EOS原始碼備忘-Push Transaction機制

這裡我們討論EOS Push Transaction 的邏輯，這塊EOS與Eosforce實現有一些區別，我們會著重點出。 關於wasm相關的內容我們會有一片專門的文件分析。

我們這裡通常將Transaction譯做交易，其實這裡應該是事務的意思。

1. Transaction與Action 在EOS中Transaction與Action是最重要的幾個型別， 在EOS中，所有的鏈上行為都是Action，Transaction是一系列Action組成的事務。

EOS中使用繼承體系劃分trx與action結構，關係圖如下：

transaction_header <- transaction <- signed_transaction <- deferred_transaction

                    |

            packed_transaction

1.1 Action

我們這裡先看一下Action的宣告：

// 許可權結構structpermission_level{account_name actor; permission_name permission; }; …structaction{account_name account; action_name name;// 執行所需的許可權vector authorization; bytes data; …// 打包成二進位制templateTdata_as()const{ … } };

Action沒有什麼特別的內容，但要注意：

!> 在EOS中一個transaction中包含很多個action，而在Eosforce中一個trx只能包括一個action。

1.2 Transaction

下面我們分析一下transaction，這裡簡寫為trx。

首先看下

/**

*  The transaction header contains the fixed-sized data

*  associated with each transaction. It is separated from

*  the transaction body to facilitate partial parsing of

*  transactions without requiring dynamic memory allocation.

*

*  All transactions have an expiration time after which they

*  may no longer be included in the blockchain. Once a block

*  with a block_header::timestamp greater than expiration is

*  deemed irreversible, then a user can safely trust the transaction

*  will never be included.

*

*  Each region is an independent blockchain, it is included as routing

*  information for inter-blockchain communication. A contract in this

*  region might generate or authorize a transaction intended for a foreign

*  region.

*/structtransaction_header{time_point_sec        expiration;///< trx超時時間uint16_tref_block_num      =0U;// 包含trx的block num 注意這個值是後2^16個塊中uint32_tref_block_prefix    =0UL;// blockid的低32位fc::unsigned_int      max_net_usage_words =0UL;// 網路資源上限uint8_tmax_cpu_usage_ms    =0;// cpu資源上限fc::unsigned_int      delay_sec          =0UL;/// 延遲交易的延遲時間/**

  * @return the absolute block number given the relative ref_block_num

  * 計算ref_block_num

  */block_num_typeget_ref_blocknum( block_num_type head_blocknum )const{return((head_blocknum/0xffff)*0xffff) + head_blocknum%0xffff;      }voidset_reference_block(constblock_id_type& reference_block );boolverify_reference_block(constblock_id_type& reference_block )const;voidvalidate()const;  };
 

transaction_header包含一個trx中固定長度的資料，這裡之所以要單獨提出來主要是為了優化。

transaction視為交易體資料，這裡主要是儲存這個trx包含的action。

/**

*  A transaction consits of a set of messages which must all be applied or

*  all are rejected. These messages have access to data within the given

*  read and write scopes.

*/

// 在EOS中一個交易中 action要麼全部執行，要麼都不執行

struct transaction : public transaction_header {

  vector<action>        context_free_actions;

  vector<action>        actions;

  extensions_type        transaction_extensions;

  // 獲取trx id

  transaction_id_type        id()const;

  digest_type                sig_digest( const chain_id_type& chain_id, const vector<bytes>& cfd = vector<bytes>() )const;

...

};

另外一個值得注意的是trx id：

transaction_id_type transaction::id()const{ digest_type::encoder enc; fc::raw::pack( enc, *this);returnenc.result();}

!> Eosforce不同

在Eosforce中為了新增手續費資訊，trx與EOS結構不同，主要是增加了fee， 在transaction中：

struct transaction : public transaction_header {

  vector<action>        context_free_actions;

  vector<action>        actions;

  extensions_type        transaction_extensions;

  asset                  fee; // EOSForce 增加的手續費，在客戶端push trx時需要寫入

  transaction_id_type        id()const;

  digest_type                sig_digest( const chain_id_type& chain_id, const vector<bytes>& cfd = vector<bytes>() )const;

  flat_set<public_key_type>  get_signature_keys( const vector<signature_type>& signatures,

                                                const chain_id_type& chain_id,

                                                const vector<bytes>& cfd = vector<bytes>(),

                                                bool allow_duplicate_keys = false,

                                                bool use_cache = true )const;

  uint32_t total_actions()const { return context_free_actions.size() + actions.size(); }

  account_name first_authorizor()const {

    for( const auto& a : actions ) {

        for( const auto& u : a.authorization )

          return u.actor;

    }

    return account_name();

  }

};

這裡計算trx id時完全使用trx的資料，這意味著，如果是兩個trx資料完全一致，特別的他們在一個區塊中，那麼這兩個trx的id就會是一樣的。

1.3 signed_transaction

一個trx簽名之後會得到一個signed_transaction，

structsigned_transaction:publictransaction { …vector signatures;// 簽名vector context_free_data;// 上下文無關的action所使用的資料// 簽名constsignature_type&sign(constprivate_key_type& key,constchain_id_type& chain_id);signature_typesign(constprivate_key_type& key,constchain_id_type& chain_id)const; flat_set get_signature_keys(constchain_id_type& chain_id,boolallow_duplicate_keys =false,booluse_cache =true)const; };

signed_transaction包含簽名資料和上下文無關的action所使用的資料，

這裡要談一下context_free_data，可以參見 https://github.com/EOSIO/eos/commit/a41b4d56b5cbfd0346de34b0e03819f72e834041 ，之前我們看過context_free_actions， 在上下文無關的action中可以去從context_free_data獲取資料，可以參見在api_tests.cpp中的測試用例：

… {// back to normal actionactionact1(pl, da); signed_transaction trx; trx.context_free_actions.push_back(act); trx.context_free_data.emplace_back(fc::raw::pack(100));// verify payload matches context free datatrx.context_free_data.emplace_back(fc::raw::pack(200)); trx.actions.push_back(act1);// attempt to access non context free apifor(uint32_ti =200; i <=211; ++i) { trx.context_free_actions.clear(); trx.context_free_data.clear(); cfa.payload = i; cfa.cfd_idx =1;actioncfa_act({}, cfa); trx.context_free_actions.emplace_back(cfa_act); trx.signatures.clear(); set_transaction_headers(trx); sigs = trx.sign(get_private_key(N(testapi),“active”), control->get_chain_id()); BOOST_CHECK_EXCEPTION(push_transaction(trx), unaccessible_api, [](constfc::exception& e) {returnexpect_assert_message(e,“only context free api’s can be used in this context”); } ); }…

這裡可以作為context_free_action的一個例子，在test_api.cpp中的合約會呼叫void test_action::test_cf_action()函式：

// 這個是測試context_free_action的action

void test_action::test_cf_action() {

eosio::action act = eosio::get_action( 0, 0 );

cf_action cfa = act.data_as<cf_action>();

if ( cfa.payload == 100 ) {

  // verify read of get_context_free_data, also verifies system api access

  // 測試在合約中通過 get_context_free_data 獲取 context_free_data

  int size = get_context_free_data( cfa.cfd_idx, nullptr, 0 );

  eosio_assert( size > 0, "size determination failed" );

  eosio::bytes cfd( static_cast<size_t>(size) );

  size = get_context_free_data( cfa.cfd_idx, &cfd[0], static_cast<size_t>(size) );

  eosio_assert(static_cast<size_t>(size) == cfd.size(), "get_context_free_data failed" );

  uint32_t v = eosio::unpack<uint32_t>( &cfd[0], cfd.size() );

  eosio_assert( v == cfa.payload, "invalid value" );

  // 以下是測試一些功能

  // verify crypto api access

  checksum256 hash;

  char test[] = "test";

  ...

  // verify context_free_system_api

  eosio_assert( true, "verify eosio_assert can be called" );

  // 下面是測試一些在上下文無關action中不能使用的功能

} else if ( cfa.payload == 200 ) {

  // attempt to access non context free api, privileged_api

  is_privileged(act.name);

  eosio_assert( false, "privileged_api should not be allowed" );

} else if ( cfa.payload == 201 ) {

  // attempt to access non context free api, producer_api

  get_active_producers( nullptr, 0 );

  eosio_assert( false, "producer_api should not be allowed" );



...

} else if ( cfa.payload == 211 ) {

  send_deferred( N(testapi), N(testapi), "hello", 6 );

  eosio_assert( false, "transaction_api should not be allowed" );

}

}

接下來我們來看一看packed_transaction，通過這個類我們可以將trx打包，這樣可以最大的節省空間，關於它的功能，會在下面使用的提到。

2. Transaction的接收和轉發流程 瞭解Transaction類定義之後，我們先來看一下trx在EOS系統中的接收和轉發流程，確定發起trx的入口， 在EOS中，大部分trx都是由使用者所操縱的客戶端發向同步節點，再通過同步網路傳送給超級節點，超級節點會把trx打包進塊，這裡我們梳理一下這裡的邏輯，

對於一個節點，trx可能是其他節點同步過來的，也可能是客戶端通過api請求的，我們先看看api：

EOS中通過http_plugin外掛響應http請求，這裡我們只看處理邏輯，在chain_api_plugin.cpp中註冊的這兩個：

voidchain_api_plugin::plugin_startup() { ilog(“starting chain_api_plugin”); my.reset(newchain_api_plugin_impl(app().get_plugin().chain()));autoro_api = app().get_plugin().get_read_only_api();autorw_api = app().get_plugin().get_read_write_api(); app().get_plugin().add_api({ … CHAIN_RW_CALL_ASYNC(push_transaction, chain_apis::read_write::push_transaction_results,202), CHAIN_RW_CALL_ASYNC(push_transactions, chain_apis::read_write::push_transactions_results,202) });}

最終實際呼叫的是這裡：

// 呼叫流程 push_transactions -> push_recurse -> push_transactionvoidread_write::push_transaction(constread_write::push_transaction_params& params, next_function next) {try{autopretty_input =std::make_shared();autoresolver = make_resolver(this, abi_serializer_max_time);try{// 這裡在使用 packed_transaction 解包abi_serializer::from_variant(params, *pretty_input, resolver, abi_serializer_max_time); } EOS_RETHROW_EXCEPTIONS(chain::packed_transaction_type_exception,“Invalid packed transaction”)// 這裡呼叫 incoming::methods::transaction_async 函式app().get_method()(pretty_input,true, [this, next](constfc::static_variant& result) ->void{ …// 返回返回值， 略去}); }catch( boost::interprocess::bad_alloc& ) { raise(SIGUSR1); } CATCH_AND_CALL(next);}

注意這裡的 persist_until_expired 引數，我們在 EOS原始碼備忘-Block Produce機制 這篇文件中分析過。 incoming::methods::transaction_async註冊的是on_incoming_transaction_async函式：

my->_incoming_transaction_async_provider = app().get_method().register_provider([this](constpacked_transaction_ptr& trx,boolpersist_until_expired, next_function next) ->void{returnmy->on_incoming_transaction_async(trx, persist_until_expired, next ); });

on_incoming_transaction_async如下：

voidon_incoming_transaction_async(constpacked_transaction_ptr& trx,boolpersist_until_expired, next_function next){ chain::controller& chain = app().get_plugin().chain();if(!chain.pending_block_state()) { _pending_incoming_transactions.emplace_back(trx, persist_until_expired, next);return; }autoblock_time = chain.pending_block_state()->header.timestamp.to_time_point();// 返回結果的回撥autosend_response = [this, &trx, &next](constfc::static_variant& response) { next(response);if(response.contains()) { _transaction_ack_channel.publish(std::pair(response.get(), trx)); }else{ _transaction_ack_channel.publish(std::pair(nullptr, trx)); } };autoid = trx->id();// 超時時間檢查if( fc::time_point(trx->expiration()) < block_time ) { send_response(std::static_pointer_cast(std::make_shared(FC_LOG_MESSAGE(error,“expired transaction ${id}”, (“id”, id)) )));return; }// 檢查是否是已處理過的trxif( chain.is_known_unexpired_transaction(id) ) { send_response(std::static_pointer_cast(std::make_shared(FC_LOG_MESSAGE(error,“duplicate transaction ${id}”, (“id”, id)) )));return; }// 看看是否超過最大的執行時間了autodeadline = fc::time_point::now() + fc::milliseconds(_max_transaction_time_ms);booldeadline_is_subjective =false;if(_max_transaction_time_ms <0|| (_pending_block_mode == pending_block_mode::producing && block_time < deadline) ) { deadline_is_subjective =true; deadline = block_time; }try{// 這裡直接呼叫push_transaction來執行trxautotrace = chain.push_transaction(std::make_shared(*trx), deadline);if(trace->except) {if(failure_is_subjective(*trace->except, deadline_is_subjective)) { _pending_incoming_transactions.emplace_back(trx, persist_until_expired, next); }else{autoe_ptr = trace->except->dynamic_copy_exception(); send_response(e_ptr); } }else{if(persist_until_expired) {// if this trx didnt fail/soft-fail and the persist flag is set, store its ID so that we can// ensure its applied to all future speculative blocks as well._persistent_transactions.insert(transaction_id_with_expiry{trx->id(), trx->expiration()}); } send_response(trace); } }catch(constguard_exception& e ) { app().get_plugin().handle_guard_exception(e); }catch( boost::interprocess::bad_alloc& ) { raise(SIGUSR1); } CATCH_AND_CALL(send_response); }

注意上面的is_known_unexpired_transaction，程式碼如下：

boolcontroller::is_known_unexpired_transaction(consttransaction_id_type& id)const{returndb().find(id);}

與之對應的是這個函式：

voidtransaction_context::record_transaction(consttransaction_id_type& id, fc::time_point_sec expire ) {try{ control.db().create([&](transaction_object& transaction) { transaction.trx_id = id; transaction.expiration = expire; }); }catch(constboost::interprocess::bad_alloc& ) {throw; }catch( … ) { EOS_ASSERT(false, tx_duplicate,“duplicate transaction ${id}”, (“id”, id ) ); } }/// record_transaction

在push_transaction中會呼叫到，記錄trx已經被處理過了。

下面我們來看看send_response這個回撥：

autosend_response = [this, &trx, &next](constfc::static_variant& response) { next(response);if(response.contains()) { _transaction_ack_channel.publish(std::pair(response.get(), trx)); }else{ _transaction_ack_channel.publish(std::pair(nullptr, trx)); } };

在執行之後會呼叫send_response，這裡是將結果傳送到_transaction_ack_channel中，對於_transaction_ack_channel， 這個實際對應的是下面這個型別：

namespacecompat {namespacechannels {usingtransaction_ack = channel_decl>; } }

在EOS中在net_plugin註冊響應這個channel的函式:

  my->incoming_transaction_ack_subscription =

        app().get_channel<channels::transaction_ack>().subscribe(

              boost::bind(&net_plugin_impl::transaction_ack, my.get(), _1));

處理的函式如下：

voidnet_plugin_impl::transaction_ack(conststd::pair& results) { transaction_id_type id = results.second->id();if(results.first) { fc_ilog(logger,“signaled NACK, trx-id = ${id} : ${why}”,(“id”, id)(“why”, results.first->to_detail_string())); dispatcher->rejected_transaction(id); }else{ fc_ilog(logger,“signaled ACK, trx-id = ${id}”,(“id”, id)); dispatcher->bcast_transaction(*results.second); } }

3. push_transaction程式碼分析

這裡我們來分析下push_transaction的過程，作為執行trx的入口，這個函式在EOS中非常重要，另一方面，這裡EOS與Eosforce有一定區別，這裡會具體介紹。

TODO 需要一個流程圖，不過部落格還不支援

3.1 transaction_metadata

我們先來看下push_transaction的transaction_metadata引數， 這個引數統一了各種不同型別，不同行為的trx：

/**

• This data structure should store context-free cached data about a transaction such as

• packed/unpacked/compressed and recovered keys

*/

class transaction_metadata {

public:

  transaction_id_type                                        id;  // trx ID

  transaction_id_type                                        signed_id; // signed trx ID

  signed_transaction                                        trx;

  packed_transaction                                        packed_trx;

  optional<pair<chain_id_type, flat_set<public_key_type>>>  signing_keys;

  bool                                                      accepted = false; // 標註是否呼叫了accepted訊號，確保只調用一次

  bool                                                      implicit = false; // 是否忽略檢查

  bool                                                      scheduled = false; // 是否是延遲trx

  explicit transaction_metadata( const signed_transaction& t, packed_transaction::compression_type c = packed_transaction::none )

  :trx(t),packed_trx(t, c) {

    id = trx.id();

    //raw_packed = fc::raw::pack( static_cast<const transaction&>(trx) );

    signed_id = digest_type::hash(packed_trx);

  }

  explicit transaction_metadata( const packed_transaction& ptrx )

  :trx( ptrx.get_signed_transaction() ), packed_trx(ptrx) {

    id = trx.id();

    //raw_packed = fc::raw::pack( static_cast<const transaction&>(trx) );

    signed_id = digest_type::hash(packed_trx);

  }

  const flat_set<public_key_type>& recover_keys( const chain_id_type& chain_id );

  uint32_t total_actions()const { return trx.context_free_actions.size() + trx.actions.size(); }

};

using transaction_metadata_ptr = std::shared_ptr<transaction_metadata>;

先看一下implicit，這個引數指示下面的邏輯是否要忽略對於trx的各種檢查，一般用於系統內部的trx， 對於EOS，主要是處理on_block_transaction（可以參見出塊文件），在start_block呼叫：

…autoonbtrx =std::make_shared( get_on_block_transaction() ); onbtrx->implicit =true;// on_block trx 會被無條件接受autoreset_in_trx_requiring_checks = fc::make_scoped_exit(old_value=in_trx_requiring_checks,this{ in_trx_requiring_checks = old_value; }); in_trx_requiring_checks =true;// 修改in_trx_requiring_checks變數達到不將trx寫入區塊，一些系統的trx沒有必要寫入區塊。push_transaction( onbtrx, fc::time_point::maximum(), self.get_global_properties().configuration.min_transaction_cpu_usage,true);…

!> Eosforce不同之處

而對於EOSForce中，除了on_block action之外，onfee合約也是被設定為implicit==true的，onfee合約是eosforce的系統合約，設計用來收取交易的手續費。

3.2 push_transaction函式

下面我們逐行分析下程式碼，EOS中push_transaction程式碼如下：

/**

*  This is the entry point for new transactions to the block state. It will check authorization and

*  determine whether to execute it now or to delay it. Lastly it inserts a transaction receipt into

*  the pending block.

*/transaction_trace_ptrpush_transaction(consttransaction_metadata_ptr& trx,                                          fc::time_point deadline,uint32_tbilled_cpu_time_us,boolexplicit_billed_cpu_time =false){// deadline必須不為空// deadline是trx執行時間的一個大上限，為了防止某些trx執行時間過長導致出塊失敗等問題，// 這裡必須有一個嚴格的上限，一旦超過上限，交易會立即失敗。EOS_ASSERT(deadline != fc::time_point(), transaction_exception,"deadline cannot be uninitialized");      transaction_trace_ptr trace;// trace主要用來儲存執行中的一些錯誤資訊。try{// trx_context是執行trx的上下文狀態，下面會專門說明transaction_contexttrx_context(self, trx->trx, trx->id);if((bool)subjective_cpu_leeway && pending->_block_status == controller::block_status::incomplete) {            trx_context.leeway = *subjective_cpu_leeway;        }// 設定資料trx_context.deadline = deadline;        trx_context.explicit_billed_cpu_time = explicit_billed_cpu_time;        trx_context.billed_cpu_time_us = billed_cpu_time_us;        trace = trx_context.trace;try{if( trx->implicit ) {// 如果是implicit的就沒有必要做下面的一些檢查和記錄，這裡的檢查主要是資源方面的trx_context.init_for_implicit_trx();              trx_context.can_subjectively_fail =false;            }else{// 如果是重放並且不是重放過程中接到的新交易，則不去使用`record_transaction`記錄boolskip_recording = replay_head_time && (time_point(trx->trx.expiration) <= *replay_head_time);// 一些trx_context的初始化操作trx_context.init_for_input_trx( trx->packed_trx.get_unprunable_size(),                                              trx->packed_trx.get_prunable_size(),                                              trx->trx.signatures.size(),                                              skip_recording);            }if( trx_context.can_subjectively_fail && pending->_block_status == controller::block_status::incomplete ) {              check_actor_list( trx_context.bill_to_accounts );// Assumes bill_to_accounts is the set of actors authorizing the transaction}            trx_context.delay = fc::seconds(trx->trx.delay_sec);if( !self.skip_auth_check() && !trx->implicit ) {// 檢測交易所需要的許可權authorization.check_authorization(                      trx->trx.actions,                      trx->recover_keys( chain_id ),                      {},                      trx_context.delay,                      [](){}/*std::bind(&transaction_context::add_cpu_usage_and_check_time, &trx_context,

                            std::placeholders::_1)*/,false);            }// 執行，注意這時trx_context包括所有資訊和狀態trx_context.exec();            trx_context.finalize();// Automatically rounds up network and CPU usage in trace and bills payers if successfulautorestore = make_block_restore_point();if(!trx->implicit) {// 如果是非implicit的交易，則需要進入區塊。transaction_receipt::status_enum s = (trx_context.delay == fc::seconds(0))                                                    ? transaction_receipt::executed                                                    : transaction_receipt::delayed;              trace->receipt = push_receipt(trx->packed_trx, s, trx_context.billed_cpu_time_us, trace->net_usage);              pending->_pending_block_state->trxs.emplace_back(trx);            }else{// 注意，這裡implicit類的交易是不會進入區塊的，只會計入資源消耗// 因為這類的trx無條件執行，所以不需要另行記錄。transaction_receipt_header r;              r.status = transaction_receipt::executed;              r.cpu_usage_us = trx_context.billed_cpu_time_us;              r.net_usage_words = trace->net_usage /8;              trace->receipt = r;            }// 這裡會將執行過的action寫入待出塊狀態的_actions之中fc::move_append(pending->_actions, move(trx_context.executed));// call the accept signal but only once for this transaction// 為這個交易呼叫accept訊號，保證只調用一次if(!trx->accepted) {              trx->accepted =true;              emit( self.accepted_transaction, trx);            }// 觸發applied_transaction訊號emit(self.applied_transaction, trace);if( read_mode != db_read_mode::SPECULATIVE && pending->_block_status == controller::block_status::incomplete ) {//this may happen automatically in destructor, but I prefere make it more explicittrx_context.undo();            }else{              restore.cancel();              trx_context.squash();            }// implicit的trx壓根沒有在unapplied_transactions中if(!trx->implicit) {              unapplied_transactions.erase( trx->signed_id );            }returntrace;        }catch(constfc::exception& e) {            trace->except = e;            trace->except_ptr =std::current_exception();        }// 注意這裡，如果成功的話上面就返回了這裡是失敗的情況// failure_is_subjective 表明if(!failure_is_subjective(*trace->except)) {            unapplied_transactions.erase( trx->signed_id );        }        emit( self.accepted_transaction, trx );        emit( self.applied_transaction, trace );returntrace;      } FC_CAPTURE_AND_RETHROW((trace))  }/// push_transaction

上面註釋中闡述了大致的流程，下面仔細分析一下：

首先是trx_context，這個物件的類宣告如下：

classtransaction_context{…// 省略voiddispatch_action( action_trace& trace,constaction& a, account_name receiver,boolcontext_free =false,uint32_trecurse_depth =0);inlinevoiddispatch_action( action_trace& trace,constaction& a,boolcontext_free =false){ dispatch_action(trace, a, a.account, context_free); };voidschedule_transaction();voidrecord_transaction(consttransaction_id_type& id, fc::time_point_sec expire );voidvalidate_cpu_usage_to_bill(int64_tu,boolcheck_minimum =true)const;public: controller& control;// controller類的引用constsigned_transaction& trx;// 要執行的trxtransaction_id_type id; optional undo_session; transaction_trace_ptr trace;// 記錄錯誤的tracefc::time_point start;// 起始時刻fc::time_point published;// publish的時刻vector executed;// 執行完成的actionflat_set bill_to_accounts; flat_set validate_ram_usage;/// the maximum number of virtual CPU instructions of the transaction that can be safely billed to the billable accountsuint64_tinitial_max_billable_cpu =0; fc::microseconds delay;boolis_input =false;boolapply_context_free =true;boolcan_subjectively_fail =true; fc::time_point deadline = fc::time_point::maximum(); fc::microseconds leeway = fc::microseconds(3000);int64_tbilled_cpu_time_us =0;boolexplicit_billed_cpu_time =false;private:boolis_initialized =false;uint64_tnet_limit =0;boolnet_limit_due_to_block =true;boolnet_limit_due_to_greylist =false;uint64_teager_net_limit =0;uint64_t& net_usage;/// reference to trace->net_usageboolcpu_limit_due_to_greylist =false; fc::microseconds initial_objective_duration_limit; fc::microseconds objective_duration_limit; fc::time_point _deadline = fc::time_point::maximum();int64_tdeadline_exception_code = block_cpu_usage_exceeded::code_value;int64_tbilling_timer_exception_code = block_cpu_usage_exceeded::code_value; fc::time_point pseudo_start; fc::microseconds billed_time; fc::microseconds billing_timer_duration_limit; };

我們先看一下init_for_input_trx：

voidtransaction_context::init_for_input_trx(uint64_tpacked_trx_unprunable_size,// 這個是指trx打包後完整的大小uint64_tpacked_trx_prunable_size,// 這個指trx額外資訊的大小uint32_tnum_signatures,// 這個引數沒用上boolskip_recording )// 是否要跳過記錄{// 根據cfg和trx初始化資源constauto& cfg = control.get_global_properties().configuration;// 利用packed_trx_unprunable_size和packed_trx_prunable_size 計算net資源消耗uint64_tdiscounted_size_for_pruned_data = packed_trx_prunable_size;if( cfg.context_free_discount_net_usage_den >0&& cfg.context_free_discount_net_usage_num < cfg.context_free_discount_net_usage_den ) { discounted_size_for_pruned_data *= cfg.context_free_discount_net_usage_num; discounted_size_for_pruned_data = ( discounted_size_for_pruned_data + cfg.context_free_discount_net_usage_den -1) / cfg.context_free_discount_net_usage_den;// rounds up}uint64_tinitial_net_usage =static_cast(cfg.base_per_transaction_net_usage) + packed_trx_unprunable_size + discounted_size_for_pruned_data;// 對於delay trx需要額外的net資源if( trx.delay_sec.value >0) {// If delayed, also charge ahead of time for the additional net usage needed to retire the delayed transaction// whether that be by successfully executing, soft failure, hard failure, or expiration.initial_net_usage +=static_cast(cfg.base_per_transaction_net_usage) +static_cast(config::transaction_id_net_usage); }// 初始化一些資訊published = control.pending_block_time(); is_input =true;if(!control.skip_trx_checks()) { control.validate_expiration(trx); control.validate_tapos(trx); control.validate_referenced_accounts(trx); } init( initial_net_usage);// 這裡呼叫init函式， 在這個函式中會處理cpu資源和ram資源if(!skip_recording)// 將trx新增入記錄中record_transaction( id, trx.expiration );/// checks for dupes}

這裡會先計算net，再在init函式中處理其他資源：

voidtransaction_context::init(uint64_tinitial_net_usage) { EOS_ASSERT( !is_initialized, transaction_exception,“cannot initialize twice”);conststaticint64_tlarge_number_no_overflow =std::numeric_limits::max()/2;constauto& cfg = control.get_global_properties().configuration;auto& rl = control.get_mutable_resource_limits_manager(); net_limit = rl.get_block_net_limit(); objective_duration_limit = fc::microseconds( rl.get_block_cpu_limit() ); _deadline = start + objective_duration_limit;// Possibly lower net_limit to the maximum net usage a transaction is allowed to be billedif( cfg.max_transaction_net_usage <= net_limit ) { net_limit = cfg.max_transaction_net_usage; net_limit_due_to_block =false; }// Possibly lower objective_duration_limit to the maximum cpu usage a transaction is allowed to be billedif( cfg.max_transaction_cpu_usage <= objective_duration_limit.count() ) { objective_duration_limit = fc::microseconds(cfg.max_transaction_cpu_usage); billing_timer_exception_code = tx_cpu_usage_exceeded::code_value; _deadline = start + objective_duration_limit; }// Possibly lower net_limit to optional limit set in the transaction headeruint64_ttrx_specified_net_usage_limit =static_cast(trx.max_net_usage_words.value) *8;if( trx_specified_net_usage_limit >0&& trx_specified_net_usage_limit <= net_limit ) { net_limit = trx_specified_net_usage_limit; net_limit_due_to_block =false; }// Possibly lower objective_duration_limit to optional limit set in transaction headerif( trx.max_cpu_usage_ms >0) {autotrx_specified_cpu_usage_limit = fc::milliseconds(trx.max_cpu_usage_ms);if( trx_specified_cpu_usage_limit <= objective_duration_limit ) { objective_duration_limit = trx_specified_cpu_usage_limit; billing_timer_exception_code = tx_cpu_usage_exceeded::code_value; _deadline = start + objective_duration_limit; } } initial_objective_duration_limit = objective_duration_limit;if( billed_cpu_time_us >0)// could also call on explicit_billed_cpu_time but it would be redundantvalidate_cpu_usage_to_bill( billed_cpu_time_us,false);// Fail early if the amount to be billed is too high// Record accounts to be billed for network and CPU usagefor(constauto& act : trx.actions ) {for(constauto& auth : act.authorization ) { bill_to_accounts.insert( auth.actor ); } } validate_ram_usage.reserve( bill_to_accounts.size() );// Update usage values of accounts to reflect new timerl.update_account_usage( bill_to_accounts, block_timestamp_type(control.pending_block_time()).slot );// Calculate the highest network usage and CPU time that all of the billed accounts can afford to be billedint64_taccount_net_limit =0;int64_taccount_cpu_limit =0;boolgreylisted_net =false, greylisted_cpu =false;std::tie( account_net_limit, account_cpu_limit, greylisted_net, greylisted_cpu) = max_bandwidth_billed_accounts_can_pay(); net_limit_due_to_greylist |= greylisted_net; cpu_limit_due_to_greylist |= greylisted_cpu; eager_net_limit = net_limit;// Possible lower eager_net_limit to what the billed accounts can pay plus some (objective) leewayautonew_eager_net_limit =std::min( eager_net_limit,static_cast(account_net_limit + cfg.net_usage_leeway) );if( new_eager_net_limit < eager_net_limit ) { eager_net_limit = new_eager_net_limit; net_limit_due_to_block =false; }// Possibly limit deadline if the duration accounts can be billed for (+ a subjective leeway) does not exceed current deltaif( (fc::microseconds(account_cpu_limit) + leeway) <= (_deadline - start) ) { _deadline = start + fc::microseconds(account_cpu_limit) + leeway; billing_timer_exception_code = leeway_deadline_exception::code_value; } billing_timer_duration_limit = _deadline - start;// Check if deadline is limited by caller-set deadline (only change deadline if billed_cpu_time_us is not set)if( explicit_billed_cpu_time || deadline < _deadline ) { _deadline = deadline; deadline_exception_code = deadline_exception::code_value; }else{ deadline_exception_code = billing_timer_exception_code; } eager_net_limit = (eager_net_limit/8)*8;// Round down to nearest multiple of word size (8 bytes) so check_net_usage can be efficientif( initial_net_usage >0) add_net_usage( initial_net_usage );// Fail early if current net usage is already greater than the calculated limitchecktime();// Fail early if deadline has already been exceededis_initialized =true; }

以上就是transaction_context初始化過程，這裡主要是處理資源消耗。

下面是exec函式，這個函式很簡單：

voidtransaction_context::exec() { EOS_ASSERT( is_initialized, transaction_exception,“must first initialize”);// 呼叫dispatch_action，這裡並沒有對上下文無關trx進行特別的操作，只是引數不同if( apply_context_free ) {for(constauto& act : trx.context_free_actions ) { trace->action_traces.emplace_back(); dispatch_action( trace->action_traces.back(), act,true); } }if( delay == fc::microseconds() ) {for(constauto& act : trx.actions ) { trace->action_traces.emplace_back(); dispatch_action( trace->action_traces.back(), act ); } }else{// 對於延遲交易，這裡特別處理schedule_transaction(); } }

主要執行在dispatch_action中，這裡會根據action不同分別觸發對應的呼叫：

voidtransaction_context::dispatch_action( action_trace& trace,constaction& a, account_name receiver,boolcontext_free,uint32_trecurse_depth ) {// 構建apply_context執行action， apply_context的分析在下節進行apply_contextacontext( control, *this, a, recurse_depth ); acontext.context_free = context_free; acontext.receiver = receiver;try{ acontext.exec(); }catch( … ) { trace = move(acontext.trace);throw; }// 彙總結果到tracetrace = move(acontext.trace); }

對於延遲交易，執行schedule_transaction：

voidtransaction_context::schedule_transaction() {// 因為交易延遲執行，會消耗額外的net和ram資源// Charge ahead of time for the additional net usage needed to retire the delayed transaction// whether that be by successfully executing, soft failure, hard failure, or expiration.if( trx.delay_sec.value ==0) {// Do not double bill. Only charge if we have not already charged for the delay.constauto& cfg = control.get_global_properties().configuration; add_net_usage(static_cast(cfg.base_per_transaction_net_usage) +static_cast(config::transaction_id_net_usage) );// Will exit early if net usage cannot be payed.}autofirst_auth = trx.first_authorizor();// 將延遲交易寫入節點執行時狀態資料庫中，到時會從這裡查找出來執行uint32_ttrx_size =0;constauto& cgto = control.db().create( [&](auto& gto ) { gto.trx_id = id; gto.payer = first_auth; gto.sender = account_name();/// delayed transactions have no sendergto.sender_id = transaction_id_to_sender_id( gto.trx_id ); gto.published = control.pending_block_time(); gto.delay_until = gto.published + delay; gto.expiration = gto.delay_until + fc::seconds(control.get_global_properties().configuration.deferred_trx_expiration_window); trx_size = gto.set( trx ); });// 因為要寫記憶體記錄，所以也消耗了一定的ramadd_ram_usage( cgto.payer, (config::billable_size_v + trx_size) ); }

呼叫完exec之後會呼叫transaction_context::finalize()：

// 這裡主要是處理資源消耗voidtransaction_context::finalize() { EOS_ASSERT( is_initialized, transaction_exception,“must first initialize”);if( is_input ) {auto& am = control.get_mutable_authorization_manager();for(constauto& act : trx.actions ) {for(constauto& auth : act.authorization ) { am.update_permission_usage( am.get_permission(auth) ); } } }auto& rl = control.get_mutable_resource_limits_manager();for(autoa : validate_ram_usage ) { rl.verify_account_ram_usage( a ); }// Calculate the new highest network usage and CPU time that all of the billed accounts can afford to be billedint64_taccount_net_limit =0;int64_taccount_cpu_limit =0;boolgreylisted_net =false, greylisted_cpu =false;std::tie( account_net_limit, account_cpu_limit, greylisted_net, greylisted_cpu) = max_bandwidth_billed_accounts_can_pay(); net_limit_due_to_greylist |= greylisted_net; cpu_limit_due_to_greylist |= greylisted_cpu;// Possibly lower net_limit to what the billed accounts can payif(static_cast(account_net_limit) <= net_limit ) {//NOTE:net_limit may possibly not be objective anymore due to net greylisting, but it should still be no greater than the truly objective net_limitnet_limit =static_cast(account_net_limit); net_limit_due_to_block =false; }// Possibly lower objective_duration_limit to what the billed accounts can payif( account_cpu_limit <= objective_duration_limit.count() ) {//NOTE:objective_duration_limit may possibly not be objective anymore due to cpu greylisting, but it should still be no greater than the truly objective objective_duration_limitobjective_duration_limit = fc::microseconds(account_cpu_limit); billing_timer_exception_code = tx_cpu_usage_exceeded::code_value; } net_usage = ((net_usage +7)/8)*8;// Round up to nearest multiple of word size (8 bytes)eager_net_limit = net_limit; check_net_usage();autonow = fc::time_point::now(); trace->elapsed = now - start; update_billed_cpu_time( now ); validate_cpu_usage_to_bill( billed_cpu_time_us ); rl.add_transaction_usage( bill_to_accounts,static_cast(billed_cpu_time_us), net_usage, block_timestamp_type(control.pending_block_time()).slot );// Should never fail}

接下來make_block_restore_point，這裡添加了一個檢查點：

// The returned scoped_exit should not exceed the lifetime of the pending which existed when make_block_restore_point was called.fc::scoped_exit> make_block_restore_point() {autoorig_block_transactions_size = pending->_pending_block_state->block->transactions.size();autoorig_state_transactions_size = pending->_pending_block_state->trxs.size();autoorig_state_actions_size = pending->_actions.size();std::function callback = this, orig_block_transactions_size, orig_state_transactions_size, orig_state_actions_size { pending->_pending_block_state->block->transactions.resize(orig_block_transactions_size); pending->_pending_block_state->trxs.resize(orig_state_transactions_size); pending->_actions.resize(orig_state_actions_size); };returnfc::make_scoped_exit(std::move(callback) ); }

而後對於不是implicit的交易會呼叫push_receipt，這裡會將trx寫入區塊資料中，這也意味著implicit為true的交易雖然執行了，但不會在區塊中。

/**

*  Adds the transaction receipt to the pending block and returns it.

*/templateconsttransaction_receipt&push_receipt(constT& trx, transaction_receipt_header::status_enum status,uint64_tcpu_usage_us,uint64_tnet_usage ){uint64_tnet_usage_words = net_usage /8;      EOS_ASSERT( net_usage_words*8== net_usage, transaction_exception,"net_usage is not divisible by 8");      pending->_pending_block_state->block->transactions.emplace_back( trx );      transaction_receipt& r = pending->_pending_block_state->block->transactions.back();      r.cpu_usage_us        = cpu_usage_us;      r.net_usage_words      = net_usage_words;      r.status              = status;returnr;  }

上面的邏輯很大程度上和implicit為true時的邏輯重複，估計以後會重構。

接下來值得注意的是這裡：

if( read_mode != db_read_mode::SPECULATIVE && pending->_block_status == controller::block_status::incomplete ) {//this may happen automatically in destructor, but I prefere make it more explicittrx_context.undo(); }else{ restore.cancel(); trx_context.squash(); }

TODO trx_context.undo

這裡呼叫database::session對應的函式，

!> Eosforce不同之處

以上是EOS的流程，這裡我們再來看看Eosforce的不同之處，Eosforce與EOS一個明顯的不同是Eosforce採用了基於手續費的資源模型， 這種模型意味著，如果一個交易在超級節點打包進塊時失敗了，此時也要收取手續費，否則會造成潛在的攻擊風險，所以Eosforce中，執行失敗的交易也會寫入區塊中，這樣每次執行時會呼叫對應onfee。 另一方面, Eosforce雖然使用手續費，但是還是區分cpu，net，ram資源，並且在大的限制上依然進行檢查。 後續Eosforce會完成新的資源模型，這裡會有所改動。

Eosforce中的push_transaction函式如下：

transaction_trace_ptrpush_transaction(consttransaction_metadata_ptr& trx, fc::time_point deadline,uint32_tbilled_cpu_time_us,boolexplicit_billed_cpu_time =false){ EOS_ASSERT(deadline != fc::time_point(), transaction_exception,“deadline cannot be uninitialized”);// eosforce暫時沒有開放延遲交易和上下文無關交易EOS_ASSERT(trx->trx.delay_sec.value ==0UL, transaction_exception,“delay,transaction failed”); EOS_ASSERT(trx->trx.context_free_actions.size()==0, transaction_exception,“context free actions size should be zero!”);// 在eosforce中，為了安全性，對於特定一些交易進行了額外的驗證，主要是考慮到，系統會將執行錯誤的交易寫入區塊// 此時就要先驗證下交易內容，特別是大小上有沒有超出限制，否則將會帶來安全問題。check_action(trx->trx.actions); transaction_trace_ptr trace;try{// 一樣的程式碼 略去…try{// 一樣的程式碼 略去…// 處理手續費EOS_ASSERT(trx->trx.fee == txfee.get_required_fee(trx->trx), transaction_exception,“set tx fee failed”); EOS_ASSERT(txfee.check_transaction(trx->trx) ==true, transaction_exception,“transaction include actor more than one”);try{// 這裡會執行onfee合約，也是通過push_transaction實現的autoonftrx =std::make_shared( get_on_fee_transaction(trx->trx.fee, trx->trx.actions[0].authorization[0].actor) ); onftrx->implicit =true;autoonftrace = push_transaction( onftrx, fc::time_point::maximum(), config::default_min_transaction_cpu_usage,true);// 這裡如果執行失敗直接丟擲異常，不會執行下面的東西if( onftrace->except )throw*onftrace->except; }catch(constfc::exception &e) { EOS_ASSERT(false, transaction_exception,“on fee transaction failed, exception: ${e}”, (“e”, e)); }catch( … ) { EOS_ASSERT(false, transaction_exception,“on fee transaction failed, but shouldn’t enough asset to pay for transaction fee”); } }// 注意這一層try catch，因為eos中出錯的交易會被拋棄，所以eos的異常會被直接丟擲到外層// 而在eosforce中出錯的交易會進入區塊// 但是要注意，這裡如果這裡並不是在超級節點出塊時呼叫，雖然也會執行下面的邏輯，但是不會被轉發給超級節點。try{if(explicit_billed_cpu_time && billed_cpu_time_us ==0){// 在eosforce中 因為超級節點打包區塊時失敗的交易也會被寫入區塊中，// 而很多交易失敗的原因不是交易本身有問題，而是在執行交易時，資源上限被觸發，導致交易被直接判定為失敗，// 這時寫入區塊的交易的cpu消耗是0, 這裡是需要失敗的，否則重跑區塊時會出現不同步的情況EOS_ASSERT(false, transaction_exception,“billed_cpu_time_us is 0”); } trx_context.exec(); trx_context.finalize();// Automatically rounds up network and CPU usage in trace and bills payers if successful}catch(constfc::exception &e) { trace->except = e; trace->except_ptr =std::current_exception();// eosforce加了一些日誌if(head->block_num !=1) { elog("—trnasction exe failed--------trace: ${trace}", (“trace”, trace)); } }autorestore = make_block_restore_point();if(!trx->implicit) {// 這裡不太好的地方是，對於出錯的交易也被標為executed（嚴格說也確實是executed），後續eosforce將會重構這裡transaction_receipt::status_enum s = (trx_context.delay == fc::seconds(0)) ? transaction_receipt::executed : transaction_receipt::delayed; trace->receipt = push_receipt(trx->packed_trx, s, trx_context.billed_cpu_time_us, trace->net_usage); pending->_pending_block_state->trxs.emplace_back(trx); }else{ transaction_receipt_header r; r.status = transaction_receipt::executed; r.cpu_usage_us = trx_context.billed_cpu_time_us; r.net_usage_words = trace->net_usage /8; trace->receipt = r; }// 以下是相同的} FC_CAPTURE_AND_RETHROW((trace)) }/// push_transaction

可以看出主要不同就是手續費導致的，這裡必須要注意，就是eosforce中區塊內會包括一些出錯的交易。

4. apply_context程式碼分析

這裡我們來看看action的執行過程，上面在dispatch_action中建立apply_context執行action，我們這裡分析這一塊的程式碼。

apply_context結構比較大，主要是資料結構實現內容很多，這裡我們只分析功能點，從這方面入手看結構，先從exec開始， 在上面push_trx最終呼叫的就是這個函式，執行actions：

voidapply_context::exec(){// 先新增receiver，關於_notified下面分析_notified.push_back(receiver);// 執行exec_one，這裡是實際執行action的地方，下面單獨分析trace = exec_one();// 下面處理inline action// 注意不是從0開始，會繞過上面新增的receiverfor(uint32_ti =1; i < _notified.size(); ++i ) { receiver = _notified[i];// 通知指定的賬戶 關於_notified下面分析trace.inline_traces.emplace_back( exec_one() ); }// 防止呼叫inline action過深if( _cfa_inline_actions.size() >0|| _inline_actions.size() >0) { EOS_ASSERT( recurse_depth < control.get_global_properties().configuration.max_inline_action_depth, transaction_exception,“inline action recursion depth reached”); }// 先執行_cfa_inline_actionsfor(constauto& inline_action : _cfa_inline_actions ) { trace.inline_traces.emplace_back(); trx_context.dispatch_action( trace.inline_traces.back(), inline_action, inline_action.account,true, recurse_depth +1); }// 再執行_inline_actionsfor(constauto& inline_action : _inline_actions ) { trace.inline_traces.emplace_back(); trx_context.dispatch_action( trace.inline_traces.back(), inline_action, inline_action.account,false, recurse_depth +1); }}/// exec()

這裡的邏輯基本都是處理inline action，inline action允許在一個合約中觸發另外一個合約的呼叫，需要注意的是這裡與程式語言中的函式呼叫並不相同，從上面程式碼也可以看出，系統會先執行合約對應的action，再執行合約中的宣告呼叫的inline action，注意recurse_depth，顯然迴圈呼叫合約次數深度過高會引起錯誤。

為了更好的理解程式碼過程我們先來仔細看下 inline action。在合約中可以這樣使用，程式碼出自dice：

//@abi actionvoiddeposit(constaccount_name from,constasset& quantity ){ … action( permission_level{ from, N(active) }, N(eosio.token), N(transfer),std::make_tuple(from, _self, quantity,std::string("")) ).send(); … }

這裡send會把action打包並呼叫下面的send_inline：

voidsend_inline( array_ptr data,size_tdata_len ){//TODO:Why is this limit even needed? And why is it not consistently checked on actions in input or deferred transactionsEOS_ASSERT( data_len < context.control.get_global_properties().configuration.max_inline_action_size, inline_action_too_big,“inline action too big”); action act; fc::raw::unpack(data, data_len, act); context.execute_inline(std::move(act)); }

可以看到這裡呼叫的是內部的execute_inline函式：

/**

• This will execute an action after checking the authorization. Inline transactions are

• implicitly authorized by the current receiver (running code). This method has significant

• security considerations and several options have been considered:

• 1. priviledged accounts (those marked as such by block producers) can authorize any action
• 2. all other actions are only authorized by ‘receiver’ which means the following:

•    a. the user must set permissions on their account to allow the 'receiver' to act on their behalf
  

• Discarded Implemenation: at one point we allowed any account that authorized the current transaction

• to implicitly authorize an inline transaction. This approach would allow privelege escalation and

• make it unsafe for users to interact with certain contracts. We opted instead to have applications

• ask the user for permission to take certain actions rather than making it implicit. This way users

• can better understand the security risk.

/voidapply_context::execute_inline( action&& a ) {// 先做了一些檢查auto code = control.db().find(a.account); EOS_ASSERT( code !=nullptr, action_validate_exception,“inline action’s code account ${account} does not exist”, (“account”, a.account) );for(constauto& auth : a.authorization ) {auto* actor = control.db().find(auth.actor); EOS_ASSERT( actor !=nullptr, action_validate_exception,“inline action’s authorizing actor ${account} does not exist”, (“account”, auth.actor) ); EOS_ASSERT( control.get_authorization_manager().find_permission(auth) !=nullptr, action_validate_exception,“inline action’s authorizations include a non-existent permission: ${permission}”, (“permission”, auth) ); }// No need to check authorization if: replaying irreversible blocks; contract is privileged; or, contract is calling itself.// 上面幾種情況下不需要做許可權檢查if( !control.skip_auth_check() && !privileged && a.account != receiver ) { control.get_authorization_manager() .check_authorization( {a}, {}, {{receiver, config::eosio_code_name}}, control.pending_block_time() - trx_context.published,std::bind(&transaction_context::checktime, &this->trx_context),false);//QUESTION: Is it smart to allow a deferred transaction that has been delayed for some time to get away// with sending an inline action that requires a delay even though the decision to send that inline// action was made at the moment the deferred transaction was executed with potentially no forewarning?}// 這裡只是把這個act放入_inline_actions列表中，並沒有執行。_inline_actions.emplace_back( move(a) );}

注意上面程式碼中最後的_inline_actions，這裡面放著執行action時所觸發的所有action的資料，回到exec中：

// 防止呼叫inline action過深if( _cfa_inline_actions.size() >0|| _inline_actions.size() >0) { EOS_ASSERT( recurse_depth < control.get_global_properties().configuration.max_inline_action_depth, transaction_exception,“inline action recursion depth reached”); }// 先執行_cfa_inline_actionsfor(constauto& inline_action : _cfa_inline_actions ) { trace.inline_traces.emplace_back(); trx_context.dispatch_action( trace.inline_traces.back(), inline_action, inline_action.account,true, recurse_depth +1); }// 再執行_inline_actionsfor(constauto& inline_action : _inline_actions ) { trace.inline_traces.emplace_back(); trx_context.dispatch_action( trace.inline_traces.back(), inline_action, inline_action.account,false, recurse_depth +1); }

這後半部分就是執行action，注意上面我們沒有跟蹤_cfa_inline_actions的流程，這裡和_inline_actions的流程是一致的，區別是在合約中由send_context_free觸發。

以上我們看了下inline action的處理，上面exec中沒有提及的是_notified，下面來看看這個， 在合約中可以呼叫require_recipient：

// 把賬戶新增至通知賬戶列表中voidapply_context::require_recipient( account_name recipient ) {if( !has_recipient(recipient) ) { _notified.push_back(recipient); }}

在執行完action之後，執行inline action之前（嚴格上說inline action 不是action的一部分，所以在這之前）會通知所有在執行合約過程中新增入_notified的賬戶：

// 注意不是從0開始，會繞過上面新增的receiverfor(uint32_ti =1; i < _notified.size(); ++i ) { receiver = _notified[i]; trace.inline_traces.emplace_back( exec_one() ); }

這裡可能有疑問的是為什麼又執行了一次exec_one，下面分析exec_one時會說明。

以上我們分析了一下exec，這裡主要是呼叫exec_one來執行合約，下面就來看看exec_one：

// 執行action，注意receiveraction_trace apply_context::exec_one(){autostart = fc::time_point::now();constauto& cfg = control.get_global_properties().configuration;try{// 這裡是receiver是作為一個合約賬戶的情況constauto& a = control.get_account( receiver ); privileged = a.privileged;// 這裡檢查action是不是系統內部的合約，關於這方面下面會單獨分析autonative = control.find_apply_handler( receiver, act.account, act.name );if( native ) {if( trx_context.can_subjectively_fail && control.is_producing_block()) { control.check_contract_list( receiver ); control.check_action_list( act.account, act.name ); }// 這裡會執行cpp中定義的程式碼(*native)( *this); }// 如果是合約賬戶的話，這裡會執行if( a.code.size() >0// 這裡對 setcode 單獨處理了一下，這是因為setcode和其他合約都使用了code資料// 但是 setcode 是在cpp層呼叫的，code作為引數，所以這裡就不會呼叫code。&& !(act.account == config::system_account_name && act.name == N( setcode ) && receiver == config::system_account_name)) {if( trx_context.can_subjectively_fail && control.is_producing_block()) {// 各種黑白名單檢查control.check_contract_list( receiver );// 這裡主要是account黑白名單，不再細細說明control.check_action_list( act.account, act.name );// 這裡主要是action黑名單，不再細細說明}try{// 這裡就會呼叫虛擬機器執行code，關於這方面，我們會單獨寫一篇分析文件control.get_wasm_interface().apply( a.code_version, a.code, *this); }catch(constwasm_exit& ) {} } } FC_RETHROW_EXCEPTIONS(warn,“pending console output: ${console}”, (“console”, _pending_console_output.str()))// 這裡的程式碼分成了兩部分，這裡其實應該重構一下，下面的邏輯應該單獨提出一個函式。// 上面對於_notified其實就是從這裡開始// 整理action_receipt資料action_receipt r; r.receiver = receiver; r.act_digest = digest_type::hash(act); r.global_sequence = next_global_sequence(); r.recv_sequence = next_recv_sequence( receiver );constauto& account_sequence = db.get(act.account); r.code_sequence = account_sequence.code_sequence; r.abi_sequence = account_sequence.abi_sequence;for(constauto& auth : act.authorization ) { r.auth_sequence[auth.actor] = next_auth_sequence( auth.actor ); }// 這裡會生成一個action_trace結構直接用來標誌action_tracet®; t.trx_id = trx_context.id; t.act = act; t.console = _pending_console_output.str();// 放入以執行的列表中trx_context.executed.emplace_back( move® );// 日誌if( control.contracts_console() ) { print_debug(receiver, t); } reset_console(); t.elapsed = fc::time_point::now() - start;returnt;}

這裡先看看對於加入_notified的賬戶的處理， 正常的邏輯中，執行的結果中會產生所有_notified（不包含最初的receiver）中賬戶對應的action_trace的列表， 這些會存入inline_traces中，這裡其實是把通知賬戶的過程也當作了一種“inline action”。

這些trace資訊會被其他外掛利用，目前主要是history外掛中的on_action_trace函式，這裡會將所有action的執行資訊和結果存入action_history_object供api呼叫，具體的過程這裡不再訊息描述。

以上就是整個apply_context執行合約的過程。

5. 幾個內建的action

在EOS中有一些action的實現是在cpp層的，這裡單獨看下。

如果看合約中，會有這樣幾個只有定義而沒有實現的合約：

/*

* Method parameters commented out to prevent generation of code that parses input data.

*/classnative:publiceosio::contract {public:usingeosio::contract::contract;/**

      *  Called after a new account is created. This code enforces resource-limits rules

      *  for new accounts as well as new account naming conventions.

      *

      *  1. accounts cannot contain '.' symbols which forces all acccounts to be 12

      *  characters long without '.' until a future account auction process is implemented

      *  which prevents name squatting.

      *

      *  2. new accounts must stake a minimal number of tokens (as set in system parameters)

      *    therefore, this method will execute an inline buyram from receiver for newacnt in

      *    an amount equal to the current new account creation fee.

      */voidnewaccount( account_name    creator,                          account_name    newact/*  no need to parse authorites

                      const authority& owner,

                      const authority& active*/);voidupdateauth(/*account_name    account,

                            permission_name  permission,

                            permission_name  parent,

                            const authority& data*/){}voiddeleteauth(/*account_name account, permission_name permission*/){}voidlinkauth(/*account_name    account,

                          account_name    code,

                          action_name    type,

                          permission_name requirement*/){}voidunlinkauth(/*account_name account,

                            account_name code,

                            action_name  type*/){}voidcanceldelay(/*permission_level canceling_auth, transaction_id_type trx_id*/){}voidonerror(/*const bytes&*/){}  };

這些合約是在eos專案的cpp中實現的，這裡的宣告是為了適配合約名相關的api， 這裡Eosforce有個問題，就是在最初的實現中，將這些宣告刪去了，導致json_to_bin api出錯，這裡後續會修正這個問題。

對於這些合約，在上面我們指出是在exec_one中處理的，實際的註冊在這裡：

voidset_apply_handler( account_name receiver, account_name contract, action_name action, apply_handler v ){ apply_handlers[receiver][make_pair(contract,action)] = v; } …#defineSET_APP_HANDLER( receiver, contract, action) \ set_apply_handler( #receiver, #contract, #action, &BOOST_PP_CAT(apply_, BOOST_PP_CAT(contract, BOOST_PP_CAT(_,action) ) ) )SET_APP_HANDLER( eosio, eosio, newaccount ); SET_APP_HANDLER( eosio, eosio, setcode ); SET_APP_HANDLER( eosio, eosio, setabi ); SET_APP_HANDLER( eosio, eosio, updateauth ); SET_APP_HANDLER( eosio, eosio, deleteauth ); SET_APP_HANDLER( eosio, eosio, linkauth ); SET_APP_HANDLER( eosio, eosio, unlinkauth );/*

SET_APP_HANDLER( eosio, eosio, postrecovery );

SET_APP_HANDLER( eosio, eosio, passrecovery );

SET_APP_HANDLER( eosio, eosio, veto