[ISSUE #6781] Fix stale proxy selector data after empty HTTP refresh.

[lymerin]

Fixes #6781.

This PR clears stale proxy selector runtime data when HTTP synchronization receives an empty full snapshot.

Changes:

• propagate empty proxy selector snapshots to subscribers through refresh();
• propagate refresh operations to proxy selector handlers;
• shut down and remove cached TCP bootstrap servers;
• continue clearing remaining servers when one shutdown fails;
• avoid a null-pointer race between individual deletion and full refresh;
• add unit, integration, and public HTTP synchronization path tests.

Although the issue is triggered by HTTP synchronization, CommonProxySelectorDataSubscriber is shared. Any synchronization mode that invokes refresh() will now clear the TCP proxy selector runtime cache.

Tests:

• full repository clean install passed;
• affected 14-module Maven reactor passed;
• Checkstyle passed with 0 violations;
• git diff --check passed.

Make sure that:

• You have read the [contribution guidelines](https://shenyu.apache.org/community/contributor-guide).
• You submit test cases (unit or integration tests) that back your changes.
• Your local test passed ./mvnw clean install -Dmaven.javadoc.skip=true.

[Copilot]

Pull request overview

This PR fixes stale TCP proxy selector runtime state when HTTP synchronization receives an empty full snapshot by ensuring empty snapshots trigger refresh() propagation through proxy selector subscribers/handlers, and by clearing/shutting down cached TCP bootstrap servers.

Changes:

• Invoke ProxySelectorDataSubscriber.refresh() when ProxySelectorRefresh.refresh(...) receives an empty snapshot.
• Propagate refresh from CommonProxySelectorDataSubscriber into ProxySelectorDataHandler.refresh() and implement TCP handler refresh to clear the bootstrap cache.
• Add unit/integration tests covering empty snapshot refresh propagation and TCP bootstrap cache shutdown/clearing behavior (including failure tolerance).

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
shenyu-sync-data-center/shenyu-sync-data-http/src/main/java/org/apache/shenyu/sync/data/http/refresh/ProxySelectorRefresh.java	Ensures empty proxy selector snapshots propagate refresh to subscribers to clear stale runtime state.
shenyu-sync-data-center/shenyu-sync-data-http/src/test/java/org/apache/shenyu/sync/data/http/refresh/ProxySelectorRefreshTest.java	Adds unit coverage verifying empty snapshot triggers subscriber.refresh() and non-empty snapshots subscribe data.
shenyu-sync-data-center/shenyu-sync-data-http/src/test/java/org/apache/shenyu/sync/data/http/HttpSyncDataServiceTest.java	Extends HTTP sync test fixture/expectations to include PROXY_SELECTOR group and verify refresh is invoked.
shenyu-plugin/shenyu-plugin-base/src/main/java/org/apache/shenyu/plugin/base/handler/ProxySelectorDataHandler.java	Adds a default refresh() hook for proxy selector handlers.
shenyu-plugin/shenyu-plugin-base/src/main/java/org/apache/shenyu/plugin/base/cache/CommonProxySelectorDataSubscriber.java	Implements subscriber-level refresh() by delegating to all handler refresh operations.
shenyu-plugin/shenyu-plugin-base/src/test/java/org/apache/shenyu/plugin/base/cache/CommonProxySelectorDataSubscriberTest.java	Adds tests asserting refresh() is propagated to all handlers and is safe with no handlers.
shenyu-plugin/shenyu-plugin-proxy/shenyu-plugin-tcp/src/main/java/org/apache/shenyu/plugin/tcp/handler/TcpProxySelectorDataHandler.java	Makes TCP handler refresh clear the bootstrap cache; hardens removal against null cache entries.
shenyu-plugin/shenyu-plugin-proxy/shenyu-plugin-tcp/src/main/java/org/apache/shenyu/plugin/tcp/handler/TcpBootstrapFactory.java	Adds cache clearing that shuts down servers, removes entries, and continues on shutdown failures.
shenyu-plugin/shenyu-plugin-proxy/shenyu-plugin-tcp/src/test/java/org/apache/shenyu/plugin/tcp/handler/TcpProxySelectorDataHandlerTest.java	Adds coverage for refresh-driven shutdown/removal, failure-tolerant shutdown, and idempotent selector removal.

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[Aias00]

Review: #6909 — [ISSUE #6781] Fix stale proxy selector data after empty HTTP refresh

Verdict: ✅ Approve (with minor non-blocking notes)

This is a clean, well-scoped fix for #6781. Good work.

What's correct

• Root cause addressed. CommonProxySelectorDataSubscriber.refresh() previously just called ProxySelectorDataSubscriber.super.refresh(), which I verified is a no-op (default void refresh() {} in the interface). So an empty full snapshot never cleared proxy-selector runtime data. The new implementation delegates to each ProxySelectorDataHandler.refresh(), which actually tears down state. This is strictly an improvement with no behavior lost from the (empty) interface default.
• ProxySelectorDataHandler.refresh() added as a default method → existing handlers keep compiling; only the TCP handler overrides it. Good backward-compat design.
• TcpBootstrapFactory.clearCache() shuts down each cached BootstrapServer with a try/catch so one failing shutdown doesn't abort the rest — exactly the "continue clearing remaining servers when one fails" goal. Using the value-conditional cache.remove(name, server) is the safe way to mutate a ConcurrentHashMap during iteration (no CME, no stale removal).
• TcpProxySelectorDataHandler.removeProxySelector now does removeCache() + null-check before .shutdown(), closing a TOCTOU race where the old inCache()-then-removeCache().shutdown() could NPE if another thread removed the entry in between.
• Propagation wired through ProxySelectorRefresh: empty snapshot now calls proxySelectorDataSubscribers.forEach(ProxySelectorDataSubscriber::refresh).
• Test coverage is solid: subscriber refresh (with/without handlers), TCP handler refresh incl. the "continues when shutdown fails" case and removeProxySelector, the HTTP sync data-service path, and a dedicated ProxySelectorRefreshTest asserting empty→clear and non-empty→subscribe.

Non-blocking suggestions

1. Empty-snapshot semantics are global. Any sync mode that sends an empty PROXY_SELECTOR snapshot will now hard-stop all TCP bootstrap servers. That matches the documented intent (#6781), but it's worth a one-line comment in ProxySelectorRefresh.refresh() noting that an empty snapshot = "clear everything", so future readers don't treat it as a no-op/clear-local-only path.
2. clearCache() mutates the map from inside forEach. Current implementation is safe for ConcurrentHashMap, but if shutdown() ever triggers re-registration (a lifecycle listener), a server could be missed. Not an issue today — just flagging the invariant to preserve.

Verdict

Approving. The fix is correct, the NPE race is real, and the regression tests back the behavior. Nice job.

[Aias00]

thx for contribution, pls add my wechat: aias00