added email notification text content support

.gitignore

@@ -6,6 +6,7 @@
 /.build
 /.release
 /.tarballs
+/.idea
 
 !/doc/examples/simple.yml
 !/circle.yml

config/notifiers.go

@@ -33,6 +33,7 @@ var (
 			VSendResolved: false,
 		},
 		HTML: `{{ template "email.default.html" . }}`,
+		TEXT: ``,
 	}
 
 	// DefaultEmailSubject defines the default Subject header of an Email.
@@ -142,6 +143,7 @@ type EmailConfig struct {
 	AuthIdentity string            `yaml:"auth_identity,omitempty" json:"auth_identity,omitempty"`
 	Headers      map[string]string `yaml:"headers,omitempty" json:"headers,omitempty"`
 	HTML         string            `yaml:"html,omitempty" json:"html,omitempty"`
+	TEXT         string            `yaml:"text,omitempty" json:"text,omitempty"`
 	RequireTLS   *bool             `yaml:"require_tls,omitempty" json:"require_tls,omitempty"`
 
 	// Catches all undefined fields and must be empty after parsing.

notify/impl.go

@@ -365,14 +365,18 @@ func (n *Email) Notify(ctx context.Context, as ...*types.Alert) (bool, error) {
 		fmt.Fprintf(wc, "%s: %s\r\n", header, mime.QEncoding.Encode("utf-8", value))
 	}
 
-	fmt.Fprintf(wc, "Content-Type: text/html; charset=UTF-8\r\n")
 	fmt.Fprintf(wc, "Date: %s\r\n", time.Now().Format(time.RFC1123Z))
+	boundary := "=_NextPart_57bb889e057d551696ff582664f96f502da361c88cdc32a9e603f0af4b1c2b17" // SHA-256 of random string
+	fmt.Fprintf(wc, "Content-Type: multipart/alternative;  boundary=\"%s\"\r\n", boundary)
+
 
 	// TODO: Add some useful headers here, such as URL of the alertmanager
 	// and active/resolved.
 	fmt.Fprintf(wc, "\r\n")
 
-	// TODO(fabxc): do a multipart write that considers the plain template.
+	// Html template
+	fmt.Fprintf(wc, "--%s\r\n", boundary)
+	fmt.Fprintf(wc, "Content-Type: text/html; charset=UTF-8\r\n")
 	body, err := n.tmpl.ExecuteHTMLString(n.conf.HTML, data)
 	if err != nil {
 		return false, fmt.Errorf("executing email html template: %s", err)
@@ -382,6 +386,23 @@ func (n *Email) Notify(ctx context.Context, as ...*types.Alert) (bool, error) {
 		return true, err
 	}
 
+	// Text template
+	// Last alternative based on recommendation in section 7.2.3
+	// https://www.w3.org/Protocols/rfc1341/7_2_Multipart.html
+	fmt.Fprintf(wc, "--%s\r\n", boundary)
+	fmt.Fprintf(wc, "Content-Type: text/plain; charset=UTF-8\r\n\r\n")
+	body, err = n.tmpl.ExecuteTextString(n.conf.TEXT, data)
+	if err != nil {
+		return false, fmt.Errorf("executing email text template: %s", err)
+	}
+	_, err = io.WriteString(wc, body)
+	if err != nil {
+		return true, err
+	}
+
+	// closing multi-part content
+	fmt.Fprintf(wc, "--%s--\r\n", boundary)
+
 	return false, nil
 }