as per lunny

Signed-off-by: Andrew Thornton <[email protected]>

Author: zeripath

modules/util/truncate.go

@@ -0,0 +1,34 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package util
+
+import "unicode/utf8"
+
+func SplitStringAtByteN(input string, n int) (left, right string) {
+	if len(input) <= n {
+		left = input
+		return
+	}
+
+	if !utf8.ValidString(input) {
+		left = input[:n-3] + "..."
+		right = "..." + input[n-3:]
+		return
+	}
+
+	// in UTF8 "…" is 3 bytes so doesn't really gain us anything...
+	end := 0
+	for end <= n-3 {
+		_, size := utf8.DecodeRuneInString(input[end:])
+		if end+size > n-3 {
+			break
+		}
+		end += size
+	}
+
+	left = input[:end] + "…"
+	right = "…" + input[end:]
+	return
+}

routers/web/repo/compare.go

@@ -24,6 +24,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/upload"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/services/gitdiff"
 )
 
@@ -568,12 +569,15 @@ func PrepareCompareDiff(
 		title = headBranch
 	}
 	if len(title) > 255 {
-		if ctx.Data["content"] != nil {
-			ctx.Data["content"] = fmt.Sprintf("…%s\n\n%s", title[254:], ctx.Data["content"])
-		} else {
-			ctx.Data["content"] = "…" + title[254:] + "\n"
+		var trailer string
+		title, trailer = util.SplitStringAtByteN(title, 255)
+		if len(trailer) > 0 {
+			if ctx.Data["content"] != nil {
+				ctx.Data["content"] = fmt.Sprintf("%s\n\n%s", trailer, ctx.Data["content"])
+			} else {
+				ctx.Data["content"] = trailer + "\n"
+			}
 		}
-		title = title[:254] + "…"
 	}
 
 	ctx.Data["title"] = title

routers/web/repo/pull.go

@@ -1042,8 +1042,10 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 		}
 
 		if len(form.Title) > 255 {
-			form.Content = "…" + form.Title[254:] + "\n\n" + form.Content
-			form.Title = form.Title[:254] + "…"
+			var trailer string
+			form.Title, trailer = util.SplitStringAtByteN(form.Title, 255)
+
+			form.Content = trailer + "\n\n" + form.Content
 		}
 		middleware.AssignForm(form, ctx.Data)