feat(policy): case-insensitive address and domain matching

internal/policy/address_test.go

@@ -0,0 +1,30 @@
+package policy
+
+import "testing"
+
+func TestMatchAddress(t *testing.T) {
+	wl := []string{"bob@example.com", "@trusted.com"}
+	cases := []struct {
+		addr string
+		want bool
+	}{
+		{"bob@example.com", true},
+		{"BOB@Example.com", true},
+		{`"Bob" <bob@example.com>`, true},
+		{"alice@trusted.com", true},
+		{"alice@untrusted.com", false},
+		{"eve@example.com", false},
+		{"", false},
+	}
+	for _, c := range cases {
+		if got := MatchAddress(wl, c.addr); got != c.want {
+			t.Fatalf("MatchAddress(%q)=%v want %v", c.addr, got, c.want)
+		}
+	}
+}
+
+func TestNormalizeAddr(t *testing.T) {
+	if got := NormalizeAddr(`"Bob Smith" <Bob@Example.COM>`); got != "bob@example.com" {
+		t.Fatalf("got %q", got)
+	}
+}

internal/policy/policy.go

@@ -0,0 +1,44 @@
+// Package policy holds pure enforcement functions: address matching,
+// inbound filtering, and (in a later phase) outbound checks.
+package policy
+
+import (
+	"net/mail"
+	"strings"
+)
+
+// NormalizeAddr lower-cases an address and strips any display name/brackets.
+func NormalizeAddr(addr string) string {
+	addr = strings.TrimSpace(addr)
+	if a, err := mail.ParseAddress(addr); err == nil {
+		return strings.ToLower(a.Address)
+	}
+	return strings.ToLower(strings.Trim(addr, "<> "))
+}
+
+// MatchAddress reports whether addr matches any whitelist entry.
+// Entries beginning with '@' match a whole domain; others match exactly.
+func MatchAddress(entries []string, addr string) bool {
+	norm := NormalizeAddr(addr)
+	if norm == "" {
+		return false
+	}
+	at := strings.LastIndex(norm, "@")
+	domain := ""
+	if at >= 0 {
+		domain = norm[at:] // includes '@'
+	}
+	for _, e := range entries {
+		e = strings.ToLower(strings.TrimSpace(e))
+		if strings.HasPrefix(e, "@") {
+			if e == domain {
+				return true
+			}
+			continue
+		}
+		if e == norm {
+			return true
+		}
+	}
+	return false
+}