feat: add domain validator pkg

pkg/validators/domain_validator.go

@@ -0,0 +1,159 @@
+// Package validators provides validators for various types of data.
+//
+// Domain validator is a simple utility that ensures two domains are exact
+// matches while ensuring that techniques used to bypass such checks do
+// not impact the validation.
+
+package validators
+
+import (
+	"fmt"
+	"net"
+	"net/url"
+	"slices"
+	"strings"
+
+	"golang.org/x/net/idna"
+)
+
+// DomainValidatorOptions is a set of options for DomainValidator.
+type DomainValidatorOptions struct {
+	// Ensure domains have the same scheme.
+	WithScheme bool
+	// Ensure domains have the same port.
+	WithPort bool
+	// Specify a list of allowed schemes IF WithScheme is set to true.
+	AllowedSchemes []string
+}
+
+// DomainValidator is a simple utility that ensures two domains are exact
+// matches while ensuring that techniques used to bypass such checks do
+// not impact the validation.
+type DomainValidator struct {
+	opts DomainValidatorOptions
+}
+
+// NewDomainValidator creates a new DomainValidator.
+func NewDomainValidator(opts DomainValidatorOptions) *DomainValidator {
+	return &DomainValidator{
+		opts: opts,
+	}
+}
+
+func (v *DomainValidator) getURL(i string) (*url.URL, error) {
+	u, err := url.Parse(i)
+
+	if !v.opts.WithScheme && (err != nil || u.Host == "") {
+		u, err = url.Parse("tinyauth://" + i)
+	}
+
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse input url: %w", err)
+	}
+
+	if u.Host == "" {
+		return nil, fmt.Errorf("input url is invalid")
+	}
+
+	if v.opts.WithPort && !v.opts.WithScheme && u.Port() == "" {
+		return nil, fmt.Errorf("port validation is enabled but port is missing in input url and schemes are not enabled")
+	}
+
+	if v.opts.WithScheme {
+		// Empty scheme means that we parsed the url with the tinyauth:// placeholder
+		if u.Scheme == "tinyauth" {
+			return nil, fmt.Errorf("input url is missing scheme")
+		}
+		if !slices.Contains(v.opts.AllowedSchemes, u.Scheme) {
+			return nil, fmt.Errorf("scheme %s not allowed", u.Scheme)
+		}
+	}
+
+	return u, nil
+}
+
+func (v *DomainValidator) getEffectivePort(u *url.URL) string {
+	if u.Port() != "" {
+		return u.Port()
+	}
+	if u.Scheme == "https" {
+		return "443"
+	}
+	return "80"
+}
+
+func (v *DomainValidator) formatHostname(hostname string) (string, error) {
+	hostname = strings.ToLower(hostname)
+	hostname = strings.TrimSuffix(hostname, ".")
+	if net.ParseIP(hostname) != nil {
+		return "", fmt.Errorf("ip addresses are not supported")
+	}
+	hostname, err := idna.Lookup.ToASCII(hostname)
+	if err != nil {
+		return "", fmt.Errorf("failed to convert hostname to ascii: %w", err)
+	}
+	return hostname, nil
+}
+
+// Validate ensures that two domains are exact matches with the
+// options defined in the DomainValidatorOptions. It ensures that the
+// inputs are proper URLs and contain a host. It lowercases the hostnames
+// and removes the trailing dot. Finally, it checks that the hostnames are
+// equal unless WithScheme or WithPort is set to true where it also
+// validates the scheme and port respectively.
+func (v *DomainValidator) Validate(expected, actual string) error {
+	eu, err := v.getURL(expected)
+
+	if err != nil {
+		return err
+	}
+
+	au, err := v.getURL(actual)
+
+	if err != nil {
+		return err
+	}
+
+	if v.opts.WithScheme {
+		if eu.Scheme != au.Scheme {
+			return fmt.Errorf("expected scheme %s, got %s", eu.Scheme, au.Scheme)
+		}
+	}
+
+	if v.opts.WithPort {
+		if v.getEffectivePort(eu) != v.getEffectivePort(au) {
+			return fmt.Errorf("expected port %s, got %s", v.getEffectivePort(eu), v.getEffectivePort(au))
+		}
+	}
+
+	euf, err := v.formatHostname(eu.Hostname())
+
+	if err != nil {
+		return err
+	}
+
+	auf, err := v.formatHostname(au.Hostname())
+
+	if err != nil {
+		return err
+	}
+
+	if euf != auf {
+		return fmt.Errorf("expected hostname %s, got %s", euf, auf)
+	}
+
+	return nil
+}
+
+// SafeHostname uses the internal validation for domains that Validator uses
+// to parse a hostname. It ensures the input URL is a valid URL, that a host
+// is present and that the hostname is lowercased and without a trailing dot.
+func (v *DomainValidator) SafeHostname(input string) (string, error) {
+	u, err := v.getURL(input)
+
+	if err != nil {
+		return "", err
+	}
+
+	return v.formatHostname(u.Hostname())
+}