Implement SMTP handler

```
$ kubewatch  config  add smtp
CLI setters not implemented yet, please edit ~/.kubewatch.yaml directly. Example:

handler:
  smtp:
    to: "[email protected]"
    from: "[email protected]"
    smarthost: smtp.mycompany.com:2525
    subject: Test notification
    auth:
      username: myusername
      password: mypassword
    requireTLS: true
```

Author: Marko Mikulicic

README.md

@@ -13,8 +13,8 @@ $ kubewatch -h
 
 Kubewatch: A watcher for Kubernetes
 
-kubewatch is a Kubernetes watcher that publishes notifications 
-to Slack/hipchat/mattermost/flock channels. It watches the cluster 
+kubewatch is a Kubernetes watcher that publishes notifications
+to Slack/hipchat/mattermost/flock channels. It watches the cluster
 for resource changes and notifies them through webhooks.
 
 supported webhooks:
@@ -23,6 +23,7 @@ supported webhooks:
  - mattermost
  - flock
  - webhook
+ - smtp
 
 Usage:
   kubewatch [flags]

cmd/config.go

@@ -22,9 +22,9 @@ import (
 	"os"
 	"path/filepath"
 
-	"github.com/sirupsen/logrus"
 	"github.com/bitnami-labs/kubewatch/config"
 	"github.com/bitnami-labs/kubewatch/pkg/client"
+	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
 )
 
@@ -98,5 +98,6 @@ func init() {
 		flockConfigCmd,
 		webhookConfigCmd,
 		msteamsConfigCmd,
+		smtpConfigCmd,
 	)
 }

cmd/smtp.go

@@ -0,0 +1,38 @@
+/*
+Copyright 2020 VMware
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/bitnami-labs/kubewatch/pkg/handlers/smtp"
+	"github.com/spf13/cobra"
+)
+
+// smtpConfigCmd represents the smtp subcommand
+var smtpConfigCmd = &cobra.Command{
+	Use:   "smtp",
+	Short: "specific smtp configuration",
+	Long:  `specific smtp configuration`,
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Fprintf(os.Stderr, "CLI setters not implemented yet, please edit ~/.kubewatch.yaml directly. Example:\n\n%s", smtp.ConfigExample)
+	},
+}
+
+func init() {
+}

config/config.go

@@ -36,6 +36,7 @@ type Handler struct {
 	Flock      Flock      `json:"flock"`
 	Webhook    Webhook    `json:"webhook"`
 	MSTeams    MSTeams    `json:"msteams"`
+	SMTP       SMTP       `json:"smtp"`
 }
 
 // Resource contains resource configuration
@@ -100,6 +101,25 @@ type MSTeams struct {
 	WebhookURL string `json:"webhookurl"`
 }
 
+// SMTP contains SMTP configuration.
+type SMTP struct {
+	To         string            `json:"to" yaml:"to,omitempty"`
+	From       string            `json:"from" yaml:"from,omitempty"`
+	Hello      string            `json:"hello" yaml:"hello,omitempty"`
+	Smarthost  string            `json:"smarthost" yaml:"smarthost,omitempty"`
+	Subject    string            `json:"subject" yaml:"subject,omitempty"`
+	Headers    map[string]string `json:"headers" yaml:"headers,omitempty"`
+	Auth       SMTPAuth          `json:"auth" yaml:"auth,omitempty"`
+	RequireTLS bool              `json:"requireTLS" yaml:"requireTLS"`
+}
+
+type SMTPAuth struct {
+	Username string `json:"username" yaml:"username,omitempty"`
+	Password string `json:"password" yaml:"password,omitempty"`
+	Secret   string `json:"secret" yaml:"secret,omitempty"`
+	Identity string `json:"identity" yaml:"identity,omitempty"`
+}
+
 // New creates new config object
 func New() (*Config, error) {
 	c := &Config{}

docs/design.md

@@ -27,6 +27,7 @@ With each event get from k8s and matched filtering from configuration, it is pas
  - `Hipchat`: which send notification to Hipchat room based on information from config
  - `Mattermost`: which send notification to Mattermost channel based on information from config
  - `Flock`: which send notification to Flock channel based on information from config
+ - 'Smtp': which sends notifications to email recipients using a SMTP server obtained from config
 
 More handlers will be added in future.
 

go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/inconshreveable/mousetrap v1.0.0 // indirect
 	github.com/magiconair/properties v1.7.4 // indirect
 	github.com/mitchellh/mapstructure v0.0.0-20180111000720-b4575eea38cc // indirect
+	github.com/mkmik/multierror v0.3.0
 	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
 	github.com/pelletier/go-toml v1.0.1 // indirect
 	github.com/sirupsen/logrus v1.6.0

go.sum

@@ -91,6 +91,7 @@ github.com/magiconair/properties v1.7.4/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czP
 github.com/mailru/easyjson v0.0.0-20160728113105-d5b7844b561a/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=
 github.com/mitchellh/mapstructure v0.0.0-20180111000720-b4575eea38cc h1:5T6hzGUO5OrL6MdYXYoLQtRWJDDgjdlOVBn9mIqGY1g=
 github.com/mitchellh/mapstructure v0.0.0-20180111000720-b4575eea38cc/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
+github.com/mkmik/multierror v0.3.0/go.mod h1:wjBYXRpDhh+8mIp+iLBOq0kZ3Y4ICTncojwvP8LUYLQ=
 github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
 github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
 github.com/modern-go/reflect2 v0.0.0-20180320133207-05fbef0ca5da/go.mod h1:bx2lNnkwVCuqBIxFjflWJWanXIb3RllmbCylyMrvgv0=

pkg/client/run.go

@@ -27,6 +27,7 @@ import (
 	"github.com/bitnami-labs/kubewatch/pkg/handlers/mattermost"
 	"github.com/bitnami-labs/kubewatch/pkg/handlers/msteam"
 	"github.com/bitnami-labs/kubewatch/pkg/handlers/slack"
+	"github.com/bitnami-labs/kubewatch/pkg/handlers/smtp"
 	"github.com/bitnami-labs/kubewatch/pkg/handlers/webhook"
 )
 
@@ -54,6 +55,8 @@ func ParseEventHandler(conf *config.Config) handlers.Handler {
 		eventHandler = new(webhook.Webhook)
 	case len(conf.Handler.MSTeams.WebhookURL) > 0:
 		eventHandler = new(msteam.MSTeams)
+	case len(conf.Handler.SMTP.Smarthost) > 0 || len(conf.Handler.SMTP.To) > 0:
+		eventHandler = new(smtp.SMTP)
 	default:
 		eventHandler = new(handlers.Default)
 	}

pkg/handlers/handler.go

@@ -23,6 +23,7 @@ import (
 	"github.com/bitnami-labs/kubewatch/pkg/handlers/mattermost"
 	"github.com/bitnami-labs/kubewatch/pkg/handlers/msteam"
 	"github.com/bitnami-labs/kubewatch/pkg/handlers/slack"
+	"github.com/bitnami-labs/kubewatch/pkg/handlers/smtp"
 	"github.com/bitnami-labs/kubewatch/pkg/handlers/webhook"
 )
 
@@ -45,6 +46,7 @@ var Map = map[string]interface{}{
 	"flock":      &flock.Flock{},
 	"webhook":    &webhook.Webhook{},
 	"ms-teams":   &msteam.MSTeams{},
+	"smtp":       &smtp.SMTP{},
 }
 
 // Default handler implements Handler interface,