Truncate: Be explicit on truncation of runes or bytes.

While most integrations set a limit by UTF-8 compatible characters (some like Webex) use runes - as pointed out in https://github.com/prometheus/alertmanager/pull/3132. This PR makes it explicit wether the truncation is happening at a byte or rune level.

Signed-off-by: gotjosh <josue.abreu@gmail.com>

notify/opsgenie/opsgenie.go

@@ -171,7 +171,8 @@ func (n *Notifier) createRequests(ctx context.Context, as ...*types.Alert) ([]*h
 		}
 		requests = append(requests, req.WithContext(ctx))
 	default:
-		message, truncated := notify.Truncate(tmpl(n.conf.Message), 130)
+		// https://docs.opsgenie.com/docs/alert-api - 130 characters meaning runes.
+		message, truncated := notify.TruncateInRunes(tmpl(n.conf.Message), 130)
 		if truncated {
 			level.Debug(n.logger).Log("msg", "truncated message", "truncated_message", message, "alert", key)
 		}

notify/pagerduty/pagerduty.go

@@ -149,7 +149,8 @@ func (n *Notifier) notifyV1(
 	var tmplErr error
 	tmpl := notify.TmplText(n.tmpl, data, &tmplErr)
 
-	description, truncated := notify.Truncate(tmpl(n.conf.Description), 1024)
+	// https://developer.pagerduty.com/docs/ZG9jOjExMDI5NTgx-send-an-alert-event - 1204 characters or runes.
+	description, truncated := notify.TruncateInRunes(tmpl(n.conf.Description), 1024)
 	if truncated {
 		level.Debug(n.logger).Log("msg", "Truncated description", "description", description, "key", key)
 	}
@@ -214,7 +215,8 @@ func (n *Notifier) notifyV2(
 		n.conf.Severity = "error"
 	}
 
-	summary, truncated := notify.Truncate(tmpl(n.conf.Description), 1024)
+	// https://developer.pagerduty.com/docs/ZG9jOjExMDI5NTgx-send-an-alert-event - 1204 characters or runes.
+	summary, truncated := notify.TruncateInRunes(tmpl(n.conf.Description), 1024)
 	if truncated {
 		level.Debug(n.logger).Log("msg", "Truncated summary", "summary", summary, "key", key)
 	}

notify/pushover/pushover.go

@@ -78,7 +78,8 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 	parameters.Add("token", tmpl(string(n.conf.Token)))
 	parameters.Add("user", tmpl(string(n.conf.UserKey)))
 
-	title, truncated := notify.Truncate(tmpl(n.conf.Title), 250)
+	// https://pushover.net/api#limits - 250 characters or runes.
+	title, truncated := notify.TruncateInRunes(tmpl(n.conf.Title), 250)
 	if truncated {
 		level.Debug(n.logger).Log("msg", "Truncated title", "truncated_title", title, "incident", key)
 	}
@@ -91,7 +92,8 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 		message = tmpl(n.conf.Message)
 	}
 
-	message, truncated = notify.Truncate(message, 1024)
+	// https://pushover.net/api#limits - 1024 characters or runes.
+	message, truncated = notify.TruncateInRunes(message, 1024)
 	if truncated {
 		level.Debug(n.logger).Log("msg", "Truncated message", "truncated_message", message, "incident", key)
 	}
@@ -102,7 +104,8 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 	}
 	parameters.Add("message", message)
 
-	supplementaryURL, truncated := notify.Truncate(tmpl(n.conf.URL), 512)
+	// https://pushover.net/api#limits - 512 characters or runes.
+	supplementaryURL, truncated := notify.TruncateInRunes(tmpl(n.conf.URL), 512)
 	if truncated {
 		level.Debug(n.logger).Log("msg", "Truncated URL", "truncated_url", supplementaryURL, "incident", key)
 	}

notify/slack/slack.go

@@ -99,7 +99,8 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 	} else {
 		markdownIn = n.conf.MrkdwnIn
 	}
-	title, truncated := notify.Truncate(tmplText(n.conf.Title), 1024)
+	// No refernce in https://api.slack.com/reference/messaging/attachments#legacy_fields - assuming runes or characters.
+	title, truncated := notify.TruncateInRunes(tmplText(n.conf.Title), 1024)
 	if truncated {
 		key, err := notify.ExtractGroupKey(ctx)
 		if err != nil {

notify/telegram/telegram.go

@@ -65,8 +65,8 @@ func (n *Notifier) Notify(ctx context.Context, alert ...*types.Alert) (bool, err
 		tmpl = notify.TmplText(n.tmpl, data, &err)
 	)
 
-	// Telegram supports 4096 chars max
-	messageText, truncated := notify.Truncate(tmpl(n.conf.Message), 4096)
+	// Telegram supports 4096 chars max - from https://limits.tginfo.me/en.
+	messageText, truncated := notify.TruncateInRunes(tmpl(n.conf.Message), 4096)
 	if truncated {
 		level.Debug(n.logger).Log("msg", "truncated message", "truncated_message", messageText)
 	}

notify/util.go

@@ -81,18 +81,33 @@ func Drain(r *http.Response) {
 	r.Body.Close()
 }
 
-// Truncate truncates a string to fit the given size.
-func Truncate(s string, n int) (string, bool) {
+// Truncate truncates a string to fit the given size in Bytes.
+func TruncateInRunes(s string, n int) (string, bool) {
 	r := []rune(s)
 	if len(r) <= n {
 		return s, false
 	}
+
 	if n <= 3 {
 		return string(r[:n]), true
 	}
+
 	return string(r[:n-1]) + "…", true
 }
 
+// Truncate truncates a string to fit the given size in Runes.
+func TruncateInBytes(s string, n int) (string, bool) {
+	if len(s) <= n {
+		return s, false
+	}
+
+	if n <= 3 {
+		return string(s[:n]), true
+	}
+
+	return string(s[:n-3]) + "…", true // This rune
+}
+
 // TmplText is using monadic error handling in order to make string templating
 // less verbose. Use with care as the final error checking is easily missed.
 func TmplText(tmpl *template.Template, data *template.Data, err *error) func(string) string {

notify/util_test.go

@@ -18,69 +18,109 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"path"
+	"reflect"
+	"runtime"
 	"testing"
 
 	"github.com/stretchr/testify/require"
 )
 
 func TestTruncate(t *testing.T) {
+	type expect struct {
+		out   string
+		trunc bool
+	}
+
 	testCases := []struct {
 		in string
 		n  int
 
-		out   string
-		trunc bool
+		runes expect
+		bytes expect
 	}{
 		{
 			in:    "",
 			n:     5,
-			out:   "",
-			trunc: false,
+			runes: expect{out: "", trunc: false},
+			bytes: expect{out: "", trunc: false},
 		},
 		{
 			in:    "abcde",
 			n:     2,
-			out:   "ab",
-			trunc: true,
+			runes: expect{out: "ab", trunc: true},
+			bytes: expect{out: "ab", trunc: true},
 		},
 		{
 			in:    "abcde",
 			n:     4,
-			out:   "abc…",
-			trunc: true,
+			runes: expect{out: "abc…", trunc: true},
+			bytes: expect{out: "a…", trunc: true},
 		},
 		{
 			in:    "abcde",
 			n:     5,
-			out:   "abcde",
-			trunc: false,
+			runes: expect{out: "abcde", trunc: false},
+			bytes: expect{out: "abcde", trunc: false},
 		},
 		{
 			in:    "abcdefgh",
 			n:     5,
-			out:   "abcd…",
-			trunc: true,
+			runes: expect{out: "abcd…", trunc: true},
+			bytes: expect{out: "ab…", trunc: true},
 		},
 		{
 			in:    "a⌘cde",
 			n:     5,
-			out:   "a⌘cde",
-			trunc: false,
+			runes: expect{out: "a⌘cde", trunc: false},
+			bytes: expect{out: "a\xe2…", trunc: true},
 		},
 		{
 			in:    "a⌘cdef",
 			n:     5,
-			out:   "a⌘cd…",
-			trunc: true,
+			runes: expect{out: "a⌘cd…", trunc: true},
+			bytes: expect{out: "a\xe2…", trunc: true},
+		},
+		{
+			in:    "世界cdef",
+			n:     3,
+			runes: expect{out: "世界c", trunc: true},
+			bytes: expect{out: "世", trunc: true},
+		},
+		{
+			in:    "❤️✅🚀🔥❌",
+			n:     4,
+			runes: expect{out: "❤️✅…", trunc: true},
+			bytes: expect{out: "\xe2…", trunc: true},
 		},
 	}
 
+	type truncateFunc func(string, int) (string, bool)
+
 	for _, tc := range testCases {
-		t.Run(fmt.Sprintf("truncate(%s,%d)", tc.in, tc.n), func(t *testing.T) {
-			s, trunc := Truncate(tc.in, tc.n)
-			require.Equal(t, tc.trunc, trunc)
-			require.Equal(t, tc.out, s)
-		})
+		for _, fn := range []truncateFunc{TruncateInBytes, TruncateInRunes} {
+			var truncated bool
+			var out string
+
+			fnPath := runtime.FuncForPC(reflect.ValueOf(fn).Pointer()).Name()
+			fnName := path.Base(fnPath)
+			switch fnName {
+			case "notify.TruncateInRunes":
+				truncated = tc.runes.trunc
+				out = tc.runes.out
+			case "notify.TruncateInBytes":
+				truncated = tc.bytes.trunc
+				out = tc.bytes.out
+			default:
+				t.Fatalf("unknown function")
+			}
+
+			t.Run(fmt.Sprintf("%s(%s,%d)", fnName, tc.in, tc.n), func(t *testing.T) {
+				s, trunc := fn(tc.in, tc.n)
+				require.Equal(t, truncated, trunc)
+				require.Equal(t, out, s)
+			})
+		}
 	}
 }
 

notify/victorops/victorops.go

@@ -134,7 +134,8 @@ func (n *Notifier) createVictorOpsPayload(ctx context.Context, as ...*types.Aler
 		messageType = victorOpsEventResolve
 	}
 
-	stateMessage, truncated := notify.Truncate(stateMessage, 20480)
+	// https://help.victorops.com/knowledge-base/incident-fields-glossary/ - 20480 characters.
+	stateMessage, truncated := notify.TruncateInRunes(stateMessage, 20480)
 	if truncated {
 		level.Debug(n.logger).Log("msg", "truncated stateMessage", "truncated_state_message", stateMessage, "incident", key)
 	}