implement compression support

lib/response.ml

@@ -11,7 +11,7 @@ let parse_header reader =
 ;;
 
 let rec parse_question reader =
-  let name, offset_name = decode_name_simple reader in
+  let name, offset_name = decode_name reader in
   let data = bytes_forward reader.data (reader.pointer + offset_name) in
   let max_size = 2 in
   match List.init max_size (fun offset -> unpack_short_be data (offset * 2)) with
@@ -20,7 +20,7 @@ let rec parse_question reader =
     , { name; type_; class_ } )
   | _ -> failwith "Invalid number of fields"
 
-and decode_name_simple reader =
+and decode_name reader =
   let rec read_parts parts pos =
     let length = int_of_char (Bytes.get reader.data (reader.pointer + pos)) in
     if length = 0
@@ -37,38 +37,15 @@ and decode_name_simple reader =
   let offset, parts = read_parts [] 0 in
   String.to_bytes (String.concat "." parts), offset
 
-(*
----
-def decode_compressed_name(length, reader):
-    pointer_bytes = bytes([length & 0b0011_1111]) + reader.read(1)
-    pointer = struct.unpack("!H", pointer_bytes)[0]
-    current_pos = reader.tell()
-    reader.seek(pointer)
-    result = decode_name(reader)
-    reader.seek(current_pos)
-    return result
----
-*)
-and decode_compressed_name _reader _length =
-  (* TODO *)
-  String.empty
+and decode_compressed_name reader length =
+  let pointer =
+    (length land 0b0011_1111) + int_of_char (Bytes.get reader.data (reader.pointer + 1))
+  in
+  String.of_bytes (fst (decode_name { reader with pointer }))
 ;;
 
-(*
----
-def parse_record(reader):
-    name = decode_name_simple(reader)
-    # the the type, class, TTL, and data length together are 10 bytes (2 + 2 + 4 + 2 = 10)
-    # so we read 10 bytes
-    data = reader.read(10)
-    # HHIH means 2-byte int, 2-byte-int, 4-byte int, 2-byte int
-    type_, class_, ttl, data_len = struct.unpack("!HHIH", data)
-    data = reader.read(data_len)
-    return DNSRecord(name, type_, class_, ttl, data)
----
-*)
 let parse_record reader =
-  let name, _offset_name = decode_name_simple reader in
+  let name, _offset_name = decode_name reader in
   (* TODO *)
   let type_, class_, ttl, data = 0, 0, 0, Bytes.empty in
   { name; type_; class_; ttl; data }