// Smoldot

// Copyright (C) 2019-2022  Parity Technologies (UK) Ltd.

// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program is free software: you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation, either version 3 of the License, or

// (at your option) any later version.

// This program is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

//! The identify protocol is a request-response protocol.

//!

//! The request's body is empty. Contrary to other request-response protocols, it doesn't even

//! contain a message length. As soon as the protocol has been negotiated, the other side should

//! send back the response.

//!

//! The response's body consists in various useful general-purpose information about the node.

//! See [`IdentifyResponse`] for details.

//!

//! The two most important fields are [`IdentifyResponse::listen_addrs`] and

//! [`IdentifyResponse::observed_addr`]. They are necessary in order for nodes to discover their

//! public address, and in order to insert peers in the Kademlia k-buckets.

//!

//! See also [the official specification](https://github.com/libp2p/specs/tree/69e57d59dc5d59d3979d79842b577ec2c483f7fa/identify).

use crate::{

    libp2p::peer_id::{FromProtobufEncodingError, PublicKey},

    util::protobuf,

};

use alloc::vec::{self, Vec};

/// Description of a response to an identify request.

#[derive(Debug, Clone, PartialEq, Eq)]

pub struct IdentifyResponse<'a, TLaIter, TProtoIter> {

    /// Name of the set of protocols supposed by the node.

    pub protocol_version: &'a str,

    /// Name and version of the software that responds. Similar to `User-Agent` in the HTTP

    /// protocol. Used for debugging purposes.

    pub agent_version: &'a str,

    /// Ed25519 public key of the local node.

    pub ed25519_public_key: [u8; 32],

    /// List of multiaddresses the local node is listening on. This should include first and

    /// foremost addresses that are publicly-reachable.

    ///

    /// > **Note**: Each item should be decoded into a multiaddr, but keep in mind that it might

    /// >           not be valid.

    pub listen_addrs: TLaIter,

    /// Multiaddress of the sender of the identify request, as seen from the receiver.

    ///

    /// > **Note**: This should be decoded into a multiaddr, but keep in mind that it might not

    /// >           be valid.

    pub observed_addr: &'a [u8],

    /// Names of the protocols supported by the local node.

    pub protocols: TProtoIter,

}

// See https://github.com/libp2p/specs/tree/master/identify#the-identify-message for the protobuf

// message format.

/// Builds the bytes corresponding to a block request.

pub fn build_identify_response<'a>(

    config: IdentifyResponse<

        'a,

        impl Iterator<Item = &'a [u8]> + 'a,

        impl Iterator<Item = &'a str> + 'a,

    >,

) -> impl Iterator<Item = impl AsRef<[u8]> + 'a> + 'a {

    protobuf::string_tag_encode(5, config.protocol_version)

        .map(either::Left)

        .map(either::Left)

        .map(either::Left)

        .chain(

            protobuf::string_tag_encode(6, config.agent_version)

                .map(either::Right)

                .map(either::Left)

                .map(either::Left),

        )

        .chain(

            protobuf::bytes_tag_encode(

                1,

                PublicKey::Ed25519(config.ed25519_public_key).to_protobuf_encoding(),

            )

            .map(either::Left)

            .map(either::Right)

            .map(either::Left),

        )

        .chain(

            config

                .listen_addrs

                .flat_map(|addr| protobuf::bytes_tag_encode(2, addr))

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                .map(either::Right)

                .map(either::Right)

                .map(either::Left),

        )

        .chain(

            protobuf::bytes_tag_encode(4, config.observed_addr)

                .map(either::Left)

                .map(either::Right),

        )

        .chain(

            config

                .protocols

                .flat_map(|p| protobuf::string_tag_encode(3, p))

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                .map(either::Right)

                .map(either::Right),

        )

}

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/// Decodes a response to an identify request.

pub fn decode_identify_response(

    response_bytes: &'_ [u8],

) -> Result<

    IdentifyResponse<'_, vec::IntoIter<&'_ [u8]>, vec::IntoIter<&'_ str>>,

    DecodeIdentifyResponseError,

> {

    let mut parser = nom::combinator::all_consuming::<_, _, nom::error::Error<&[u8]>, _>(

        nom::combinator::complete(protobuf::message_decode! {

            #[optional] protocol_version = 5 => protobuf::string_tag_decode,

            #[optional] agent_version = 6 => protobuf::string_tag_decode,

            #[optional] ed25519_public_key = 1 => protobuf::bytes_tag_decode,

            #[repeated(max = 1024)] listen_addrs = 2 => protobuf::bytes_tag_decode,

            #[optional] observed_addr = 4 => protobuf::bytes_tag_decode,

            #[repeated(max = 1024)] protocols = 3 => protobuf::string_tag_decode,

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        }),

    );

    let decoded = match nom::Finish::finish(parser(response_bytes)) {

        Ok((_, out)) => out,

        Err(_) => return Err(DecodeIdentifyResponseError::ProtobufDecode),

    };

    Ok(IdentifyResponse {

        agent_version: decoded.agent_version.unwrap_or_default(),

        protocol_version: decoded.protocol_version.unwrap_or_default(),

        ed25519_public_key: match PublicKey::from_protobuf_encoding(

            decoded.ed25519_public_key.unwrap_or_default(),

        )

        .map_err(DecodeIdentifyResponseError::InvalidPublicKey)?

        {

            PublicKey::Ed25519(key) => key,

        },

        listen_addrs: decoded.listen_addrs.into_iter(),

        observed_addr: decoded.observed_addr.unwrap_or_default(),

        protocols: decoded.protocols.into_iter(),

    })

}

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/// Error potentially returned by [`decode_identify_response`].

#[derive(Debug, derive_more::Display)]

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pub enum DecodeIdentifyResponseError {

    /// Error while decoding the Protobuf encoding.

    ProtobufDecode,

    /// Couldn't decode the public key of the remote.

    #[display(fmt = "Failed to decode remote public key: {_0}")]

    InvalidPublicKey(FromProtobufEncodingError),

}