refactor(tracex): do not depend on strings for event names (#777)

Rather than matching a string, match a type.

This is more robust considering future refactorings.

We're confident the names did not change in _this_ refactoring
because we're still testing the same strings in the tests.

Part of https://github.com/ooni/probe/issues/2121

internal/engine/netx/tracex/event.go

@@ -4,10 +4,268 @@ import (
 	"crypto/x509"
 	"net/http"
 	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 
+// Event is one of the events within a trace.
+type Event interface {
+	// Value returns the event value
+	Value() *EventValue
+
+	// Name returns the event name
+	Name() string
+}
+
+// EventTLSHandshakeStart is the beginning of the TLS handshake.
+type EventTLSHandshakeStart struct {
+	V *EventValue
+}
+
+func (ev *EventTLSHandshakeStart) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventTLSHandshakeStart) Name() string {
+	return "tls_handshake_start"
+}
+
+// EventTLSHandshakeDone is the end of the TLS handshake.
+type EventTLSHandshakeDone struct {
+	V *EventValue
+}
+
+func (ev *EventTLSHandshakeDone) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventTLSHandshakeDone) Name() string {
+	return "tls_handshake_done"
+}
+
+// EventResolveStart is the beginning of a DNS lookup operation.
+type EventResolveStart struct {
+	V *EventValue
+}
+
+func (ev *EventResolveStart) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventResolveStart) Name() string {
+	return "resolve_start"
+}
+
+// EventResolveDone is the end of a DNS lookup operation.
+type EventResolveDone struct {
+	V *EventValue
+}
+
+func (ev *EventResolveDone) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventResolveDone) Name() string {
+	return "resolve_done"
+}
+
+// EventDNSRoundTripStart is the start of a DNS round trip.
+type EventDNSRoundTripStart struct {
+	V *EventValue
+}
+
+func (ev *EventDNSRoundTripStart) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventDNSRoundTripStart) Name() string {
+	return "dns_round_trip_start"
+}
+
+// EventDNSRoundTripDone is the end of a DNS round trip.
+type EventDNSRoundTripDone struct {
+	V *EventValue
+}
+
+func (ev *EventDNSRoundTripDone) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventDNSRoundTripDone) Name() string {
+	return "dns_round_trip_done"
+}
+
+// EventQUICHandshakeStart is the start of a QUIC handshake.
+type EventQUICHandshakeStart struct {
+	V *EventValue
+}
+
+func (ev *EventQUICHandshakeStart) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventQUICHandshakeStart) Name() string {
+	return "quic_handshake_start"
+}
+
+// EventQUICHandshakeDone is the end of a QUIC handshake.
+type EventQUICHandshakeDone struct {
+	V *EventValue
+}
+
+func (ev *EventQUICHandshakeDone) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventQUICHandshakeDone) Name() string {
+	return "quic_handshake_done"
+}
+
+// EventWriteToOperation summarizes the WriteTo operation.
+type EventWriteToOperation struct {
+	V *EventValue
+}
+
+func (ev *EventWriteToOperation) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventWriteToOperation) Name() string {
+	return netxlite.WriteToOperation
+}
+
+// EventReadFromOperation summarizes the ReadFrom operation.
+type EventReadFromOperation struct {
+	V *EventValue
+}
+
+func (ev *EventReadFromOperation) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventReadFromOperation) Name() string {
+	return netxlite.ReadFromOperation
+}
+
+// EventHTTPRequestMetadata contains HTTP request metadata.
+type EventHTTPRequestMetadata struct {
+	V *EventValue
+}
+
+func (ev *EventHTTPRequestMetadata) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventHTTPRequestMetadata) Name() string {
+	return "http_request_metadata"
+}
+
+// EventHTTPResponseMetadata contains HTTP response metadata.
+type EventHTTPResponseMetadata struct {
+	V *EventValue
+}
+
+func (ev *EventHTTPResponseMetadata) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventHTTPResponseMetadata) Name() string {
+	return "http_response_metadata"
+}
+
+// EventHTTPTransactionStart is the beginning of an HTTP transaction.
+type EventHTTPTransactionStart struct {
+	V *EventValue
+}
+
+func (ev *EventHTTPTransactionStart) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventHTTPTransactionStart) Name() string {
+	return "http_transaction_start"
+}
+
+// EventHTTPTransactionDone is the end of an HTTP transaction.
+type EventHTTPTransactionDone struct {
+	V *EventValue
+}
+
+func (ev *EventHTTPTransactionDone) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventHTTPTransactionDone) Name() string {
+	return "http_transaction_done"
+}
+
+// EventHTTPRequestBodySnapshot contains a snapshot of the request body.
+type EventHTTPRequestBodySnapshot struct {
+	V *EventValue
+}
+
+func (ev *EventHTTPRequestBodySnapshot) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventHTTPRequestBodySnapshot) Name() string {
+	return "http_request_body_snapshot"
+}
+
+// EventHTTPResponseBodySnapshot contains a snapshot of the response body.
+type EventHTTPResponseBodySnapshot struct {
+	V *EventValue
+}
+
+func (ev *EventHTTPResponseBodySnapshot) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventHTTPResponseBodySnapshot) Name() string {
+	return "http_response_body_snapshot"
+}
+
+// EventConnectOperation contains information about the connect operation.
+type EventConnectOperation struct {
+	V *EventValue
+}
+
+func (ev *EventConnectOperation) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventConnectOperation) Name() string {
+	return netxlite.ConnectOperation
+}
+
+// EventReadOperation contains information about a read operation.
+type EventReadOperation struct {
+	V *EventValue
+}
+
+func (ev *EventReadOperation) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventReadOperation) Name() string {
+	return netxlite.ReadOperation
+}
+
+// EventWriteOperation contains information about a write operation.
+type EventWriteOperation struct {
+	V *EventValue
+}
+
+func (ev *EventWriteOperation) Value() *EventValue {
+	return ev.V
+}
+
+func (ev *EventWriteOperation) Name() string {
+	return netxlite.WriteOperation
+}
+
 // Event is one of the events within a trace
-type Event struct {
+type EventValue struct {
 	Addresses          []string            `json:",omitempty"`
 	Address            string              `json:",omitempty"`
 	DNSQuery           []byte              `json:",omitempty"`
@@ -21,7 +279,6 @@ type Event struct {
 	HTTPStatusCode     int                 `json:",omitempty"`
 	HTTPURL            string              `json:",omitempty"`
 	Hostname           string              `json:",omitempty"`
-	Name               string              `json:",omitempty"`
 	NoTLSVerify        bool                `json:",omitempty"`
 	NumBytes           int                 `json:",omitempty"`
 	Proto              string              `json:",omitempty"`