PLT-7599: webhook post splitting (#7707)

* webhook post splitting

* style fix

* update old webhook test

app/webhook_test.go

@@ -4,8 +4,12 @@
 package app
 
 import (
+	"strings"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/utils"
 )
@@ -50,3 +54,95 @@ func TestCreateWebhookPost(t *testing.T) {
 		t.Fatal("should have failed - bad post type")
 	}
 }
+
+func TestSplitWebhookPost(t *testing.T) {
+	type TestCase struct {
+		Post     *model.Post
+		Expected []*model.Post
+	}
+
+	for name, tc := range map[string]TestCase{
+		"LongPost": {
+			Post: &model.Post{
+				Message: strings.Repeat("本", model.POST_MESSAGE_MAX_RUNES*3/2),
+			},
+			Expected: []*model.Post{
+				{
+					Message: strings.Repeat("本", model.POST_MESSAGE_MAX_RUNES),
+				},
+				{
+					Message: strings.Repeat("本", model.POST_MESSAGE_MAX_RUNES/2),
+				},
+			},
+		},
+		"LongPostAndMultipleAttachments": {
+			Post: &model.Post{
+				Message: strings.Repeat("本", model.POST_MESSAGE_MAX_RUNES*3/2),
+				Props: map[string]interface{}{
+					"attachments": []*model.SlackAttachment{
+						&model.SlackAttachment{
+							Text: strings.Repeat("本", 1000),
+						},
+						&model.SlackAttachment{
+							Text: strings.Repeat("本", 2000),
+						},
+						&model.SlackAttachment{
+							Text: strings.Repeat("本", model.POST_PROPS_MAX_USER_RUNES-1000),
+						},
+					},
+				},
+			},
+			Expected: []*model.Post{
+				{
+					Message: strings.Repeat("本", model.POST_MESSAGE_MAX_RUNES),
+				},
+				{
+					Message: strings.Repeat("本", model.POST_MESSAGE_MAX_RUNES/2),
+					Props: map[string]interface{}{
+						"attachments": []*model.SlackAttachment{
+							&model.SlackAttachment{
+								Text: strings.Repeat("本", 1000),
+							},
+							&model.SlackAttachment{
+								Text: strings.Repeat("本", 2000),
+							},
+						},
+					},
+				},
+				{
+					Props: map[string]interface{}{
+						"attachments": []*model.SlackAttachment{
+							&model.SlackAttachment{
+								Text: strings.Repeat("本", model.POST_PROPS_MAX_USER_RUNES-1000),
+							},
+						},
+					},
+				},
+			},
+		},
+		"UnsplittableProps": {
+			Post: &model.Post{
+				Message: "foo",
+				Props: map[string]interface{}{
+					"foo": strings.Repeat("x", model.POST_PROPS_MAX_USER_RUNES*2),
+				},
+			},
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			splits, err := SplitWebhookPost(tc.Post)
+			if tc.Expected == nil {
+				require.NotNil(t, err)
+			} else {
+				require.Nil(t, err)
+			}
+			assert.Equal(t, len(tc.Expected), len(splits))
+			for i, split := range splits {
+				if i < len(tc.Expected) {
+					assert.Equal(t, tc.Expected[i].Message, split.Message)
+					assert.Equal(t, tc.Expected[i].Props["attachments"], split.Props["attachments"])
+				}
+			}
+		})
+	}
+}