fix(analytics): isolate AnalyticsMessages and HttpService per instance [SDK-109]

[tylerjroach]

Summary

Two MixpanelAPI instances configured with different tokens and no explicit instanceName silently shared a single AnalyticsMessages worker (and therefore its MPConfig and HttpService), so events for the second instance were POSTed to the first instance's server URL. Independently, runtime setServerURL calls updated MPConfig endpoints but never refreshed the HttpService serverHost captured at construction.

Changes

• AnalyticsMessages.getInstance now takes a token and keys sInstances by MPConfig.resolveInstanceKey(instanceName, token), mirroring MixpanelAPI.getInstance and matching iOS MixpanelManager behavior.
• AnalyticsMessages.getPoster re-syncs serverHost (in addition to backupHost and the error listener) on every call, so setServerURL propagates to the poster.
• Added HttpService.setServerHost / getServerHost; the constructor delegates to setServerHost so the empty-check + DEFAULT_SERVER_HOST fallback lives in one place.
• Extracted the instanceName ?? token fallback into MPConfig.resolveInstanceKey — the five prior inline copies (plus three in tests) now call it, avoiding future drift.
• Removed the dead mInstanceName field on AnalyticsMessages.

Workaround

Users on older SDK versions can side-step both bugs by giving each MixpanelOptions a distinct instanceName and setting the server URL via MixpanelOptions.serverURL(...) (which is applied before the first getPoster() call, so HttpService is constructed with the right host on first creation).

[linear-code]

SDK-109

[greptile-apps]

Confidence Score: 5/5

Safe to merge — the changes are well-scoped bug fixes with direct regression tests, and no new error paths are introduced.

The instance-isolation and setServerURL-propagation fixes are correct and consistent with how MixpanelAPI already keyed its own map. The resolveInstanceKey refactor is mechanical. No logic is removed that could leave a code path uncovered, and the new MultiInstanceIsolationTest directly exercises both fixed scenarios.

No files require special attention.

Important Files Changed

Filename	Overview
analytics/src/main/java/com/mixpanel/android/mpmetrics/AnalyticsMessages.java	Core fix: sInstances now keyed by resolveInstanceKey(instanceName, token); getPoster() re-syncs serverHost unconditionally; dead mInstanceName field removed.
analytics/src/main/java/com/mixpanel/android/mpmetrics/MPConfig.java	New package-private resolveInstanceKey consolidates the instanceName??token fallback in one place.
analytics/src/main/java/com/mixpanel/android/mpmetrics/MixpanelAPI.java	Passes mToken to AnalyticsMessages.getInstance; replaces inline instanceName??token copies with resolveInstanceKey.
analytics/src/main/java/com/mixpanel/android/util/HttpService.java	Adds setServerHost/getServerHost; constructor delegates to setServerHost centralising the empty-string fallback.
analytics/src/test/java/com/mixpanel/android/mpmetrics/MultiInstanceIsolationTest.java	New regression tests covering token-isolated workers and setServerURL propagation to the poster.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant App
    participant MixpanelAPI
    participant AnalyticsMessages
    participant MPConfig
    participant HttpService

    App->>MixpanelAPI: getInstance(ctx, token, options)
    MixpanelAPI->>MPConfig: resolveInstanceKey(instanceName, token)
    MPConfig-->>MixpanelAPI: key
    MixpanelAPI->>AnalyticsMessages: getInstance(ctx, config, token)
    AnalyticsMessages->>MPConfig: resolveInstanceKey(instanceName, token)
    MPConfig-->>AnalyticsMessages: key (same as MixpanelAPI key)
    AnalyticsMessages-->>MixpanelAPI: isolated worker per key

    App->>MixpanelAPI: setServerURL(newUrl)
    MixpanelAPI->>MPConfig: setEventsEndpoint(newUrl)
    App->>MixpanelAPI: track(event)
    MixpanelAPI->>AnalyticsMessages: eventsMessage(...)
    AnalyticsMessages->>AnalyticsMessages: getPoster()
    AnalyticsMessages->>HttpService: setServerHost(extractHost(newUrl))
    Note over HttpService: host updated on every getPoster() call

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sequenceDiagram
    participant App
    participant MixpanelAPI
    participant AnalyticsMessages
    participant MPConfig
    participant HttpService

    App->>MixpanelAPI: getInstance(ctx, token, options)
    MixpanelAPI->>MPConfig: resolveInstanceKey(instanceName, token)
    MPConfig-->>MixpanelAPI: key
    MixpanelAPI->>AnalyticsMessages: getInstance(ctx, config, token)
    AnalyticsMessages->>MPConfig: resolveInstanceKey(instanceName, token)
    MPConfig-->>AnalyticsMessages: key (same as MixpanelAPI key)
    AnalyticsMessages-->>MixpanelAPI: isolated worker per key

    App->>MixpanelAPI: setServerURL(newUrl)
    MixpanelAPI->>MPConfig: setEventsEndpoint(newUrl)
    App->>MixpanelAPI: track(event)
    MixpanelAPI->>AnalyticsMessages: eventsMessage(...)
    AnalyticsMessages->>AnalyticsMessages: getPoster()
    AnalyticsMessages->>HttpService: setServerHost(extractHost(newUrl))
    Note over HttpService: host updated on every getPoster() call

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_{Reviews (2): Last reviewed commit: "test(analytics): use assertSame for Http..." | Re-trigger Greptile}

[tylerjroach]

Pushed f9407b5 — swapped assertEquals → assertSame and imported the helper. 2 tests pass locally.