Split internal/web into subpackages before domain-admin growth.

Lay out view, auth, validate, and handlers under internal/web while keeping
the cmd/panel API unchanged; update roadmap and changelog for web-split closure.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/web/validate/validate.go

@@ -0,0 +1,148 @@
+// Package validate holds shared server-side form validation for the panel.
+package validate
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+)
+
+// MinAdminPasswordLen is the floor for the administrator password. The panel is
+// public (security.md), so this is deliberately not tiny.
+const MinAdminPasswordLen = 12
+
+const (
+	minUsernameLen = 3
+	maxUsernameLen = 64
+)
+
+// MinSecretFilePasswordLen is the floor for the password protecting an
+// encrypted backup or domain export. Such a file is offline and can be attacked
+// at leisure, so the floor matches the administrator password's rather than the
+// weaker "any password is better than none".
+const MinSecretFilePasswordLen = MinAdminPasswordLen
+
+// Username enforces a strict server-side whitelist (security.md): letters,
+// digits, dot, dash, underscore. Client validation is never trusted.
+func Username(u string) error {
+	if len(u) < minUsernameLen || len(u) > maxUsernameLen {
+		return fmt.Errorf("username must be %d-%d characters", minUsernameLen, maxUsernameLen)
+	}
+	for _, r := range u {
+		if r > unicode.MaxASCII || (!isASCIILetterOrDigit(r) && r != '.' && r != '-' && r != '_') {
+			return fmt.Errorf("username may contain only letters, digits, '.', '-' and '_'")
+		}
+	}
+	return nil
+}
+
+// AdminPassword enforces a minimum length. Composition rules beyond length tend
+// to reduce entropy in practice, so length is the sole gate.
+func AdminPassword(p string) error {
+	if len(p) < MinAdminPasswordLen {
+		return fmt.Errorf("password must be at least %d characters", MinAdminPasswordLen)
+	}
+	return nil
+}
+
+func isASCIILetterOrDigit(r rune) bool {
+	return (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9')
+}
+
+const maxDomainLen = 253 // RFC 1035 limit on a fully-qualified name
+
+// NormalizeDomain lower-cases and trims a domain name. Domain names are
+// case-insensitive, and the generated OpenDKIM tables/keys use the canonical
+// lower-case form, so we normalise before both validation and storage.
+func NormalizeDomain(name string) string {
+	return strings.ToLower(strings.TrimSpace(name))
+}
+
+// Domain enforces a strict server-side whitelist for sending-domain names
+// (security.md). The result is safe to write verbatim into the OpenDKIM
+// KeyTable/SigningTable and to use as a filesystem path segment: only
+// lower-case letters, digits, '.' and '-' are allowed, in valid DNS label
+// shape. Input must already be normalised with NormalizeDomain.
+func Domain(name string) error {
+	if name == "" {
+		return fmt.Errorf("domain is required")
+	}
+	if len(name) > maxDomainLen {
+		return fmt.Errorf("domain must be at most %d characters", maxDomainLen)
+	}
+	labels := strings.Split(name, ".")
+	if len(labels) < 2 {
+		return fmt.Errorf("domain must include at least one dot (e.g. example.com)")
+	}
+	for _, label := range labels {
+		if err := domainLabel(label); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func domainLabel(label string) error {
+	if len(label) == 0 {
+		return fmt.Errorf("domain must not contain an empty label")
+	}
+	if len(label) > 63 {
+		return fmt.Errorf("each domain label must be at most 63 characters")
+	}
+	if label[0] == '-' || label[len(label)-1] == '-' {
+		return fmt.Errorf("domain labels must not start or end with '-'")
+	}
+	for i := 0; i < len(label); i++ {
+		c := label[i]
+		lower := c >= 'a' && c <= 'z'
+		digit := c >= '0' && c <= '9'
+		if !lower && !digit && c != '-' {
+			return fmt.Errorf("domain may contain only lower-case letters, digits, '.' and '-'")
+		}
+	}
+	return nil
+}
+
+// freemailDomains lists public mail hosts that cannot publish _report._dmarc
+// authorisation for third-party sending domains.
+var freemailDomains = map[string]struct{}{
+	"gmail.com":      {},
+	"googlemail.com": {},
+	"outlook.com":    {},
+	"hotmail.com":    {},
+	"live.com":       {},
+	"yahoo.com":      {},
+	"icloud.com":     {},
+	"me.com":         {},
+	"proton.me":      {},
+	"protonmail.com": {},
+}
+
+// Email checks a DMARC rua= mailbox. Empty is allowed (policy-only).
+func Email(addr string) error {
+	addr = strings.TrimSpace(addr)
+	if addr == "" {
+		return nil
+	}
+	at := strings.LastIndex(addr, "@")
+	if at <= 0 || at >= len(addr)-1 {
+		return fmt.Errorf("enter a valid email address")
+	}
+	local := addr[:at]
+	domain := NormalizeDomain(addr[at+1:])
+	if err := Domain(domain); err != nil {
+		return fmt.Errorf("email domain is invalid: %w", err)
+	}
+	for _, r := range local {
+		if r > unicode.MaxASCII {
+			return fmt.Errorf("email address must be ASCII")
+		}
+		if !isASCIILetterOrDigit(r) && r != '.' && r != '-' && r != '_' && r != '+' {
+			return fmt.Errorf("email address contains invalid characters")
+		}
+	}
+	if _, blocked := freemailDomains[domain]; blocked {
+		return fmt.Errorf("use an address on a domain you control; public mail hosts cannot receive authorised DMARC reports")
+	}
+	return nil
+}