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fix(rpc): version-immune payload-0 CBOR decode (tolerate CheckPack pad) #45

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fix(rpc): version-immune payload-0 CBOR decode (tolerate CheckPack pad) #45

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11 changes: 10 additions & 1 deletion rpc/rpc.go
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package rpc

import (
"bytes"
"crypto/rand"
"encoding/json"
"fmt"
Expand Down Expand Up @@ -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
}

Expand Down