Initial commit: multi-peer torrent download engine

Reactor/loop-pool engine with TCP/µTP/MSE transports, per-connection
pipelining, priority-driven piece selection with endgame, and the Python
FFI test harness.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

interop/seed_transmission.py

@@ -0,0 +1,109 @@
+from __future__ import annotations
+
+import argparse
+import json
+import os
+import shutil
+import signal
+import subprocess
+import time
+
+from common import touch_ready, wait_for_tcp
+
+
+def run_remote(rpc_port: int, *args: str, check: bool = True) -> subprocess.CompletedProcess:
+    return subprocess.run(
+        ["transmission-remote", f"127.0.0.1:{rpc_port}", *args],
+        text=True,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        check=check,
+    )
+
+
+def write_settings(config_dir: str, peer_port: int, rpc_port: int, data_dir: str) -> None:
+    os.makedirs(config_dir, exist_ok=True)
+    settings = {
+        "download-dir": data_dir,
+        "incomplete-dir-enabled": False,
+        "dht-enabled": False,
+        "pex-enabled": False,
+        "lpd-enabled": False,
+        "utp-enabled": False,
+        "port-forwarding-enabled": False,
+        "peer-port": peer_port,
+        "peer-port-random-on-start": False,
+        "rpc-enabled": True,
+        "rpc-bind-address": "127.0.0.1",
+        "rpc-port": rpc_port,
+        "rpc-whitelist-enabled": False,
+        "start-added-torrents": True,
+        "trash-original-torrent-files": False,
+    }
+    with open(os.path.join(config_dir, "settings.json"), "w", encoding="utf-8") as f:
+        json.dump(settings, f, indent=2, sort_keys=True)
+
+
+def main() -> int:
+    ap = argparse.ArgumentParser(description="Seed a fixture with Transmission.")
+    ap.add_argument("--torrent", required=True)
+    ap.add_argument("--data", required=True)
+    ap.add_argument("--peer-port", type=int, required=True)
+    ap.add_argument("--rpc-port", type=int, required=True)
+    ap.add_argument("--utp", action="store_true")
+    ap.add_argument("--encryption", choices=["tolerated", "preferred", "required"],
+                    default="tolerated")
+    args = ap.parse_args()
+
+    config_dir = "/tmp/transmission-config"
+    shutil.rmtree(config_dir, ignore_errors=True)
+    write_settings(config_dir, args.peer_port, args.rpc_port, args.data)
+
+    proc = subprocess.Popen(["transmission-daemon", "-f", "-g", config_dir])
+    stop = False
+
+    def _stop(signum, frame):
+        nonlocal stop
+        stop = True
+        proc.terminate()
+
+    signal.signal(signal.SIGTERM, _stop)
+    signal.signal(signal.SIGINT, _stop)
+
+    try:
+        wait_for_tcp("127.0.0.1", args.rpc_port, timeout=30)
+        run_remote(args.rpc_port, "--no-dht", "--no-pex", "--no-lpd", "--no-portmap")
+        run_remote(args.rpc_port, "--utp" if args.utp else "--no-utp")
+        run_remote(args.rpc_port, {
+            "tolerated": "--encryption-tolerated",
+            "preferred": "--encryption-preferred",
+            "required": "--encryption-required",
+        }[args.encryption])
+        run_remote(args.rpc_port, "-a", args.torrent, "-w", args.data)
+        run_remote(args.rpc_port, "-t", "all", "--start")
+        wait_for_tcp("127.0.0.1", args.peer_port, timeout=30)
+        deadline = time.time() + 60
+        while time.time() < deadline:
+            info = run_remote(args.rpc_port, "-t", "all", "-i", check=False).stdout
+            if "Percent Done: 100%" in info or "Seeding" in info:
+                touch_ready()
+                print(f"transmission seeding on {args.peer_port}", flush=True)
+                break
+            time.sleep(1)
+        else:
+            raise TimeoutError("Transmission did not report a complete seed")
+
+        while not stop and proc.poll() is None:
+            time.sleep(1)
+        return proc.returncode or 0
+    finally:
+        if proc.poll() is None:
+            proc.terminate()
+            try:
+                proc.wait(timeout=10)
+            except subprocess.TimeoutExpired:
+                proc.kill()
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())