How to check if a username exists in my Golang chain code for Hyperledger Fabric?

Question

In the chain code for Hyperledger Fabric, is it possible to check if an identity exists with a given name? that is, something like this:

func (c *SmartContract) UserExists(ctx contractapi.TransactionContextInterface, username string) bool {
     // if an identity exists with the username, then return true, otherwise return false.
}

Answer 1

You can do it with the IdentityService provided contractapi.TransactionContextInterface. However, in fact identities in Hyperledger Fabric are typically managed by the MSP and not directly accessible within the chaincode. If you use identity-based access control within your Fabric network, then you can try the following approach.

//assuming that you've imported necessary packages

 func (c *SmartContract) UserExists(ctx contractapi.TransactionContextInterface, 
 username string) (bool, error) {
// Get the identity service from the transaction context
identityService, err := 
ctx.GetClientIdentity().GetSigningIdentity().CreateAccessControl()
if err != nil {
    return false, err
}

// Check if the identity exists with the given username
exists, err := identityService.GetState(username)
if err != nil {
    return false, err
}

return exists != nil, nil
}