MM-13826 Webhooks: Allow "true"/"false" for bool values in payload body (#10114)

* Webhooks: Allow "true"/"false" for bool values in payload body

Some slack integrations encode bool fields as "true"/"false", which
was previously unsupported in mattermost due to how encoding/json works.
This commit adds an aliased type for bool that implements json.Unmarshaler
to maintain compatibility with Slack.

* Add missing copyright header to added files

model/slack_attachment.go

@@ -31,9 +31,9 @@ type SlackAttachment struct {
 }
 
 type SlackAttachmentField struct {
-	Title string      `json:"title"`
-	Value interface{} `json:"value"`
-	Short bool        `json:"short"`
+	Title string              `json:"title"`
+	Value interface{}         `json:"value"`
+	Short SlackCompatibleBool `json:"short"`
 }
 
 func StringifySlackFieldValue(a []*SlackAttachment) []*SlackAttachment {

model/slack_compatibility.go

@@ -0,0 +1,30 @@
+// Copyright (c) 2019-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+import (
+	"fmt"
+	"strings"
+)
+
+// SlackCompatibleBool is an alias for bool that implements json.Unmarshaler
+type SlackCompatibleBool bool
+
+// UnmarshalJSON implements json.Unmarshaler
+//
+// Slack allows bool values to be represented as strings ("true"/"false") or
+// literals (true/false). To maintain compatibility, we define an Unmarshaler
+// that supports both.
+func (b *SlackCompatibleBool) UnmarshalJSON(data []byte) error {
+	value := strings.ToLower(string(data))
+	if value == "true" || value == `"true"` {
+		*b = true
+	} else if value == "false" || value == `"false"` {
+		*b = false
+	} else {
+		return fmt.Errorf("unmarshal: unable to convert %s to bool", data)
+	}
+
+	return nil
+}

model/slack_compatibility_test.go

@@ -0,0 +1,57 @@
+// Copyright (c) 2019-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSlackCompatibleBool_UnmarshalJSON_True(t *testing.T) {
+	cases := []struct {
+		name    string
+		payload string
+	}{
+		{name: "literal", payload: `{"title": "Foo", "value": "Bar", "short": true}`},
+		{name: "stringLower", payload: `{"title": "Foo", "value": "Bar", "short": "true"}`},
+		{name: "stringMixed", payload: `{"title": "Foo", "value": "Bar", "short": "True"}`},
+		{name: "stringUpper", payload: `{"title": "Foo", "value": "Bar", "short": "TRUE"}`},
+	}
+
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			field := &SlackAttachmentField{}
+
+			err := json.Unmarshal([]byte(tt.payload), field)
+
+			require.NoError(t, err)
+			require.True(t, bool(field.Short))
+		})
+	}
+}
+
+func TestSlackCompatibleBool_UnmarshalJSON_False(t *testing.T) {
+	cases := []struct {
+		name    string
+		payload string
+	}{
+		{name: "literal", payload: `{"title": "Foo", "value": "Bar", "short": false}`},
+		{name: "stringLower", payload: `{"title": "Foo", "value": "Bar", "short": "false"}`},
+		{name: "stringMixed", payload: `{"title": "Foo", "value": "Bar", "short": "False"}`},
+		{name: "stringUpper", payload: `{"title": "Foo", "value": "Bar", "short": "FALSE"}`},
+	}
+
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			field := &SlackAttachmentField{}
+
+			err := json.Unmarshal([]byte(tt.payload), field)
+
+			require.NoError(t, err)
+			require.False(t, bool(field.Short))
+		})
+	}
+}