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|
//! Optional endpoint encoding that retains unchanged terminal cells across projections.
use super::{CellData, PaneSurfaceFrame, ServerMessage};
use serde::{Deserialize, Serialize};
pub(crate) const CAPABILITY: &str = "surface_reuse";
pub(crate) const MESSAGE_KIND: &str = "endpoint.surface-reuse.v1";
#[derive(Serialize, Deserialize)]
struct SurfaceReuse<S> {
base_surface_revision: u64,
surface: S,
}
pub(crate) fn message(
base_surface_revision: u64,
surface: &mut PaneSurfaceFrame,
) -> serde_json::Result<Option<ServerMessage>> {
let cells = std::mem::take(&mut surface.frame.cells);
let data = serde_json::to_string(&SurfaceReuse {
base_surface_revision,
surface: &*surface,
});
surface.frame.cells = cells;
let message = ServerMessage::EndpointControl {
kind: MESSAGE_KIND.into(),
data: data?,
};
// JSON can expand non-cell data (for example escaped hyperlink URLs). A
// failed compact encoding must fall back, not strand a newer snapshot.
let size = bincode::serde::encode_into_std_write(
&message,
&mut std::io::sink(),
bincode::config::standard(),
);
match size {
Ok(size) => Ok((size <= super::MAX_FRAME_SIZE).then_some(message)),
Err(error) => {
tracing::warn!(%error, "failed to size surface reuse");
Ok(None)
}
}
}
#[derive(Default)]
struct CellBaseline {
boot_id: String,
projection_revision: u64,
surface_revision: u64,
width: u16,
height: u16,
cells: Vec<CellData>,
}
/// Connection-local decoding happens before activation and presentation filtering, so
/// switching endpoints cannot discard a baseline needed by the next wire message.
#[derive(Default)]
pub(crate) struct Decoder {
baseline: Option<CellBaseline>,
}
impl Decoder {
pub(crate) fn decode(&mut self, message: ServerMessage) -> Result<ServerMessage, String> {
let message = match message {
ServerMessage::EndpointControl { kind, data } if kind == MESSAGE_KIND => {
let reuse: SurfaceReuse<PaneSurfaceFrame> = serde_json::from_str(&data)
.map_err(|error| format!("invalid surface reuse: {error}"))?;
let Some(base) = &mut self.baseline else {
return Err("surface reuse without a baseline".into());
};
let mut surface = reuse.surface;
if base.boot_id != surface.boot_id
|| base.surface_revision != reuse.base_surface_revision
|| surface.surface_revision != base.surface_revision.saturating_add(1)
|| base.width != surface.frame.width
|| base.height != surface.frame.height
|| !surface.frame.cells.is_empty()
{
return Err("surface reuse does not match its baseline".into());
}
surface.frame.cells.clone_from(&base.cells);
base.projection_revision = surface.projection_revision;
base.surface_revision = surface.surface_revision;
return Ok(ServerMessage::PaneSurface(surface));
}
message => message,
};
match &message {
ServerMessage::PaneSurface(surface) => {
let base = self.baseline.get_or_insert_with(CellBaseline::default);
base.boot_id.clone_from(&surface.boot_id);
base.projection_revision = surface.projection_revision;
base.surface_revision = surface.surface_revision;
base.width = surface.frame.width;
base.height = surface.frame.height;
base.cells.clone_from(&surface.frame.cells);
}
ServerMessage::PaneSurfacePatch(patch) => {
if let Some(base) = &mut self.baseline {
if patch.boot_id != base.boot_id
|| patch.projection_revision != base.projection_revision
|| patch.base_surface_revision != base.surface_revision
|| patch.surface_revision != base.surface_revision.saturating_add(1)
{
self.baseline = None;
} else {
for row in &patch.rows {
let start =
usize::from(row.y) * usize::from(base.width) + usize::from(row.x);
let end = start.saturating_add(row.cells.len());
if row.y >= base.height
|| usize::from(row.x) + row.cells.len() > usize::from(base.width)
|| end > base.cells.len()
{
return Err("surface patch exceeds the cell baseline".into());
}
base.cells[start..end].clone_from_slice(&row.cells);
}
base.surface_revision = patch.surface_revision;
}
}
}
_ => {}
}
Ok(message)
}
}
|
