refactor(netx): towards removing connid, dialid, etc (#369)

I have verified that experiment/tor does not depend on this
functionality, therefore we can safely remove it.

Part of https://github.com/ooni/probe-engine/issues/897

internal/engine/legacy/netx/emitterdialer.go

@@ -0,0 +1,116 @@
+package netx
+
+import (
+	"context"
+	"net"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/connid"
+	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/dialid"
+	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/modelx"
+	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/transactionid"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/dialer"
+)
+
+// EmitterDialer is a Dialer that emits events
+type EmitterDialer struct {
+	dialer.Dialer
+}
+
+// DialContext implements Dialer.DialContext
+func (d EmitterDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	start := time.Now()
+	conn, err := d.Dialer.DialContext(ctx, network, address)
+	stop := time.Now()
+	root := modelx.ContextMeasurementRootOrDefault(ctx)
+	root.Handler.OnMeasurement(modelx.Measurement{
+		Connect: &modelx.ConnectEvent{
+			ConnID:                 safeConnID(network, conn),
+			DialID:                 dialid.ContextDialID(ctx),
+			DurationSinceBeginning: stop.Sub(root.Beginning),
+			Error:                  err,
+			Network:                network,
+			RemoteAddress:          address,
+			SyscallDuration:        stop.Sub(start),
+			TransactionID:          transactionid.ContextTransactionID(ctx),
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+	return EmitterConn{
+		Conn:      conn,
+		Beginning: root.Beginning,
+		Handler:   root.Handler,
+		ID:        safeConnID(network, conn),
+	}, nil
+}
+
+// EmitterConn is a net.Conn used to emit events
+type EmitterConn struct {
+	net.Conn
+	Beginning time.Time
+	Handler   modelx.Handler
+	ID        int64
+}
+
+// Read implements net.Conn.Read
+func (c EmitterConn) Read(b []byte) (n int, err error) {
+	start := time.Now()
+	n, err = c.Conn.Read(b)
+	stop := time.Now()
+	c.Handler.OnMeasurement(modelx.Measurement{
+		Read: &modelx.ReadEvent{
+			ConnID:                 c.ID,
+			DurationSinceBeginning: stop.Sub(c.Beginning),
+			Error:                  err,
+			NumBytes:               int64(n),
+			SyscallDuration:        stop.Sub(start),
+		},
+	})
+	return
+}
+
+// Write implements net.Conn.Write
+func (c EmitterConn) Write(b []byte) (n int, err error) {
+	start := time.Now()
+	n, err = c.Conn.Write(b)
+	stop := time.Now()
+	c.Handler.OnMeasurement(modelx.Measurement{
+		Write: &modelx.WriteEvent{
+			ConnID:                 c.ID,
+			DurationSinceBeginning: stop.Sub(c.Beginning),
+			Error:                  err,
+			NumBytes:               int64(n),
+			SyscallDuration:        stop.Sub(start),
+		},
+	})
+	return
+}
+
+// Close implements net.Conn.Close
+func (c EmitterConn) Close() (err error) {
+	start := time.Now()
+	err = c.Conn.Close()
+	stop := time.Now()
+	c.Handler.OnMeasurement(modelx.Measurement{
+		Close: &modelx.CloseEvent{
+			ConnID:                 c.ID,
+			DurationSinceBeginning: stop.Sub(c.Beginning),
+			Error:                  err,
+			SyscallDuration:        stop.Sub(start),
+		},
+	})
+	return
+}
+
+func safeLocalAddress(conn net.Conn) (s string) {
+	if conn != nil && conn.LocalAddr() != nil {
+		s = conn.LocalAddr().String()
+	}
+	return
+}
+
+func safeConnID(network string, conn net.Conn) int64 {
+	return connid.Compute(network, safeLocalAddress(conn))
+}