#42: the compress functions can write pass the end of the slice via copy. Make sure the capacity of the buffer used for compression is the same as its length.

reader.go

@@ -101,7 +101,7 @@ func (z *Reader) readHeader(first bool) error {
 	z.data = z.zdata[:cap(z.zdata)][bSize:]
 	z.idx = len(z.data)
 
-	z.checksum.Write(buf[0:2])
+	_, _ = z.checksum.Write(buf[0:2])
 
 	if frameSize {
 		buf := buf[:8]
@@ -110,7 +110,7 @@ func (z *Reader) readHeader(first bool) error {
 		}
 		z.Size = binary.LittleEndian.Uint64(buf)
 		z.pos += 8
-		z.checksum.Write(buf)
+		_, _ = z.checksum.Write(buf)
 	}
 
 	// Header checksum.
@@ -258,7 +258,7 @@ func (z *Reader) Read(buf []byte) (int, error) {
 		}
 
 		if !z.NoChecksum {
-			z.checksum.Write(z.data)
+			_, _ = z.checksum.Write(z.data)
 			if debugFlag {
 				debug("current frame checksum %x", z.checksum.Sum32())
 			}

writer.go

@@ -46,8 +46,8 @@ func (z *Writer) writeHeader() error {
 	if n := 2 * bSize; cap(z.zdata) < n {
 		z.zdata = make([]byte, n, n)
 	}
-	z.zdata = z.zdata[:bSize]
-	z.data = z.zdata[:cap(z.zdata)][bSize:]
+	z.data = z.zdata[:bSize]
+	z.zdata = z.zdata[:cap(z.zdata)][bSize:]
 	z.idx = 0
 
 	// Size is optional.

writer_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"os"
 	"reflect"
 	"testing"
 
@@ -96,3 +97,28 @@ func TestIssue41(t *testing.T) {
 		t.Fatal("uncompressed data does not match original")
 	}
 }
+
+func TestIssue42(t *testing.T) {
+	r, w := io.Pipe()
+	go func() {
+		defer w.Close()
+
+		f, err := os.Open("testdata/issue42.data")
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer f.Close()
+
+		zw := lz4.NewWriter(w)
+		defer zw.Close()
+
+		_, err = io.Copy(zw, f)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+	_, err := io.Copy(ioutil.Discard, lz4.NewReader(r))
+	if err != nil {
+		t.Fatal(err)
+	}
+}