milestone 18: collapse duplicated infrastructure into shared listener core, crud list helper, resource shells, transport race, name and line helpers, ui modules

src/dns/name.zig

@@ -134,6 +134,34 @@ pub fn fromText(text: []const u8) FromTextError!Name {
     return name;
 }
 
+pub const NormalizeError = error{BadName};
+
+/// Lowercases over ASCII into `buf`, strips one trailing dot, and checks the
+/// result is a name `fromText` accepts. Returns the normalized text, borrowed
+/// from `buf`.
+///
+/// A byte ≥ 0x80 is rejected: query names arrive ASCII-lowercased, so a high
+/// byte here could never be matched, and configuration that can never match is
+/// worth reporting rather than storing. The root name is rejected for the same
+/// reason — a configured entry that matches everything, or nothing, is not what
+/// either caller means.
+///
+/// `filter/rules.zig`, `filter/compiler.zig` and `cache/dns_cache.zig` keep
+/// their own variants on purpose; each says why beside its copy.
+pub fn normalizeText(text: []const u8, buf: *[types.max_name_len]u8) NormalizeError![]const u8 {
+    var rest = text;
+    if (rest.len > 0 and rest[rest.len - 1] == '.') rest = rest[0 .. rest.len - 1];
+    if (rest.len == 0 or rest.len > types.max_name_len) return error.BadName;
+
+    for (rest, 0..) |byte, i| {
+        if (byte >= 0x80) return error.BadName;
+        buf[i] = std.ascii.toLower(byte);
+    }
+    const normalized = buf[0..rest.len];
+    _ = fromText(normalized) catch return error.BadName;
+    return normalized;
+}
+
 /// Writes presentation form: labels joined by dots, no trailing dot. The root
 /// name writes as ".".
 pub fn formatText(name: Name, w: *Writer) Writer.Error!void {
@@ -392,3 +420,22 @@ test "labelCount" {
     try testing.expectEqual(@as(usize, 1), (try fromText("com")).labelCount());
     try testing.expectEqual(@as(usize, 3), (try fromText("www.example.com")).labelCount());
 }
+
+test "normalizeText lowercases and strips one trailing dot" {
+    var buf: [types.max_name_len]u8 = undefined;
+    try testing.expectEqualStrings("example.com", try normalizeText("Example.COM", &buf));
+    try testing.expectEqualStrings("example.com", try normalizeText("example.com.", &buf));
+    try testing.expectEqualStrings("a", try normalizeText("A", &buf));
+}
+
+test "normalizeText rejects the root, high bytes and names fromText refuses" {
+    var buf: [types.max_name_len]u8 = undefined;
+    try testing.expectError(error.BadName, normalizeText("", &buf));
+    try testing.expectError(error.BadName, normalizeText(".", &buf));
+    try testing.expectError(error.BadName, normalizeText("caf\xc3\xa9.example.com", &buf));
+    try testing.expectError(error.BadName, normalizeText("a..b", &buf));
+    try testing.expectError(error.BadName, normalizeText("a." ** 200 ++ "com", &buf));
+
+    // A label of 64 bytes is one over the wire limit.
+    try testing.expectError(error.BadName, normalizeText("a" ** 64 ++ ".com", &buf));
+}