Ref #88 Review updates: check retval of intrinsic

Ensure the buffer was adequately large for the response and if not,
allocate sufficient space and call intrinsic again.

libraries/eosiolib/contracts/eosio/action.hpp

@@ -174,18 +174,38 @@ namespace eosio {
  inline checksum256 get_code_hash( name account, code_hash_result* full_result = nullptr ) {
  if (full_result == nullptr)
  full_result = (code_hash_result*)alloca(sizeof(code_hash_result));
+ constexpr size_t max_stack_buffer_size = 50;
 
- // Packed size is dynamic, so we don't know what it'll be. Try to have plenty of space.
- auto struct_buffer_size = sizeof(code_hash_result)*2;
+ // Packed size of this struct will virtually always be less than the struct size; always less after padding
+ auto struct_buffer_size = sizeof(code_hash_result);
  char* struct_buffer = (char*)alloca(struct_buffer_size);
 
  using VersionType = decltype(code_hash_result::struct_version);
  const VersionType STRUCT_VERSION = 0;
- internal_use_do_not_use::get_code_hash(account.value, STRUCT_VERSION, struct_buffer, struct_buffer_size);
+ auto response_size =
+ internal_use_do_not_use::get_code_hash(account.value, STRUCT_VERSION, struct_buffer, struct_buffer_size);
+ // Safety check: in this case, response size should never exceed our buffer, but just in case...
+ bool buffer_on_heap = false;
+ if (response_size > struct_buffer_size) {
+ // Slow path: allocate an adequate buffer and try again
+ // No need to deallocate struct_buffer since it was alloca'd
+ if (response_size > max_stack_buffer_size) {
+ struct_buffer = (char*)malloc(response_size);
+ buffer_on_heap = true;
+ } else {
+ struct_buffer = (char*)alloca(response_size);
+ }
+ internal_use_do_not_use::get_code_hash(account.value, STRUCT_VERSION, struct_buffer, struct_buffer_size);
+ }
+
  check(unpack<VersionType>(struct_buffer, struct_buffer_size) == STRUCT_VERSION,
  "Hypervisor returned unexpected code hash struct version");
  unpack(*full_result, struct_buffer, struct_buffer_size);
 
+ // If struct_buffer is heap allocated, we must free it
+ if (buffer_on_heap)
+ free(struct_buffer);
+
  return full_result->code_hash;
  }