first commit

internal/user/nostr_sync.go

@@ -0,0 +1,101 @@
+package user
+
+import (
+	"strings"
+)
+
+// SanitizeForUsername coerces an arbitrary profile string into a candidate
+// that matches usernameRE: lowercase ASCII alphanumerics, `_`, and `-`,
+// length <= 30, with an alphanumeric first character. Returns "" when no
+// usable handle can be derived.
+func SanitizeForUsername(s string) string {
+	s = strings.ToLower(strings.TrimSpace(s))
+	if s == "" {
+		return ""
+	}
+
+	var b strings.Builder
+	b.Grow(len(s))
+	prevSep := false
+	for _, r := range s {
+		switch {
+		case (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9'):
+			b.WriteRune(r)
+			prevSep = false
+		case r == '-' || r == '_':
+			if b.Len() == 0 {
+				continue
+			}
+			if prevSep {
+				continue
+			}
+			b.WriteRune(r)
+			prevSep = true
+		default:
+			if b.Len() == 0 {
+				continue
+			}
+			if prevSep {
+				continue
+			}
+			b.WriteRune('_')
+			prevSep = true
+		}
+	}
+	out := strings.TrimRight(b.String(), "_-")
+	if len(out) > 30 {
+		out = strings.TrimRight(out[:30], "_-")
+	}
+	return out
+}
+
+// nip05LocalPart returns the local part of a NIP-05 identifier (`local@domain`)
+// when its domain matches `serviceDomain` (case-insensitive). The bare form
+// `local` (no `@`) per NIP-05 implies `_@domain`, which we ignore for sync
+// since we cannot prove the domain match.
+func nip05LocalPart(nip05, serviceDomain string) string {
+	nip05 = strings.TrimSpace(nip05)
+	if nip05 == "" || serviceDomain == "" {
+		return ""
+	}
+	at := strings.LastIndex(nip05, "@")
+	if at <= 0 || at == len(nip05)-1 {
+		return ""
+	}
+	local := nip05[:at]
+	domain := nip05[at+1:]
+	if !strings.EqualFold(domain, serviceDomain) {
+		return ""
+	}
+	return local
+}
+
+// CandidateFromMetadata returns a sanitized, validated username derived from a
+// kind:0 profile, or "" if no field yields a usable handle. Precedence:
+//  1. NIP-05 local part when its domain matches serviceDomain.
+//  2. `name` (NIP-01).
+//  3. `display_name` / `displayName` (NIP-24).
+//  4. Deprecated `username` field.
+func CandidateFromMetadata(name, displayName, displayNameAlt, username, nip05, serviceDomain string, reserved []string) string {
+	tryFields := []string{
+		nip05LocalPart(nip05, serviceDomain),
+		name,
+		displayName,
+		displayNameAlt,
+		username,
+	}
+	for _, raw := range tryFields {
+		if raw == "" {
+			continue
+		}
+		c := SanitizeForUsername(raw)
+		if c == "" {
+			continue
+		}
+		if err := ValidateUsername(c, reserved); err != nil {
+			continue
+		}
+		return c
+	}
+	return ""
+}