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* Import Full Stack Asset Transfer Guide at commit fb554befdbbeff9e69159b54fce0b811603f29c7 Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> * Update the workshop with a new WORKSHOP_PATH under fabric-samples Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> * Update the workshop with a new WORKSHOP_PATH under fabric-samples Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> * missed a .git ignored directory on add Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> * Updates to run the workshop on the Apple M1 Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> * Workaround for https://github.com/eslint/eslint/issues/15299 in the contract tslinter Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> * Build an arch-specific CC images on M1 Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> * empty commit - force a build Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> * revert an accidental commit that was building the top-level asset-transfer as arm64 Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com> Signed-off-by: Josh Kneubuhl <jkneubuh@us.ibm.com>
20 lines
2.3 KiB
Markdown
20 lines
2.3 KiB
Markdown
# Chaincode events
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A smart contract transaction function can emit a chaincode event to communicate business events. These events are emitted only after a transaction is successfully committed and updates the ledger. Transactions that fail validation do not emit chaincode events.
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Client applications can listen for chaincode events and trigger external business processes in response to ledger updates. An example might be to schedule collection of a parcel after a delivery order is received. Events can either be replayed from any point in the blockchain, or received in realtime.
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When emitting a chaincode event, the smart contract can specify an arbitrary **payload** to be included in the event. The **payload** is used to communicate business context to client applications receiving the chaincode events.
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The [Network](https://hyperledger.github.io/fabric-gateway/main/api/node/interfaces/Network.html) object in the Gateway API provides methods to obtain chaincode events.
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To ensure the correct operation of business processes, it is important that each chaincode event is received exactly once. We don't want to collect the same parcel twice, or to miss a parcel collection!
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The Gateway API allows a [Checkpointer](https://hyperledger.github.io/fabric-gateway/main/api/node/interfaces/Checkpointer.html) to be used to track (or checkpoint) successfully processed events, and for eventing to be resumed exactly after the last checkpointed event if a failure or application restart occurs.
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For convenience, the Gateway API provides two checkpointer implementations:
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1. [File checkpointer](https://hyperledger.github.io/fabric-gateway/main/api/node/functions/checkpointers.file.html) that persists its state to the file-system. This can be used to resume eventing, even after an application restart.
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1. [In-memory checkpointer](https://hyperledger.github.io/fabric-gateway/main/api/node/functions/checkpointers.inMemory.html) that stores its state only in-memory. This can be used to recover from transient failures, such as a network communication error, during a single application run.
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Client applications can also use their own checkpointer implementations, which persist their state in suitable storage such as a database, provided they conform to the simple [Checkpoint](https://hyperledger.github.io/fabric-gateway/main/api/node/interfaces/Checkpoint.html) interface.
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