我可以在hyperledger-fabric中生成事件吗？

Question

我之前在Ethereum上工作过，它可以在函数被调用或状态改变时生成“事件”，这些事件可以通过观察状态变化从应用程序中捕获。Hyperledger有这个功能吗？我可以在hyperledger-fabric中看到“事件”，但是当状态发生变化时，我如何生成自己的事件并在节点应用程序中捕获它们？

Answer 1

在Hyperledger Fabric中，有一个名为的shim.ChaincodeStubInterface应用编程接口方法：

// SetEvent allows the chaincode to set an event on the response to the
// proposal to be included as part of a transaction. The event will be
// available within the transaction in the committed block regardless of the
// validity of the transaction.
SetEvent(name string, payload []byte) error

它允许您在调用链代码(也称为smartcontract)期间指定事件。稍后，您可以注册到event hub以获取这些事件。

Answer 2

您可以在链代码中设置事件，如以下代码所示：

APIstub.SetEvent("evtsender", []byte("abcdef"))

然后，在您用来执行查询的文件中，您应该使用registerChaincodeEvent()；请参阅以下官方文档：

https://fabric-sdk-node.github.io/EventHub.html#registerChaincodeEvent__anchor

这可能是一个示例：

let event_monitor = new Promise((resolve, reject) => {
        let regid = null;
        let handle = setTimeout(() => {
            if (regid) {
                // might need to do the clean up this listener
                eh.unregisterChaincodeEvent(regid);
                console.log('Timeout - Failed to receive the chaincode event');
            }
            reject(new Error('Timed out waiting for chaincode event'));
        }, 20000);
        eh.connect();
        regid = eh.registerChaincodeEvent('fabcar', 'evtsender',
            (event, block_num, txnid, status) => {
                // This callback will be called when there is a chaincode event name
                // within a block that will match on the second parameter in the registration
                // from the chaincode with the ID of the first parameter.
                console.log('Successfully got a chaincode event with transid:' + txnid + ' with status:' + status);

                // might be good to store the block number to be able to resume if offline
                storeBlockNumForLater(block_num);

                // to see the event payload, the channel_event_hub must be connected(true)
                let event_payload = event.payload.toString('utf8');
                if (event_payload.indexOf('CHAINCODE') > -1) {
                    clearTimeout(handle);
                    // Chaincode event listeners are meant to run continuously
                    // Therefore the default to automatically unregister is false
                    // So in this case we want to shutdown the event listener once
                    // we see the event with the correct payload
                    event_hub.unregisterChaincodeEvent(regid);
                    console.log('Successfully received the chaincode event on block number ' + block_num);
                    resolve('RECEIVED');
                } else {
                    console.log('Successfully got chaincode event ... just not the one we are looking for on block number ' + block_num);
                }
            }, (error) => {
                clearTimeout(handle);


                   console.log('Failed to receive the chaincode event ::' + error);
                    reject(error);
                }
                // no options specified
                // startBlock will default to latest
                // endBlock will default to MAX
                // unregister will default to false
                // disconnect will default to false
            );
})

无论如何，我在测试它时遇到了一些问题。