Adding a new api for smart contracts to WASM

Question

I'm trying to add a new smart contract API to wasm_interface.cpp.

I did the same things like context_free_transaction_api::tapos_block_prefix(), https://github.com/EOSIO/eos/pull/1217, adding max_net_usage() function to eosiolib/transaction.h and its implementation on wasm_interface.cpp, and built nodeos and hello contract as API caller using eosio_build.sh.

diff --git a/contracts/eosiolib/transaction.h b/contracts/eosiolib/transaction.h
index bb29f159a..f7d2654c4 100644
--- a/contracts/eosiolib/transaction.h
+++ b/contracts/eosiolib/transaction.h
@@ -115,5 +115,7 @@ extern "C" {
     */
    int get_context_free_data( uint32_t index, char* buff, size_t size );

+   int max_net_usage();
+
    ///@ } transactioncapi
 }
diff --git a/contracts/hello/hello.cpp b/contracts/hello/hello.cpp
index 7c52afa9b..4b9f1d09d 100644
--- a/contracts/hello/hello.cpp
+++ b/contracts/hello/hello.cpp
@@ -1,4 +1,5 @@
 #include <eosiolib/eosio.hpp>
+#include <eosiolib/transaction.h>
 using namespace eosio;

 class hello : public eosio::contract {
@@ -8,6 +9,8 @@ class hello : public eosio::contract {
       /// @abi action
       void hi( account_name user ) {
          print( "Hello, ", name{user} );
+         print("\n");
+         print("max_net_usage=", max_net_usage());
       }
 };

diff --git a/libraries/chain/wasm_interface.cpp b/libraries/chain/wasm_interface.cpp
index 18cf81362..0833a21e6 100644
--- a/libraries/chain/wasm_interface.cpp
+++ b/libraries/chain/wasm_interface.cpp
@@ -1368,6 +1368,10 @@ class context_free_transaction_api : public context_aware_api {
       int get_action( uint32_t type, uint32_t index, array_ptr<char> buffer, size_t buffer_size )const {
          return context.get_action( type, index, buffer, buffer_size );
       }
+
+      int max_net_usage() const {
+         return context.trx_context.trx.max_net_usage_words;
+      }
 };

 class compiler_builtins : public context_aware_api {
@@ -1819,6 +1823,7 @@ REGISTER_INTRINSICS(context_free_transaction_api,
    (tapos_block_prefix,     int()                    )
    (tapos_block_num,        int()                    )
    (get_action,             int (int, int, int, int) )
+   (max_net_usage,          int()                    )
 );

 REGISTER_INTRINSICS(transaction_api,

Build was successful, but contract deployment was failed with this error.

$ cleos set contract hello build/contracts/hello -p hello Reading WAST/WASM from build/contracts/hello/hello.wasm... Using already assembled WASM... Publishing contract... 689825ms thread-0
main.cpp:2659 main ] Failed with error: Assert Exception (10) !"unresolvable": env.max_net_usage

What am I missing? Is there a WASM command to add max_net_usage symbol up to env?

Answer 1

At that point you posted this question, you need to add max_net_usage to eosio.imports, but now eosio_wasm_import attribute can do same thing.

Add __attribute__((eosio_wasm_import)) before function declaration:

diff --git a/contracts/eosiolib/transaction.h b/contracts/eosiolib/transaction.h
index bb29f159a..f7d2654c4 100644
--- a/contracts/eosiolib/transaction.h
+++ b/contracts/eosiolib/transaction.h
@@ -115,5 +115,7 @@ extern "C" {
     */
    int get_context_free_data( uint32_t index, char* buff, size_t size );

+   __attribute__((eosio_wasm_import)) // add here
+   int max_net_usage();
+
    ///@ } transactioncapi
 }

Answer 2

I think change transaction.h to .hpp will help you avoid of this problem.

BTW, all the implemented code seems to be correct.