cleanup: remove ConnID, DialID, TransactionID (#395)

We are not using them anymore. The only nettest still using the
legacy netx implementation is tor, for which setting these fields
is useless, because it performs each measurement into a separate
goroutine. Hence, let us start removing this part of the legacy
netx codebase, which is hampering progress in other areas.

Occurred to me while doing testing for the recent changes in
error mapping (https://github.com/ooni/probe/issues/1505).

internal/engine/legacy/oonitemplates/oonitemplates.go

@@ -71,45 +71,8 @@ type Results struct {
 	TLSHandshakes []*modelx.TLSHandshakeDoneEvent
 }
 
-type connmapper struct {
-	counter int64
-	mu      sync.Mutex
-	once    sync.Once
-	table   map[int64]int64
-}
-
-// scramble maps a ConnID to a different number to avoid emitting
-// the port numbers. We preserve the sign because it's used to
-// distinguish between TCP (positive) and UDP (negative). A special
-// case is zero, which is always mapped to zero, since the zero
-// port means "unspecified" in netx code.
-func (m *connmapper) scramble(cid int64) int64 {
-	m.once.Do(func() {
-		m.table = make(map[int64]int64)
-		m.table[0] = 0 // means unspecified in netx
-	})
-	// See https://stackoverflow.com/a/38140573/4354461
-	m.mu.Lock()
-	defer m.mu.Unlock()
-	if value, found := m.table[cid]; found {
-		return value
-	}
-	var factor int64 = 1
-	if cid < 0 {
-		factor = -1
-	}
-	m.counter++ // we must never emit zero
-	value := factor * m.counter
-	m.table[cid] = value
-	return value
-}
-
-// cm is the global connmapper
-var cm connmapper
-
 func (r *Results) onMeasurement(m modelx.Measurement, lowLevel bool) {
 	if m.Connect != nil {
-		m.Connect.ConnID = cm.scramble(m.Connect.ConnID)
 		r.Connects = append(r.Connects, m.Connect)
 		if lowLevel {
 			r.NetworkEvents = append(r.NetworkEvents, &m)
@@ -122,17 +85,14 @@ func (r *Results) onMeasurement(m modelx.Measurement, lowLevel bool) {
 		r.Resolves = append(r.Resolves, m.ResolveDone)
 	}
 	if m.TLSHandshakeDone != nil {
-		m.TLSHandshakeDone.ConnID = cm.scramble(m.TLSHandshakeDone.ConnID)
 		r.TLSHandshakes = append(r.TLSHandshakes, m.TLSHandshakeDone)
 	}
 	if m.Read != nil {
-		m.Read.ConnID = cm.scramble(m.Read.ConnID)
 		if lowLevel {
 			r.NetworkEvents = append(r.NetworkEvents, &m)
 		}
 	}
 	if m.Write != nil {
-		m.Write.ConnID = cm.scramble(m.Write.ConnID)
 		if lowLevel {
 			r.NetworkEvents = append(r.NetworkEvents, &m)
 		}

internal/engine/legacy/oonitemplates/oonitemplates_test.go

@@ -387,22 +387,3 @@ func (txp *faketransport) ClientFactory(stateDir string) (obfs4base.ClientFactor
 func (txp *faketransport) ServerFactory(stateDir string, args *goptlib.Args) (obfs4base.ServerFactory, error) {
 	return txp.txp.ServerFactory(stateDir, args)
 }
-
-func TestConnmapper(t *testing.T) {
-	var mapper connmapper
-	if mapper.scramble(-1) >= 0 {
-		t.Fatal("unexpected value for negative input")
-	}
-	if mapper.scramble(1234) != 2 {
-		t.Fatal("unexpected second value")
-	}
-	if mapper.scramble(12) != 3 {
-		t.Fatal("unexpected third value")
-	}
-	if mapper.scramble(12) != mapper.scramble(12) {
-		t.Fatal("not idempotent")
-	}
-	if mapper.scramble(0) != 0 {
-		t.Fatal("unexpected value for zero input")
-	}
-}