fix(slack): limit attachments to 100 (#241)

also removes last attachment if text is empty

Author: piksel

pkg/services/slack/slack_json.go

@@ -73,13 +73,24 @@ type APIResponse struct {
 func CreateJSONPayload(config *Config, message string) interface{} {
 
 	var atts []attachment
-	for _, line := range strings.Split(message, "\n") {
+	for i, line := range strings.Split(message, "\n") {
+		// When 100 attachments have been reached, append the remaining line to the last
+		// attachment to prevent reaching the slack API limit
+		if i >= 100 {
+			atts[len(atts)-1].Text += "\n" + line
+			continue
+		}
 		atts = append(atts, attachment{
 			Text:  line,
 			Color: config.Color,
 		})
 	}
 
+	// Remove last attachment if empty
+	if atts[len(atts)-1].Text == "" {
+		atts = atts[:len(atts)-1]
+	}
+
 	payload := MessagePayload{
 		ThreadTS:    config.ThreadTS,
 		Text:        config.Title,

pkg/services/slack/slack_test.go

@@ -2,7 +2,9 @@ package slack_test
 
 import (
 	"errors"
+	"fmt"
 	"log"
+	"strings"
 
 	"github.com/containrrr/shoutrrr/internal/testutils"
 	. "github.com/containrrr/shoutrrr/pkg/services/slack"
@@ -163,7 +165,29 @@ var _ = Describe("the slack service", func() {
 				Expect(payload.IconURL).To(BeEmpty())
 			})
 		})
-
+		When("when more than 99 lines are being sent", func() {
+			It("should append the exceeding lines to the last attachment", func() {
+				config := Config{}
+				sb := strings.Builder{}
+				for i := 1; i <= 110; i++ {
+					sb.WriteString(fmt.Sprintf("Line %d\n", i))
+				}
+				payload := CreateJSONPayload(&config, sb.String()).(MessagePayload)
+				atts := payload.Attachments
+
+				fmt.Printf("\nLines: %d, Last: %#v\n", len(atts), atts[len(atts)-1])
+
+				Expect(atts).To(HaveLen(100))
+				Expect(atts[len(atts)-1].Text).To(ContainSubstring("Line 110"))
+			})
+		})
+		When("when the last message line ends with a newline", func() {
+			It("should not send an empty attachment", func() {
+				payload := CreateJSONPayload(&Config{}, "One\nTwo\nThree\n").(MessagePayload)
+				atts := payload.Attachments
+				Expect(atts[len(atts)-1].Text).NotTo(BeEmpty())
+			})
+		})
 	})
 
 	Describe("sending the payload", func() {