1. 概述

官方關(guān)于智能合約介紹的文檔：
https://developers.eos.io/eosio-cpp/docs/introduction

Hello World智能合約文檔：
https://developers.eos.io/eosio-cpp/docs/hello-world

基于EOSIO的區(qū)塊鏈?zhǔn)褂?a target="_blank" rel="nofollow">WebAssembly（WASM）執(zhí)行用戶生成的應(yīng)用程序和代碼。WASM是一種新興的Web標(biāo)準(zhǔn)力试，得到了Google，Microsoft饲做，Apple和其他公司的廣泛支持鸥昏。目前，用于構(gòu)建編譯為WASM的應(yīng)用程序的最成熟的工具鏈?zhǔn)?a target="_blank" rel="nofollow">clang / llvm及其C / C ++編譯器。為獲得最佳兼容性脂矫，建議使用EOSIO工具鏈。

第三方開發(fā)的其他工具鏈包括：Rust霉晕，Python和Solidity羹唠。雖然這些其他語言可能看起來更簡(jiǎn)單，但它們的性能可能會(huì)影響可以構(gòu)建的應(yīng)用程序的規(guī)模娄昆。我們希望C ++將成為開發(fā)高性能和安全智能合約的最佳語言佩微，并計(jì)劃在可預(yù)見的未來使用C ++。

在使用C++編寫完成合約代碼后萌焰，通過EOSIO軟件中提供的eosiocpp工具哺眯，將C++代碼編譯生成WASM（wasm的文本格式是后綴是wast）文件和abi文件，再利用cleos工具（將代碼部署到鏈上扒俯，也就是存到區(qū)塊數(shù)據(jù)中奶卓。

2. EOS智能合約與以太坊智能合約的區(qū)別

以下內(nèi)容節(jié)選自全面理解EOS——4.測(cè)試智能合約與EOS發(fā)幣

1.名稱不同

在EOS中具有賬號(hào)的概念，智能合約名也就是賬號(hào)名撼玄。而以太坊中的合約是一個(gè)個(gè)不同的地址夺姑。

2.升級(jí)方式不同

以太坊的合約不可升級(jí)，一旦部署之后掌猛，代碼不可修改盏浙。如果需要修改，只能在一個(gè)新的地址上重新部署荔茬。而EOS的智能合約和賬號(hào)綁定后废膘，賬號(hào)可直接升級(jí)智能合約的代碼，其實(shí)就相當(dāng)于向鏈上重新上傳了代碼慕蔚。

3.資源消耗不同

以太坊智能合約的執(zhí)行需要消耗gas丐黄，也就是每個(gè)步驟都有手續(xù)費(fèi)，手續(xù)費(fèi)不夠就不會(huì)繼續(xù)執(zhí)行孔飒，之前的操作也會(huì)被回滾灌闺，而且手續(xù)費(fèi)也不退艰争。而EOS的智能合約不需要首先費(fèi)，但是部署合約要消耗RAM桂对，傳送信息和執(zhí)行合約需要消耗抵押而得的CPU和網(wǎng)絡(luò)帶寬园细。

3.文件結(jié)構(gòu)

eosiocpp工具可以初始化一份新的合約，簡(jiǎn)化我們的工作接校。

使用eosiocpp創(chuàng)建一份智能合約：

yuyangdeMacBook-Pro:eos yuyang$ eosiocpp -n hello

此命令會(huì)在當(dāng)前目錄創(chuàng)建一個(gè)名為hello的文件夾猛频，里面包含三個(gè)文件：

hello.abi

abi文件

hello.cpp

包含合同函數(shù)實(shí)現(xiàn)的源文件

hello.hpp

頭文件：包含變量，常量蛛勉，和cpp文件的函數(shù)引用

如果.cpp文件是使用eosiocpp工具生成的鹿寻，則生成的.cpp文件將類似于以下內(nèi)容：

#include 

using namespace eosio;

class hello : public eosio::contract {
  public:
      using contract::contract;

      /// @abi action
      void hi( account_name user ) {
         print( "Hello, ", name{user} );
      }
};

EOSIO_ABI( hello, (hi) )

可能官方文檔沒更新，我這里的.cpp文件的內(nèi)容如下：

/**
 *  @file
 *  @copyright defined in eos/LICENSE.txt
 */
#include <hello.hpp>

/**
 *  The init() and apply() methods must have C calling convention so that the blockchain can lookup and
 *  call these methods.
 */
extern "C" {

    /// The apply method implements the dispatch of events to this contract
    void apply( uint64_t receiver, uint64_t code, uint64_t action ) {
       eosio::print( "Hello World: ", eosio::name(code), "->", eosio::name(action), "\n" );
    }

} // extern "C"

4.Hello World智能合約

4.1 創(chuàng)建賬號(hào)

創(chuàng)建名為hello.code的賬號(hào)用于部署合約：

打開并解鎖錢包：

yuyangdeMacBook-Pro:cleos yuyang$ cleos wallet open
Opened: default
yuyangdeMacBook-Pro:cleos yuyang$ cleos wallet list
Wallets:
[
  "default"
]
yuyangdeMacBook-Pro:cleos yuyang$ cleos wallet unlock --password PW5KQwfoDJDUUTTEdZzTpSHYfmvSWxL23jefVHLi6UL74Uw9em6WA
Unlocked: default
yuyangdeMacBook-Pro:cleos yuyang$ cleos wallet list
Wallets:
[
  "default *"
]

生成密鑰對(duì)：

yuyangdeMacBook-Pro:cleos yuyang$ cleos create key --to-console
Private key: 5JixXRHHAnxL68LnyvSBTKszZiZgHFAQctHVVYAFp4fwijFE8SZ
Public key: EOS64rVEsvzXnTiGSoYaMockxcvxdj7eM57anUoW1eNcSgxmijXTK
yuyangdeMacBook-Pro:cleos yuyang$ cleos create key --to-console
Private key: 5KhJsLuwzQ8ShdrTVnvgmXZT4J1iGHF16YAyyGFPxeMNVgWVyZF
Public key: EOS8JLJVwbQv9Dp4nnLg8Bso4RvXgsY3MeNBTU5LfLcD8WgKL5jUT

導(dǎo)入密鑰對(duì)到錢包：

yuyangdeMacBook-Pro:cleos yuyang$ cleos wallet import --private-key 5JixXRHHAnxL68LnyvSBTKszZiZgHFAQctHVVYAFp4fwijFE8SZ
imported private key for: EOS64rVEsvzXnTiGSoYaMockxcvxdj7eM57anUoW1eNcSgxmijXTK
yuyangdeMacBook-Pro:cleos yuyang$ cleos wallet import --private-key 5KhJsLuwzQ8ShdrTVnvgmXZT4J1iGHF16YAyyGFPxeMNVgWVyZF
imported private key for: EOS8JLJVwbQv9Dp4nnLg8Bso4RvXgsY3MeNBTU5LfLcD8WgKL5jUT

創(chuàng)建賬號(hào)：

yuyangdeMacBook-Pro:cleos yuyang$ cleos create account eosio hello.code EOS64rVEsvzXnTiGSoYaMockxcvxdj7eM57anUoW1eNcSgxmijXTK EOS8JLJVwbQv9Dp4nnLg8Bso4RvXgsY3MeNBTU5LfLcD8WgKL5jUT
executed transaction: 7904dc63327d21b01b097f80ec6272a4ca656b3120efe5e9f39738cd5b5c263f  200 bytes  3394 us
#         eosio <= eosio::newaccount            {"creator":"eosio","name":"hello.code","owner":{"threshold":1,"keys":[{"key":"EOS64rVEsvzXnTiGSoYaMo...
2018-08-29T03:35:56.708 thread-0   main.cpp:455                  print_result   warning: transaction executed locally, but may not be confirmed by the network yet

查看賬號(hào)：

yuyangdeMacBook-Pro:cleos yuyang$ cleos get account hello.code
permissions: 
    owner     1:    1 EOS64rVEsvzXnTiGSoYaMockxcvxdj7eM57anUoW1eNcSgxmijXTK
       active     1:    1 EOS8JLJVwbQv9Dp4nnLg8Bso4RvXgsY3MeNBTU5LfLcD8WgKL5jUT
memory: 
    quota:       unlimited  used:      2.66 KiB  

net bandwidth: 
    used:               unlimited
    available:          unlimited
    limit:              unlimited

cpu bandwidth:
    used:               unlimited
    available:          unlimited
    limit:              unlimited

4.2 編寫代碼并生成wast和abi文件

使用下面代碼覆蓋hello.cpp中的內(nèi)容：

#include <eosiolib/eosio.hpp>
#include <eosiolib/print.hpp>
using namespace eosio;

class hello : public eosio::contract {
  public:
      using contract::contract;

      /// @abi action 
      void hi( account_name user ) {
         print( "Hello, ", name{user} );
      }
};

EOSIO_ABI( hello, (hi) )

EOSIO_ABI中定義了對(duì)外可調(diào)用的函數(shù)hi方法诽凌，在hi方法中打印了調(diào)用者的賬戶名

生成.wast文件

yuyangdeMacBook-Pro:eos yuyang$ cd hello
yuyangdeMacBook-Pro:hello yuyang$ eosiocpp -o hello.wast hello.cpp

多了hello.wasm和hello.wast文件

將剛才創(chuàng)建的hello文件夾中的hello.abi文件刪除毡熏，我們要重新生成abi文件

yuyangdeMacBook-Pro:hello yuyang$ eosiocpp -g hello.abi hello.cpp
2018-08-29T03:45:49.132 thread-0   abi_generator.hpp:68          ricardian_contracts  ] Warning, no ricardian clauses found for hello

2018-08-29T03:45:49.133 thread-0   abi_generator.hpp:75          ricardian_contracts  ] Warning, no ricardian contract found for hi

Generated hello.abi ...

ABI
應(yīng)用程序二進(jìn)制接口（ABI）是一個(gè)基于JSON的描述，介紹如何在JSON和二進(jìn)制表示之間轉(zhuǎn)換用戶操作侣诵。ABI還描述了如何將數(shù)據(jù)庫狀態(tài)轉(zhuǎn)換為JSON或從JSON轉(zhuǎn)換痢法。通過ABI描述合同后，開發(fā)人員和用戶將能夠通過JSON無縫地與您的合同進(jìn)行交互杜顺。

4.3 部署合約

yuyangdeMacBook-Pro:cleos yuyang$ cleos set contract hello.code ../../../hello -p hello.code@active
Reading WASM from ../../../hello/hello.wasm...
Publishing contract...
executed transaction: 14fc91fcdb35775b42a98e71267959aae508d0858406610da7b59520f20aebd3  1800 bytes  5738 us
#         eosio <= eosio::setcode               {"account":"hello.code","vmtype":0,"vmversion":0,"code":"0061736d01000000013b0c60027f7e006000017e600...
#         eosio <= eosio::setabi                {"account":"hello.code","abi":"0e656f73696f3a3a6162692f312e30000102686900010475736572046e616d6501000...
2018-08-29T06:22:51.809 thread-0   main.cpp:455                  print_result   warning: transaction executed locally, but may not be confirmed by the network yet

4.4 合約交互

在執(zhí)行調(diào)用命令之前财搁，我們先簡(jiǎn)單地了解EOS中的一個(gè)概念：transaction和action。

qction表示單個(gè)操作躬络，而transaction是一個(gè)或多個(gè)action的集合尖奔。action是合約和賬戶之間進(jìn)行通信的方式。action可以單獨(dú)執(zhí)行穷当，或者組合起來作為一個(gè)整體執(zhí)行提茁。EOS中的action就相當(dāng)于以太坊中的transaction。

調(diào)用合約hi方法：

yuyangdeMacBook-Pro:cleos yuyang$ cleos push action hello.code hi '["user"]' -p user@active
executed transaction: 9f109157ea7ea19bd069b6befa28c707cd5a40777c8827a9e474c926f5d9d0e0  104 bytes  2159 us
#    hello.code <= hello.code::hi               {"user":"user"}
2018-08-29T06:43:16.925 thread-0   main.cpp:455                  print_result   warning: transaction executed locally, but may not be confirmed by the network yet

如果看不到合約執(zhí)行時(shí)的打印內(nèi)容馁菜≤畋猓可以重啟nodeos，并且加上--contracts-console參數(shù)啟動(dòng)汪疮，以查看合約的輸出內(nèi)容：

yuyangdeMacBook-Pro:nodeos yuyang$ nodeos --contracts-console

或者編輯配置文件~/Library/Application Support/eosio/nodeos/config中的config.ini峭火，找到以下內(nèi)容：

# print contract's output to console (eosio::chain_plugin)
contracts-console = false

將false改為true

再次調(diào)用合約hi方法：

yuyangdeMacBook-Pro:cleos yuyang$ cleos push action hello.code hi '["user"]' -p user@active
executed transaction: 89eed32e56d38ef91db92633568f40343f8e9389ceb0df5c15c7c46c51319d23  104 bytes  7449 us
#    hello.code <= hello.code::hi               {"user":"user"}
>> Hello, user
2018-08-29T06:48:46.087 thread-0   main.cpp:455                  print_result   warning: transaction executed locally, but may not be confirmed by the network yet

可以看到>> Hello, user的打印內(nèi)容

再查看nodeos中的輸出：

2018-08-29T06:48:46.005 thread-0   producer_plugin.cpp:1302      produce_block        ] Produced block 0000d235ac33678d... #53813 @ 2018-08-29T06:48:46.000 signed by eosio [trxs: 0, lib: 53812, confirmed: 0]
2018-08-29T06:48:46.085 thread-0   apply_context.cpp:28          print_debug          ] 
[(hello.code,hi)->hello.code]: CONSOLE OUTPUT BEGIN =====================
Hello, user
[(hello.code,hi)->hello.code]: CONSOLE OUTPUT END   =====================
2018-08-29T06:48:46.503 thread-0   producer_plugin.cpp:1302      produce_block        ] Produced block 0000d236ab3eb059... #53814 @ 2018-08-29T06:48:46.500 signed by eosio [trxs: 1, lib: 53813, confirmed: 0]

由于此時(shí)合約授權(quán)所有人調(diào)用hi方法，所以也可以進(jìn)行如下操作：

yuyangdeMacBook-Pro:cleos yuyang$ cleos push action hello.code hi '["user"]' -p tester@active
executed transaction: 5c5232d118c8cf60d593435fdaeef6905163cfeeb30473fe97050e71459d7095  104 bytes  303 us
#    hello.code <= hello.code::hi               {"user":"user"}
>> Hello, user
2018-08-29T07:41:36.166 thread-0   main.cpp:455                  print_result   warning: transaction executed locally, but may not be confirmed by the network yet

如果我們希望授權(quán)者和調(diào)用者為同一個(gè)賬戶铲咨，可以加入以下代碼：

void hi( account_name user ) {
   require_auth( user );
   print( "Hello, ", name{user} );
}

重新編譯wast文件躲胳，生成abi文件，再次部署合約并調(diào)用纤勒，如果此時(shí)授權(quán)者和調(diào)用者并非同一個(gè)賬戶，合約會(huì)拋出錯(cuò)誤：

yuyangdeMacBook-Pro:cleos yuyang$ cleos push action hello.code hi '["tester"]' -p user@active
Error 3090004: Missing required authority
Ensure that you have the related authority inside your transaction!;
If you are currently using 'cleos push action' command, try to add the relevant authority using -p option.

nodeos日記輸出：

2018-08-29T08:15:36.002 thread-0   producer_plugin.cpp:1302      produce_block        ] Produced block 0000fae9ce9a18be... #64233 @ 2018-08-29T08:15:36.000 signed by eosio [trxs: 0, lib: 64232, confirmed: 0]
2018-08-29T08:15:36.436 thread-0   http_plugin.cpp:472           handle_exception     ] FC Exception encountered while processing chain.push_transaction
2018-08-29T08:15:36.436 thread-0   http_plugin.cpp:473           handle_exception     ] Exception Details: 3090004 missing_auth_exception: Missing required authority
missing authority of tester
    {"account":"tester"}
    thread-0  apply_context.cpp:131 require_authorization
pending console output: 
    {"console":""}
    thread-0  apply_context.cpp:61 exec_one
2018-08-29T08:15:36.503 thread-0   producer_plugin.cpp:1302      produce_block        ] Produced block 0000faea889f31c9... #64234 @ 2018-08-29T08:15:36.500 signed by eosio [trxs: 0, lib: 64233, confirmed: 0]

我們重新將授權(quán)者設(shè)為tester隆檀，正常

yuyangdeMacBook-Pro:cleos yuyang$ cleos push action hello.code hi '["tester"]' -p tester@active
executed transaction: bd9ed2dd386de13ce622c6c6184acd7085c8cc84a5ee0f86d58ae1abbaa5100e  104 bytes  332 us
#    hello.code <= hello.code::hi               {"user":"tester"}
>> Hello, tester
2018-08-29T08:16:59.641 thread-0   main.cpp:455                  print_result   warning: transaction executed locally, but may not be confirmed by the network yet

將授權(quán)者設(shè)為user摇天，正常

yuyangdeMacBook-Pro:cleos yuyang$ cleos push action hello.code hi '["user"]' -p user@active
executed transaction: aabe5baab544c9386f5162b8327e34735fa2530e6497d64b356dfe380f53587a  104 bytes  293 us
#    hello.code <= hello.code::hi               {"user":"user"}
>> Hello, user
2018-08-29T08:18:10.926 thread-0   main.cpp:455                  print_result   warning: transaction executed locally, but may not be confirmed by the network yet