From 70b4e5ffaf46592bfa297c94b4ee7793e05c658d Mon Sep 17 00:00:00 2001
From: Tai Groot <tai@taigrr.com>
Date: Sun, 30 Aug 2026 09:34:08 +0000
Subject: [PATCH] fix(attachment): skip unexported payload fields

---
 attachment.go      |  6 ++++++
 attachment_test.go | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/attachment.go b/attachment.go
index 1617647..da20935 100644
--- a/attachment.go
+++ b/attachment.go
@@ -47,6 +47,9 @@ func encodeAttachmentValue(v reflect.Value, index *int) []io.Reader {
 	if !v.IsValid() {
 		return ret
 	}
+	if !v.CanInterface() {
+		return ret
+	}
 	switch v.Kind() {
 	case reflect.Struct:
 		if v.Type().Name() == "Attachment" {
@@ -96,6 +99,9 @@ func decodeAttachmentValue(v reflect.Value, binary [][]byte) error {
 	if !v.IsValid() {
 		return fmt.Errorf("invalid value")
 	}
+	if !v.CanInterface() {
+		return nil
+	}
 	switch v.Kind() {
 	case reflect.Struct:
 		if v.Type().Name() == "Attachment" {
diff --git a/attachment_test.go b/attachment_test.go
index e63b88b..aa7e791 100644
--- a/attachment_test.go
+++ b/attachment_test.go
@@ -19,6 +19,11 @@ type HaveAttachment struct {
 	A *Attachment `json:"a"`
 }
 
+type HavePrivateAttachment struct {
+	A      *Attachment `json:"a"`
+	hidden any
+}
+
 func TestEncodeAttachments(t *testing.T) {
 	var input any
 	var target []io.Reader
@@ -103,6 +108,21 @@ func TestEncodeAttachments(t *testing.T) {
 		So(string(b), ShouldEqual, `{"test":{"i":0,"a":{"_placeholder":true,"num":0}}}`)
 	})
 
+	Convey("Unexported fields are ignored", t, func() {
+		hidden := &Attachment{Data: buf2}
+		hidden.num = -1
+		input = HavePrivateAttachment{
+			A:      attachment1,
+			hidden: hidden,
+		}
+		target = []io.Reader{buf1}
+
+		test()
+
+		So(attachment1.num, ShouldEqual, 0)
+		So(hidden.num, ShouldEqual, -1)
+	})
+
 }
 
 func TestDecodeAttachments(t *testing.T) {
@@ -182,4 +202,21 @@ func TestDecodeAttachments(t *testing.T) {
 		So(err, ShouldBeNil)
 		So(v.A.num, ShouldEqual, 2)
 	})
+
+	Convey("Unexported fields are ignored", t, func() {
+		input = [][]byte{[]byte("data1"), []byte("data2")}
+		hidden := &Attachment{Data: buf2}
+		hidden.num = 1
+		attachment1 = &Attachment{Data: buf1}
+		attachment2 = nil
+		attachment1.num = 0
+		v = HavePrivateAttachment{
+			A:      attachment1,
+			hidden: hidden,
+		}
+
+		test()
+
+		So(buf2.String(), ShouldBeEmpty)
+	})
 }