System Chaincode Plugins¶
System chaincodes are specialized chaincodes that run as part of the peer process as opposed to user chaincodes that run in separate docker containers. As such they have more access to resources in the peer and can be used for implementing features that are difficult or impossible to be implemented through user chaincodes. Examples of System Chaincodes are ESCC (Endorser System Chaincode) for endorsing proposals, QSCC (Query System Chaincode) for ledger and other fabric related queries and VSCC (Validation System Chaincode) for validating a transaction at commit time respectively.
Unlike a user chaincode, a system chaincode is not installed and instantiated using proposals from SDKs or CLI. It is registered and deployed by the peer at start-up.
System chaincodes can be linked to a peer in two ways: statically and dynamically using Go plugins. This tutorial will outline how to develop and load system chaincodes as plugins.
A plugin includes a main package with exported symbols and is built with the command
go build -buildmode=plugin.
Every system chaincode must implement the Chaincode Interface
and export a constructor method that matches the signature
func New() shim.Chaincode in the main package.
An example can be found in the repository at
Existing chaincodes such as the QSCC can also serve as templates for certain features - such as access control - that are typically implemented through system chaincodes. The existing system chaincodes also serve as a reference for best-practices on things like logging and testing.
On imported packages: the Go standard library requires that a plugin must include the same version of imported packages as the host application (fabric, in this case)
Plugins are configured in the
chaincode.systemPlugin section in core.yaml:
chaincode: systemPlugins: - enabled: true name: mysyscc path: /opt/lib/syscc.so invokableExternal: true invokableCC2CC: true
A system chaincode must also be whitelisted in the
chaincode.system section in core.yaml:
chaincode: system: mysyscc: enable