From cf92a2a9a3db2b11ee2aafce4ce176d4ecbdded6 Mon Sep 17 00:00:00 2001
From: "M. J. Fromberger" <fromberger@tailscale.com>
Date: Wed, 25 Mar 2026 10:48:54 -0700
Subject: [PATCH] add discard method for the disk cache

Change-Id: I7f597e3b1ad5319c0baf82079b248be948bf4b22
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>
---
 ipn/ipnlocal/diskcache.go | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/ipn/ipnlocal/diskcache.go b/ipn/ipnlocal/diskcache.go
index 0b1b7b448..f04829e98 100644
--- a/ipn/ipnlocal/diskcache.go
+++ b/ipn/ipnlocal/diskcache.go
@@ -54,3 +54,29 @@ func (b *LocalBackend) loadDiskCacheLocked() (om *netmap.NetworkMap, ok bool) {
 	}
 	return nm, true
 }
+
+func (b *LocalBackend) discardDiskCacheLocked() {
+	if !buildfeatures.HasCacheNetMap {
+		return
+	}
+	if b.diskCache.cache == nil {
+		return // nothing to do, we do not have a cache
+	}
+
+	// Reaching here, we have a cache directory that needs to be purged.
+	// Log errors but do not fail for them.
+	store := netmapcache.FileStore(b.diskCache.dir)
+	ctx := b.currentNode().Context()
+	for key, err := range store.List(ctx, "") {
+		if err != nil {
+			b.logf("listing cache contents: %v", err)
+			break
+		}
+		if err := store.Remove(ctx, key); err != nil {
+			b.logf("discarding cache key %q: %v", key, err)
+		}
+	}
+
+	b.diskCache.cache = nil // drop reference
+	b.diskCache.dir = ""
+}