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//! The session layer: the backend's own type and its [`SessionBackend`]
//! implementation.
use super::cli::default_command;
use super::policy::{TernRef, session_label, split_word};
use crate::backend::*;
use std::collections::BTreeMap;
use std::sync::Arc;
pub struct TernBackend {
pub(super) runner: Arc<dyn Runner>,
pub(super) command: String,
pub(super) env: BTreeMap<String, String>,
}
impl TernBackend {
pub fn new(runner: Arc<dyn Runner>) -> Self {
Self::with_env(runner, process_env())
}
pub fn with_env(runner: Arc<dyn Runner>, env: BTreeMap<String, String>) -> Self {
let command = env
.get("TERN_COMMAND")
.cloned()
.filter(|value| !value.is_empty())
.unwrap_or_else(default_command);
Self {
runner,
command,
env,
}
}
}
impl SessionBackend for TernBackend {
fn name(&self) -> &'static str {
"tern"
}
fn capabilities(&self) -> Capabilities {
Capabilities {
spawn: true,
attach: true,
probe: true,
close: true,
focus: true,
// `tern rename BLOCK NAME` renames the block's *tab*, measured: a
// block id renames the tab that holds it, and a tab id is refused
// with `no block is called`. Renaming one session's pane would
// therefore rename every pane in that role's tab, so this backend
// answers unsupported rather than do it.
rename: false,
}
}
fn available(&self) -> Result<bool> {
// The only honest test: run the read every other call here begins with.
// A window key in the environment proves the client is inside a pane,
// not that the binary answers — and a `PATH` `tern` would fail this
// where a spawned pane's `ls` would too.
Ok(self.json(vec!["ls".into(), "--json".into()]).is_ok())
}
fn spawn(&self, spec: SpawnSpec) -> Result<SessionRef> {
if spec.command.is_empty() {
anyhow::bail!("tern spawn requires a command");
}
let label = session_label(&spec);
let session_id = self.find_or_create_session(&spec)?;
let tab = self.find_or_create_tab(&session_id, &spec)?;
// Tern takes no ratio, so the placement contributes its direction and
// nothing else. The pane count still decides the default direction, as
// it did for herdr: a split bringing the count to a power of two goes
// right, every other one down.
let placement = spec
.placement
.unwrap_or_else(|| PanePlacement::from_pane_count(tab.pane_count));
tracing::info!(
pane_count = tab.pane_count,
direction = split_word(placement.direction),
"tern block split (tern takes no split ratio)"
);
let pane_id =
self.split_and_start(&tab.base_pane, &spec, placement, &session_id, &tab.tab_id)?;
Ok(SessionRef {
task_id: spec.task_id.clone(),
backend: self.name().into(),
backend_ref: TernRef {
session_id,
tab_id: tab.tab_id,
pane_id,
session_label: label,
base_pane: tab.base_pane,
split_direction: split_word(placement.direction).to_string(),
}
.to_value(),
generation: 1,
})
}
fn attach(&self, session: &SessionRef) -> Result<SessionRef> {
let probe = self.probe(session)?;
if !probe.alive {
anyhow::bail!("tern block is gone");
}
Ok(session.clone())
}
fn probe(&self, session: &SessionRef) -> Result<ResourceProbe> {
let reference = TernRef::from_session(session)?;
// A listing that cannot be read is a probe that could not answer, not
// a verdict: the block's own state is unknown, so it reports the
// failure rather than claiming the pane died.
let listing = self.listing()?;
let Some((block, tab, host)) = listing.block(&reference.pane_id) else {
// The block is in no tab of any session: gone, or detached by the
// daemon. Both read the same to this backend, which can address
// neither.
return Ok(ResourceProbe {
alive: false,
attached: false,
detail: Some(serde_json::json!({
"pane_id": reference.pane_id,
"error": "block is in no tab",
})),
});
};
// Liveness from the block's own row: `exited` is null while the
// program runs and holds an exit code once it returns, and `live` says
// whether the daemon still holds the pty. A `--keep-open` block whose
// command has ended stays listed with `exited` set — the pane is
// addressable, and the session that owned it is over. So `exited`
// ends a session and `live` is the fallback for a build that reports
// one without the other.
let alive = block.exited.is_none() && block.live;
let mut detail = serde_json::json!({
"pane": {
"id": block.id,
"title": block.title,
"cwd": block.cwd,
"program": block.program,
"command": block.command,
"exited": block.exited,
"keep_open": block.keep_open,
"focused": block.focused,
"live": block.live,
},
"tab_id": tab.id,
"session_id": host.id,
"session_label": host.name,
});
if let Some(process) = self.process_of(&reference.pane_id) {
if let Some(map) = detail.as_object_mut() {
map.insert("process".into(), process);
}
}
Ok(ResourceProbe {
alive,
// A block still listed is one the daemon holds, so a live one is
// attached to a pty. A block whose program exited under
// `--keep-open` is addressable but holds nothing: attached follows
// `live`, which is what separates the two.
attached: block.live,
detail: Some(detail),
})
}
fn close(&self, session: &SessionRef, reason: CloseReason, force: bool) -> Result<()> {
// `tern close` has no force flag and no reason; both close paths are
// the same command.
tracing::debug!(task = %session.task_id, ?reason, force, "closing tern block");
let reference = TernRef::from_session(session)?;
match self.json(vec![
"close".into(),
reference.pane_id.clone(),
"--json".into(),
]) {
Ok(_) => Ok(()),
// Measured: a closed block is refused with `no block is called
// \`N\`` and exit 1, with no JSON body to carry a code. Closing
// again is a no-op, which is what lets the client end a session
// twice without the second end failing.
Err(error) if self.is_gone(&error) => {
tracing::debug!(
task = %session.task_id,
pane = %reference.pane_id,
"tern block already closed"
);
Ok(())
}
Err(error) => Err(error),
}
}
fn rename(&self, _session: &SessionRef, _title: &str) -> Result<()> {
// `tern rename BLOCK NAME` renames the block's tab, so one session's
// title would land on every pane in the role's tab. Tern offers no
// block title of its own — the listing's `title` is the pane's
// working directory or its program — so this is unsupported, and the
// capability says so.
Err(unsupported(
self.name(),
"rename",
"tern renames a block's tab, so renaming one session's block would rename the \
whole role tab",
))
}
fn focus(&self, session: &SessionRef) -> Result<()> {
let reference = TernRef::from_session(session)?;
let listing = self.listing()?;
if let Some(site) = self.focus_here(&listing) {
if site.pane_id == reference.pane_id
&& site.tab_id == reference.tab_id
&& site.session_id == reference.session_id
{
return Ok(());
}
}
self.focus_block(&reference.pane_id)?;
// Confirm the block took focus, naming the one that holds it. The
// listing can drift when an operator closes or moves blocks, and a
// focus that lands elsewhere sends the operator's keyboard to another
// session — a wrong block holding focus is reported, not passed off as
// success.
let after = self.listing()?;
match self.focus_here(&after) {
Some(site) if site.pane_id == reference.pane_id => Ok(()),
Some(site) => Err(anyhow::anyhow!(
"tern left block {} unfocused (focused block {})",
reference.pane_id,
site.pane_id
)),
None => Err(anyhow::anyhow!(
"tern left block {} unfocused (no block holds focus)",
reference.pane_id
)),
}
}
}