Alerts to Slack and ntfy, each destination with its own queue (closes #90)

Each alert is posted as a message to the Slack incoming webhook
SWWAF_ALERT_SLACK_WEBHOOK_URL names, and published to the ntfy topic
SWWAF_ALERT_NTFY_URL names, with SWWAF_ALERT_NTFY_TOKEN as a bearer
token and a priority and tag by event. The cooldown and the hourly
limit stay shared; past them, each destination has its own bounded
queue and backoff, and its own sent, failed and dropped counts.
alerts.json keeps the alerts waiting by destination; one whose waiting
is still a list stops the start, saying what to change. A control
character in the ntfy token, or in the instance name ntfy is sent,
stops the start.

Judgement call: messages also give the detail's file, source, error and mode.
Judgement call: alerts_suppressed_total is the same for every destination.

Model: opus-5-5

README.md

@@ -361,7 +361,10 @@ effective settings are logged at start.
   to all can read it.
 - `SWWAF_ALERT_NTFY_TOKEN` (default unset): an ntfy access token, sent to ntfy
   with each alert as `Authorization: Bearer <token>`, for a topic that needs
-  one. The settings logged at start show `********` in its place.
+  one. The settings logged at start show `********` in its place. A control
+  character in it, such as the carriage return of a file saved with Windows line
+  ends, stops the start, and while `SWWAF_ALERT_NTFY_URL` is set, so does one in
+  `SWWAF_INSTANCE_NAME`, which ntfy is sent in the title.
 - `SWWAF_ALERT_EVENTS` (default
   `ban,permanent_ban,waf_block,anomaly,reputation_hit,source_failure,file_error`):
   the events alerts are sent for. `waf_block`, `anomaly` and `reputation_hit`
@@ -731,7 +734,9 @@ entries by client address, but for the alerts waiting, with times in UTC.
   `webhook`, `slack` or `ntfy`, the alerts still waiting to be sent to it, the
   oldest first, each as the webhook is sent it. As an hour ends, the cooldowns
   that have run out with no repeat held back are dropped. As the file is read,
-  the alerts waiting for a destination you no longer name are dropped.
+  the alerts waiting for a destination you no longer name are dropped. A file
+  whose `waiting` is a list, as it was before alerts went to Slack and ntfy too,
+  stops the start: put the list under `"webhook"`, or remove the file.
 
 `bans.json` is written `SWWAF_STATE_WRITE_DELAY` after a ban is made, lifted
 through `DELETE /_smallwebwaf/bans/<client>`, or made permanent, with every such

internal/alerts/alerts_test.go

@@ -172,6 +172,27 @@ func TestWouldSendNothingWithoutADestination(t *testing.T) {
 	}
 }
 
+func TestWouldSendWithOnlySlackOrOnlyNtfySet(t *testing.T) {
+	t.Parallel()
+
+	onlySlack := newParams()
+	onlySlack.WebhookURL = nil
+	onlySlack.SlackURL = parseURL(slackURL)
+
+	onlyNtfy := newParams()
+	onlyNtfy.WebhookURL = nil
+	onlyNtfy.NtfyURL = parseURL(ntfyURL)
+
+	for setting, params := range map[string]alerts.Params{
+		"SWWAF_ALERT_SLACK_WEBHOOK_URL": onlySlack,
+		"SWWAF_ALERT_NTFY_URL":          onlyNtfy,
+	} {
+		if !alerts.New(params).WouldSend(alerts.EventBan, netblock(1)) {
+			t.Errorf("a ban alert would not be sent with only %s set", setting)
+		}
+	}
+}
+
 func TestRepeatWithinTheCooldownIsHeldBackAndCountedInTheNext(t *testing.T) {
 	t.Parallel()
 

internal/config/config.go

@@ -20,6 +20,7 @@ import (
 	"strconv"
 	"strings"
 	"time"
+	"unicode"
 	"unicode/utf8"
 
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
@@ -260,6 +261,8 @@ var (
 	errNotWebhookHeader = errors.New(
 		"is not a header name followed by : and the header's value, " +
 			"such as Authorization:Bearer <token>")
+	errControlCharacter = errors.New(
+		"holds a control character, such as the carriage return of a Windows line end")
 	errNotAlertEvent = errors.New(
 		"is not ban, permanent_ban, waf_block, anomaly, reputation_hit, " +
 			"source_failure or file_error")
@@ -334,6 +337,8 @@ func FromEnvironment(lookupEnv func(string) (string, bool)) (*Config, error) {
 	cfg.LogRemoteAppName = env.appName("SWWAF_LOG_REMOTE_APP_NAME",
 		cfg.InstanceName, cfg.LogRemoteURL != nil)
 
+	env.checkInstanceNameForNtfy(cfg.InstanceName, cfg.AlertNtfyURL != nil)
+
 	for _, country := range cfg.ExclusivelyAllowedCountries {
 		if slices.Contains(cfg.DeniedCountries, country) {
 			env.check("SWWAF_EXCLUSIVELY_ALLOWED_COUNTRIES",
@@ -678,6 +683,17 @@ func (e *environment) appName(name, instanceName string, sending bool) string {
 	return value
 }
 
+// checkInstanceNameForNtfy refuses an instance name that holds a control
+// character while ntfySet, SWWAF_ALERT_NTFY_URL being set: ntfy is sent
+// the instance name in a header, which cannot hold one.
+func (e *environment) checkInstanceNameForNtfy(instanceName string, ntfySet bool) {
+	if ntfySet && strings.ContainsFunc(instanceName, unicode.IsControl) {
+		e.check("SWWAF_INSTANCE_NAME", fmt.Errorf(
+			"%q %w, and is sent to ntfy in a header while SWWAF_ALERT_NTFY_URL is set",
+			instanceName, errControlCharacter))
+	}
+}
+
 // webhookURL reads a setting that is a URL each alert is posted to:
 // SWWAF_ALERT_WEBHOOK_URL, SWWAF_ALERT_SLACK_WEBHOOK_URL or
 // SWWAF_ALERT_NTFY_URL. Unset or empty, it is nil, and no alert is posted
@@ -706,8 +722,10 @@ func (e *environment) webhookHeaders(name string) http.Header {
 }
 
 // secret reads a setting that is a secret another service gave, such as
-// an ntfy token, "" while it is unset. The log shows ******** in place of
-// a value that is not empty.
+// an ntfy token, "" while it is unset. It is sent in a header, which
+// cannot hold a control character, so one in it is an error. The log
+// shows ******** in place of a value that is not empty, and an error
+// shows none of it.
 func (e *environment) secret(name string) string {
 	value, _ := e.lookup(name)
 
@@ -718,6 +736,10 @@ func (e *environment) secret(name string) string {
 
 	e.settings = append(e.settings, slog.String(name, logged))
 
+	if strings.ContainsFunc(value, unicode.IsControl) {
+		e.check(name, errControlCharacter)
+	}
+
 	return value
 }
 

internal/config/config_test.go

@@ -697,6 +697,46 @@ func TestSlackAndNtfySettingsAreLoggedWithoutTheirSecrets(t *testing.T) {
 	}
 }
 
+func TestNtfyTokenWithAControlCharacterStopsTheStartWithoutShowingIt(t *testing.T) {
+	t.Parallel()
+
+	// A file saved with Windows line ends keeps the carriage return.
+	for name, env := range map[string]environment{
+		"set":       {alertNtfyToken: token + "\r"},
+		"in a file": {alertNtfyToken + "_FILE": writeFile(t, token+"\r\n")},
+	} {
+		_, err := config.FromEnvironment(env.lookupEnv)
+
+		want := alertNtfyToken + ": holds a control character, such as the " +
+			"carriage return of a Windows line end"
+		if err == nil || err.Error() != want {
+			t.Errorf("%s: error %v, want %s", name, err, want)
+		}
+	}
+}
+
+func TestInstanceNameWithAControlCharacterStopsTheStartOnlyWithNtfySet(t *testing.T) {
+	t.Parallel()
+
+	const name = "fsn1app1\r"
+
+	_, err := config.FromEnvironment(environment{
+		instanceName: name, alertNtfyURL: "https://ntfy.example/smallwebwaf-alerts",
+	}.lookupEnv)
+
+	want := instanceName + `: "fsn1app1\r" holds a control character, such as the ` +
+		`carriage return of a Windows line end, and is sent to ntfy in a header ` +
+		`while ` + alertNtfyURL + ` is set`
+	if err == nil || err.Error() != want {
+		t.Errorf("error %v, want %s", err, want)
+	}
+
+	cfg := fromEnvironment(t, environment{instanceName: name})
+	if cfg.InstanceName != name {
+		t.Errorf("not sending to ntfy, %s is %q", instanceName, cfg.InstanceName)
+	}
+}
+
 func TestCodeOnBothCountryListsStopsTheStart(t *testing.T) {
 	t.Parallel()
 

internal/state/state.go

@@ -56,6 +56,9 @@ var (
 	errMissing     = errors.New("has no")
 	errCause       = errors.New("is not limit, attack or admin")
 	errDestination = errors.New("is not webhook, slack or ntfy")
+	errWaitingList = errors.New(`waiting is a list, but now lists the alerts by ` +
+		`destination: put the list under "webhook", as "waiting": {"webhook": [...]}, ` +
+		`or remove the file`)
 )
 
 // Params are what Load needs.
@@ -396,6 +399,17 @@ func (f *Files) takeIn(name string, data []byte, edit bool) (int, error) {
 		f.params.GeoJS.Load(file.Lookups)
 		entries = len(file.Lookups)
 	case alertsJSON:
+		// waiting was a list, of the alerts waiting for the webhook, before
+		// alerts went to Slack and ntfy too.
+		var written struct {
+			Waiting json.RawMessage `json:"waiting"`
+		}
+
+		if json.Unmarshal(data, &written) == nil &&
+			bytes.HasPrefix(written.Waiting, []byte("[")) {
+			return 0, fmt.Errorf("%s: %w", path, errWaitingList)
+		}
+
 		var file alertsFile
 
 		err := parse(path, data, &file)

internal/state/state_test.go

@@ -450,6 +450,23 @@ func TestAlertsJSONEntryWithoutAFieldItNeedsStopsTheStart(t *testing.T) {
 	}
 }
 
+func TestAlertsJSONWithWaitingAsAListStopsTheStartSayingWhatToChange(t *testing.T) {
+	t.Parallel()
+
+	// alerts.json as it was written before alerts went to Slack and ntfy too,
+	// with no alert waiting, or one.
+	for _, waiting := range []string{
+		`[]`,
+		`[{"event": "ban", "time": "2026-10-06T00:00:00Z"}]`,
+	} {
+		wantRefused(t, alertsJSON, `{"version": 1, "cooldowns": [], `+
+			`"hour": {"start": "2026-10-06T00:00:00Z", "sent": 0, "held_back": {}}, `+
+			`"waiting": `+waiting+`}`,
+			`: waiting is a list, but now lists the alerts by destination: put the `+
+				`list under "webhook", as "waiting": {"webhook": [...]}, or remove the file`)
+	}
+}
+
 func TestBanWithAnotherCauseStopsTheStart(t *testing.T) {
 	t.Parallel()