Application

blockchain › Hyperledger-Fabric › Key Concepts
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官方文档：Application

Basic Flow

develop.diagram.3A PaperNet application invokes the commercial paper smart contract to submit an issue transaction request.

An application has to follow six basic steps to submit a transaction:

  • Select an identity from a wallet
  • Connect to a gateway
  • Access the desired network
  • Construct a transaction request for a smart contract
  • Submit the transaction to the network
  • Process the response

Wallet

Think of a wallet holding the digital equivalents of your government ID, driving license or ATM card. The X.509 digital certificates within it will associate the holder with a organization, thereby entitling them to rights in a network channel. For example, Isabella might be an administrator in MagnetoCorp, and this could give her more privileges than a different user – Balaji from DigiBank. Moreover, a smart contract can retrieve this identity during smart contract processing using the transaction context.

钱包是保管了很多身份信息的钱包。

（个人理解：就好像谍战电影里面的间谍，打开一个抽屉里面有这个间谍的不同身份的护照。）

Gateway

The second key class is a Fabric Gateway. Most importantly, a gateway identifies one or more peers that provide access to a network。 in our case, PaperNet. See how issue.js connects to its gateway:

网关标识一个或多个提供对网络访问的节点。

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await gateway.connect(connectionProfile, connectionOptions);

gateway.connect() has two important parameters:

  • connectionProfile: the file system location of a connection profile that identifies a set of peers as a gateway to PaperNet

    连接配置文件的文件系统位置，该文件将一组peer标识为PaperNet的gateway

  • connectionOptions: a set of options used to control how issue.js interacts with PaperNet

See how the client application uses a gateway to insulate itself from the network topology, which might change. The gateway takes care of sending the transaction proposal to the right peer nodes in the network using the connection profile and connection options.

Network channel

The peers defined in the gateway connectionProfile.yaml provide issue.js with access to PaperNet. Because these peers can be joined to multiple network channels, the gateway actually provides the application with access to multiple network channels!

We can see here a powerful feature of Hyperledger Fabric – applications can participate in a network of networks, by connecting to multiple gateway peers, each of which is joined to multiple network channels. Applications will have different rights in different channels according to their wallet identity provided in gateway.connect().

Construct request

The application is now ready to issue a commercial paper. To do this, it’s going to use CommercialPaperContract and again, its fairly straightforward to access this smart contract:

Submit transaction

Note that the submitTransaction API includes a process for listening for transaction commits. Listening for commits is required because without it, you will not know whether your transaction has successfully been orderered, validated, and committed to the ledger.

Process response