PTY has no flow control: yes command pegs the server, grows memory without bound, and starves input #53473

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1. github-actions

   assigned

   kitlangton

   on Oct 6, 2026
2. github-actions commented on Oct 6, 2026

   

   github-actionsBot

   on Oct 6, 2026 – with GitHub Actions

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   This issue might be a duplicate of existing issues. Please check:

   • #50699: opencode serve leaves orphaned PTY shell processes when PTY connection is denied; this issue also reports orphaned PTY children, though the trigger differs.
3. opencodejr commented on Oct 27, 2026

   

   opencodejrBot

   on Oct 27, 2026

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   Thanks for the detailed report. I reproduced this on 2.0.23 using the server API, and it still happens on the latest dev (f7d0ce1).

   The script below creates a PTY with POST /api/pty, connects over the WebSocket, sends yes, and samples the server process for 10 seconds:

   • Memory: on 2.0.23 the server grew from about 270 MB to about 860 MB, and on dev to about 1 GB.
   • Output: in those 10 seconds the client received only 5 MB (2.0.23) and 0.5 MB (dev) of output, so the rest was piling up on the server.
   • Ctrl-C: after Ctrl-C, a follow-up echo took about 20 s to come back on 2.0.23 and about 12 s on dev. The server stayed around 100% CPU afterwards.

   This matches your first three points: the retained buffer is re-sliced on every chunk once it passes 2 MB, and output goes into an unbounded queue for each subscriber with nothing slowing the PTY down. I didn't reproduce the orphaned serve --stdio case: in my non-stdio test, yes exited once the client closed. The smaller gaps you listed (attaching to exited PTYs, location eviction, environment cleanup, size on create) read more like separate feature requests.

   The linked issue search didn't work during triage, so I couldn't check for existing duplicates.

   Reproduction script (pty-flood.ts)

   // Reproduces #53473: `yes` in a PTY floods the v2 server (CPU, memory) and starves Ctrl-C.
   // Usage: start `opencode serve --port 4199` in a project dir, then:
   //   OC_PASSWORD=<server password> OC_DIR=<project dir> SERVER_PID=<pid> bun pty-flood.ts
   const base = process.env.OC_URL ?? "http://127.0.0.1:4199"
   const dir = process.env.OC_DIR ?? process.cwd()
   const auth = "Basic " + btoa(`${process.env.OC_USER ?? "opencode"}:${process.env.OC_PASSWORD ?? ""}`)
   const loc = `location%5Bdirectory%5D=${encodeURIComponent(dir)}`
   const pid = process.env.SERVER_PID
   
   const rss = async () => {
     if (!pid) return "?"
     const out = await Bun.$`ps -o rss=,pcpu= -p ${pid}`.nothrow().text()
     const [kb, cpu] = out.trim().split(/\s+/)
     return `rss=${Math.round(Number(kb) / 1024)}MB cpu=${cpu}%`
   }
   
   const created = await fetch(`${base}/api/pty?${loc}`, {
     method: "POST",
     headers: { authorization: auth, "content-type": "application/json" },
     body: JSON.stringify({ command: "/bin/bash", args: ["--norc", "--noprofile"] }),
   }).then((r) => r.json() as any)
   const id = created.data?.id ?? created.id
   console.log("created pty", id)
   
   const ws = new WebSocket(`${base.replace("http", "ws")}/api/pty/${id}/connect?${loc}`, {
     headers: { authorization: auth },
   } as any)
   let bytes = 0
   let tail = ""
   ws.binaryType = "arraybuffer"
   ws.onmessage = (e) => {
     const s = typeof e.data === "string" ? e.data : new TextDecoder().decode(e.data)
     bytes += s.length
     tail = (tail + s).slice(-200)
   }
   ws.onclose = (e) => console.log("closed", e.code, e.reason)
   await new Promise((r) => (ws.onopen = r))
   console.log("connected; baseline", await rss())
   ws.send("yes\n")
   for (let i = 1; i <= 10; i++) {
     await Bun.sleep(1000)
     console.log(`t=${i}s received=${(bytes / 1e6).toFixed(1)}MB`, await rss())
   }
   console.log("sending Ctrl-C")
   ws.send("\x03")
   ws.send("echo MARKER_$((40+2))\n")
   const t0 = Date.now()
   while (Date.now() - t0 < 30000) {
     if (tail.includes("MARKER_42")) break
     await Bun.sleep(100)
   }
   const ok = tail.includes("MARKER_42")
   console.log(ok ? `prompt back after ${Date.now() - t0}ms` : "NO prompt within 30s after Ctrl-C", await rss())
   ws.close()
   await Bun.sleep(3000)
   console.log("after client close", await rss())
   console.log("yes processes still running:", (await Bun.$`pgrep -x yes`.nothrow().text()).trim().split("\n").filter(Boolean).length)
   process.exit(0)

   Run it: bun pty-flood.ts
4. opencodejr

   added

   reproduced

   on Oct 27, 2026