.rd = rd
+
 	for i := 0; i < WindowSize; i++ {
 		c.window[i] = 0
 	}
@@ -92,6 +95,7 @@ func (c *Chunker) reset() {
 	c.digest = 0
 	c.wpos = 0
 	c.pos = 0
+	c.start = 0
 	c.count = 0
 	c.slide(1)
 
@@ -230,9 +234,9 @@ func (c *Chunker) Next() (*Chunk, error) {
 
 				c.resetHash()
 
-				// keep position
+				// reset chunker, but keep position
 				pos := c.pos
-				c.reset()
+				c.Reset(c.rd)
 				c.pos = pos
 				c.start = pos
 				c.pre = MinSize - WindowSize

chunker/chunker_test.go

@@ -91,22 +91,22 @@ func test_with_data(t *testing.T, chnker *chunker.Chunker, testChunks []chunk) [
 		if c != nil {
 			if c.Start != pos {
 				t.Fatalf("Start for chunk %d does not match: expected %d, got %d",
-					i, c.Start, pos)
+					i, pos, c.Start)
 			}
 
 			if c.Length != chunk.Length {
 				t.Fatalf("Length for chunk %d does not match: expected %d, got %d",
-					i, c.Length, chunk.Length)
+					i, chunk.Length, c.Length)
 			}
 
 			if c.Cut != chunk.CutFP {
 				t.Fatalf("Cut fingerprint for chunk %d/%d does not match: expected %016x, got %016x",
-					i, len(chunks)-1, c.Cut, chunk.CutFP)
+					i, len(chunks)-1, chunk.CutFP, c.Cut)
 			}
 
 			if !bytes.Equal(c.Digest, chunk.Digest) {
-				t.Fatalf("Digest fingerprint for chunk %d/%d does not match: expected %q, got %q",
+				t.Fatalf("Digest fingerprint for chunk %d/%d does not match: expected %02x, got %02x",
-					i, len(chunks)-1, hex.EncodeToString(c.Digest), hex.EncodeToString(chunk.Digest))
+					i, len(chunks)-1, chunk.Digest, c.Digest)
 			}
 
 			pos += c.Length
@@ -179,9 +179,11 @@ func TestChunker(t *testing.T) {
 
 func TestChunkerReuse(t *testing.T) {
 	// test multiple uses of the same chunker
-	for i := 0; i < 4; i++ {
+	ch := chunker.New(nil, *testBufSize, sha256.New)
 	buf := get_random(23, 32*1024*1024)
-		ch := chunker.New(bytes.NewReader(buf), *testBufSize, sha256.New)
+
+	for i := 0; i < 4; i++ {
+		ch.Reset(bytes.NewReader(buf))
 		test_with_data(t, ch, chunks1)
 	}
 }