From 3ddf111092f85bd37ec0a6bf0e94798705407334 Mon Sep 17 00:00:00 2001 From: Md Mushfiqur Rahim <20mahin2020@gmail.com> Date: Sat, 13 Jun 2026 09:38:33 +0000 Subject: [PATCH] fix: encode non-BMP characters as UTF-16 surrogate pairs in AsciiJSON The AsciiJSON Render method used fmt.Appendf(buf, "\u%04x", r) for all non-ASCII runes. For non-BMP characters (code points > 0xFFFF, e.g. emoji), this produced invalid JSON with raw 5+ hex digit sequences like \u1f389. Fix: use utf16.Encode([]rune{r}) to convert non-BMP runes into UTF-16 surrogate pairs, producing valid JSON like \ud83c\udf89. Fixes #4688 Signed-off-by: Md Mushfiqur Rahim <20mahin2020@gmail.com> --- render/json.go | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/render/json.go b/render/json.go index 2f98676c..6902c94d 100644 --- a/render/json.go +++ b/render/json.go @@ -10,6 +10,7 @@ import ( "html/template" "net/http" "unicode" + "unicode/utf16" "github.com/gin-gonic/gin/codec/json" "github.com/gin-gonic/gin/internal/bytesconv" @@ -160,11 +161,16 @@ func (r AsciiJSON) Render(w http.ResponseWriter) error { } var buffer bytes.Buffer - escapeBuf := make([]byte, 0, 6) // Preallocate 6 bytes for Unicode escape sequences + escapeBuf := make([]byte, 0, 12) // Preallocate for up to two \uXXXX sequences for _, r := range bytesconv.BytesToString(ret) { if r > unicode.MaxASCII { - escapeBuf = fmt.Appendf(escapeBuf[:0], "\\u%04x", r) // Reuse escapeBuf + if r > 0xFFFF { + surrogates := utf16.Encode([]rune{r}) + escapeBuf = fmt.Appendf(escapeBuf[:0], "\\u%04x\\u%04x", surrogates[0], surrogates[1]) + } else { + escapeBuf = fmt.Appendf(escapeBuf[:0], "\\u%04x", r) + } buffer.Write(escapeBuf) } else { buffer.WriteByte(byte(r))