[omaha-client] Don't overwrite cohort if it's missing from response.

Bug: 102304
Change-Id: I35043f3010605991e8bc6166694cbde78d7552d9
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/690663
Fuchsia-Auto-Submit: Sen Jiang <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>
Reviewed-by: Aaron Wood <[email protected]>

Author: JayXon

src/sys/pkg/lib/omaha-client/src/protocol.rs

@@ -48,9 +48,18 @@ impl Cohort {
     }
 
     pub fn update_from_omaha(&mut self, omaha_cohort: Self) {
-        // Do not overwrite cohort hint, because Omaha should never send cohort hint back.
-        self.id = omaha_cohort.id;
-        self.name = omaha_cohort.name;
+        // From Omaha spec:
+        // If this attribute is transmitted in the response (even if the value is empty-string),
+        // the client should overwrite the current cohort of this app with the sent value.
+        if omaha_cohort.id != None {
+            self.id = omaha_cohort.id;
+        }
+        if omaha_cohort.hint != None {
+            self.hint = omaha_cohort.hint;
+        }
+        if omaha_cohort.name != None {
+            self.name = omaha_cohort.name;
+        }
     }
 
     /// A validation function to test that a given Cohort hint or name is valid per the Omaha spec:
@@ -84,6 +93,18 @@ mod tests {
         assert_eq!(None, cohort.name);
     }
 
+    #[test]
+    fn test_cohort_update_from_omaha_none() {
+        let mut cohort = Cohort {
+            id: Some("id".to_string()),
+            hint: Some("hint".to_string()),
+            name: Some("name".to_string()),
+        };
+        let expected_cohort = cohort.clone();
+        cohort.update_from_omaha(Cohort::default());
+        assert_eq!(cohort, expected_cohort);
+    }
+
     #[test]
     fn test_valid_cohort_names() {
         assert!(Cohort::validate_name("some-channel"));