Add Codex JSON sessions and usage limits

server/src/session/transport.rs

@@ -101,6 +101,83 @@ pub enum Transport {
 }
 
 impl Transport {
+    /// Exchanges newline-delimited JSON requests with a short-lived stdio
+    /// server. `initial` is written first; after its response arrives,
+    /// `requests` is written and the response bearing `wanted_id` is returned.
+    ///
+    /// This is the shape Codex's app-server requires for a usage read: an
+    /// initialize round trip must finish before the initialized notification
+    /// and account request are accepted.
+    pub fn request_json_blocking(
+        &self,
+        launch: &Launch,
+        initial: &serde_json::Value,
+        requests: &[serde_json::Value],
+        wanted_id: u64,
+    ) -> Result<serde_json::Value> {
+        use std::io::{BufRead, BufReader, Write};
+
+        let host = match self {
+            Self::Here => None,
+            Self::Ssh { ssh, .. } => Some(ssh),
+        };
+        let mut command = crate::ssh::command(
+            host,
+            &launch.program,
+            &launch.args,
+            launch.cwd.as_deref(),
+            launch.forward,
+        );
+        command
+            .stdin(Stdio::piped())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::piped());
+        let mut child = command
+            .spawn()
+            .with_context(|| format!("couldn't run \"{}\" {}", launch.program, self.describe()))?;
+        let mut stdin = child.stdin.take().context("the JSON server has no stdin")?;
+        let stdout = child
+            .stdout
+            .take()
+            .context("the JSON server has no stdout")?;
+        writeln!(stdin, "{initial}")?;
+        stdin.flush()?;
+        let mut reader = BufReader::new(stdout);
+        let mut line = String::new();
+        loop {
+            line.clear();
+            if reader.read_line(&mut line)? == 0 {
+                anyhow::bail!("the JSON server exited before initialization completed");
+            }
+            let Ok(value) = serde_json::from_str::<serde_json::Value>(&line) else {
+                continue;
+            };
+            if value.get("id").and_then(serde_json::Value::as_u64)
+                == initial.get("id").and_then(serde_json::Value::as_u64)
+            {
+                break;
+            }
+        }
+        for request in requests {
+            writeln!(stdin, "{request}")?;
+        }
+        stdin.flush()?;
+        loop {
+            line.clear();
+            if reader.read_line(&mut line)? == 0 {
+                anyhow::bail!("the JSON server exited before answering request {wanted_id}");
+            }
+            let Ok(value) = serde_json::from_str::<serde_json::Value>(&line) else {
+                continue;
+            };
+            if value.get("id").and_then(serde_json::Value::as_u64) == Some(wanted_id) {
+                let _ = child.kill();
+                let _ = child.wait();
+                return Ok(value);
+            }
+        }
+    }
+
     /// The transport a setup describes; a setup with no `ssh` is here.
     pub fn for_setup(setup: &crate::config::SetupConfig) -> Self {
         match &setup.ssh {