Handling “flags” types in telegram's TL schema language

问题

I wrote a tl parser so can now use the latest layer (53). But I am unsure how to handle "flags" types. They are only mentioned in the tl docs but not defined (as far as I can tell) at the bottom of the page here: link.

For example, when a method returns a 'message' type it should look like this: message#c09be45f flags:# out:flags.1?true mentioned:flags.4?true media_unread:flags.5?true silent:flags.13?true post:flags.14?true id:int from_id:flags.8?int to_id:Peer fwd_from:flags.2?MessageFwdHeader via_bot_id:flags.11?int reply_to_msg_id:flags.3?int date:int message:string media:flags.9?MessageMedia reply_markup:flags.6?ReplyMarkup entities:flags.7?Vector<MessageEntity> views:flags.10?int edit_date:flags.15?int = Message;

If I understand correctly each flag is a bit set in some variable, right?

My parser breaks out the 'message' type like this:

     id: -1063525281
     params:
             name: flags
             type:
                     name: out
                     bit: 1
                     type: true

                     name: mentioned
                     bit: 4
                     type: true

                     name: media_unread
                     bit: 5
                     type: true

                     name: silent
                     bit: 13
                     type: true

                     name: post
                     bit: 14
                     type: true

                     name: from_id
                     bit: 8
                     type: int

                     name: fwd_from
                     bit: 2
                     type: MessageFwdHeader

                     name: via_bot_id
                     bit: 11
                     type: int

                     name: reply_to_msg_id
                     bit: 3
                     type: int

                     name: media
                     bit: 9
                     type: MessageMedia

                     name: reply_markup
                     bit: 6
                     type: ReplyMarkup

                     name: entities
                     bit: 7
                     type: Vector<MessageEntity>

                     name: views
                     bit: 10
                     type: int

                     name: edit_date
                     bit: 15
                     type: int

             name: id
             type: int

             name: to_id
             type: Peer

             name: date
             type: int

             name: message
             type: string

     predicate: message
     type: Message

But if the flags are bits in some variable, which variable?

Related: is tl based on a formal, standardized language spec or was it created specifically for telegram? I ask because if it is a subset of a formal language (like yaml) it might be better to use an already known parser for tl instead of reinventing the wheel.

回答1:

But if the flags are bits in some variable, which variable?

Message#c09be45f flags:# out:flags.1?true mentioned:flags.4?true media_unread:flags.5?true silent:flags.13?true post:flags.14?true id:int from_id:flags.8?int to_id:Peer fwd_from:flags.2?MessageFwdHeader via_bot_id:flags.11?int reply_to_msg_id:flags.3?int date:int message:string media:flags.9?MessageMedia reply_markup:flags.6?ReplyMarkup entities:flags.7?Vector<MessageEntity> views:flags.10?int edit_date:flags.15?int = Message;

Example: flags:# out:flags.1?true

Decoding Flags: BinaryAND(flags, 2^ix) === 2^ix --> this will help you determine if a field is included or not

flags = The value if the flags field, this is usually the first field for objects with flags

ix == flag index, this is a number that indicates flag position, e.g. out:flags.1?true here out is the field in flag position 1, and the type is true

For the example above out will have a value of true if BAND(flags,2^N) == 2^N otherwise, out field is ignored

Code - Message Encoding (Elixir)

def encode(%Message{} = x), do: <<95, 228, 155, 192, encode(:Int, x.flags)::binary, enc_f(:True, x.out, x.flags, 2)::binary, enc_f(:True, x.mentioned, x.flags, 16)::binary, enc_f(:True, x.media_unread, x.flags, 32)::binary, enc_f(:True, x.silent, x.flags, 8192)::binary, enc_f(:True, x.post, x.flags, 16384)::binary, encode(:Int, x.id)::binary, enc_f(:Int, x.from_id, x.flags, 256)::binary, encode(x.to_id)::binary, enc_f(x.fwd_from, x.flags, 4)::binary, enc_f(:Int, x.via_bot_id, x.flags, 2048)::binary, enc_f(:Int, x.reply_to_msg_id, x.flags, 8)::binary, encode(:Int, x.date)::binary, encode(:String, x.message)::binary, enc_f(x.media, x.flags, 512)::binary, enc_f(x.reply_markup, x.flags, 64)::binary, enc_vf(x.entities, x.flags, 128)::binary, enc_f(:Int, x.views, x.flags, 1024)::binary, enc_f(:Int, x.edit_date, x.flags, 32768)::binary>>

Code - Message Decode (Elixir)

  def decode(<<95, 228, 155, 192, bin::binary>>) do
    {flags, bin} = decode(:Int, bin)
    {out, bin} = decode(:True, bin, flags, 2) # 1
    {mentioned, bin} = decode(:True, bin, flags, 16) # 4
    {media_unread, bin} = decode(:True, bin, flags, 32) # 5
    {silent, bin} = decode(:True, bin, flags, 8192) # 13
    {post, bin} = decode(:True, bin, flags, 16384) # 14
    {id, bin} = decode(:Int, bin)
    {from_id, bin} = decode(:Int, bin, flags, 256) # 8
    {to_id, bin} = decode(bin)
    {fwd_from, bin} = decode(bin, flags, 4) # 2
    {via_bot_id, bin} = decode(:Int, bin, flags, 2048) # 11
    {reply_to_msg_id, bin} = decode(:Int, bin, flags, 8) # 3
    {date, bin} = decode(:Int, bin)
    {message, bin} = decode(:String, bin)
    {media, bin} = decode(bin, flags, 512) # 9
    {reply_markup, bin} = decode(bin, flags, 64) # 6
    {entities, bin} = decode([:MessageEntity], bin, flags, 128) # 7
    {views, bin} = decode(:Int, bin, flags, 1024) # 10
    {edit_date, bin} = decode(:Int, bin, flags, 32768) # 15
    {%Message{flags: flags, out: out, mentioned: mentioned, media_unread: media_unread, silent: silent, post: post, id: id, from_id: from_id, to_id: to_id, fwd_from: fwd_from, via_bot_id: via_bot_id, reply_to_msg_id: reply_to_msg_id, date: date, message: message, media: media, reply_markup: reply_markup, entities: entities, views: views, edit_date: edit_date}, bin}
  end

#5 == 2^5 == 32
#4 == 2^4 == 16

so basically N == 2^N, where N == ix

来源：https://stackoverflow.com/questions/38903321/handling-flags-types-in-telegrams-tl-schema-language