PLT-7599: webhook post splitting (#7707)

* webhook post splitting

* style fix

* update old webhook test

5 files changed, 187 insertions, 36 deletions

diff --git a/api/webhook_test.go b/api/webhook_test.go
index 285650b5c..68dc4f4e7 100644
--- a/api/webhook_test.go
+++ b/api/webhook_test.go
@@ -1065,8 +1065,8 @@ func TestIncomingWebhooks(t *testing.T) {
 	       ]
 	   }`
 
-	if _, err := Client.DoPost(url, attachmentPayload, "application/json"); err == nil || err.StatusCode != http.StatusBadRequest {
-		t.Fatal("should have failed with bad request - attachment too long")
+	if _, err := Client.DoPost(url, attachmentPayload, "application/json"); err != nil {
+		t.Fatal(err)
 	}
 
 	th.App.UpdateConfig(func(cfg *model.Config) { cfg.ServiceSettings.EnableIncomingWebhooks = false })
diff --git a/app/webhook.go b/app/webhook.go
index e8f9936f8..56f1f0875 100644
--- a/app/webhook.go
+++ b/app/webhook.go
@@ -123,6 +123,86 @@ func (a *App) TriggerWebhook(payload *model.OutgoingWebhookPayload, hook *model.
 	}
 }
 
+func SplitWebhookPost(post *model.Post) ([]*model.Post, *model.AppError) {
+	splits := make([]*model.Post, 0)
+	remainingText := post.Message
+
+	base := *post
+	base.Message = ""
+	base.Props = make(map[string]interface{})
+	for k, v := range post.Props {
+		if k != "attachments" {
+			base.Props[k] = v
+		}
+	}
+	if utf8.RuneCountInString(model.StringInterfaceToJson(base.Props)) > model.POST_PROPS_MAX_USER_RUNES {
+		return nil, model.NewAppError("SplitWebhookPost", "web.incoming_webhook.split_props_length.app_error", map[string]interface{}{"Max": model.POST_PROPS_MAX_USER_RUNES}, "", http.StatusBadRequest)
+	}
+
+	for utf8.RuneCountInString(remainingText) > model.POST_MESSAGE_MAX_RUNES {
+		split := base
+		x := 0
+		for index := range remainingText {
+			x++
+			if x > model.POST_MESSAGE_MAX_RUNES {
+				split.Message = remainingText[:index]
+				remainingText = remainingText[index:]
+				break
+			}
+		}
+		splits = append(splits, &split)
+	}
+
+	split := base
+	split.Message = remainingText
+	splits = append(splits, &split)
+
+	attachments, _ := post.Props["attachments"].([]*model.SlackAttachment)
+	for _, attachment := range attachments {
+		newAttachment := *attachment
+		for {
+			lastSplit := splits[len(splits)-1]
+			newProps := make(map[string]interface{})
+			for k, v := range lastSplit.Props {
+				newProps[k] = v
+			}
+			origAttachments, _ := newProps["attachments"].([]*model.SlackAttachment)
+			newProps["attachments"] = append(origAttachments, &newAttachment)
+			newPropsString := model.StringInterfaceToJson(newProps)
+			runeCount := utf8.RuneCountInString(newPropsString)
+
+			if runeCount <= model.POST_PROPS_MAX_USER_RUNES {
+				lastSplit.Props = newProps
+				break
+			}
+
+			if len(origAttachments) > 0 {
+				newSplit := base
+				splits = append(splits, &newSplit)
+				continue
+			}
+
+			truncationNeeded := runeCount - model.POST_PROPS_MAX_USER_RUNES
+			textRuneCount := utf8.RuneCountInString(attachment.Text)
+			if textRuneCount < truncationNeeded {
+				return nil, model.NewAppError("SplitWebhookPost", "web.incoming_webhook.split_props_length.app_error", map[string]interface{}{"Max": model.POST_PROPS_MAX_USER_RUNES}, "", http.StatusBadRequest)
+			}
+			x := 0
+			for index := range attachment.Text {
+				x++
+				if x > textRuneCount-truncationNeeded {
+					newAttachment.Text = newAttachment.Text[:index]
+					break
+				}
+			}
+			lastSplit.Props = newProps
+			break
+		}
+	}
+
+	return splits, nil
+}
+
 func (a *App) CreateWebhookPost(userId string, channel *model.Channel, text, overrideUsername, overrideIconUrl string, props model.StringInterface, postType string) (*model.Post, *model.AppError) {
 	// parse links into Markdown format
 	linkWithTextRegex := regexp.MustCompile(`<([^<\|]+)\|([^>]+)>`)
@@ -166,37 +246,18 @@ func (a *App) CreateWebhookPost(userId string, channel *model.Channel, text, ove
 		}
 	}
 
-	splits := make([]string, 0)
-	remainingText := post.Message
-
-	for len(remainingText) > model.POST_MESSAGE_MAX_RUNES {
-		splits = append(splits, remainingText[:model.POST_MESSAGE_MAX_RUNES])
-		remainingText = remainingText[model.POST_MESSAGE_MAX_RUNES:]
+	splits, err := SplitWebhookPost(post)
+	if err != nil {
+		return nil, err
 	}
 
-	splits = append(splits, remainingText)
-
-	var firstPost *model.Post = nil
-
-	for _, txt := range splits {
-		post.Id = ""
-		post.UpdateAt = 0
-		post.CreateAt = 0
-		post.Message = txt
-		if _, err := a.CreatePostMissingChannel(post, false); err != nil {
+	for _, split := range splits {
+		if _, err := a.CreatePostMissingChannel(split, false); err != nil {
 			return nil, model.NewAppError("CreateWebhookPost", "api.post.create_webhook_post.creating.app_error", nil, "err="+err.Message, http.StatusInternalServerError)
 		}
-
-		if firstPost == nil {
-			if len(splits) > 1 {
-				firstPost = model.PostFromJson(strings.NewReader(post.ToJson()))
-			} else {
-				firstPost = post
-			}
-		}
 	}
 
-	return firstPost, nil
+	return splits[0], nil
 }
 
 func (a *App) CreateIncomingWebhookForChannel(creatorId string, channel *model.Channel, hook *model.IncomingWebhook) (*model.IncomingWebhook, *model.AppError) {
@@ -482,13 +543,6 @@ func (a *App) HandleIncomingWebhook(hookId string, req *model.IncomingWebhookReq
 			req.Props = make(model.StringInterface)
 		}
 		req.Props["attachments"] = req.Attachments
-
-		attachmentSize := utf8.RuneCountInString(model.StringInterfaceToJson(req.Props))
-		// Minus 100 to leave room for setting post type in the Props
-		if attachmentSize > model.POST_PROPS_MAX_RUNES-100 {
-			return model.NewAppError("HandleIncomingWebhook", "web.incoming_webhook.attachment.app_error", map[string]interface{}{"Max": model.POST_PROPS_MAX_RUNES - 100, "Actual": attachmentSize}, "", http.StatusBadRequest)
-		}
-
 		webhookType = model.POST_SLACK_ATTACHMENT
 	}
 
diff --git a/app/webhook_test.go b/app/webhook_test.go
index d6293e2b7..8dc90b49b 100644
--- a/app/webhook_test.go
+++ b/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"])
+				}
+			}
+		})
+	}
+}
diff --git a/i18n/en.json b/i18n/en.json
index 7a8c8f4c1..e20edf2f2 100644
--- a/i18n/en.json
+++ b/i18n/en.json
@@ -6860,8 +6860,8 @@
     "translation": "Back"
   },
   {
-    "id": "web.incoming_webhook.attachment.app_error",
-    "translation": "Maximum attachments length is {{.Max}} characters, received size is {{.Actual}}"
+    "id": "web.incoming_webhook.split_props_length.app_error",
+    "translation": "Unable to split webhook props into {{.Max}} character parts."
   },
   {
     "id": "web.incoming_webhook.channel.app_error",
diff --git a/model/post.go b/model/post.go
index a5ae0b82a..a7be63432 100644
--- a/model/post.go
+++ b/model/post.go
@@ -32,6 +32,7 @@ const (
 	POST_HASHTAGS_MAX_RUNES    = 1000
 	POST_MESSAGE_MAX_RUNES     = 4000
 	POST_PROPS_MAX_RUNES       = 8000
+	POST_PROPS_MAX_USER_RUNES  = POST_PROPS_MAX_RUNES - 400 // Leave some room for system / pre-save modifications
 	POST_CUSTOM_TYPE_PREFIX    = "custom_"
 	PROPS_ADD_CHANNEL_MEMBER   = "add_channel_member"
 )