fix(buffer): make buffer capacity atleast defaultCapacity (#273)

Author: NamanJain8

z/buffer.go

@@ -57,7 +57,7 @@ type Buffer struct {
 }
 
 func NewBuffer(capacity int, tag string) *Buffer {
-	if capacity == 0 {
+	if capacity < defaultCapacity {
 		capacity = defaultCapacity
 	}
 	if tag == "" {
@@ -100,7 +100,7 @@ func NewBufferTmp(dir string, capacity int) (*Buffer, error) {
 }
 
 func newBufferFile(file *os.File, capacity int) (*Buffer, error) {
-	if capacity == 0 {
+	if capacity < defaultCapacity {
 		capacity = defaultCapacity
 	}
 	mmapFile, err := OpenMmapFileUsing(file, capacity, true)

z/buffer_test.go

@@ -286,3 +286,18 @@ func newTestBuffers(t *testing.T, capacity int) []*Buffer {
 
 	return bufs
 }
+
+func TestSmallBuffer(t *testing.T) {
+	buf := NewBuffer(5, "test")
+	t.Cleanup(func() {
+		require.NoError(t, buf.Release())
+	})
+	// Write something to buffer so sort actually happens.
+	buf.WriteSlice([]byte("abc"))
+	// This test fails if the buffer has offset > currSz.
+	require.NotPanics(t, func() {
+		buf.SortSlice(func(left, right []byte) bool {
+			return true
+		})
+	})
+}