fix(netxlite): prefer composition over embedding (#733)

This diff has been extracted and adapted from 8848c8c516

The reason to prefer composition over embedding is that we want the
build to break if we add new methods to interfaces we define. If the build
does not break, we may forget about wrapping methods we should
actually be wrapping. I noticed this issue inside netxlite when I was working
on websteps-illustrated and I added support for NS and PTR queries.

See https://github.com/ooni/probe/issues/2096

While there, perform comprehensive netxlite code review
and apply minor changes and improve the docs.

internal/netxlite/http.go

@@ -1,5 +1,9 @@
 package netxlite
 
+//
+// HTTP/1.1 and HTTP2 code
+//
+
 import (
 	"context"
 	"errors"
@@ -13,9 +17,11 @@ import (
 
 // httpTransportErrWrapper is an HTTPTransport with error wrapping.
 type httpTransportErrWrapper struct {
-	model.HTTPTransport
+	HTTPTransport model.HTTPTransport
 }
 
+var _ model.HTTPTransport = &httpTransportErrWrapper{}
+
 func (txp *httpTransportErrWrapper) RoundTrip(req *http.Request) (*http.Response, error) {
 	resp, err := txp.HTTPTransport.RoundTrip(req)
 	if err != nil {
@@ -24,10 +30,18 @@ func (txp *httpTransportErrWrapper) RoundTrip(req *http.Request) (*http.Response
 	return resp, nil
 }
 
+func (txp *httpTransportErrWrapper) CloseIdleConnections() {
+	txp.HTTPTransport.CloseIdleConnections()
+}
+
+func (txp *httpTransportErrWrapper) Network() string {
+	return txp.HTTPTransport.Network()
+}
+
 // httpTransportLogger is an HTTPTransport with logging.
 type httpTransportLogger struct {
 	// HTTPTransport is the underlying HTTP transport.
-	model.HTTPTransport
+	HTTPTransport model.HTTPTransport
 
 	// Logger is the underlying logger.
 	Logger model.DebugLogger
@@ -62,12 +76,26 @@ func (txp *httpTransportLogger) CloseIdleConnections() {
 	txp.HTTPTransport.CloseIdleConnections()
 }
 
+func (txp *httpTransportLogger) Network() string {
+	return txp.HTTPTransport.Network()
+}
+
 // httpTransportConnectionsCloser is an HTTPTransport that
 // correctly forwards CloseIdleConnections calls.
 type httpTransportConnectionsCloser struct {
-	model.HTTPTransport
-	model.Dialer
-	model.TLSDialer
+	HTTPTransport model.HTTPTransport
+	Dialer        model.Dialer
+	TLSDialer     model.TLSDialer
+}
+
+var _ model.HTTPTransport = &httpTransportConnectionsCloser{}
+
+func (txp *httpTransportConnectionsCloser) RoundTrip(req *http.Request) (*http.Response, error) {
+	return txp.HTTPTransport.RoundTrip(req)
+}
+
+func (txp *httpTransportConnectionsCloser) Network() string {
+	return txp.HTTPTransport.Network()
 }
 
 // CloseIdleConnections forwards the CloseIdleConnections calls.
@@ -148,7 +176,17 @@ func NewOOHTTPBaseTransport(dialer model.Dialer, tlsDialer model.TLSDialer) mode
 
 // stdlibTransport wraps oohttp.StdlibTransport to add .Network()
 type stdlibTransport struct {
-	*oohttp.StdlibTransport
+	StdlibTransport *oohttp.StdlibTransport
+}
+
+var _ model.HTTPTransport = &stdlibTransport{}
+
+func (txp *stdlibTransport) CloseIdleConnections() {
+	txp.StdlibTransport.CloseIdleConnections()
+}
+
+func (txp *stdlibTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	return txp.StdlibTransport.RoundTrip(req)
 }
 
 // Network implements HTTPTransport.Network.
@@ -170,7 +208,13 @@ func WrapHTTPTransport(logger model.DebugLogger, txp model.HTTPTransport) model.
 // httpDialerWithReadTimeout enforces a read timeout for all HTTP
 // connections. See https://github.com/ooni/probe/issues/1609.
 type httpDialerWithReadTimeout struct {
-	model.Dialer
+	Dialer model.Dialer
+}
+
+var _ model.Dialer = &httpDialerWithReadTimeout{}
+
+func (d *httpDialerWithReadTimeout) CloseIdleConnections() {
+	d.Dialer.CloseIdleConnections()
 }
 
 // DialContext implements Dialer.DialContext.
@@ -186,7 +230,13 @@ func (d *httpDialerWithReadTimeout) DialContext(
 // httpTLSDialerWithReadTimeout enforces a read timeout for all HTTP
 // connections. See https://github.com/ooni/probe/issues/1609.
 type httpTLSDialerWithReadTimeout struct {
-	model.TLSDialer
+	TLSDialer model.TLSDialer
+}
+
+var _ model.TLSDialer = &httpTLSDialerWithReadTimeout{}
+
+func (d *httpTLSDialerWithReadTimeout) CloseIdleConnections() {
+	d.TLSDialer.CloseIdleConnections()
 }
 
 // ErrNotTLSConn occur when an interface accepts a net.Conn but
@@ -280,7 +330,7 @@ func WrapHTTPClient(clnt model.HTTPClient) model.HTTPClient {
 }
 
 type httpClientErrWrapper struct {
-	model.HTTPClient
+	HTTPClient model.HTTPClient
 }
 
 func (c *httpClientErrWrapper) Do(req *http.Request) (*http.Response, error) {
@@ -290,3 +340,7 @@ func (c *httpClientErrWrapper) Do(req *http.Request) (*http.Response, error) {
 	}
 	return resp, nil
 }
+
+func (c *httpClientErrWrapper) CloseIdleConnections() {
+	c.HTTPClient.CloseIdleConnections()
+}