Support unix_ms_now in rhai engine (#5181)

Co-authored-by: Gary Pennington <gary@apollographql.com>

.changesets/feat_feature_shaika_add_ms_support_to_rhai_engine.md

@@ -0,0 +1,4 @@
+### Support unix_ms_now in rhai engine ([Issue #5182](https://github.com/apollographql/router/issues/5182))
+
+
+By [@shaikatzz](https://github.com/shaikatzz) in https://github.com/apollographql/router/pull/5181

apollo-router/src/plugins/rhai/engine.rs

@@ -1233,6 +1233,14 @@ mod router_plugin {
             .map(|x| x.as_secs() as i64)
     }
 
+    #[rhai_fn(return_raw)]
+    pub(crate) fn unix_ms_now() -> Result<i64, Box<EvalAltResult>> {
+        SystemTime::now()
+            .duration_since(SystemTime::UNIX_EPOCH)
+            .map_err(|e| e.to_string().into())
+            .map(|x| x.as_millis() as i64)
+    }
+
     // Add query plan getter to execution request
     #[rhai_fn(get = "query_plan")]
     pub(crate) fn execution_request_query_plan_get(

apollo-router/src/plugins/rhai/tests.rs

@@ -579,6 +579,21 @@ fn it_can_create_unix_now() {
     assert!(st <= unix_now && unix_now <= st + 1);
 }
 
+#[test]
+fn it_can_create_unix_ms_now() {
+    let engine = new_rhai_test_engine();
+    let st = SystemTime::now()
+        .duration_since(SystemTime::UNIX_EPOCH)
+        .expect("can get system time")
+        .as_millis() as i64;
+    let unix_ms_now: i64 = engine
+        .eval(r#"unix_ms_now()"#)
+        .expect("can get unix_ms_now() timestamp");
+    // Always difficult to do timing tests. unix_ms_now() should execute within a second of st,
+    // so...
+    assert!(st <= unix_ms_now && unix_ms_now <= st + 1000);
+}
+
 #[test]
 fn it_can_generate_uuid() {
     let engine = new_rhai_test_engine();

docs/source/customizations/rhai-api.mdx

@@ -306,6 +306,16 @@ fn supergraph_service(service) {
 }
 ```
 
+## Unix timestamp (in milliseconds)
+
+Your Rhai customization can use the function `unix_ms_now()` to obtain the current Unix timestamp in milliseconds since the Unix epoch. 
+
+```rhai
+fn supergraph_service(service) {
+    let now = unix_ms_now();
+}
+```
+
 ## Unique IDs (UUID)
 
 Your Rhai customization can use the function `uuid_v4()` to obtain a UUIDv4 ID.