[relay] Use instanceURL instead of Exposed address. (#4905)

Replaces string-based exposed address handling with URL-based InstanceURL() (type url.URL) across relay/server and relay/healthcheck; adds SchemeREL/SchemeRELS constants; updates getInstanceURL to return *url.URL with scheme and TLS validation; adjusts WS dialing and health-check logic to use URL fields.

relay/server/url.go

@@ -6,9 +6,14 @@ import (
 	"strings"
 )
 
+const (
+	SchemeREL  = "rel"
+	SchemeRELS = "rels"
+)
+
 // getInstanceURL checks if user supplied a URL scheme otherwise adds to the
 // provided address according to TLS definition and parses the address before returning it
-func getInstanceURL(exposedAddress string, tlsSupported bool) (string, error) {
+func getInstanceURL(exposedAddress string, tlsSupported bool) (*url.URL, error) {
 	addr := exposedAddress
 	split := strings.Split(exposedAddress, "://")
 	switch {
@@ -17,17 +22,22 @@ func getInstanceURL(exposedAddress string, tlsSupported bool) (string, error) {
 	case len(split) == 1 && !tlsSupported:
 		addr = "rel://" + exposedAddress
 	case len(split) > 2:
-		return "", fmt.Errorf("invalid exposed address: %s", exposedAddress)
+		return nil, fmt.Errorf("invalid exposed address: %s", exposedAddress)
 	}
 
 	parsedURL, err := url.ParseRequestURI(addr)
 	if err != nil {
-		return "", fmt.Errorf("invalid exposed address: %v", err)
+		return nil, fmt.Errorf("invalid exposed address: %v", err)
 	}
 
-	if parsedURL.Scheme != "rel" && parsedURL.Scheme != "rels" {
-		return "", fmt.Errorf("invalid scheme: %s", parsedURL.Scheme)
+	if parsedURL.Scheme != SchemeREL && parsedURL.Scheme != SchemeRELS {
+		return nil, fmt.Errorf("invalid scheme: %s", parsedURL.Scheme)
 	}
 
-	return parsedURL.String(), nil
+	// Validate scheme matches TLS configuration
+	if tlsSupported && parsedURL.Scheme == SchemeREL {
+		return nil, fmt.Errorf("non-TLS scheme '%s' provided but TLS is supported", SchemeREL)
+	}
+
+	return parsedURL, nil
 }