From f51f51ec723f680ac4be5068b47d727fa0f80818 Mon Sep 17 00:00:00 2001
From: gotjosh <josue.abreu@gmail.com>
Date: Fri, 11 Nov 2022 15:14:35 +0000
Subject: [PATCH] Use the new truncation in bytes functions to ensure strings
 are not butchered

Signed-off-by: gotjosh <josue.abreu@gmail.com>
---
 notify/util.go        | 22 ++++++++++++++++++++--
 notify/util_test.go   | 18 +++++++++---------
 notify/webex/webex.go |  2 +-
 3 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/notify/util.go b/notify/util.go
index c127913e..6b71ac7b 100644
--- a/notify/util.go
+++ b/notify/util.go
@@ -20,6 +20,7 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"strings"
 
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
@@ -100,15 +101,32 @@ func TruncateInRunes(s string, n int) (string, bool) {
 
 // TruncateInBytes truncates a string to fit the given size in Bytes.
 func TruncateInBytes(s string, n int) (string, bool) {
+	// First, measure the string the w/o a to-rune conversion.
 	if len(s) <= n {
 		return s, false
 	}
 
+	// The truncationMarker itself is 3 bytes, we can't return any part of the string when it's less than 3.
 	if n <= 3 {
-		return string(s[:n]), true
+		switch n {
+		case 3:
+			return truncationMarker, true
+		default:
+			return strings.Repeat(".", n), true
+		}
 	}
 
-	return string(s[:n-3]) + truncationMarker, true // In bytes, the truncation marker is 3 bytes.
+	// Now, to ensure we don't butcher the string we need to remove using runes.
+	r := []rune(s)
+	truncationTarget := n - 3
+
+	// Next, let's truncate the runes to the lower possible number.
+	truncatedRunes := r[:truncationTarget]
+	for len(string(truncatedRunes)) > truncationTarget {
+		truncatedRunes = r[:len(truncatedRunes)-1]
+	}
+
+	return string(truncatedRunes) + truncationMarker, true
 }
 
 // TmplText is using monadic error handling in order to make string templating
diff --git a/notify/util_test.go b/notify/util_test.go
index 434e8c55..032fc515 100644
--- a/notify/util_test.go
+++ b/notify/util_test.go
@@ -49,7 +49,7 @@ func TestTruncate(t *testing.T) {
 			in:    "abcde",
 			n:     2,
 			runes: expect{out: "ab", trunc: true},
-			bytes: expect{out: "ab", trunc: true},
+			bytes: expect{out: "..", trunc: true},
 		},
 		{
 			in:    "abcde",
@@ -73,25 +73,25 @@ func TestTruncate(t *testing.T) {
 			in:    "a⌘cde",
 			n:     5,
 			runes: expect{out: "a⌘cde", trunc: false},
-			bytes: expect{out: "a\xe2…", trunc: true},
+			bytes: expect{out: "a…", trunc: true},
 		},
 		{
 			in:    "a⌘cdef",
 			n:     5,
 			runes: expect{out: "a⌘cd…", trunc: true},
-			bytes: expect{out: "a\xe2…", trunc: true},
+			bytes: expect{out: "a…", trunc: true},
 		},
 		{
 			in:    "世界cdef",
 			n:     3,
 			runes: expect{out: "世界c", trunc: true},
-			bytes: expect{out: "世", trunc: true},
+			bytes: expect{out: "…", trunc: true},
 		},
 		{
-			in:    "❤️✅🚀🔥❌",
-			n:     4,
-			runes: expect{out: "❤️✅…", trunc: true},
-			bytes: expect{out: "\xe2…", trunc: true},
+			in:    "❤️✅🚀🔥❌❤️✅🚀🔥❌❤️✅🚀🔥❌❤️✅🚀🔥❌",
+			n:     19,
+			runes: expect{out: "❤️✅🚀🔥❌❤️✅🚀🔥❌❤️✅🚀🔥❌…", trunc: true},
+			bytes: expect{out: "❤️✅🚀…", trunc: true},
 		},
 	}
 
@@ -117,8 +117,8 @@ func TestTruncate(t *testing.T) {
 
 			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)
+				require.Equal(t, truncated, trunc)
 			})
 		}
 	}
diff --git a/notify/webex/webex.go b/notify/webex/webex.go
index 968fac4b..a19f6eac 100644
--- a/notify/webex/webex.go
+++ b/notify/webex/webex.go
@@ -94,7 +94,7 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 		return false, err
 	}
 
-	message, truncated := notify.Truncate(message, maxMessageSize)
+	message, truncated := notify.TruncateInBytes(message, maxMessageSize)
 	if truncated {
 		level.Debug(n.logger).Log("msg", "message truncated due to exceeding maximum allowed length by webex", "truncated_message", message)
 	}