refactor: move httptransport w/ logging to netxlite (#411)

Part of https://github.com/ooni/probe/issues/1505

internal/netxlite/http.go

@@ -0,0 +1,62 @@
+package netxlite
+
+import "net/http"
+
+// HTTPTransport is an http.Transport-like structure.
+type HTTPTransport interface {
+	// RoundTrip performs the HTTP round trip.
+	RoundTrip(req *http.Request) (*http.Response, error)
+
+	// CloseIdleConnections closes idle connections.
+	CloseIdleConnections()
+}
+
+// HTTPTransportLogger is an HTTPTransport with logging.
+type HTTPTransportLogger struct {
+	// HTTPTransport is the underlying HTTP transport.
+	HTTPTransport HTTPTransport
+
+	// Logger is the underlying logger.
+	Logger Logger
+}
+
+var _ HTTPTransport = &HTTPTransportLogger{}
+
+// RoundTrip implements HTTPTransport.RoundTrip.
+func (txp *HTTPTransportLogger) RoundTrip(req *http.Request) (*http.Response, error) {
+	host := req.Host
+	if host == "" {
+		host = req.URL.Host
+	}
+	req.Header.Set("Host", host) // anticipate what Go would do
+	return txp.logTrip(req)
+}
+
+// logTrip is an HTTP round trip with logging.
+func (txp *HTTPTransportLogger) logTrip(req *http.Request) (*http.Response, error) {
+	txp.Logger.Debugf("> %s %s", req.Method, req.URL.String())
+	for key, values := range req.Header {
+		for _, value := range values {
+			txp.Logger.Debugf("> %s: %s", key, value)
+		}
+	}
+	txp.Logger.Debug(">")
+	resp, err := txp.HTTPTransport.RoundTrip(req)
+	if err != nil {
+		txp.Logger.Debugf("< %s", err)
+		return nil, err
+	}
+	txp.Logger.Debugf("< %d", resp.StatusCode)
+	for key, values := range resp.Header {
+		for _, value := range values {
+			txp.Logger.Debugf("< %s: %s", key, value)
+		}
+	}
+	txp.Logger.Debug("<")
+	return resp, nil
+}
+
+// CloseIdleConnections implement HTTPTransport.CloseIdleConnections.
+func (txp *HTTPTransportLogger) CloseIdleConnections() {
+	txp.HTTPTransport.CloseIdleConnections()
+}