feat(webconnectivity): long-term-evolution prototype (#882)

See https://github.com/ooni/probe/issues/2237

internal/experiment/webconnectivity/dnswhoami.go

@@ -0,0 +1,79 @@
+package webconnectivity
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/netxlite"
+)
+
+// TODO(bassosimone): this code needs refining before we can merge it inside
+// master. For one, we already have systemv4 info. Additionally, it would
+// be neat to avoid additional AAAA queries. Furthermore, we should also see
+// to implement support for IPv6 only clients as well.
+
+// DNSWhoamiService is a service that performs DNS whoami lookups.
+type DNSWhoamiService struct {
+	// mu provides mutual exclusion
+	mu *sync.Mutex
+
+	// systemv4 contains systemv4 results
+	systemv4 []DNSWhoamiInfoEntry
+
+	// udpv4 contains udpv4 results
+	udpv4 map[string][]DNSWhoamiInfoEntry
+}
+
+// SystemV4 returns the results of querying using the system resolver and IPv4.
+func (svc *DNSWhoamiService) SystemV4(ctx context.Context) ([]DNSWhoamiInfoEntry, bool) {
+	svc.mu.Lock()
+	defer svc.mu.Unlock()
+	if len(svc.systemv4) <= 0 {
+		ctx, cancel := context.WithTimeout(ctx, 4*time.Second)
+		defer cancel()
+		reso := netxlite.NewStdlibResolver(model.DiscardLogger)
+		addrs, err := reso.LookupHost(ctx, "whoami.v4.powerdns.org")
+		if err != nil || len(addrs) < 1 {
+			return nil, false
+		}
+		svc.systemv4 = []DNSWhoamiInfoEntry{{
+			Address: addrs[0],
+		}}
+	}
+	return svc.systemv4, len(svc.systemv4) > 0
+}
+
+// UDPv4 returns the results of querying a given UDP resolver and IPv4.
+func (svc *DNSWhoamiService) UDPv4(ctx context.Context, address string) ([]DNSWhoamiInfoEntry, bool) {
+	svc.mu.Lock()
+	defer svc.mu.Unlock()
+	if len(svc.udpv4[address]) <= 0 {
+		ctx, cancel := context.WithTimeout(ctx, 4*time.Second)
+		defer cancel()
+		dialer := netxlite.NewDialerWithStdlibResolver(model.DiscardLogger)
+		reso := netxlite.NewParallelUDPResolver(model.DiscardLogger, dialer, address)
+		// TODO(bassosimone): this should actually only send an A query. Sending an AAAA
+		// query is _way_ unnecessary since we know that only A is going to work.
+		addrs, err := reso.LookupHost(ctx, "whoami.v4.powerdns.org")
+		if err != nil || len(addrs) < 1 {
+			return nil, false
+		}
+		svc.udpv4[address] = []DNSWhoamiInfoEntry{{
+			Address: addrs[0],
+		}}
+	}
+	value := svc.udpv4[address]
+	return value, len(value) > 0
+}
+
+// TODO(bassosimone): consider factoring this code and keeping state
+// on disk rather than on memory.
+
+// DNSWhoamiSingleton is the DNSWhoamiService singleton.
+var DNSWhoamiSingleton = &DNSWhoamiService{
+	mu:       &sync.Mutex{},
+	systemv4: []DNSWhoamiInfoEntry{},
+	udpv4:    map[string][]DNSWhoamiInfoEntry{},
+}