From 211671e48c4b9bdd57e32fe36c396e52c159872d Mon Sep 17 00:00:00 2001
From: Rico Huijbers <rix0rrr@gmail.com>
Date: Mon, 7 Dec 2020 15:06:48 +0100
Subject: [PATCH] fix(core): autogenerated exports do not account for stack
 name length

Autogenerated IDs are limited to 248 characters. However, for exports
these are combined with a stack name, which may make the combination
exceed the maximum length of 255 characters.

Account for the stack name length while generating these IDs.

Fixes #9733.
---
 packages/@aws-cdk/core/lib/cfn-output.ts   |  8 ++++++
 packages/@aws-cdk/core/lib/private/refs.ts |  5 ++--
 packages/@aws-cdk/core/test/output.test.ts | 14 ++++++++-
 packages/@aws-cdk/core/test/stack.test.ts  | 33 ++++++++++++++++++++++
 4 files changed, 57 insertions(+), 3 deletions(-)

diff --git a/packages/@aws-cdk/core/lib/cfn-output.ts b/packages/@aws-cdk/core/lib/cfn-output.ts
index 480de577db06c..e296ecce34375 100644
--- a/packages/@aws-cdk/core/lib/cfn-output.ts
+++ b/packages/@aws-cdk/core/lib/cfn-output.ts
@@ -163,10 +163,18 @@ export class CfnOutput extends CfnElement {
       },
     };
   }
+
+  protected validate(): string[] {
+    if (this._exportName && !Token.isUnresolved(this._exportName) && this._exportName.length > 255) {
+      return [`Export name cannot exceed 255 characters (got ${this._exportName.length} characters)`];
+    }
+    return [];
+  }
 }
 
 import { CfnCondition } from './cfn-condition';
 import { Fn } from './cfn-fn';
 import { Lazy } from './lazy';
 import { Stack } from './stack';
+import { Token } from './token';
 
diff --git a/packages/@aws-cdk/core/lib/private/refs.ts b/packages/@aws-cdk/core/lib/private/refs.ts
index 05bb7930bc34f..46d44563b4a96 100644
--- a/packages/@aws-cdk/core/lib/private/refs.ts
+++ b/packages/@aws-cdk/core/lib/private/refs.ts
@@ -213,8 +213,9 @@ function generateExportName(stackExports: Construct, id: string) {
     id,
   ];
   const prefix = stack.stackName ? stack.stackName + ':' : '';
-  const exportName = prefix + makeUniqueId(components);
-  return exportName;
+  const localPart = makeUniqueId(components);
+  const maxLength = 255;
+  return prefix + localPart.slice(Math.max(0, localPart.length - maxLength + prefix.length));
 }
 
 // ------------------------------------------------------------------------------------------------
diff --git a/packages/@aws-cdk/core/test/output.test.ts b/packages/@aws-cdk/core/test/output.test.ts
index 1179c3111c0c9..0359049756946 100644
--- a/packages/@aws-cdk/core/test/output.test.ts
+++ b/packages/@aws-cdk/core/test/output.test.ts
@@ -1,5 +1,5 @@
 import { nodeunitShim, Test } from 'nodeunit-shim';
-import { App, CfnOutput, CfnResource, Stack } from '../lib';
+import { App, CfnOutput, CfnResource, ConstructNode, Stack, ValidationError } from '../lib';
 import { toCloudFormation } from './util';
 
 let app: App;
@@ -113,4 +113,16 @@ nodeunitShim({
 
     test.done();
   },
+
+  'Verify maximum length of export name'(test: Test) {
+    new CfnOutput(stack, 'SomeOutput', { value: 'x', exportName: 'x'.repeat(260) });
+
+    const errors = ConstructNode.validate(stack.node).map((v: ValidationError) => v.message);
+
+    expect(errors).toEqual([
+      expect.stringContaining('Export name cannot exceed 255 characters'),
+    ]);
+
+    test.done();
+  },
 });
diff --git a/packages/@aws-cdk/core/test/stack.test.ts b/packages/@aws-cdk/core/test/stack.test.ts
index dad2a64b3235c..63c04be2e81de 100644
--- a/packages/@aws-cdk/core/test/stack.test.ts
+++ b/packages/@aws-cdk/core/test/stack.test.ts
@@ -261,6 +261,39 @@ nodeunitShim({
     test.done();
   },
 
+  'Cross-stack export names account for stack name lengths'(test: Test) {
+    // GIVEN
+    const app = new App();
+    const stack1 = new Stack(app, 'Stack1', {
+      stackName: 'SoThisCouldPotentiallyBeAVeryLongStackName',
+    });
+    let scope: Construct = stack1;
+
+    // WHEN - deeply nested
+    for (let i = 0; i < 50; i++) {
+      scope = new Construct(scope, `ChildConstruct${i}`);
+    }
+
+    const resource1 = new CfnResource(scope, 'Resource', { type: 'BLA' });
+    const stack2 = new Stack(app, 'Stack2');
+
+    // WHEN - used in another resource
+    new CfnResource(stack2, 'SomeResource', {
+      type: 'AWS::Some::Resource',
+      properties: {
+        someProperty: new Intrinsic(resource1.ref),
+      },
+    });
+
+    // THEN
+    const assembly = app.synth();
+    const template1 = assembly.getStackByName(stack1.stackName).template;
+
+    const theOutput = template1.Outputs[Object.keys(template1.Outputs)[0]];
+    expect(theOutput.Export.Name.length).toEqual(255);
+    test.done();
+  },
+
   'Cross-stack reference export names are relative to the stack (when the flag is set)'(test: Test) {
     // GIVEN
     const app = new App({