refactor(netxlite): introduce the getaddrinfo transport (#775)

This diff modifies the system resolver to use a getaddrinf transport.

Obviously the transport is a fake, but its existence will allow us
to observe DNS events more naturally.

A lookup using the system resolver would be a ANY lookup that will
contain all the resolved IP addresses into the same response.

This change was also part of websteps-illustrated, albeit the way in
which I did it there was less clean than what we have here.

Ref issue: https://github.com/ooni/probe/issues/2096

internal/netxlite/parallelresolver.go

@@ -1,125 +0,0 @@
-package netxlite
-
-//
-// Parallel DNS resolver implementation
-//
-
-import (
-	"context"
-	"net"
-
-	"github.com/miekg/dns"
-	"github.com/ooni/probe-cli/v3/internal/model"
-)
-
-// ParallelResolver uses a transport and performs a LookupHost
-// operation in a parallel fashion, hence its name.
-//
-// You should probably use NewUnwrappedParallelResolver to
-// create a new instance of this type.
-type ParallelResolver struct {
-	// Txp is the MANDATORY underlying DNS transport.
-	Txp model.DNSTransport
-}
-
-// UnwrappedParallelResolver creates a new ParallelResolver instance. This instance is
-// not wrapped and you should wrap if before using it.
-func NewUnwrappedParallelResolver(t model.DNSTransport) *ParallelResolver {
-	return &ParallelResolver{
-		Txp: t,
-	}
-}
-
-// Transport returns the transport being used.
-func (r *ParallelResolver) Transport() model.DNSTransport {
-	return r.Txp
-}
-
-// Network returns the "network" of the underlying transport.
-func (r *ParallelResolver) Network() string {
-	return r.Txp.Network()
-}
-
-// Address returns the "address" of the underlying transport.
-func (r *ParallelResolver) Address() string {
-	return r.Txp.Address()
-}
-
-// CloseIdleConnections closes idle connections, if any.
-func (r *ParallelResolver) CloseIdleConnections() {
-	r.Txp.CloseIdleConnections()
-}
-
-// LookupHost performs an A lookup in parallel with an AAAA lookup.
-func (r *ParallelResolver) LookupHost(ctx context.Context, hostname string) ([]string, error) {
-	ach := make(chan *parallelResolverResult)
-	go r.lookupHost(ctx, hostname, dns.TypeA, ach)
-	aaaach := make(chan *parallelResolverResult)
-	go r.lookupHost(ctx, hostname, dns.TypeAAAA, aaaach)
-	ares := <-ach
-	aaaares := <-aaaach
-	if ares.err != nil && aaaares.err != nil {
-		// Note: we choose to return the A error because we assume that
-		// it's the more meaningful one: the AAAA error may just be telling
-		// us that there is no AAAA record for the website.
-		return nil, ares.err
-	}
-	var addrs []string
-	addrs = append(addrs, ares.addrs...)
-	addrs = append(addrs, aaaares.addrs...)
-	if len(addrs) < 1 {
-		return nil, ErrOODNSNoAnswer
-	}
-	return addrs, nil
-}
-
-// LookupHTTPS implements Resolver.LookupHTTPS.
-func (r *ParallelResolver) LookupHTTPS(
-	ctx context.Context, hostname string) (*model.HTTPSSvc, error) {
-	encoder := &DNSEncoderMiekg{}
-	query := encoder.Encode(hostname, dns.TypeHTTPS, r.Txp.RequiresPadding())
-	response, err := r.Txp.RoundTrip(ctx, query)
-	if err != nil {
-		return nil, err
-	}
-	return response.DecodeHTTPS()
-}
-
-// parallelResolverResult is the internal representation of a
-// lookup using either the A or the AAAA query type.
-type parallelResolverResult struct {
-	addrs []string
-	err   error
-}
-
-// lookupHost issues a lookup host query for the specified qtype (e.g., dns.A).
-func (r *ParallelResolver) lookupHost(ctx context.Context, hostname string,
-	qtype uint16, out chan<- *parallelResolverResult) {
-	encoder := &DNSEncoderMiekg{}
-	query := encoder.Encode(hostname, qtype, r.Txp.RequiresPadding())
-	response, err := r.Txp.RoundTrip(ctx, query)
-	if err != nil {
-		out <- &parallelResolverResult{
-			addrs: []string{},
-			err:   err,
-		}
-		return
-	}
-	addrs, err := response.DecodeLookupHost()
-	out <- &parallelResolverResult{
-		addrs: addrs,
-		err:   err,
-	}
-}
-
-// LookupNS implements Resolver.LookupNS.
-func (r *ParallelResolver) LookupNS(
-	ctx context.Context, hostname string) ([]*net.NS, error) {
-	encoder := &DNSEncoderMiekg{}
-	query := encoder.Encode(hostname, dns.TypeNS, r.Txp.RequiresPadding())
-	response, err := r.Txp.RoundTrip(ctx, query)
-	if err != nil {
-		return nil, err
-	}
-	return response.DecodeNS()
-}