proxy: imp code, docs

proxy/dns_context.go

@@ -80,39 +80,39 @@ type DNSContext struct {
 }
 
 // calcFlagsAndSize lazily calculates some values required for Resolve method.
-func (ctx *DNSContext) calcFlagsAndSize() {
-	if ctx.udpSize != 0 || ctx.Req == nil {
+func (dctx *DNSContext) calcFlagsAndSize() {
+	if dctx.udpSize != 0 || dctx.Req == nil {
 		return
 	}
 
-	ctx.adBit = ctx.Req.AuthenticatedData
-	ctx.udpSize = defaultUDPBufSize
-	if o := ctx.Req.IsEdns0(); o != nil {
-		ctx.hasEDNS0 = true
-		ctx.doBit = o.Do()
-		ctx.udpSize = o.UDPSize()
+	dctx.adBit = dctx.Req.AuthenticatedData
+	dctx.udpSize = defaultUDPBufSize
+	if o := dctx.Req.IsEdns0(); o != nil {
+		dctx.hasEDNS0 = true
+		dctx.doBit = o.Do()
+		dctx.udpSize = o.UDPSize()
 	}
 }
 
 // scrub prepares the d.Res to be written.  Truncation is applied as well if
 // necessary.
-func (ctx *DNSContext) scrub() {
-	if ctx.Res == nil || ctx.Req == nil {
+func (dctx *DNSContext) scrub() {
+	if dctx.Res == nil || dctx.Req == nil {
 		return
 	}
 
 	// We should guarantee that all the values we need are calculated.
-	ctx.calcFlagsAndSize()
+	dctx.calcFlagsAndSize()
 
 	// RFC-6891 (https://tools.ietf.org/html/rfc6891) states that response
 	// mustn't contain an EDNS0 RR if the request doesn't include it.
 	//
 	// See https://github.com/AdguardTeam/dnsproxy/issues/132.
-	if ctx.hasEDNS0 && ctx.Res.IsEdns0() == nil {
-		ctx.Res.SetEdns0(ctx.udpSize, ctx.doBit)
+	if dctx.hasEDNS0 && dctx.Res.IsEdns0() == nil {
+		dctx.Res.SetEdns0(dctx.udpSize, dctx.doBit)
 	}
 
-	ctx.Res.Truncate(proxyutil.DNSSize(ctx.Proto == ProtoUDP, ctx.Req))
+	dctx.Res.Truncate(proxyutil.DNSSize(dctx.Proto == ProtoUDP, dctx.Req))
 	// Some devices require DNS message compression.
-	ctx.Res.Compress = true
+	dctx.Res.Compress = true
 }

proxy/helpers.go

@@ -144,7 +144,11 @@ func setECS(m *dns.Msg, ip net.IP, scope uint8) (net.IP, uint8) {
 	return e.Address, e.SourceNetmask
 }
 
-// Return TRUE if IP is within public Internet IP range
+// isPublicIP returns true if ip is within public Internet IP range.
+//
+// TODO(e.burkov, a.garipov):  Add an interface-based subnet detector to the
+// netutil.
+//
 // nolint (gocyclo)
 func isPublicIP(ip net.IP) (ok bool) {
 	if ip = ip.To4(); ip == nil {
@@ -153,29 +157,39 @@ func isPublicIP(ip net.IP) (ok bool) {
 
 	switch ip[0] {
 	case 0, 10, 127:
+		// Software, private network, loopback.
 		return false
 	case 169:
+		// Link-local.
 		return ip[1] != 254
 	case 172:
+		// Private network.
 		return ip[1] < 16 || ip[1] > 31
 	case 192:
 		switch ip[1] {
 		case 0:
+			// Private network, documentation.
 			return ip[2] != 0 && ip[2] != 2
 		case 88:
+			// Reserved.
 			return ip[2] != 99
 		case 168:
+			// Private network.
 			return false
 		default:
 			return true
 		}
 	case 198:
+		// Private network, documentation.
 		return (ip[1] != 18 && ip[2] != 19) && (ip[1] != 51 && ip[2] != 100)
 	case 203:
+		// Documentation.
 		return ip[1] != 0 || ip[2] != 113
 	case 224:
+		// Multicast.
 		return ip[1] != 0 || ip[2] != 0
 	case 255:
+		// Broadcast.
 		return ip[1] != 255 || ip[2] != 255 || ip[3] != 255
 	default:
 		return true

proxy/proxy.go

@@ -507,28 +507,28 @@ func (p *Proxy) Resolve(d *DNSContext) (err error) {
 }
 
 // processECS adds EDNS Client-Subnet data into the request from d.
-func (d *DNSContext) processECS(cliIP net.IP) {
-	d.ECSReqIP, d.ECSReqMask, _ = parseECS(d.Req)
-	if d.ECSReqMask != 0 {
-		log.Debug("passing through ecs: %s/%d", d.ECSReqIP, d.ECSReqMask)
+func (dctx *DNSContext) processECS(cliIP net.IP) {
+	dctx.ECSReqIP, dctx.ECSReqMask, _ = parseECS(dctx.Req)
+	if dctx.ECSReqMask != 0 {
+		log.Debug("passing through ecs: %s/%d", dctx.ECSReqIP, dctx.ECSReqMask)
 
 		return
 	}
 
 	// Set ECS.
-	d.ECSReqIP = nil
+	dctx.ECSReqIP = nil
 
 	if cliIP == nil {
-		cliIP, _ = netutil.IPAndPortFromAddr(d.Addr)
+		cliIP, _ = netutil.IPAndPortFromAddr(dctx.Addr)
 		if cliIP == nil {
 			return
 		}
 	}
 
 	if isPublicIP(cliIP) {
-		d.ECSReqIP, d.ECSReqMask = setECS(d.Req, cliIP, 0)
+		dctx.ECSReqIP, dctx.ECSReqMask = setECS(dctx.Req, cliIP, 0)
 
-		log.Debug("setting ecs: %s/%d", d.ECSReqIP, d.ECSReqMask)
+		log.Debug("setting ecs: %s/%d", dctx.ECSReqIP, dctx.ECSReqMask)
 	}
 }