From cfaaba7e467dc495f306c91815765b44a468daf8 Mon Sep 17 00:00:00 2001
From: DHEBP <152355273+DHEBP@users.noreply.github.com>
Date: Thu, 9 Jul 2026 13:26:26 -0400
Subject: [PATCH] fix(rpc): version-immune payload-0 CBOR decode (tolerate
 CheckPack pad)
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Decode exactly the FIRST CBOR item in Arguments.UnmarshalBinary and ignore
trailing bytes. CheckPack pads every payload-0 to its size limit with random
trailing bytes; fxamacker/cbor v2.4.0's Unmarshal tolerated that pad, but
v2.7+ returns ExtraneousDataError on remaining bytes. A streaming Decoder
reads a single item and stops — version-agnostic, no dependency pin. Without
this, a cbor bump past ~v2.7 silently orphans all payload-0 messaging.
---
 rpc/rpc.go | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/rpc/rpc.go b/rpc/rpc.go
index 51e6438a..c9b9ec98 100644
--- a/rpc/rpc.go
+++ b/rpc/rpc.go
@@ -1,6 +1,7 @@
 package rpc
 
 import (
+	"bytes"
 	"crypto/rand"
 	"encoding/json"
 	"fmt"
@@ -223,7 +224,15 @@ func (args Arguments) MarshalBinary() (data []byte, err error) {
 func (args *Arguments) UnmarshalBinary(data []byte) (err error) {
 	localmap := map[string]interface{}{}
 
-	if err = dec.Unmarshal(data, &localmap); err != nil {
+	// Decode exactly the FIRST CBOR item and ignore any trailing bytes. CheckPack pads
+	// every payload-0 to its size limit with random trailing bytes, so the packed buffer
+	// is one CBOR map followed by pad. fxamacker/cbor v2.4.0's Unmarshal tolerates that
+	// trailing pad, but v2.7+ made Unmarshal return ExtraneousDataError on remaining bytes
+	// (UnmarshalFirst became the opt-in tolerant API). A version bump past ~v2.7 would make
+	// dec.Unmarshal here fail on EVERY padded payload-0, silently orphaning all messaging.
+	// A Decoder reads a single item and stops, so this is tolerant of the pad in EVERY cbor
+	// version with no dependency pin — the version-agnostic equivalent of UnmarshalFirst.
+	if err = dec.NewDecoder(bytes.NewReader(data)).Decode(&localmap); err != nil {
 		return err
 	}