add dns_header, question, bytes to string, header and question to bytes and encode dns name

lib/utils.ml

@@ -0,0 +1,75 @@
+type dns_header =
+  { id : int
+  ; flags : int
+  ; num_questions : int
+  ; num_answers : int
+  ; num_authorities : int
+  ; num_additionals : int
+  }
+
+type dns_question =
+  { name : bytes
+  ; type_ : int
+  ; class_ : int
+  }
+
+let get_bytecode data =
+  let result =
+    List.map
+      (fun byte ->
+        let code = Char.code byte in
+        if code >= 65 && code <= 122
+        then String.make 1 byte
+        else Printf.sprintf "\\x%02X" code)
+      (List.of_seq (Bytes.to_seq data))
+  in
+  String.concat "" result
+;;
+
+let new_buffer obj list =
+  let size = 2 * Obj.size (Obj.repr obj) in
+  let buffer = Bytes.create size in
+  let verification =
+    List.fold_left
+      (fun acc field ->
+        Bytes.set_uint16_be buffer acc field;
+        acc + 2)
+      0
+      list
+  in
+  if verification != size then failwith "Issue converting header to bytes";
+  buffer
+;;
+
+let header_to_bytes header =
+  new_buffer
+    header
+    [ header.id
+    ; header.flags
+    ; header.num_questions
+    ; header.num_answers
+    ; header.num_authorities
+    ; header.num_additionals
+    ]
+;;
+
+let question_to_bytes question =
+  let buffer1 = new_buffer question [ question.type_; question.class_ ] in
+  let buffer2 = Buffer.create (Bytes.length question.name + Bytes.length buffer1) in
+  Buffer.add_bytes buffer2 question.name;
+  Buffer.add_bytes buffer2 buffer1;
+  buffer2
+;;
+
+let encode_dns_name domain_name =
+  let parts = String.split_on_char '.' domain_name in
+  let encoded_parts =
+    List.map
+      (fun part ->
+        let len_part = String.length part in
+        let len_byte = Char.chr len_part in
+        Bytes.cat (Bytes.of_string (String.make 1 len_byte)) (Bytes.of_string part))
+      parts
+  in
+  Bytes.cat (Bytes.concat Bytes.empty encoded_parts) (Bytes.of_string "\x00")
+;;