feat: implement webhook_url_file for discord

implements prometheus#3482

Signed-off-by: Philipp Born <git@pborn.eu>

config/notifiers.go

@@ -216,8 +216,9 @@ func (c *WebexConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 type DiscordConfig struct {
 	NotifierConfig `yaml:",inline" json:",inline"`
 
-	HTTPConfig *commoncfg.HTTPClientConfig `yaml:"http_config,omitempty" json:"http_config,omitempty"`
-	WebhookURL *SecretURL                  `yaml:"webhook_url,omitempty" json:"webhook_url,omitempty"`
+	HTTPConfig     *commoncfg.HTTPClientConfig `yaml:"http_config,omitempty" json:"http_config,omitempty"`
+	WebhookURL     *SecretURL                  `yaml:"webhook_url,omitempty" json:"webhook_url,omitempty"`
+	WebhookURLFile string                      `yaml:"webhook_url_file,omitempty" json:"webhook_url_file,omitempty"`
 
 	Title   string `yaml:"title,omitempty" json:"title,omitempty"`
 	Message string `yaml:"message,omitempty" json:"message,omitempty"`
@@ -227,7 +228,15 @@ type DiscordConfig struct {
 func (c *DiscordConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	*c = DefaultDiscordConfig
 	type plain DiscordConfig
-	return unmarshal((*plain)(c))
+	if err := unmarshal((*plain)(c)); err != nil {
+		return err
+	}
+
+	if c.WebhookURL != nil && len(c.WebhookURLFile) > 0 {
+		return fmt.Errorf("at most one of webhook_url & webhook_url_file must be configured")
+	}
+
+	return nil
 }
 
 // EmailConfig configures notifications via mail.

docs/configuration.md

@@ -666,7 +666,9 @@ Discord notifications are sent via the [Discord webhook API](https://discord.com
 [ send_resolved: <boolean> | default = true ]
 
 # The Discord webhook URL.
+# webhook_url and webhook_url_file are mutually exclusive.
 webhook_url: <secret>
+webhook_url_file: <filepath>
 
 # Message title template.
 [ title: <tmpl_string> | default = '{{ template "discord.default.title" . }}' ]

notify/discord/discord.go

@@ -17,7 +17,10 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/http"
+	"os"
+	"strings"
 
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
@@ -107,6 +110,17 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 		color = colorGreen
 	}
 
+	var url string
+	if n.conf.WebhookURL != nil {
+		url = n.conf.WebhookURL.String()
+	} else {
+		content, err := os.ReadFile(n.conf.WebhookURLFile)
+		if err != nil {
+			return false, fmt.Errorf("read webhook_url_file: %w", err)
+		}
+		url = strings.TrimSpace(string(content))
+	}
+
 	w := webhook{
 		Embeds: []webhookEmbed{{
 			Title:       title,
@@ -120,7 +134,7 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 		return false, err
 	}
 
-	resp, err := notify.PostJSON(ctx, n.client, n.webhookURL.String(), &payload)
+	resp, err := notify.PostJSON(ctx, n.client, url, &payload)
 	if err != nil {
 		return true, notify.RedactURL(err)
 	}

notify/discord/discord_test.go

@@ -20,6 +20,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"os"
 	"testing"
 	"time"
 
@@ -127,3 +128,43 @@ func TestDiscordTemplating(t *testing.T) {
 		})
 	}
 }
+
+func TestDiscordRedactedURL(t *testing.T) {
+	ctx, u, fn := test.GetContextWithCancelingURL()
+	defer fn()
+
+	secret := "secret"
+	notifier, err := New(
+		&config.DiscordConfig{
+			WebhookURL: &config.SecretURL{URL: u},
+			HTTPConfig: &commoncfg.HTTPClientConfig{},
+		},
+		test.CreateTmpl(t),
+		log.NewNopLogger(),
+	)
+	require.NoError(t, err)
+
+	test.AssertNotifyLeaksNoSecret(ctx, t, notifier, secret)
+}
+
+func TestDiscordReadingURLFromFile(t *testing.T) {
+	ctx, u, fn := test.GetContextWithCancelingURL()
+	defer fn()
+
+	f, err := os.CreateTemp("", "webhook_url")
+	require.NoError(t, err, "creating temp file failed")
+	_, err = f.WriteString(u.String() + "\n")
+	require.NoError(t, err, "writing to temp file failed")
+
+	notifier, err := New(
+		&config.DiscordConfig{
+			WebhookURLFile: f.Name(),
+			HTTPConfig:     &commoncfg.HTTPClientConfig{},
+		},
+		test.CreateTmpl(t),
+		log.NewNopLogger(),
+	)
+	require.NoError(t, err)
+
+	test.AssertNotifyLeaksNoSecret(ctx, t, notifier, u.String())
+}