Blockchain Framework Tendermint Getting Started Tutorial

Tendermint is a modular blockchain application framework that can achieve Byzantine Fault Tolerance (BFT). It mainly includes two parts:

• Tendermint Core：

  • Implemented a p2p network; shared blocks and transactions between nodes;

  • The Byzantine fault-tolerant consensus algorithm is implemented, and the transaction order that does not change is determined;

• ABCI Interface, the specific logic processing layer, can be implemented based on different languages ​​(Golang, JS); at this layer, operations such as transaction verification processing and query are implemented.

These two parts will correspond to two different processes respectively. Core and ABCI establish three connections:

• A connection used to verify the transaction, after the transaction verification is passed, it will be broadcast to the mempoll;

• a proposal for the block;

• The last connection is used to query the status of the application;

The following figure is the Workflow of the two:

Core and ABCI communication

Tendermint-based Key-Value Storage Example

Tendermint has a built-in KV storage application example, we can run this example:

Install

You need to install tendermint and abci-cli first:

go get -u github.com/tendermint/tendermint/cmd/tendermint
go get -u github.com/tendermint/abci
cd $GOPATH/src/github.com/tendermint/abci
make install

Verify that the installation was successful:

➜  blog git:(hexo) ✗ which tendermint
/Users/hbliu/go/bin/tendermint
➜  blog git:(hexo) ✗ which abci-cli
/Users/hbliu/go/bin/abci-cli

start up

Initialize node configuration:

tendermint init

Start the KV storage application:

abci-cli kvstore

Start the Tendermint node:

tendermint node --consensus.create_empty_blocks=false

The latter parameter is to prohibit the Tendermint node from periodically generating empty blocks.

Create transaction

Create a storage with key name and value hbliu in Tendermint:

➜  blog git:(hexo) ✗ curl -s 'localhost:46657/broadcast_tx_commit?tx="name=hbliu"'
{
  "jsonrpc": "2.0",
  "id": "",
  "result": {
    "check_tx": {
      "fee": {}
    },
    "deliver_tx": {
      "tags": [
        {
          "key": "YXBwLmNyZWF0b3I=",
          "value": "amFl"
        },
        {
          "key": "YXBwLmtleQ==",
          "value": "bmFtZQ=="
        }
      ],
      "fee": {}
    },
    "hash": "BA0C60A3F391B35DEAE8A7E6E0491E9B2E0BA497",
    "height": 2
  }
}

返回的 Response 中的 key 和 value 使用了 base64 进行了编码, 我们可以通过命令 base64 对其进行解码：

➜  blog git:(hexo) ✗ echo "YXBwLmtleQ==" | base64 -D
app.key
➜  blog git:(hexo) ✗ echo "bmFtZQ==" | base64 -D
name

查询下我们之前的信息有没有成功写入：

➜  blog git:(hexo) ✗ curl -s 'localhost:46657/abci_query?data="name"'
{
  "jsonrpc": "2.0",
  "id": "",
  "result": {
    "response": {
      "log": "exists",
      "index": "-1",
      "key": "bmFtZQ==",
      "value": "aGJsaXU="
    }
  }
}
➜  blog git:(hexo) ✗ echo "bmFtZQ==" | base64 -D
name
➜  blog git:(hexo) ✗ echo "aGJsaXU=" | base64 -D
hbliu

在浏览器中打开 http://localhost:46657 可以显示当前所有支持的 API。

示例代码介绍

上述示例的代码存储在 Github（https://github.com/tendermint/abci/blob/master/example/kvstore/kvstore.go） 上。下面我们对这部分代码做一个简单的介绍。

在我们调用 broadcast_tx_commit 的时候，会先调用 CheckTx，验证通过后会把 TX 加入到 mempool 里。在 kvstore 示例中没有对 transaction 做检查，直接通过：

func (app *KVStoreApplication) CheckTx(tx []byte) types.ResponseCheckTx {
    return types.ResponseCheckTx{Code: code.CodeTypeOK}
}

放到 mempool 里的 TX 会被定期广播到所有节点。当 Tendermint 选出了 Proposal 节点后，它便会从 mempool 里选出一系列的 TXs，将它们组成一个 Block，广播给所有的节点。节点在收到 Block 后，会对 Block 里的所有 TX 执行 DeliverTX 操作，同时对 Block 执行 Commit 操作。

我们调用 broadcast_tx_commit 返回的结果其实就是 DeliverTX 返回的结果：

func (app *KVStoreApplication) DeliverTx(tx []byte) types.ResponseDeliverTx {
    var key, value []byte
    parts := bytes.Split(tx, []byte("="))
    if len(parts) == 2 {
        key, value = parts[0], parts[1]
    } else {
        key, value = tx, tx
    }
    app.state.db.Set(prefixKey(key), value)
    app.state.Size += 1
    tags := []cmn.KVPair{
        {[]byte("app.creator"), []byte("jae")},
        {[]byte("app.key"), key},
    }
    return types.ResponseDeliverTx{Code: code.CodeTypeOK, Tags: tags}
}

可以看出它会从输入参数中解析出 key 和 value，最后保存在应用的 State 中。

当所有的 TX 被处理完之后需要调用 Commit 来更新整个区块的状态，包括高度加 1 等：

func (app *KVStoreApplication) Commit() types.ResponseCommit {
    // Using a memdb - just return the big endian size of the db
    appHash := make([]byte, 8)
    binary.PutVarint(appHash, app.state.Size)
    app.state.AppHash = appHash
    app.state.Height += 1
    saveState(app.state)
    return types.ResponseCommit{Data: appHash}
}

References

• Tendermint Introduction（http://tendermint.readthedocs.io/projects/tools/en/develop/introduction.html）

出处：https://hiberabyss.github.io/2018/04/02/tendermint-introduction-1/

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