refactor(netxlite): expose useful HTTPTransport/DNSTransport factories (#813)

These factories will soon be useful to finish with
https://github.com/ooni/probe/issues/2135.

internal/netxlite/http.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"net"
 	"net/http"
+	"net/url"
 	"time"
 
 	oohttp "github.com/ooni/oohttp"
@@ -105,6 +106,25 @@ func (txp *httpTransportConnectionsCloser) CloseIdleConnections() {
 	txp.TLSDialer.CloseIdleConnections()
 }
 
+// NewHTTPTransportWithLoggerResolverAndOptionalProxyURL creates an HTTPTransport using
+// the given logger and resolver and an optional proxy URL.
+//
+// Arguments:
+//
+// - logger is the MANDATORY logger;
+//
+// - resolver is the MANDATORY resolver;
+//
+// - purl is the OPTIONAL proxy URL.
+func NewHTTPTransportWithLoggerResolverAndOptionalProxyURL(
+	logger model.DebugLogger, resolver model.Resolver, purl *url.URL) model.HTTPTransport {
+	dialer := NewDialerWithResolver(logger, resolver)
+	dialer = MaybeWrapWithProxyDialer(dialer, purl)
+	handshaker := NewTLSHandshakerStdlib(logger)
+	tlsDialer := NewTLSDialer(dialer, handshaker)
+	return NewHTTPTransport(logger, dialer, tlsDialer)
+}
+
 // NewHTTPTransportWithResolver creates a new HTTP transport using
 // the stdlib for everything but the given resolver.
 func NewHTTPTransportWithResolver(logger model.DebugLogger, reso model.Resolver) model.HTTPTransport {
@@ -335,6 +355,12 @@ func NewHTTPClientStdlib(logger model.DebugLogger) model.HTTPClient {
 	return NewHTTPClient(txp)
 }
 
+// NewHTTPClientWithResolver creates a new HTTPTransport using the
+// given resolver and then from that builds an HTTPClient.
+func NewHTTPClientWithResolver(logger model.Logger, reso model.Resolver) model.HTTPClient {
+	return NewHTTPClient(NewHTTPTransportWithResolver(logger, reso))
+}
+
 // NewHTTPClient creates a new, wrapped HTTPClient using the given transport.
 func NewHTTPClient(txp model.HTTPTransport) model.HTTPClient {
 	return WrapHTTPClient(&http.Client{Transport: txp})