test(storage): unflake PostPolicyV4 test

This test verifies that the upload works using a basic net/http
client, so we need to account for the fact that that client doesn't
include retries.

Fixes googleapis#6212

storage/integration_test.go

@@ -4588,74 +4588,83 @@ func verifySignedURL(url string, headers map[string][]string, expectedFileBody [
 // verifies that it was uploaded correctly
 func verifyPostPolicy(pv4 *PostPolicyV4, obj *ObjectHandle, bytesToWrite []byte, statusCodeOnSuccess int) error {
 	ctx := context.Background()
-	formBuf := new(bytes.Buffer)
-	mw := multipart.NewWriter(formBuf)
-	for fieldName, value := range pv4.Fields {
-		if err := mw.WriteField(fieldName, value); err != nil {
-			return fmt.Errorf("Failed to write form field: %q: %v", fieldName, err)
-		}
-	}
-
-	// Now let's perform the upload
-	mf, err := mw.CreateFormFile("file", "myfile.txt")
-	if err != nil {
-		return err
-	}
-	if _, err := mf.Write(bytesToWrite); err != nil {
-		return err
-	}
-	if err := mw.Close(); err != nil {
-		return err
-	}
+	var res *http.Response
+
+	// Request is sent using a vanilla net/http client, so there are no built-in
+	// retries. We must wrap with a retry to prevent flakes.
+	return retry(ctx,
+		func() error{
+			formBuf := new(bytes.Buffer)
+			mw := multipart.NewWriter(formBuf)
+			for fieldName, value := range pv4.Fields {
+				if err := mw.WriteField(fieldName, value); err != nil {
+					return fmt.Errorf("Failed to write form field: %q: %v", fieldName, err)
+				}
+			}
 
-	// Compose the HTTP request
-	req, err := http.NewRequest("POST", pv4.URL, formBuf)
-	if err != nil {
-		return fmt.Errorf("Failed to compose HTTP request: %v", err)
-	}
+			// Now let's perform the upload
+			mf, err := mw.CreateFormFile("file", "myfile.txt")
+			if err != nil {
+				return err
+			}
+			if _, err := mf.Write(bytesToWrite); err != nil {
+				return err
+			}
+			if err := mw.Close(); err != nil {
+				return err
+			}
 
-	// Ensure the Content-Type is derived from the writer
-	req.Header.Set("Content-Type", mw.FormDataContentType())
+			// Compose the HTTP request
+			req, err := http.NewRequest("POST", pv4.URL, formBuf)
+			if err != nil {
+				return fmt.Errorf("Failed to compose HTTP request: %v", err)
+			}
 
-	// Send request
-	res, err := http.DefaultClient.Do(req)
-	if err != nil {
-		return err
-	}
+			// Ensure the Content-Type is derived from the writer
+			req.Header.Set("Content-Type", mw.FormDataContentType())
 
-	// Check response
-	if g, w := res.StatusCode, statusCodeOnSuccess; g != w {
-		blob, _ := httputil.DumpResponse(res, true)
-		return fmt.Errorf("Status code in response mismatch: got %d want %d\nBody: %s", g, w, blob)
-	}
-	io.Copy(ioutil.Discard, res.Body)
+			// Send request
+			res, err = http.DefaultClient.Do(req)
+			if err != nil {
+				return err
+			}
+			return nil
+		},
+		func() error {
+			// Check response
+			if g, w := res.StatusCode, statusCodeOnSuccess; g != w {
+				blob, _ := httputil.DumpResponse(res, true)
+				return fmt.Errorf("Status code in response mismatch: got %d want %d\nBody: %s", g, w, blob)
+			}
+			io.Copy(ioutil.Discard, res.Body)
 
-	// Verify that the file was properly uploaded
-	// by reading back its attributes and content
-	attrs, err := obj.Attrs(ctx)
-	if err != nil {
-		return fmt.Errorf("Failed to retrieve attributes: %v", err)
-	}
-	if g, w := attrs.Size, int64(len(bytesToWrite)); g != w {
-		return fmt.Errorf("ContentLength mismatch: got %d want %d", g, w)
-	}
-	if g, w := attrs.MD5, md5.Sum(bytesToWrite); !bytes.Equal(g, w[:]) {
-		return fmt.Errorf("MD5Checksum mismatch\nGot:  %x\nWant: %x", g, w)
-	}
+			// Verify that the file was properly uploaded
+			// by reading back its attributes and content
+			attrs, err := obj.Attrs(ctx)
+			if err != nil {
+				return fmt.Errorf("Failed to retrieve attributes: %v", err)
+			}
+			if g, w := attrs.Size, int64(len(bytesToWrite)); g != w {
+				return fmt.Errorf("ContentLength mismatch: got %d want %d", g, w)
+			}
+			if g, w := attrs.MD5, md5.Sum(bytesToWrite); !bytes.Equal(g, w[:]) {
+				return fmt.Errorf("MD5Checksum mismatch\nGot:  %x\nWant: %x", g, w)
+			}
 
-	// Compare the uploaded body with the expected
-	rd, err := obj.NewReader(ctx)
-	if err != nil {
-		return fmt.Errorf("Failed to create a reader: %v", err)
-	}
-	gotBody, err := ioutil.ReadAll(rd)
-	if err != nil {
-		return fmt.Errorf("Failed to read the body: %v", err)
-	}
-	if diff := testutil.Diff(string(gotBody), string(bytesToWrite)); diff != "" {
-		return fmt.Errorf("Body mismatch: got - want +\n%s", diff)
-	}
-	return nil
+			// Compare the uploaded body with the expected
+			rd, err := obj.NewReader(ctx)
+			if err != nil {
+				return fmt.Errorf("Failed to create a reader: %v", err)
+			}
+			gotBody, err := ioutil.ReadAll(rd)
+			if err != nil {
+				return fmt.Errorf("Failed to read the body: %v", err)
+			}
+			if diff := testutil.Diff(string(gotBody), string(bytesToWrite)); diff != "" {
+				return fmt.Errorf("Body mismatch: got - want +\n%s", diff)
+			}
+			return nil
+		})
 }
 
 func newTestClientWithExplicitCredentials(ctx context.Context, t *testing.T) *Client {