Function UpdateCache

net/dnsfallback/dnsfallback.go:233–258

UpdateCache stores the DERP map cache back to disk. The caller must not mutate 'c' after calling this function.

(c *tailcfg.DERPMap, logf logger.Logf)

//
// The caller must not mutate 'c' after calling this function.
func UpdateCache(c *tailcfg.DERPMap, logf logger.Logf) {
	// Don't do anything if nothing changed.
	curr := cachedDERPMap.Load()
	if reflect.DeepEqual(curr, c) {
		return
	}

	d, err := json.Marshal(c)
	if err != nil {
		logf("[v1] dnsfallback: UpdateCache error marshaling: %v", err)
		return
	}

	// Only store after we're confident this is at least valid JSON
	cachedDERPMap.Store(c)

	// Don't try writing if we don't have a cache path set; this can happen
	// when we don't have a state path (e.g. /var/lib/tailscale) configured.
	if cachePath != "" {
		err = atomicfile.WriteFile(cachePath, d, 0600)
		if err != nil {
			logf("[v1] dnsfallback: UpdateCache error writing: %v", err)
			return
		}
	}
}

// SetCachePath sets the path to the on-disk DERP map cache that we store and
// update. Additionally, if a file at this path exists, we load it and merge it