From e9c17581010f148f00c5bee1126c49406df0cbde Mon Sep 17 00:00:00 2001
From: CJ van den Berg <cj@vdbonline.com>
Date: Wed, 4 Mar 2026 21:42:30 +0100
Subject: [PATCH] feat: add thespian_unexpected to C API

---
 include/thespian/c/instance.h   |  1 +
 src/c/instance.cpp              | 12 ++++++++++++
 test/ip_tcp_client_server_c.cpp |  8 ++++----
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/thespian/c/instance.h b/include/thespian/c/instance.h
index 8e48239..09d3bd8 100644
--- a/include/thespian/c/instance.h
+++ b/include/thespian/c/instance.h
@@ -17,6 +17,7 @@ void thespian_receive(thespian_receiver, thespian_behaviour_state,
                       thespian_receiver_dtor);
 
 thespian_result thespian_exit(const char *status);
+thespian_result thespian_unexpected(cbor_buffer msg);
 
 bool thespian_get_trap();
 bool thespian_set_trap(bool);
diff --git a/src/c/instance.cpp b/src/c/instance.cpp
index a8b058b..7b25aec 100644
--- a/src/c/instance.cpp
+++ b/src/c/instance.cpp
@@ -47,6 +47,18 @@ auto thespian_exit(const char *status) -> thespian_result {
   return &exit_error_buf;
 }
 
+auto thespian_unexpected(cbor_buffer m) -> thespian_result {
+  cbor::buffer buf;
+  const uint8_t *data = m.base;
+  std::copy(data, data + m.len, back_inserter(buf)); // NOLINT
+  auto r = thespian::unexpected(buf);
+  if (r)
+    return nullptr;
+  exit_msg_buf = r.error();
+  exit_error_buf = {exit_msg_buf.data(), exit_msg_buf.size()};
+  return &exit_error_buf;
+}
+
 void thespian_link(thespian_handle h) {
   thespian::handle *h_{
       reinterpret_cast<thespian::handle *>( // NOLINT(*-reinterpret-cast)
diff --git a/test/ip_tcp_client_server_c.cpp b/test/ip_tcp_client_server_c.cpp
index 548d749..6f53142 100644
--- a/test/ip_tcp_client_server_c.cpp
+++ b/test/ip_tcp_client_server_c.cpp
@@ -79,7 +79,7 @@ static thespian_result cc_receive(thespian_behaviour_state s, thespian_handle,
     send(st->client, cbor::array("client_connection", "done"));
     return thespian_exit("normal");
   } else {
-    LOG("cc_receive: UNEXPECTED msg=%s\n", msg_json);
+    return thespian_unexpected(m);
   }
   return nullptr;
 }
@@ -131,7 +131,7 @@ static thespian_result client_receive(thespian_behaviour_state s,
     send(st->server, cbor::array("client", "done"));
     return thespian_exit("normal");
   } else {
-    LOG("client_receive: UNEXPECTED msg=%s\n", msg_json);
+    return thespian_unexpected(m);
   }
   return nullptr;
 }
@@ -184,7 +184,7 @@ static thespian_result sc_receive(thespian_behaviour_state s, thespian_handle,
     send(st->server, cbor::array("server_connection", "done"));
     return thespian_exit("normal");
   } else {
-    LOG("sc_receive: UNEXPECTED msg=%s\n", msg_json);
+    return thespian_unexpected(m);
   }
   return nullptr;
 }
@@ -245,7 +245,7 @@ static thespian_result server_receive(thespian_behaviour_state s,
         st->acceptor_closed, st->client_done);
     st->server_conn_done = true;
   } else {
-    LOG("server_receive: UNEXPECTED msg=%s\n", msg_json);
+    return thespian_unexpected(m);
   }
   if (st->acceptor_closed && st->client_done && st->server_conn_done) {
     LOG("server_receive: all done, exiting success\n");