Merge pull request kubernetes#123620 from benluddy/json-frame-reader-underlying-array-reuse

Remove shared ref to underlying array of JSONFrameReader's Read arg.

Author: k8s-ci-robot

staging/src/k8s.io/apimachinery/pkg/util/framer/framer.go

@@ -147,7 +147,6 @@ func (r *jsonFrameReader) Read(data []byte) (int, error) {
 
 	// RawMessage#Unmarshal appends to data - we reset the slice down to 0 and will either see
 	// data written to data, or be larger than data and a different array.
-	n := len(data)
 	m := json.RawMessage(data[:0])
 	if err := r.decoder.Decode(&m); err != nil {
 		return 0, err
@@ -156,12 +155,19 @@ func (r *jsonFrameReader) Read(data []byte) (int, error) {
 	// If capacity of data is less than length of the message, decoder will allocate a new slice
 	// and set m to it, which means we need to copy the partial result back into data and preserve
 	// the remaining result for subsequent reads.
-	if len(m) > n {
-		//nolint:staticcheck // SA4006,SA4010 underlying array of data is modified here.
-		data = append(data[0:0], m[:n]...)
-		r.remaining = m[n:]
-		return n, io.ErrShortBuffer
+	if len(m) > cap(data) {
+		copy(data, m)
+		r.remaining = m[len(data):]
+		return len(data), io.ErrShortBuffer
 	}
+
+	if len(m) > len(data) {
+		// The bytes beyond len(data) were stored in data's underlying array, which we do
+		// not own after this function returns.
+		r.remaining = append([]byte(nil), m[len(data):]...)
+		return len(data), io.ErrShortBuffer
+	}
+
 	return len(m), nil
 }
 

staging/src/k8s.io/apimachinery/pkg/util/framer/framer_test.go

@@ -18,6 +18,7 @@ package framer
 
 import (
 	"bytes"
+	"errors"
 	"io"
 	"testing"
 )
@@ -173,3 +174,17 @@ func TestJSONFrameReaderShortBuffer(t *testing.T) {
 		t.Fatalf("unexpected: %v %d %q", err, n, buf)
 	}
 }
+
+func TestJSONFrameReaderShortBufferNoUnderlyingArrayReuse(t *testing.T) {
+	b := bytes.NewBufferString("{}")
+	r := NewJSONFramedReader(io.NopCloser(b))
+	buf := make([]byte, 1, 2) // cap(buf) > len(buf) && cap(buf) <= len("{}")
+
+	if n, err := r.Read(buf); !errors.Is(err, io.ErrShortBuffer) || n != 1 || string(buf[:n]) != "{" {
+		t.Fatalf("unexpected: %v %d %q", err, n, buf)
+	}
+	buf = append(buf, make([]byte, 1)...) // stomps the second byte of the backing array
+	if n, err := r.Read(buf[1:]); err != nil || n != 1 || string(buf[1:1+n]) != "}" {
+		t.Fatalf("unexpected: %v %d %q", err, n, buf)
+	}
+}