When using the NewWriterV2 function for compressing data, an error occurs during decompression if the data size is an exact multiple of blocksize.

[newacorn]

Test

func TestBrotliWriteMultiplyBlockData(t *testing.T) {
	tmpW := brotli.NewWriterV2(nil, 4)
	blockSize := tmpW.BlockSize
	for i := 0; i < 5; i++ {
		t.Run("compress data length: "+strconv.Itoa(i*blockSize)+"bytes", func(t *testing.T) {
			dataStr := randomstring.HumanFriendlyString(i * blockSize)
			dataBytes := []byte(dataStr)
			buf := bytes.Buffer{}
			w := brotli.NewWriterV2(&buf, 4)
			n, err := w.Write(dataBytes)
			err = w.Close()
			assert.NoErr(t, err)
			assert.Eq(t, n, len(dataBytes))
			assert.NoErr(t, err)
			r := brotli.NewReader(&buf)
			dst := make([]byte, len(dataBytes)+1000)
			p := dst
			total := 0
			for {
				n1, err1 := r.Read(p)
				if err1 != nil {
					if err1 != io.EOF {
						t.Fatal(err1)
					}
					break
				}
				total += n1
				p = p[n1:]
			}
			assert.Eq(t, dataBytes, dst[:total])
		})
	}

}

sum

Respceting p‘s length the observed errors are: either a PADDING_1 error is returned during reading, or the io.EOF error is not correctly returned, resulting in incorrect decompression of data or an infinite loop.

Fix: matchfinder Encode method bug