Add Slack additional "fields" to notifications (#1135)

* impl slack fields

* wrap title and value in tmplText

config/notifiers.go

@@ -238,6 +238,8 @@ type SlackConfig struct {
 	TitleLink   string              `yaml:"title_link,omitempty" json:"title_link,omitempty"`
 	Pretext     string              `yaml:"pretext,omitempty" json:"pretext,omitempty"`
 	Text        string              `yaml:"text,omitempty" json:"text,omitempty"`
+	Fields      []map[string]string `yaml:"fields,omitempty" json:"fields,omitempty"`
+	ShortFields bool                `yaml:"short_fields,omitempty" json:"short_fields,omitempty"`
 	Footer      string              `yaml:"footer,omitempty" json:"footer,omitempty"`
 	Fallback    string              `yaml:"fallback,omitempty" json:"fallback,omitempty"`
 	IconEmoji   string              `yaml:"icon_emoji,omitempty" json:"icon_emoji,omitempty"`

notify/impl.go

@@ -631,6 +631,7 @@ type slackAttachment struct {
 	Pretext   string                 `json:"pretext,omitempty"`
 	Text      string                 `json:"text"`
 	Fallback  string                 `json:"fallback"`
+	Fields    []slackAttachmentField `json:"fields"`
 	Footer    string                 `json:"footer"`
 
 	Color    string   `json:"color,omitempty"`
@@ -662,6 +663,20 @@ func (n *Slack) Notify(ctx context.Context, as ...*types.Alert) (bool, error) {
 		Color:     tmplText(n.conf.Color),
 		MrkdwnIn:  []string{"fallback", "pretext", "text"},
 	}
+
+	var numFields = len(n.conf.Fields)
+	if numFields > 0 {
+		var fields = make([]slackAttachmentField, numFields)
+		for k, v := range n.conf.Fields {
+			fields[k] = slackAttachmentField{
+				tmplText(v["title"]),
+				tmplText(v["value"]),
+				n.conf.ShortFields,
+			}
+		}
+		attachment.Fields = fields
+	}
+
 	req := &slackReq{
 		Channel:     tmplText(n.conf.Channel),
 		Username:    tmplText(n.conf.Username),