已在IBM Cloud部署composer-rest-server，如何用GoLang获取链码？

Hey there! You’ve already checked off two big milestones—getting the Composer REST Server up on IBM Cloud and writing your custom Go logic for interacting with chaincode. Nice work! Let’s break down the next steps to get that Go code talking to your Hyperledger Fabric chaincode properly.

First things first—make sure your Go chaincode is actually live on your IBM Cloud Fabric network:

• Log into the IBM Cloud console, navigate to your Hyperledger Fabric instance.
• Head to the Channel Management section, pick the channel you want to use.
• If you haven’t installed your chaincode yet: Click Install Chaincode, upload your packaged Go chaincode (zip it up into a .tar.gz file first).
• Once installed, click Instantiate Chaincode on the same channel. Specify your chaincode name, version, and any initialization parameters your chaincode’s Init function requires.

Your Go code needs to use the Hyperledger Fabric Go SDK to connect to the IBM Cloud network. Here’s how to set that up:

• Create a connection profile: Grab the connection profile YAML file from your IBM Cloud Fabric instance (look for a "Download Connection Profile" option in the console). This file has all the details for peers, orderers, CA, and channels in your network.
• Initialize the SDK in your code: Load the connection profile, create a gateway, and authenticate with a valid user identity. You’ll need the user’s certificate and private key—you can get these from the IBM Cloud Fabric’s identity registry.
• Query/Invoke your chaincode: Once connected, use the gateway to access your channel and chaincode. Here’s a quick example snippet:

  // Load the connection profile and create a gateway
  gateway, err := gateway.Connect(
      gateway.WithConfigFile("connection.yaml"),
      gateway.WithIdentity(yourWallet, "your-user-id"),
  )
  if err != nil {
      panic(fmt.Errorf("failed to connect gateway: %v", err))
  }
  defer gateway.Close()
  
  // Access your target channel
  network, err := gateway.GetNetwork("your-channel-name")
  if err != nil {
      panic(fmt.Errorf("failed to get network: %v", err))
  }
  
  // Get a reference to your chaincode
  chaincode := network.GetContract("your-chaincode-name")
  
  // Example: Run a query transaction
  queryResult, err := chaincode.EvaluateTransaction("your-query-function", "param1")
  if err != nil {
      panic(fmt.Errorf("query failed: %v", err))
  }
  fmt.Println("Query result:", string(queryResult))
  
  // Example: Run an invoke transaction (writes to ledger)
  _, err = chaincode.SubmitTransaction("your-invoke-function", "param1", "param2")
  if err != nil {
      panic(fmt.Errorf("invoke failed: %v", err))
  }
  fmt.Println("Transaction submitted successfully")
  

If you want to expose your chaincode functions as REST endpoints via the Composer REST Server, you’ll need to link your external Go chaincode to your Composer Business Network Definition (BND):

• Update your BND: In your Composer project, add asset/transaction definitions that map to your chaincode functions. Use the @ExternalChaincode annotation to specify the chaincode name and channel. For example:

  transaction MyInvokeTransaction {
      @ExternalChaincode(chaincodeName: "your-chaincode-name", channel: "your-channel-name")
      o String param1
      o String param2
  }
  

• Repackage and deploy the BND: Package your updated BND into a .bna file, install it on your IBM Cloud Fabric network, and upgrade the business network.
• Restart the Composer REST Server: After upgrading the BND, restart the server—it will now expose your chaincode functions as REST endpoints that you can call directly.

• Test your Go code: Run your script and check if it can successfully query or invoke the chaincode. If you hit errors, check the peer logs in the IBM Cloud Fabric console for clues.
• Test the REST Server: Use tools like Postman or curl to send requests to the REST endpoints. Verify that the responses match what you expect from your chaincode.

• Permission issues: Make sure the user identity you’re using has the right ACL permissions on the channel and chaincode (check IBM Cloud Fabric’s ACL settings).
• Version mismatch: Ensure the chaincode version in your code matches the one you instantiated on the network.
• Connection profile errors: Double-check that your connection.yaml has the correct URLs for peers/orderers/CA, and that the certificate paths point to valid files.

内容的提问来源于stack exchange，提问作者shiv simplyfi