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95 lines
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4.5 KiB
Markdown
95 lines
No EOL
4.5 KiB
Markdown
# Off-chain data store sample
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The off-chain data store sample demonstrates:
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- Receiving block events in a client application.
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- Using a checkpointer to resume event listening after a failure or application restart.
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- Extracting ledger updates from block events in order to build an off-chain data store.
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## About the sample
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This sample shows how to replicate the data in your blockchain network to an off-chain data store. Using an off-chain data store allows you to analyze the data from your network or build a dashboard without degrading the performance of your application.
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This sample uses the block event listening capability of the [Fabric Gateway client API](https://hyperledger.github.io/fabric-gateway/) for Fabric v2.4 and later.
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### Application
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The client application provides several "commands" that can be invoked using the command-line:
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- **getAllAssets**: Retrieve the current details of all assets recorded on the ledger. See `application-typescript/src/getAllAssets.ts`.
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- **listen**: Listen for block events, and use them to replicate ledger updates in an off-chain data store. See `application-typescript/src/listen.ts`.
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- **transact**: Submit a set of transactions to create, modify and delete assets. See `application-typescript/src/transact.ts`.
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To keep the sample code concise, the **listen** command writes ledger updates to an output file named `store.log` in the current working directory. A real implementation could write ledger updates directly to an off-chain data store of choice. You can inspect the information captured in this file as you run the sample.
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Note that the **listen** command is is restartable and will resume event listening after the last successfully processed block / transaction. This is achieved using a checkpointer to persist the current listening position. Checkpoint state is persisted to a file named `checkpoint.json` in the current working directory. If no checkpoint state is present, event listening begins from the start of the ledger (block number zero).
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### Smart Contract
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The asset-transfer-basic smart contract is used to generate transactions and associated ledger updates.
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## Running the sample
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The Fabric test network is used to deploy and run this sample. Follow these steps in order:
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1. Create the test network and a channel (from the `test-network` folder).
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```
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./network.sh up createChannel -c mychannel -ca
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```
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1. Deploy one of the asset-transfer-basic smart contract implementations (from the `test-network` folder).
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```
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# To deploy the TypeScript chaincode implementation
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./network.sh deployCC -ccn basic -ccp ../asset-transfer-basic/chaincode-typescript/ -ccl typescript
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# To deploy the Go chaincode implementation
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./network.sh deployCC -ccn basic -ccp ../asset-transfer-basic/chaincode-go/ -ccl go
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# To deploy the Java chaincode implementation
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./network.sh deployCC -ccn basic -ccp ../asset-transfer-basic/chaincode-java/ -ccl java
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```
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1. Populate the ledger with some assets and use eventing to capture ledger updates (from the `off_chain_data` folder).
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```
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# To run the TypeScript sample application
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cd application-typescript
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npm install
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npm start transact listen
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```
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1. Interrupt the listener process using **Control-C**.
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1. View the current world state of the blockchain (from the `off_chain_data` folder). You may want to compare the results to the ledger updates captured by the listener in the `store.log` file.
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```
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# To run the TypeScript sample application
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cd application-typescript
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npm --silent start getAllAssets
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```
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1. Make some more ledger updates, then observe listener resume capability (from the `off_chain_data` folder). Note from the transaction IDs recorded to the console that the listener resumes from exactly after the last successfully processed transaction.
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```
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# To run the TypeScript sample application
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cd application-typescript
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npm start transact
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SIMULATED_FAILURE_COUNT=5 npm start listen
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npm start listen
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```
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1. Interrupt the listener process using **Control-C**.
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## Clean up
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The persisted event checkpoint position can be removed by deleting the `checkpoint.json` file while the listener is stopped.
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The recorded ledger updates can be removed by deleting the `store.log` file.
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When you are finished, you can bring down the test network (from the `test-network` folder). The command will remove all the nodes of the test network, and delete any ledger data that you created. Be sure to remove the `checkpoint.json` and `store.log` files before attempting to run the application with a new network.
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```
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./network.sh down
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``` |