72 lines
2.7 KiB
OCaml
72 lines
2.7 KiB
OCaml
open Types
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open Utils
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let parse_header (reader : reader) =
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let max_size = 6 in
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match List.init max_size (fun offset -> unpack_short_be reader.data (offset * 2)) with
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| [ id; flags; num_questions; num_answers; num_authorities; num_additionals ] ->
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( { reader with pointer = reader.pointer + (max_size * 2) }
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, { id; flags; num_questions; num_answers; num_authorities; num_additionals } )
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| _ -> failwith "Invalid number of fields"
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;;
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let rec parse_question (reader : reader) =
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let name, offset_name = decode_name reader in
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let data = bytes_forward reader.data (reader.pointer + offset_name) in
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let max_size = 2 in
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match List.init max_size (fun offset -> unpack_short_be data (offset * 2)) with
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| [ type_; class_ ] ->
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( { reader with pointer = reader.pointer + offset_name + (max_size * 2) }
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, { name; type_; class_ } )
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| _ -> failwith "Invalid number of fields"
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and decode_name reader =
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let rec read_parts parts pos =
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let length = int_of_char (Bytes.get reader.data (reader.pointer + pos)) in
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if length = 0
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then 1, parts
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else if length land 0b1100_0000 <> 0
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then (
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let decoded_name = decode_compressed_name reader length in
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2, decoded_name :: parts)
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else (
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let part = Bytes.sub_string reader.data (reader.pointer + pos + 1) length in
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let last_length, parts' = read_parts (parts @ [ part ]) (pos + 1 + length) in
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last_length + length + 1, parts')
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in
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let offset, parts = read_parts [] 0 in
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String.to_bytes (String.concat "." parts), offset
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and decode_compressed_name reader length =
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let pointer =
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(length land 0b0011_1111) + int_of_char (Bytes.get reader.data (reader.pointer + 1))
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in
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String.of_bytes (fst (decode_name { reader with pointer }))
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;;
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let parse_record reader =
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let name, offset_name = decode_name reader in
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let data = bytes_forward reader.data (offset_name + reader.pointer) in
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let data_len = unpack_short_be data 8 in
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let record_len = 10 in
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( { reader with pointer = reader.pointer + offset_name + record_len + data_len }
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, { name
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; type_ = unpack_short_be data 0
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; class_ = unpack_short_be data 2
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; ttl = unpack_int_be data 4
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; data = Bytes.sub data record_len data_len
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} )
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;;
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let parse_dns_packet data =
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let reader, dns_header = parse_header { data; pointer = 0 } in
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(* Quid du pointeur du reader, pas récupéré à chaque itération... *)
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{ header = dns_header
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; questions = List.init dns_header.num_questions (fun _ -> snd (parse_question reader))
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; answers = List.init dns_header.num_answers (fun _ -> snd (parse_record reader))
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; authorities =
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List.init dns_header.num_authorities (fun _ -> snd (parse_record reader))
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; additionals =
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List.init dns_header.num_additionals (fun _ -> snd (parse_record reader))
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}
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;;
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