#42: the compress functions can write pass the end of the slice via c…

…opy. 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)
+	}
+}