feat(ads-client): ignore context_id in HTTP cache key generation (#7214)

Remove cycle_context_id() API and modify cache to ignore context_id
field in request bodies when generating cache keys. This prevents
unnecessary cache invalidation when context_id rotates automatically.

- Remove cycle_context_id() public API (breaking change)
- Strip context_id from request body before hashing for cache key
- Add tests for context_id-agnostic caching behavior
- Update documentation to remove cycle_context_id() method

Author: Almaju

CHANGELOG.md

@@ -37,6 +37,8 @@
 * Enable staging environment support for all platforms (previously feature-gated)
 * Temporarily disable cache invalidation on click and impression recording (will be re-enabled behind Nimbus experiment)
 * Enable automatic context_id rotation every 3 days
+* **BREAKING**: Removed `cycle_context_id()` API method - context_id rotation is now automatic
+* Modified HTTP cache to ignore `context_id` field in request bodies when generating cache keys, preventing unnecessary cache invalidation on rotation
 
 ### Android
 * Upgraded Kotlin compiler from 2.2.21 to 2.3.0 ([#7183](https://github.com/mozilla/application-services/pull/7183))

components/ads-client/docs/usage.md

@@ -52,7 +52,6 @@ let client = MozAdsClientBuilder::new()
 | Method                                                                                                                  | Return Type                                            | Description                                                                                                                                                                          |
 | ----------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
 | `clear_cache(&self)`                                                                                                    | `AdsClientApiResult<()>`                               | Clears the client's HTTP cache. Returns an error if clearing fails.                                                                                                                  |
-| `cycle_context_id(&self)`                                                                                               | `AdsClientApiResult<String>`                           | Rotates the client's context ID and returns the **previous** ID.                                                                                                                     |
 | `record_click(&self, click_url: String)`                                                                                | `AdsClientApiResult<()>`                               | Records a click using the provided callback URL (typically from `ad.callbacks.click`).                                                                                               |
 | `record_impression(&self, impression_url: String)`                                                                      | `AdsClientApiResult<()>`                               | Records an impression using the provided callback URL (typically from `ad.callbacks.impression`).                                                                                    |
 | `report_ad(&self, report_url: String)`                                                                                  | `AdsClientApiResult<()>`                               | Reports an ad using the provided callback URL (typically from `ad.callbacks.report`).                                                                                                |

components/ads-client/src/client.rs

@@ -205,13 +205,6 @@ where
         self.context_id_component.request(3)
     }
 
-    pub fn cycle_context_id(&mut self) -> context_id::ApiResult<String> {
-        let old_context_id = self.get_context_id()?;
-        self.context_id_component.force_rotation()?;
-        let _ = self.client.clear_cache();
-        Ok(old_context_id)
-    }
-
     pub fn clear_cache(&self) -> Result<(), HttpCacheError> {
         self.client.clear_cache()
     }
@@ -267,21 +260,6 @@ mod tests {
         assert!(!context_id.is_empty());
     }
 
-    #[test]
-    fn test_cycle_context_id() {
-        let config = AdsClientConfig {
-            environment: Environment::Test,
-            cache_config: None,
-            telemetry: MozAdsTelemetryWrapper::noop(),
-        };
-        let mut client = AdsClient::new(config);
-        let old_id = client.get_context_id().unwrap();
-        let previous_id = client.cycle_context_id().unwrap();
-        assert_eq!(previous_id, old_id);
-        let new_id = client.get_context_id().unwrap();
-        assert_ne!(new_id, old_id);
-    }
-
     #[test]
     fn test_request_image_ads_happy() {
         viaduct_dev::init_backend_dev();

components/ads-client/src/http_cache/request_hash.rs

@@ -22,7 +22,22 @@ impl From<&Request> for RequestHash {
             header.value.hash(&mut hasher);
         }
 
-        request.body.hash(&mut hasher);
+        // Strip context_id before hashing — it rotates on client re-instantiation
+        // and should not invalidate cached responses.
+        // NOTE: This couples ads-client domain logic to the cache. When the cache
+        // is extracted into its own module, this should move to the caller side.
+        let body_for_hash = request.body.as_deref().and_then(|bytes| {
+            serde_json::from_slice::<serde_json::Value>(bytes)
+                .ok()
+                .map(|mut value| {
+                    if let Some(obj) = value.as_object_mut() {
+                        obj.remove("context_id");
+                    }
+                    serde_json::to_vec(&value).unwrap_or_else(|_| bytes.to_vec())
+                })
+        });
+        body_for_hash.hash(&mut hasher);
+
         RequestHash(format!("{:x}", hasher.finish()))
     }
 }
@@ -118,6 +133,66 @@ mod tests {
         assert_eq!(h_req1.to_string(), h_req3.to_string());
     }
 
+    #[test]
+    fn test_context_id_ignored_in_hash() {
+        let url = "https://example.com/ads";
+        let body1 = serde_json::to_vec(&serde_json::json!({
+            "context_id": "aaaa-bbbb-cccc",
+            "placements": [{"placement": "tile_1", "count": 1}]
+        }))
+        .unwrap();
+        let body2 = serde_json::to_vec(&serde_json::json!({
+            "context_id": "dddd-eeee-ffff",
+            "placements": [{"placement": "tile_1", "count": 1}]
+        }))
+        .unwrap();
+
+        let req1 = Request {
+            method: Method::Post,
+            url: url.parse().unwrap(),
+            headers: Headers::new(),
+            body: Some(body1),
+        };
+        let req2 = Request {
+            method: Method::Post,
+            url: url.parse().unwrap(),
+            headers: Headers::new(),
+            body: Some(body2),
+        };
+
+        assert_eq!(RequestHash::from(&req1), RequestHash::from(&req2));
+    }
+
+    #[test]
+    fn test_different_placements_produce_different_hash() {
+        let url = "https://example.com/ads";
+        let body1 = serde_json::to_vec(&serde_json::json!({
+            "context_id": "same-id",
+            "placements": [{"placement": "tile_1", "count": 1}]
+        }))
+        .unwrap();
+        let body2 = serde_json::to_vec(&serde_json::json!({
+            "context_id": "same-id",
+            "placements": [{"placement": "tile_2", "count": 3}]
+        }))
+        .unwrap();
+
+        let req1 = Request {
+            method: Method::Post,
+            url: url.parse().unwrap(),
+            headers: Headers::new(),
+            body: Some(body1),
+        };
+        let req2 = Request {
+            method: Method::Post,
+            url: url.parse().unwrap(),
+            headers: Headers::new(),
+            body: Some(body2),
+        };
+
+        assert_ne!(RequestHash::from(&req1), RequestHash::from(&req2));
+    }
+
     #[test]
     fn test_request_hash_from_string() {
         let hash_str = "abc123def456";

components/ads-client/src/lib.rs

@@ -118,12 +118,6 @@ impl MozAdsClient {
         inner.report_ad(url).map_err(ComponentError::ReportAd)
     }
 
-    pub fn cycle_context_id(&self) -> AdsClientApiResult<String> {
-        let mut inner = self.inner.lock();
-        let previous_context_id = inner.cycle_context_id()?;
-        Ok(previous_context_id)
-    }
-
     pub fn clear_cache(&self) -> AdsClientApiResult<()> {
         let inner = self.inner.lock();
         inner