Method Resolve

proxy/proxy.go:689–750

Resolve is the default resolving method used by the DNS proxy to query upstream servers. It expects dctx is filled with the client's request.

(ctx context.Context, dctx *DNSContext)

// Resolve is the default resolving method used by the DNS proxy to query
// upstream servers.  It expects dctx is filled with the client's request.
func (p *Proxy) Resolve(ctx context.Context, dctx *DNSContext) (err error) {
	if p.EnableEDNSClientSubnet {
		dctx.processECS(p.EDNSAddr, p.logger)
	}

	dctx.calcFlagsAndSize()

	cacheWorks := p.cacheWorks(dctx)
	if cacheWorks {
		// Request for DNSSEC from the upstream to cache the
		// DNSSEC resource records as well.  In case of disabled DNSSEC,
		// requesting and therefore caching of DNSSEC resource records depends
		// on the DO bit of the initiating query.
		//
		// See https://datatracker.ietf.org/doc/html/rfc4035#section-4.5 and
		// https://datatracker.ietf.org/doc/html/rfc3225#section-3.
		p.addDO(dctx.Req)

		// Only add pending requests if the cache is enabled, since this is a
		// mitigation against cache poisoning.
		//
		// TODO(e.burkov):  Consider tracking all requests.
		var loaded bool
		loaded, err = p.pendingRequests.queue(ctx, dctx)
		if loaded {
			return err
		}
		defer func() { p.pendingRequests.done(ctx, dctx, err) }()

		if p.replyFromCache(dctx) {
			// Complete the response from cache.
			filterMsg(dctx.Res, dctx.Res, dctx.adBit, dctx.doBit, 0)
			dctx.scrub()

			return nil
		}
	}

	var ok bool
	ok, err = p.replyFromUpstream(dctx)

	// Don't cache the responses having CD flag, just like Dnsmasq does.  It
	// prevents the cache from being poisoned with unvalidated answers which may
	// differ from validated ones.
	//
	// See https://github.com/imp/dnsmasq/blob/770bce967cfc9967273d0acfb3ea018fb7b17522/src/forward.c#L1169-L1172.
	if cacheWorks && ok && !dctx.Res.CheckingDisabled {
		// Cache the response with DNSSEC RRs.
		p.cacheResp(dctx)
	}

	// It is possible that the response is nil if the upstream hasn't been
	// chosen.
	if dctx.Res != nil {
		filterMsg(dctx.Res, dctx.Res, dctx.adBit, dctx.doBit, 0)
	}

	// Complete the response.