本文基于 Fabric v2.0.1 ，与 v1.x 版不同，v2 版将 protos 定义放到一个独立仓库 fabric-protos 进行管理，并且使用 protoc 工具生成的具体语言代码也使用独立的仓库存放，如 golang 版 fabric-protos-go。

一、 Orderer

1. AtomicBroadcast

服务定义于 orderer/ab.proto

service AtomicBroadcast {
    // broadcast receives a reply of Acknowledgement for each common.Envelope in order, indicating success or type of failure
    rpc Broadcast(stream common.Envelope) returns (stream BroadcastResponse);

    // deliver first requires an Envelope of type DELIVER_SEEK_INFO with Payload data as a mashaled SeekInfo message, then a stream of block replies is received.
    rpc Deliver(stream common.Envelope) returns (stream DeliverResponse);
}

1.1 Broadcast

Broadcast 接口用于接收待排序的消息，包括普通事务 tx 消息和 channel 配置消息。
客户端将事务消息提交到 endorsing peers 预执行 chaincode 并背书读写集结果，由客户端将返回结果提交到 Orderer 进行排序。

1.2 Deliver

Deliver 接口用于向 peers 分发已经过排序 block 数据，peer 节点通过 join channel 从 Orderer 获取已排序的 block 。

2. Cluster

服务定义于 orderer/cluster.proto

// Cluster defines communication between cluster members.
service Cluster {
    // Step passes an implementation-specific message to another cluster member.
    rpc Step(stream StepRequest) returns (stream StepResponse);
}

Fabric v1.1 之后支持 EtcdRaft 共识算法，与使用 Kafka 共识算法各orderer独立连接中心化的 kafka 集群不同，使用 EtcdRaft 共识算法各 orderer 组成一个集群， Step 用于集群节点间消息交换。

二、Peer

1. Endorser

服务定义于 peer/peer.proto

service Endorser {
    rpc ProcessProposal(SignedProposal) returns (ProposalResponse);
}

ProcessProposal 接口用于客户端将已签名的事务消息提交到 endorsing peers 进行预执行并背书读写集。所谓预执行是指使用当前本地账本状态执行 chaincode 生成读写集，但执行结果不写入账本。

2. Deliver

服务定义于 peer/events.proto

service Deliver {
    // Deliver first requires an Envelope of type ab.DELIVER_SEEK_INFO with
    // Payload data as a marshaled orderer.SeekInfo message,
    // then a stream of block replies is received
    rpc Deliver (stream common.Envelope) returns (stream DeliverResponse) {
    }
    // DeliverFiltered first requires an Envelope of type ab.DELIVER_SEEK_INFO with
    // Payload data as a marshaled orderer.SeekInfo message,
    // then a stream of **filtered** block replies is received
    rpc DeliverFiltered (stream common.Envelope) returns (stream DeliverResponse) {
    }
    // DeliverWithPrivateData first requires an Envelope of type ab.DELIVER_SEEK_INFO with
    // Payload data as a marshaled orderer.SeekInfo message,
    // then a stream of block and private data replies is received
    rpc DeliverWithPrivateData (stream common.Envelope) returns (stream DeliverResponse) {
    }
}

2.1 Deliver & DeliverFiltered

Deliver 接口用于向客户端分发已写入本地账本的 block 数据。客户端将 endorsing peers 返回的结果提交给 orderer 后，等待 peer 通知事务处理完毕。

2.2 DeliverWithPrivateData

DeliverWithPrivateData v2.0 版本新增，分发带私密数据的 block 数据

三、Chaincode

1. ChaincodeSupport

服务定义于 peer/chaincode_shim.proto

// Interface that provides support to chaincode execution. ChaincodeContext
// provides the context necessary for the server to respond appropriately.
service ChaincodeSupport {
    rpc Register(stream ChaincodeMessage) returns (stream ChaincodeMessage);
}

Register 用于 Chaincode 启动时向 peer 注册当前 Chaincode

2. Chaincode

服务定义于 peer/chaincode_shim.proto

// Chaincode as a server - peer establishes a connection to the chaincode as a client
// Currently only supports a stream connection.
service Chaincode {
    rpc Connect(stream ChaincodeMessage) returns (stream ChaincodeMessage);
}

v2 新增服务，Chaincode 启动并作为服务端，由 peer 通过 Connect 接口连接 Chaincode

四、Gossip

服务定义于 gossip/message.proto

// Gossip
service Gossip {

    // GossipStream is the gRPC stream used for sending and receiving messages
    rpc GossipStream (stream Envelope) returns (stream Envelope);

    // Ping is used to probe a remote peer's aliveness
    rpc Ping (Empty) returns (Empty);
}

为减轻 Orderer 压力，组织内只有少量 peer 连接 orderer 获取最新 block，组织内各 peer 通过 Gossip 互联，通过 Gossip 交换 block 数据及私密数据。

五、Discovery

服务定义于 discovery/protocol.proto

// Discovery defines a service that serves information about the fabric network
// like which peers, orderers, chaincodes, etc.
service Discovery {
    // Discover receives a signed request, and returns a response.
    rpc Discover (SignedRequest) returns (Response);
}