feat(webconnectivity): long-term-evolution prototype (#882)

See https://github.com/ooni/probe/issues/2237

internal/experiment/webconnectivity/inputparser.go

@@ -0,0 +1,63 @@
+package webconnectivity
+
+//
+// Input parsing
+//
+
+import (
+	"errors"
+	"net"
+	"net/url"
+
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
+)
+
+// InputParser helps to print the experiment's input.
+type InputParser struct {
+	// List of accepted URL schemes.
+	AcceptedSchemes []string
+
+	// Whether to allow endpoints in input.
+	AllowEndpoints bool
+
+	// The default scheme to use if AllowEndpoints == true.
+	DefaultScheme string
+}
+
+// Parse parses the experiment input and returns the resulting URL.
+func (ip *InputParser) Parse(input string) (*url.URL, error) {
+	// put this check at top-level such that we always see the crash if needed
+	runtimex.PanicIfTrue(
+		ip.AllowEndpoints && ip.DefaultScheme == "",
+		"invalid configuration for InputParser.AllowEndpoints == true",
+	)
+	URL, err := url.Parse(input)
+	if err != nil {
+		return ip.maybeAllowEndpoints(URL, err)
+	}
+	for _, scheme := range ip.AcceptedSchemes {
+		if URL.Scheme == scheme {
+			// TODO: here you may want to perform additional parsing
+			return URL, nil
+		}
+	}
+	return nil, errors.New("cannot parse input")
+}
+
+// Conditionally allows endpoints when ip.AllowEndpoints is true.
+func (ip *InputParser) maybeAllowEndpoints(URL *url.URL, err error) (*url.URL, error) {
+	runtimex.PanicIfNil(err, "expected to be called with a non-nil error")
+	if ip.AllowEndpoints && URL.Scheme != "" && URL.Opaque != "" && URL.User == nil &&
+		URL.Host == "" && URL.Path == "" && URL.RawPath == "" &&
+		URL.RawQuery == "" && URL.Fragment == "" && URL.RawFragment == "" {
+		// See https://go.dev/play/p/Rk5pS_zGY5U
+		//
+		// Note that we know that `ip.DefaultScheme != ""` from the above runtime check.
+		out := &url.URL{
+			Scheme: ip.DefaultScheme,
+			Host:   net.JoinHostPort(URL.Scheme, URL.Opaque),
+		}
+		return out, nil
+	}
+	return nil, err
+}