1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151

use crate::codec::UserError;
use crate::error::Reason;
use crate::frame;
use crate::proto::*;
use std::task::{Context, Poll};

#[derive(Debug)]
pub(crate) struct Settings {
    /// Our local SETTINGS sync state with the remote.
    local: Local,
    /// Received SETTINGS frame pending processing. The ACK must be written to
    /// the socket first then the settings applied **before** receiving any
    /// further frames.
    remote: Option<frame::Settings>,
}

#[derive(Debug)]
enum Local {
    /// We want to send these SETTINGS to the remote when the socket is ready.
    ToSend(frame::Settings),
    /// We have sent these SETTINGS and are waiting for the remote to ACK
    /// before we apply them.
    WaitingAck(frame::Settings),
    /// Our local settings are in sync with the remote.
    Synced,
}

impl Settings {
    pub(crate) fn new(local: frame::Settings) -> Self {
        Settings {
            // We assume the initial local SETTINGS were flushed during
            // the handshake process.
            local: Local::WaitingAck(local),
            remote: None,
        }
    }

    pub(crate) fn recv_settings<T, B, C, P>(
        &mut self,
        frame: frame::Settings,
        codec: &mut Codec<T, B>,
        streams: &mut Streams<C, P>,
    ) -> Result<(), Error>
    where
        T: AsyncWrite + Unpin,
        B: Buf,
        C: Buf,
        P: Peer,
    {
        if frame.is_ack() {
            match &self.local {
                Local::WaitingAck(local) => {
                    tracing::debug!("received settings ACK; applying {:?}", local);

                    if let Some(max) = local.max_frame_size() {
                        codec.set_max_recv_frame_size(max as usize);
                    }

                    if let Some(max) = local.max_header_list_size() {
                        codec.set_max_recv_header_list_size(max as usize);
                    }

                    streams.apply_local_settings(local)?;
                    self.local = Local::Synced;
                    Ok(())
                }
                Local::ToSend(..) | Local::Synced => {
                    // We haven't sent any SETTINGS frames to be ACKed, so
                    // this is very bizarre! Remote is either buggy or malicious.
                    proto_err!(conn: "received unexpected settings ack");
                    Err(Error::library_go_away(Reason::PROTOCOL_ERROR))
                }
            }
        } else {
            // We always ACK before reading more frames, so `remote` should
            // always be none!
            assert!(self.remote.is_none());
            self.remote = Some(frame);
            Ok(())
        }
    }

    pub(crate) fn send_settings(&mut self, frame: frame::Settings) -> Result<(), UserError> {
        assert!(!frame.is_ack());
        match &self.local {
            Local::ToSend(..) | Local::WaitingAck(..) => Err(UserError::SendSettingsWhilePending),
            Local::Synced => {
                tracing::trace!("queue to send local settings: {:?}", frame);
                self.local = Local::ToSend(frame);
                Ok(())
            }
        }
    }

    pub(crate) fn poll_send<T, B, C, P>(
        &mut self,
        cx: &mut Context,
        dst: &mut Codec<T, B>,
        streams: &mut Streams<C, P>,
    ) -> Poll<Result<(), Error>>
    where
        T: AsyncWrite + Unpin,
        B: Buf,
        C: Buf,
        P: Peer,
    {
        if let Some(settings) = &self.remote {
            if !dst.poll_ready(cx)?.is_ready() {
                return Poll::Pending;
            }

            // Create an ACK settings frame
            let frame = frame::Settings::ack();

            // Buffer the settings frame
            dst.buffer(frame.into()).expect("invalid settings frame");

            tracing::trace!("ACK sent; applying settings");

            streams.apply_remote_settings(settings)?;

            if let Some(val) = settings.header_table_size() {
                dst.set_send_header_table_size(val as usize);
            }

            if let Some(val) = settings.max_frame_size() {
                dst.set_max_send_frame_size(val as usize);
            }
        }

        self.remote = None;

        match &self.local {
            Local::ToSend(settings) => {
                if !dst.poll_ready(cx)?.is_ready() {
                    return Poll::Pending;
                }

                // Buffer the settings frame
                dst.buffer(settings.clone().into())
                    .expect("invalid settings frame");
                tracing::trace!("local settings sent; waiting for ack: {:?}", settings);

                self.local = Local::WaitingAck(settings.clone());
            }
            Local::WaitingAck(..) | Local::Synced => {}
        }

        Poll::Ready(Ok(()))
    }
}