zstd: Forward read errors (#373)

* zstd: Forward read errors

Forward all read errors.

Fixes #372

zstd/blockdec.go

@@ -123,12 +123,10 @@ func newBlockDec(lowMem bool) *blockDec {
 // Input must be a start of a block and will be at the end of the block when returned.
 func (b *blockDec) reset(br byteBuffer, windowSize uint64) error {
 	b.WindowSize = windowSize
-	tmp := br.readSmall(3)
-	if tmp == nil {
-		if debug {
-			println("Reading block header:", io.ErrUnexpectedEOF)
-		}
-		return io.ErrUnexpectedEOF
+	tmp, err := br.readSmall(3)
+	if err != nil {
+		println("Reading block header:", err)
+		return err
 	}
 	bh := uint32(tmp[0]) | (uint32(tmp[1]) << 8) | (uint32(tmp[2]) << 16)
 	b.Last = bh&1 != 0
@@ -179,7 +177,6 @@ func (b *blockDec) reset(br byteBuffer, windowSize uint64) error {
 	if cap(b.dst) <= maxSize {
 		b.dst = make([]byte, 0, maxSize+1)
 	}
-	var err error
 	b.data, err = br.readBig(cSize, b.dataStorage)
 	if err != nil {
 		if debug {

zstd/bytebuf.go

@@ -12,8 +12,8 @@ import (
 
 type byteBuffer interface {
 	// Read up to 8 bytes.
-	// Returns nil if no more input is available.
-	readSmall(n int) []byte
+	// Returns io.ErrUnexpectedEOF if this cannot be satisfied.
+	readSmall(n int) ([]byte, error)
 
 	// Read >8 bytes.
 	// MAY use the destination slice.
@@ -29,17 +29,17 @@ type byteBuffer interface {
 // in-memory buffer
 type byteBuf []byte
 
-func (b *byteBuf) readSmall(n int) []byte {
+func (b *byteBuf) readSmall(n int) ([]byte, error) {
 	if debugAsserts && n > 8 {
 		panic(fmt.Errorf("small read > 8 (%d). use readBig", n))
 	}
 	bb := *b
 	if len(bb) < n {
-		return nil
+		return nil, io.ErrUnexpectedEOF
 	}
 	r := bb[:n]
 	*b = bb[n:]
-	return r
+	return r, nil
 }
 
 func (b *byteBuf) readBig(n int, dst []byte) ([]byte, error) {
@@ -81,19 +81,22 @@ type readerWrapper struct {
 	tmp [8]byte
 }
 
-func (r *readerWrapper) readSmall(n int) []byte {
+func (r *readerWrapper) readSmall(n int) ([]byte, error) {
 	if debugAsserts && n > 8 {
 		panic(fmt.Errorf("small read > 8 (%d). use readBig", n))
 	}
 	n2, err := io.ReadFull(r.r, r.tmp[:n])
 	// We only really care about the actual bytes read.
-	if n2 != n {
+	if err != nil {
+		if err == io.EOF {
+			return nil, io.ErrUnexpectedEOF
+		}
 		if debug {
 			println("readSmall: got", n2, "want", n, "err", err)
 		}
-		return nil
+		return nil, err
 	}
-	return r.tmp[:n]
+	return r.tmp[:n], nil
 }
 
 func (r *readerWrapper) readBig(n int, dst []byte) ([]byte, error) {

zstd/decoder_test.go

@@ -9,6 +9,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -142,6 +143,28 @@ func TestNewReaderMismatch(t *testing.T) {
 	t.Log("Output matched")
 }
 
+type errorReader struct {
+	err error
+}
+
+func (r *errorReader) Read(p []byte) (int, error) {
+	return 0, r.err
+}
+
+func TestErrorReader(t *testing.T) {
+	wantErr := fmt.Errorf("i'm a failure")
+	zr, err := NewReader(&errorReader{err: wantErr})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer zr.Close()
+
+	_, err = ioutil.ReadAll(zr)
+	if !errors.Is(err, wantErr) {
+		t.Errorf("want error %v, got %v", wantErr, err)
+	}
+}
+
 func TestNewDecoder(t *testing.T) {
 	defer timeout(60 * time.Second)()
 	testDecoderFile(t, "testdata/decoder.zip")
@@ -426,7 +449,7 @@ func TestDecoderRegression(t *testing.T) {
 	}
 	defer dec.Close()
 	for i, tt := range zr.File {
-		if !strings.HasSuffix(tt.Name, "") || (testing.Short() && i > 10) {
+		if !strings.HasSuffix(tt.Name, "artifact (5)") || (testing.Short() && i > 10) {
 			continue
 		}
 		t.Run("Reader-"+tt.Name, func(t *testing.T) {

zstd/framedec.go

@@ -80,9 +80,14 @@ func (d *frameDec) reset(br byteBuffer) error {
 	d.WindowSize = 0
 	var b []byte
 	for {
-		b = br.readSmall(4)
-		if b == nil {
+		var err error
+		b, err = br.readSmall(4)
+		switch err {
+		case io.EOF, io.ErrUnexpectedEOF:
 			return io.EOF
+		default:
+			return err
+		case nil:
 		}
 		if !bytes.Equal(b[1:4], skippableFrameMagic) || b[0]&0xf0 != 0x50 {
 			if debug {
@@ -92,14 +97,14 @@ func (d *frameDec) reset(br byteBuffer) error {
 			break
 		}
 		// Read size to skip
-		b = br.readSmall(4)
-		if b == nil {
-			println("Reading Frame Size EOF")
-			return io.ErrUnexpectedEOF
+		b, err = br.readSmall(4)
+		if err != nil {
+			println("Reading Frame Size", err)
+			return err
 		}
 		n := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
 		println("Skipping frame with", n, "bytes.")
-		err := br.skipN(int(n))
+		err = br.skipN(int(n))
 		if err != nil {
 			if debug {
 				println("Reading discarded frame", err)
@@ -147,12 +152,11 @@ func (d *frameDec) reset(br byteBuffer) error {
 		if size == 3 {
 			size = 4
 		}
-		b = br.readSmall(int(size))
-		if b == nil {
-			if debug {
-				println("Reading Dictionary_ID", io.ErrUnexpectedEOF)
-			}
-			return io.ErrUnexpectedEOF
+
+		b, err = br.readSmall(int(size))
+		if err != nil {
+			println("Reading Dictionary_ID", err)
+			return err
 		}
 		var id uint32
 		switch size {
@@ -187,10 +191,10 @@ func (d *frameDec) reset(br byteBuffer) error {
 	}
 	d.FrameContentSize = 0
 	if fcsSize > 0 {
-		b := br.readSmall(fcsSize)
-		if b == nil {
-			println("Reading Frame content", io.ErrUnexpectedEOF)
-			return io.ErrUnexpectedEOF
+		b, err = br.readSmall(fcsSize)
+		if err != nil {
+			println("Reading Frame content", err)
+			return err
 		}
 		switch fcsSize {
 		case 1:
@@ -307,10 +311,10 @@ func (d *frameDec) checkCRC() error {
 	tmp[3] = byte(got >> 24)
 
 	// We can overwrite upper tmp now
-	want := d.rawInput.readSmall(4)
-	if want == nil {
-		println("CRC missing?")
-		return io.ErrUnexpectedEOF
+	want, err := d.rawInput.readSmall(4)
+	if err != nil {
+		println("CRC missing?", err)
+		return err
 	}
 
 	if !bytes.Equal(tmp[:], want) {