1 files changed, 151 insertions, 0 deletions
diff --git a/third_party/rust/h2/src/proto/settings.rs b/third_party/rust/h2/src/proto/settings.rs
new file mode 100644
index 0000000000..6cc6172099
--- /dev/null
+++ b/third_party/rust/h2/src/proto/settings.rs
@@ -0,0 +1,151 @@
+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(()))
+    }
+}