rpc接口调用以太坊智能合约

在以太坊摸爬滚打有些日子了，也遇到了各种各样的问题。这几天主要研究了一下如何通过rpc接口编译、部署和调用合约。也遇到了一些困难和问题，下面将向大家分享。

rpc接口调用智能合约

先来编写一个简单的智能合约

contract Multiply7 {

   event Print(uint);

   function multiply(uint input) returns (uint) {

      Print(input * 7);

      return input * 7;

   }

}

这是输入一个无符号整数做乘法的合约，接下来想要用rpc接口编译它。编译之前先验证geth的solidity编译器是否可用

curl --data '{"jsonrpc":"2.0","method": "eth_getCompilers", "id": 3}' http://localhost:8545

返回结果

HTTP/1.1 200 OK

Content-Type: application/json

Vary: Origin

Date: Fri, 20 Apr 2018 02:59:24 GMT

Content-Length: 121

{"jsonrpc":"2.0","id":3,"error":{"code":-32601,"message":"The method eth_getCompilers does not exist/is not available"}}

这里竟然出现了eth_getCompilers方法不可用的错误，查阅资料后发现geth1.6以后的版本删除了这个功能，删除还包括eht.compile 等功能，至于删除原因详见https://github.com/ethereum/EIPs/issues/209

现在只好到remix ide上进行编译，编译通过后点击"Details"，复制"WEB3DEPLOY"中的"data"数据，接下来部署合约

curl -i -H 'Content-Type:application/json' -d '{"jsonrpc":"2.0","method": "eth_sendTransaction", "params": [{"from": "0x2a5026d44ab3de2094ec79dec074d4a8612a14aa", "gas": "0xfffff", "data": "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"}], "id": 6}' http://localhost:8545

部署合约用到eth_sendTransaction方法，其中from对应的是部署合约的账户地址，gas对应为gas消耗量，太少会报错。data对应的是之前复制的data

执行命令后返回了交易hasa

HTTP/1.1 200 OK

Content-Type: application/json

Vary: Origin

Date: Fri, 20 Apr 2018 14:00:58 GMT

Content-Length: 103

{"jsonrpc":"2.0","id":6,"result":"0xa31ad7bc958290c0b401ae4e046d6e93bc67db1cb038ba2953e2cffe6bdf60fa"}

通过这个交易hasa可以查询部署合约的详细信息，我们可以用eth_getTransactionReceipt RPC方法验证一下

curl -i -H 'Content-Type:application/json' -d '{"jsonrpc":"2.0","method": "eth_getTransactionReceipt", "params": ["0xa31ad7bc958290c0b401ae4e046d6e93bc67db1cb038ba2953e2cffe6bdf60fa"], "id": 7}' http://localhost:8545

在返回的信息中，`contractAddress`对应的内容就是合约的地址了

HTTP/1.1 200 OK

Content-Type: application/json

Vary: Origin

Date: Fri, 20 Apr 2018 14:05:03 GMT

Content-Length: 981

{"jsonrpc":"2.0","id":7,"result":{"blockHash":"0x5480323e9a5ac26ec585ca610cb15cffbfe26f2323e19fb8d8a967e11903d6a0","blockNumber":"0x5599","contractAddress":"0x21f981af36218aaf1a40621bfe1e57cf2f43455a","cumulativeGasUsed":"0x1ce23","from":"0x2a5026d44ab3de2094ec79dec074d4a8612a14aa","gasUsed":"0x1ce23","logs":[],"logsBloom":"0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000","status":"0x1","to":null,"transactionHash":"0xa31ad7bc958290c0b401ae4e046d6e93bc67db1cb038ba2953e2cffe6bdf60fa","transactionIndex":"0x0"}}

拿到合约地址后，我们可以通过eth_sendTransaction调用合约

curl -i -H 'Content-Type:application/json' -d '{"jsonrpc":"2.0","method": "eth_sendTransaction", "params": [{"from": "0x2a5026d44ab3de2094ec79dec074d4a8612a14aa","to":"0x21f981af36218aaf1a40621bfe1e57cf2f43455a","data":"0xc6888fa10000000000000000000000000000000000000000000000000000000000000007"}], "id": 6}' http://localhost:8545

`from`对应为调用合约的账户，`to`对应为要调用的合约地址。`data`对应为调用方法的签名和传入参数，那么我们怎么获取这个值呢,首先，它的编码方式是：`sha3(“multiply(uint256)”).substring(0,10)+to_32bit_Hex_str(7)`

在geth中输入：

> web3.sha3("multiply(uint256)").substring(0, 10)

"0xc6888fa1"

而参数输入为7，最后出结果为0000000000000000000000000000000000000000000000000000000000000007，加上前面的0xc6888fa1就得到了data的值。

通过eth_sendTransaction调用合约后返回：

HTTP/1.1 200 OK

Content-Type: application/json

Vary: Origin

Date: Fri, 20 Apr 2018 14:12:06 GMT

Content-Length: 103

{"jsonrpc":"2.0","id":6,"result":"0xbe0881901ee9e52c9e969a85a1367c4a8936c5ab77fa479aaee1c780fe5d1159"}

可以看到，返回了交易哈希，我们可以用这个交易哈希查询详细信息，验证是否正确，为了返回的数据格式更方便查看，我们可以在geth私有节点中输入获取交易详细信息的命令：

> eth.getTransactionReceipt("0xbe0881901ee9e52c9e969a85a1367c4a8936c5ab77fa479aaee1c780fe5d1159")

返回结果：

{

  blockHash: "0xeac4d7dd5123720ebc43fbc35778de2215738af97cf723721f0260335228eb93",

  blockNumber: 22581,

  contractAddress: null,

  cumulativeGasUsed: 22804,

  from: "0x2a5026d44ab3de2094ec79dec074d4a8612a14aa",

  gasUsed: 22804,

  logs: [{

      address: "0x21f981af36218aaf1a40621bfe1e57cf2f43455a",

      blockHash: "0xeac4d7dd5123720ebc43fbc35778de2215738af97cf723721f0260335228eb93",

      blockNumber: 22581,

      data: "0x0000000000000000000000000000000000000000000000000000000000000031",

      logIndex: 0,

      removed: false,

      topics: ["0x24abdb5865df5079dcc5ac590ff6f01d5c16edbc5fab4e195d9febd1114503da"],

      transactionHash: "0xbe0881901ee9e52c9e969a85a1367c4a8936c5ab77fa479aaee1c780fe5d1159",

      transactionIndex: 0

  }],

  logsBloom: "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000020000000000000004000000000000000000000000000002000000000000000000040000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000080000000000000000000",

  status: "0x1",

  to: "0x21f981af36218aaf1a40621bfe1e57cf2f43455a",

  transactionHash: "0xbe0881901ee9e52c9e969a85a1367c4a8936c5ab77fa479aaee1c780fe5d1159",

  transactionIndex: 0

}

重点来了：我们来看一下返回数据中的logs，其中可能包含调用合约的结果。可以看到logs中也有个data,值为0x0000000000000000000000000000000000000000000000000000000000000031，把这个十六进制转换为十进制得到数字49。49正好是7*7的结果，这说明我们调用合约的multiply方法成功了并得到了正确的结果。

以太坊的JSON RPC API的用法还有很多，在这里就不一一介绍了。无论是web3.js还是web3j，都是对以太坊JSON RPC API开发接口的封装。研究JSON RPC API主要出于学习目的，开发DApp还是用web3.js方便一些。