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//! Subscribe command: multiplexed event stream from all active sessions.
//!
//! Watches all active session JSONL files and outputs a single merged
//! event stream. This is the read-side primitive for building real
//! orchestration on top of zag.
use crate::listen;
use anyhow::{Result, bail};
use log::debug;
use std::io::{BufRead, BufReader, Seek, SeekFrom};
use zag_agent::session::SessionStore;
use zag_agent::session_log::AgentLogEvent;
/// Parameters for the subscribe command.
pub struct SubscribeParams {
pub tag: Option<String>,
pub event_type: Option<String>,
pub global: bool,
pub json: bool,
pub root: Option<String>,
}
/// A tracked log file with its current read position.
struct TrackedLog {
#[allow(dead_code)]
session_id: String,
reader: BufReader<std::fs::File>,
}
/// Discover active session log files.
fn discover_sessions(params: &SubscribeParams) -> Result<Vec<(String, std::path::PathBuf)>> {
let store = if params.global {
SessionStore::load_all()?
} else {
SessionStore::load(params.root.as_deref())?
};
let sessions: Vec<_> = if let Some(ref tag) = params.tag {
store.find_by_tag(tag).into_iter().cloned().collect()
} else {
store.sessions.clone()
};
let mut result = Vec::new();
for entry in &sessions {
match listen::resolve_session_log(
Some(&entry.session_id),
false,
false,
params.root.as_deref(),
) {
Ok(path) => {
if path.exists() {
result.push((entry.session_id.clone(), path));
}
}
Err(_) => continue,
}
}
Ok(result)
}
/// Subscribe to events from all active sessions, returning a channel.
/// Spawns a background task that polls all JSONL files and sends events.
pub fn subscribe_events(
params: &SubscribeParams,
) -> Result<tokio::sync::mpsc::Receiver<AgentLogEvent>> {
let sessions = discover_sessions(params)?;
if sessions.is_empty() {
anyhow::bail!("No active sessions found to subscribe to");
}
let (tx, rx) = tokio::sync::mpsc::channel::<AgentLogEvent>(256);
let event_type_filter = params.event_type.clone();
// Open all log files and seek to end
let mut tracked: Vec<TrackedLog> = Vec::new();
for (session_id, path) in &sessions {
match std::fs::File::open(path) {
Ok(mut file) => {
let _ = file.seek(SeekFrom::End(0));
tracked.push(TrackedLog {
session_id: session_id.clone(),
reader: BufReader::new(file),
});
}
Err(e) => {
debug!("Failed to open log for session {session_id}: {e}");
}
}
}
if tracked.is_empty() {
anyhow::bail!("Could not open any session logs");
}
tokio::spawn(async move {
loop {
let mut had_data = false;
for log in &mut tracked {
loop {
let mut line = String::new();
match log.reader.read_line(&mut line) {
Ok(0) => break,
Ok(_) => {
let trimmed = line.trim();
if trimmed.is_empty() {
continue;
}
let event: AgentLogEvent = match serde_json::from_str(trimmed) {
Ok(e) => e,
Err(_) => continue,
};
if let Some(ref type_filter) = event_type_filter {
let event_type = match &event.kind {
zag_agent::session_log::LogEventKind::SessionStarted {
..
} => "session_started",
zag_agent::session_log::LogEventKind::SessionEnded {
..
} => "session_ended",
zag_agent::session_log::LogEventKind::UserMessage {
..
} => "user_message",
zag_agent::session_log::LogEventKind::AssistantMessage {
..
} => "assistant_message",
zag_agent::session_log::LogEventKind::ToolCall { .. } => {
"tool_call"
}
zag_agent::session_log::LogEventKind::ToolResult { .. } => {
"tool_result"
}
_ => "other",
};
if event_type != type_filter.as_str() {
continue;
}
}
had_data = true;
if tx.send(event).await.is_err() {
return; // receiver dropped
}
}
Err(_) => break,
}
}
}
if !had_data {
tokio::time::sleep(std::time::Duration::from_millis(200)).await;
}
}
});
Ok(rx)
}
/// Run the subscribe command.
pub fn run_subscribe(params: SubscribeParams) -> Result<()> {
let sessions = discover_sessions(¶ms)?;
if sessions.is_empty() {
bail!("No active sessions found to subscribe to");
}
debug!("Subscribing to {} session(s)", sessions.len());
// Open all log files and seek to end
let mut tracked: Vec<TrackedLog> = Vec::new();
for (session_id, path) in &sessions {
match std::fs::File::open(path) {
Ok(mut file) => {
let _ = file.seek(SeekFrom::End(0));
tracked.push(TrackedLog {
session_id: session_id.clone(),
reader: BufReader::new(file),
});
}
Err(e) => {
debug!("Failed to open log for session {session_id}: {e}");
}
}
}
if tracked.is_empty() {
bail!("Could not open any session logs");
}
// Poll loop: read new lines from all tracked logs
loop {
let mut had_data = false;
for log in &mut tracked {
loop {
let mut line = String::new();
match log.reader.read_line(&mut line) {
Ok(0) => break, // No more data in this file
Ok(_) => {
let trimmed = line.trim();
if trimmed.is_empty() {
continue;
}
let event: AgentLogEvent = match serde_json::from_str(trimmed) {
Ok(e) => e,
Err(_) => continue,
};
// Filter by event type
if let Some(ref type_filter) = params.event_type {
let event_type = match &event.kind {
zag_agent::session_log::LogEventKind::SessionStarted { .. } => {
"session_started"
}
zag_agent::session_log::LogEventKind::SessionEnded { .. } => {
"session_ended"
}
zag_agent::session_log::LogEventKind::UserMessage { .. } => {
"user_message"
}
zag_agent::session_log::LogEventKind::AssistantMessage {
..
} => "assistant_message",
zag_agent::session_log::LogEventKind::ToolCall { .. } => {
"tool_call"
}
zag_agent::session_log::LogEventKind::ToolResult { .. } => {
"tool_result"
}
_ => "other",
};
if event_type != type_filter.as_str() {
continue;
}
}
had_data = true;
if params.json {
println!("{}", serde_json::to_string(&event).unwrap_or_default());
} else {
let id_short =
&event.wrapper_session_id[..event.wrapper_session_id.len().min(8)];
let type_name = match &event.kind {
zag_agent::session_log::LogEventKind::SessionStarted { .. } => {
"session_started"
}
zag_agent::session_log::LogEventKind::SessionEnded { .. } => {
"session_ended"
}
zag_agent::session_log::LogEventKind::AssistantMessage {
..
} => "assistant_message",
zag_agent::session_log::LogEventKind::ToolCall { .. } => {
"tool_call"
}
_ => "event",
};
println!("[{}] {} {}", id_short, event.ts, type_name);
}
}
Err(_) => break,
}
}
}
if !had_data {
std::thread::sleep(std::time::Duration::from_millis(200));
}
}
}
#[cfg(test)]
#[path = "subscribe_tests.rs"]
mod tests;