fix(lambda): version.fromVersionArn creates invalid Version object

[pahud]

Issue # (if applicable)

Closes #29813

Reason for this change

improve the fromFunctionArn() to better handle the input ARN

Description of changes

fromFunctionArn() does not handle the ARN correctly if the input ARN has trailing version or alias.

Description of how you validated changes

See unit tests

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

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[pahud]

Exemption Request - unit tests added

[GavinZZ]

LGTM

[paulhcsun]

Left a couple comments

[paulhcsun]

I'm not really a fan hardcoding this check with > 7 but I also don't really foresee this ever changing in terms of sections of an ARN so I guess it's ok. We should just add a description of what the 7 means.

[rehos]

@paulhcsun see my comment here too. It is about the fact that the functionArn can be an unresolved token instead of a literal string too (for example when it is passed as a parameter to the CloudFormation stack). I also added a code snippet on how to handle that case too.

[pahud]

fromFunctionArn only accepts functionArn as string. Should we consider that condition?

[rehos]

@pahud and @paulhcsun in the following code snippet is a stack that accepts the lambda function version arn as a parameter (for example because the actual function was created in another stack earlier in the ci/cd pipeline).

const myFunctionVersionArn = new cdk.CfnParameter(stack, 'MyFunctionVersionArn');

const version = lambda.Version.fromVersionArn(stack, 'MyVersionFunction', myFunctionVersionArn.valueAsString);

The arn that is passed to fromVersionArn is a tokenized string (value not known at compile time) and is eventually passed to fromFunctionArn because it is called by fromVersionArn under the hood. And fromVersionArn passes it down without stripping the version part from the arn.

At the moment the fix has been applied to Function.fromFunctionArn, but I think you may assume people pass the correct arn to that function. The real problem is in fromVersionArn. This function "knows" it will receive a version arn so it also should know that it should strip the version to get a valid functionArn. So I think this line should be fixed. If you do that then the Fn.join(Fn.select(.., Fn.split...) will only be generated when it is really needed.

public static fromVersionArn(scope: Construct, id: string, versionArn: string): IVersion {
      const version = extractQualifierFromArn(versionArn);

      let functionArn: string;

      if (Token.isUnresolved(versionArn)) {
            const parts =  Fn.split(':', versionArn);
            functionArn = cdk.Fn.join(':', [
                Fn.select(0, parts),
                Fn.select(1, parts),
                Fn.select(2, parts),
                Fn.select(3, parts),
                Fn.select(4, parts),
                Fn.select(5, parts),
                Fn.select(6, parts),
            ]);
      } else {
            const parts = versionArn.split(':');
            functionArn = parts.slice(0, 7).join(':');
      }

      const lambda = Function.fromFunctionArn(scope, `${id}Function`, functionArn);
  
      class Import extends QualifiedFunctionBase implements IVersion {
        public readonly version = version;
        public readonly lambda = lambda;
        public readonly functionName = `${lambda.functionName}:${version}`;
        public readonly functionArn = versionArn;
        public readonly grantPrincipal = lambda.grantPrincipal;
        public readonly role = lambda.role;
        public readonly architecture = lambda.architecture;
  
        protected readonly qualifier = version;
        protected readonly canCreatePermissions = this._isStackAccount();
  
        public addAlias(name: string, opts: AliasOptions = {}): Alias {
          return addAlias(this, this, name, opts);
        }
  
        public get edgeArn(): string {
          if (version === '$LATEST') {
            throw new Error('$LATEST function version cannot be used for Lambda@Edge');
          }
          return this.functionArn;
        }
      }
      return new Import(scope, id);
    }

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[paulhcsun]

Thanks @pahud!

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[rehos]

I reviewed the code and I don't think it works when the function arn is an unresolved token (i.e. passed as a parameter to the CloudFormation stack). See my comment and suggestions here

[mindstorms6]

I think this change is backwards incompatible - it broke our stack.

Previously, if you passed a function arn with a version, the getFunctionArn would retain that version. It no longer does - and this caused an outage for us (by causing an APIG authorizer to point to the "root" lambda function instead of a specific alias - where it didn't haver permissions)

[rehos]

Sorry to hear the change caused an outage. My issue still isn't fixed with the change (see also my comment above, in which I also suggested not to change Function.fromFunctionArn, but instead fix Version.fromVersionArn).

This still generates an invalid stack:

const DemoClientVersionArn = new cdk.CfnParameter(this, 'DemoClientVersionArn');

const demoClientVersion = lambda.Version.fromVersionArn(this, 'DemoClientVersion', DemoClientVersionArn.valueAsString);

const demoClientCurrentAlias = new lambda.Alias(this, 'DemoClientCurrentAlias', {
    aliasName: 'current',
    version: demoClientVersion,
});

// The function url resource created by the CDK causes a CloudFormation deployment error
// because the version qualifier is still part of the functionArn of the lambda.Function
// created by lambda.Version.fromVersionArn
const demoClientFunctionUrl = new lambda.FunctionUrl(this, 'DemoClientFunctionUrl', {
    authType: lambda.FunctionUrlAuthType.AWS_IAM,
    invokeMode: lambda.InvokeMode.RESPONSE_STREAM,
    function: demoClientCurrentAlias,
});