diff --git a/p2p/dnsdisc/client.go b/p2p/dnsdisc/client.go index d3e8111ab..3e4b50aad 100644 --- a/p2p/dnsdisc/client.go +++ b/p2p/dnsdisc/client.go @@ -37,9 +37,10 @@ import ( // Client discovers nodes by querying DNS servers. type Client struct { - cfg Config - clock mclock.Clock - entries *lru.Cache + cfg Config + clock mclock.Clock + entries *lru.Cache + ratelimit *rate.Limiter } // Config holds configuration options for the client. @@ -97,8 +98,12 @@ func NewClient(cfg Config) *Client { panic(err) } rlimit := rate.NewLimiter(rate.Limit(cfg.RateLimit), 10) - cfg.Resolver = &rateLimitResolver{cfg.Resolver, rlimit} - return &Client{cfg: cfg, entries: cache, clock: mclock.System{}} + return &Client{ + cfg: cfg, + entries: cache, + clock: mclock.System{}, + ratelimit: rlimit, + } } // SyncTree downloads the entire node tree at the given URL. @@ -157,6 +162,13 @@ func parseAndVerifyRoot(txt string, loc *linkEntry) (rootEntry, error) { // resolveEntry retrieves an entry from the cache or fetches it from the network // if it isn't cached. func (c *Client) resolveEntry(ctx context.Context, domain, hash string) (entry, error) { + // The rate limit always applies, even when the result might be cached. This is + // important because it avoids hot-spinning in consumers of node iterators created on + // this client. + if err := c.ratelimit.Wait(ctx); err != nil { + return nil, err + } + cacheKey := truncateHash(hash) if e, ok := c.entries.Get(cacheKey); ok { return e.(entry), nil @@ -196,19 +208,6 @@ func (c *Client) doResolveEntry(ctx context.Context, domain, hash string) (entry return nil, nameError{name, errNoEntry} } -// rateLimitResolver applies a rate limit to a Resolver. -type rateLimitResolver struct { - r Resolver - limiter *rate.Limiter -} - -func (r *rateLimitResolver) LookupTXT(ctx context.Context, domain string) ([]string, error) { - if err := r.limiter.Wait(ctx); err != nil { - return nil, err - } - return r.r.LookupTXT(ctx, domain) -} - // randomIterator traverses a set of trees and returns nodes found in them. type randomIterator struct { cur *enode.Node