Add a test to validate deferredResponseWriteron multiple write calls

Signed-off-by: nkeert <197718357+nkeert@users.noreply.github.com>

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/responsewriters/writers_test.go

@@ -19,6 +19,7 @@ package responsewriters
 import (
 	"bytes"
 	"compress/gzip"
+	"context"
 	"encoding/hex"
 	"encoding/json"
 	"errors"
@@ -32,6 +33,7 @@ import (
 	"os"
 	"reflect"
 	"strconv"
+	"strings"
 	"testing"
 	"time"
 
@@ -371,6 +373,124 @@ func TestSerializeObject(t *testing.T) {
 	}
 }
 
+func TestDeferredResponseWriter_Write(t *testing.T) {
+	smallChunk := bytes.Repeat([]byte("b"), defaultGzipThresholdBytes-1)
+	largeChunk := bytes.Repeat([]byte("b"), defaultGzipThresholdBytes+1)
+
+	tests := []struct {
+		name       string
+		chunks     [][]byte
+		expectGzip bool
+	}{
+		{
+			name:       "one small chunk write",
+			chunks:     [][]byte{smallChunk},
+			expectGzip: false,
+		},
+		{
+			name:       "two small chunk writes",
+			chunks:     [][]byte{smallChunk, smallChunk},
+			expectGzip: false,
+		},
+		{
+			name:       "one large chunk writes",
+			chunks:     [][]byte{largeChunk},
+			expectGzip: true,
+		},
+		{
+			name:       "two large chunk writes",
+			chunks:     [][]byte{largeChunk, largeChunk},
+			expectGzip: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockResponseWriter := httptest.NewRecorder()
+
+			drw := &deferredResponseWriter{
+				mediaType:       "text/plain",
+				statusCode:      200,
+				contentEncoding: "gzip",
+				hw:              mockResponseWriter,
+				ctx:             context.Background(),
+			}
+
+			fullPayload := []byte{}
+
+			for _, chunk := range tt.chunks {
+				n, err := drw.Write(chunk)
+
+				if err != nil {
+					t.Fatalf("unexpected error while writing chunk: %v", err)
+				}
+				if n != len(chunk) {
+					t.Errorf("write is not complete, expected: %d bytes, written: %d bytes", len(chunk), n)
+				}
+
+				fullPayload = append(fullPayload, chunk...)
+			}
+
+			err := drw.Close()
+			if err != nil {
+				t.Fatalf("unexpected error when closing deferredResponseWriter: %v", err)
+			}
+
+			res := mockResponseWriter.Result()
+
+			if res.StatusCode != http.StatusOK {
+				t.Fatalf("status code is not writtend properly, expected: 200, got: %d", res.StatusCode)
+			}
+			contentEncoding := res.Header.Get("Content-Encoding")
+			varyHeader := res.Header.Get("Vary")
+
+			resBytes, err := io.ReadAll(res.Body)
+			if err != nil {
+				t.Fatalf("unexpected error occurred while reading response body: %v", err)
+			}
+
+			if tt.expectGzip {
+				if contentEncoding != "gzip" {
+					t.Fatalf("content-encoding is not set properly, expected: gzip, got: %s", contentEncoding)
+				}
+
+				if !strings.Contains(varyHeader, "Accept-Encoding") {
+					t.Errorf("vary header doesn't have Accept-Encoding")
+				}
+
+				gr, err := gzip.NewReader(bytes.NewReader(resBytes))
+				if err != nil {
+					t.Fatalf("failed to create gzip reader: %v", err)
+				}
+
+				decompressed, err := io.ReadAll(gr)
+				if err != nil {
+					t.Fatalf("failed to decompress: %v", err)
+				}
+
+				if !bytes.Equal(fullPayload, decompressed) {
+					t.Errorf("payload mismatch, expected: %s, got: %s", fullPayload, decompressed)
+				}
+
+			} else {
+				if contentEncoding != "" {
+					t.Errorf("content-encoding is set unexpectedly")
+				}
+
+				if strings.Contains(varyHeader, "Accept-Encoding") {
+					t.Errorf("accept encoding is set unexpectedly")
+				}
+
+				if !bytes.Equal(fullPayload, resBytes) {
+					t.Errorf("payload mismatch, expected: %s, got: %s", fullPayload, resBytes)
+				}
+
+			}
+
+		})
+	}
+}
+
 func randTime(t *time.Time, r *rand.Rand) {
 	*t = time.Unix(r.Int63n(1000*365*24*60*60), r.Int63())
 }