fix(discov): prevent unbounded memory growth on duplicate etcd PUT events

[kevwan]

Problem

Two related bugs in core/discov cause unbounded memory growth in long-running services using zRPC with etcd service discovery.

Bug 1 — handleWatchEvents fires OnAdd on every PUT unconditionally

When etcd re-emits a PUT event for a key that already exists with the same value (lease refresh, watch reconnect), handleWatchEvents called l.OnAdd() without checking whether the value actually changed. This triggered addKv on every duplicate event.

Bug 2 — addKv appends key to slice without deduplication

container.values maps a server address (string) to a slice of etcd keys ([]string). addKv unconditionally appended the key on every OnAdd call — so a single etcd key could appear thousands of times in the slice after repeated lease refreshes, consuming unbounded memory.

Bonus: when a key's value changed (etcd key moved to a different server address), the stale c.values[oldVal] slice entry was never cleaned up, and OnDelete(old) was never fired — leaving listeners with a stale view.

Fix

core/discov/internal/registry.go — handleWatchEvents

• Duplicate PUT (same key, same value) → continue; no listener notification.
• Value change (same key, different value) → fire OnDelete(old) then OnAdd(new) to keep listeners consistent.

core/discov/subscriber.go — addKv

• Duplicate add (key already maps to same value) → early return, no slice append, no dirty-flag churn.
• Value change (key moves to new server) → call doRemoveKey first to clean up the stale c.values[oldVal] entry before inserting the new one.

Tests

Four regression tests added:

Test	File	What it verifies
TestCluster_handleWatchEvents_DuplicatePut	registry_test.go	OnAdd called exactly once for two identical PUT events
TestCluster_handleWatchEvents_ValueChange	registry_test.go	OnDelete(old) fired before OnAdd(new) when value changes
TestContainer_DuplicateAdd	subscriber_test.go	Internal slice length stays at 1 after 100 duplicate adds
TestContainer_KeyValueChange	subscriber_test.go	Key moving to new value leaves correct state after delete

Related issues

• etcd context deadline exceeded #3705 (etcd context deadline errors / reconnect behaviour)
• go-zero etcd invalid auth token, very serious #4393 (memory growth in long-running zRPC services)
• ZRpc + Etcd + Docker Env, After the ZRpc client container slept for 1 hour, An ZRpc client request was initiated again, this request will exception and could not be recovered. The error "context deadline exceeded" appeared every 4 seconds in the log #4420 (unrecoverable state after Docker sleep)

[Copilot]

Pull request overview

Fixes two related bugs in core/discov that caused unbounded memory growth in long-running zRPC services using etcd service discovery. When etcd re-emits a PUT event for an unchanged key (lease refresh, watch reconnect), the old code unconditionally appended the key to an internal slice and fired OnAdd listeners, growing memory without bound. Additionally, when a key's value changed, the stale entry was leaked and OnDelete was never emitted for the old value.

Changes:

• handleWatchEvents now skips duplicate same-value PUTs and emits OnDelete(old) before OnAdd(new) when a key's value changes.
• container.addKv short-circuits duplicate adds and calls doRemoveKey to clean up stale state when a key is reassigned to a new value.
• Four regression tests added (two in registry_test.go, two in subscriber_test.go).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
core/discov/internal/registry.go	Dedup duplicate PUTs and emit OnDelete on value change in handleWatchEvents; trailing whitespace cleanup.
core/discov/internal/registry_test.go	New tests for duplicate-PUT and value-change behavior; trailing whitespace cleanup.
core/discov/subscriber.go	addKv now skips duplicates and cleans up stale mapping on value change.
core/discov/subscriber_test.go	New tests verifying internal slice doesn't grow on duplicates and cleanup on value change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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