fix(sdk): add cron validation for cloud.Schedule (#6090)

Closes #5985

## Checklist

- [x] Title matches [Winglang's style guide](https://www.winglang.io/contributing/start-here/pull_requests#how-are-pull-request-titles-formatted)
- [x] Description explains motivation and solution
- [x] Tests added (always)
- [ ] Docs updated (only required for features)
- [ ] Added `pr/e2e-full` label if this feature requires end-to-end testing

*By submitting this pull request, I confirm that my contribution is made under the terms of the [Wing Cloud Contribution License](https://github.com/winglang/wing/blob/main/CONTRIBUTION_LICENSE.md)*.

examples/tests/sdk_tests/schedule/init.test.w

@@ -4,6 +4,7 @@ skip: true
 
 bring cloud;
 bring util;
+bring expect;
 
 new cloud.Schedule( rate: 5m ) as "s0";
 
@@ -16,27 +17,34 @@ if (util.env("WING_TARGET") != "sim") {
   } catch e {
       error = e;
   }
-  assert(error == "rate or cron need to be filled.");
+  expect.equal(error, "rate or cron need to be filled.");
 
   try {
       new cloud.Schedule( rate: 2m, cron: "* * * * *" ) as "s2";
   } catch e {
       error = e;
   }
-  assert(error == "rate and cron cannot be configured simultaneously.");
+  expect.equal(error, "rate and cron cannot be configured simultaneously.");
 
 
   try {
       new cloud.Schedule( rate: 1s ) as "s3";
   } catch e {
       error = e;
   }
-  assert(error == "rate can not be set to less than 1 minute.");
+  expect.equal(error, "rate can not be set to less than 1 minute.");
 
   try {
       new cloud.Schedule( cron: "* * * * * *" ) as "s4";
   } catch e {
       error = e;
   }
-  assert(error ==  "cron string must be UNIX cron format [minute] [hour] [day of month] [month] [day of week]");
+  expect.equal(error, "cron string must be in UNIX cron format");
+
+  try {
+      new cloud.Schedule( cron: "* * * * ?" ) as "s5";
+  } catch e {
+      error = e;
+  }
+  expect.equal(error, "cron string must be in UNIX cron format");
 }

examples/tests/sdk_tests/schedule/on_tick.test.w

@@ -2,7 +2,7 @@ bring cloud;
 bring util;
 
 // every minute
-let from_cron = new cloud.Schedule( cron: "* * * * ?" ) as "from_cron";
+let from_cron = new cloud.Schedule( cron: "* * * * *" ) as "from_cron";
 let from_rate = new cloud.Schedule( rate: 1m ) as "from_rate";
 let c1 = new cloud.Counter() as "c1";
 let c2 = new cloud.Counter() as "c2";

libs/awscdk/test/schedule.test.ts

@@ -158,9 +158,7 @@ test("cron with more than five values", () => {
       new cloud.Schedule(app, "Schedule", {
         cron: "0/1 * ? * * *",
       })
-  ).toThrow(
-    "cron string must be UNIX cron format [minute] [hour] [day of month] [month] [day of week]"
-  );
+  ).toThrow("cron string must be in UNIX cron format");
 });
 
 test("schedule without rate or cron", () => {
@@ -196,5 +194,7 @@ test("cron with day of month and day of week configured at the same time", () =>
       new cloud.Schedule(app, "Schedule", {
         cron: "* * 1 * 1",
       })
-  ).toThrow("Cannot restrict both 'day-of-month' and 'day-of-week' in a cron expression, at least one must be '*'");
+  ).toThrow(
+    "Cannot restrict both 'day-of-month' and 'day-of-week' in a cron expression, at least one must be '*'"
+  );
 });

libs/wingsdk/.projenrc.ts

@@ -82,6 +82,7 @@ const project = new cdk.JsiiProject({
     "ioredis",
     "jsonschema",
     "ajv",
+    "cron-validator",
     // fs module dependency
     "yaml",
     "toml",

libs/wingsdk/src/cloud/schedule.ts

@@ -1,4 +1,5 @@
 import { Construct } from "constructs";
+import { isValidCron } from "cron-validator";
 import { Function, FunctionProps } from "./function";
 import { fqnForType } from "../constants";
 import { AbstractMemberError } from "../core/errors";
@@ -70,10 +71,18 @@ export class Schedule extends Resource {
     if (rate && rate.seconds < 60) {
       throw new Error("rate can not be set to less than 1 minute.");
     }
-    if (cron && cron.split(" ").length > 5) {
-      throw new Error(
-        "cron string must be UNIX cron format [minute] [hour] [day of month] [month] [day of week]"
-      );
+    // Check for valid UNIX cron format
+    // https://www.ibm.com/docs/en/db2/11.5?topic=task-unix-cron-format
+    if (
+      cron &&
+      !isValidCron(cron, {
+        alias: true,
+        allowSevenAsSunday: true,
+        allowBlankDay: false,
+        seconds: false,
+      })
+    ) {
+      throw new Error("cron string must be in UNIX cron format");
     }
   }
 

libs/wingsdk/test/target-tf-aws/schedule.test.ts

@@ -241,9 +241,7 @@ test("cron with more than five values", () => {
       new cloud.Schedule(app, "Schedule", {
         cron: "0/1 * * * * *",
       })
-  ).toThrow(
-    "cron string must be UNIX cron format [minute] [hour] [day of month] [month] [day of week]"
-  );
+  ).toThrow("cron string must be in UNIX cron format");
 });
 
 test("schedule without rate or cron", () => {