P2P AppRequestFailed protobuf definition (#2111)

Signed-off-by: Joshua Kim <20001595+joshua-kim@users.noreply.github.com>
Co-authored-by: Stephen Buttolph <stephen@avalabs.org>

proto/p2p/p2p.proto

@@ -58,6 +58,7 @@ message Message {
     AppGossip app_gossip = 32;
 
     PeerListAck peer_list_ack = 33;
+    AppRequestFailed app_request_failed = 34;
   }
 }
 
@@ -385,7 +386,8 @@ message Chits {
 
 // AppRequest is a VM-defined request.
 //
-// Remote peers must respond to AppRequest with corresponding AppResponse
+// Remote peers must respond to AppRequest with a corresponding AppResponse or
+// AppRequestFailed
 message AppRequest {
   // Chain being requested from
   bytes chain_id = 1;
@@ -407,6 +409,18 @@ message AppResponse {
   bytes app_bytes = 3;
 }
 
+// AppRequestFailed is a VM-defined error sent in response to AppRequest
+message AppRequestFailed {
+  // Chain the message is for
+  bytes chain_id = 1;
+  // Request id of the original AppRequest
+  uint32 request_id = 2;
+  // VM defined error code
+  uint32 error_code = 3;
+  // VM defined error message
+  string error_message = 4;
+}
+
 // AppGossip is a VM-defined message
 message AppGossip {
   // Chain the message is for