From f6d8847bcfe97296fa80b4fc05b75cfbca839e98 Mon Sep 17 00:00:00 2001
From: Ian Gulliver <github@flamingcow.io>
Date: Fri, 10 Apr 2026 23:23:58 +0900
Subject: [PATCH] Fix packer: store span_writer by reference, not copy

---
 firmware/include/msgpack.h | 8 ++++----
 firmware/include/wire.h    | 3 ++-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/firmware/include/msgpack.h b/firmware/include/msgpack.h
index dda3aaa..115fdce 100644
--- a/firmware/include/msgpack.h
+++ b/firmware/include/msgpack.h
@@ -164,7 +164,7 @@ inline result<body_info> get_body_info(const uint8_t *p, int size) {
 
 class packer {
 private:
-  span_writer m_buf;
+  span_writer &m_buf;
 
   template <typename T> void push_big_endian(T n) {
     auto p = reinterpret_cast<std::uint8_t *>(&n) + (sizeof(T) - 1);
@@ -178,8 +178,7 @@ private:
   }
 
 public:
-  packer(uint8_t *data, size_t capacity) : m_buf(data, capacity) {}
-  packer(span_writer buf) : m_buf(buf) {}
+  packer(span_writer &buf) : m_buf(buf) {}
 
   packer(const packer &) = delete;
   packer &operator=(const packer &) = delete;
@@ -409,7 +408,8 @@ public:
     requires requires(const T &v) { { T::ext_id } -> std::convertible_to<int8_t>; v.as_tuple(); }
   pack_result pack(const T &v) {
     uint8_t ext_buf[256];
-    packer inner(ext_buf, sizeof(ext_buf));
+    span_writer ext_writer(ext_buf, sizeof(ext_buf));
+    packer inner(ext_writer);
     auto r = inner.pack(v.as_tuple());
     if (!r) return r;
     return pack_ext(T::ext_id, inner.get_payload());
diff --git a/firmware/include/wire.h b/firmware/include/wire.h
index 15e751d..920a51b 100644
--- a/firmware/include/wire.h
+++ b/firmware/include/wire.h
@@ -115,7 +115,8 @@ inline msgpack::result<size_t> encode_response_into(span_writer &out, uint32_t m
     body_p.pack(msg.as_tuple());
 
     auto inner_ext = out.subspan(envelope_hdr_len, ext16_header_len);
-    msgpack::packer(inner_ext).pack_ext16_header(T::ext_id, static_cast<uint16_t>(body.size()));
+    msgpack::packer inner_ext_p(inner_ext);
+    inner_ext_p.pack_ext16_header(T::ext_id, static_cast<uint16_t>(body.size()));
 
     size_t bin_len = inner_ext.size() + body.size();
     uint32_t checksum = halfsiphash::hash32({inner_ext.data(), bin_len}, hash_key);