Findings from porting a real client to IDA Code Mode

Notes for the ida-codemode maintainers, gathered while porting ida-tui (a Textual TUI frontend for IDA) from a private idalib worker to ida_codemode.client.DatabaseHandle.

Everything below is measured, not inferred. Where we worked around something, the workaround is named so you can judge whether the library should make it unnecessary.

Environment: ida-codemode 0.3.1, IDA 9.4 (idalib), Linux, single managed worker backend, quiet box. Target for timings: targets/echo unless stated.

What the client does, for scale: it renders a continuous disassembly listing, pseudocode, a CFG graph view and a hex view, paging over the database as the user scrolls. It is latency-sensitive in a way an agent-driven MCP client is not — a keypress must repaint. It issues ~1–8 operations per user action.

1. timeout_trace enables line tracing in every frame — 52x on IDA calls

Highest-impact item by a wide margin.

runtime.py wraps every execute_python in sys.settrace(timeout_trace) to enforce the deadline. timeout_trace ends with return timeout_trace, and returning a trace function from a 'call' event asks CPython to trace every line of that frame. So every line of every function the snippet touches pays a Python-level callback, and the specialising interpreter is disabled throughout.

Measured inside the worker, same process, same database:

Untraced matches a plain idalib process, so the trace hook accounts for essentially all of it. For us this was the single largest cost in the port — larger than HTTP, serialisation and IDA itself combined.

Reproduce inside any execute_python:

import sys, time, ida_bytes
def bench():
    t = time.perf_counter()
    for _ in range(20000): ida_bytes.get_flags(0x1000)
    return (time.perf_counter() - t) / 20000 * 1e6
traced = bench()
old = sys.gettrace(); sys.settrace(None)
try:    untraced = bench()
finally: sys.settrace(old)
result = {"traced_us": traced, "untraced_us": untraced}

Suggested fixes, cheapest first

1. return None from timeout_trace instead of itself. You keep 'call'-event deadline checks — which is enough to interrupt anything that calls a function — and drop per-line tracing entirely.
2. On 3.12+, use sys.monitoring with only the events you need; it is designed for exactly this and is far cheaper than settrace.
3. Or drop the trace and rely on the threading.Timer → ida_kernwin.set_cancelled() path you already have, accepting that a pure-Python loop with no calls in it cannot be interrupted.

Our workaround (we would rather not ship it): the snippet detaches the trace and restores it in a finally. That gives up deadline enforcement for pure-Python loops inside our own code; your native cancel timer is unaffected and still fires. Every client that does real work per call will eventually find this and do the same, which is an argument for fixing it in the runtime.

2. to_jsonable dominates any large result

execute_python runs to_jsonable() over whatever the snippet returns. Our answers are already JSON-safe and they are big — a 200-row listing page is roughly 10k small objects.

That is 114x, and it was 72% of the page's total cost before we changed it.

Suggested fixes

• Fast-path values that are already JSON-safe (a cheap recursive type check that bails to the original object beats rebuilding it), or
• let a snippet opt out by returning an already-serialised payload — a documented envelope such as {"__json__": "<...>"}, or simply passing str/bytes through untouched.

Our workaround: snippets json.dumps inside the database process and return one string, which the client parses. to_jsonable then walks a single scalar. Cost went 66.2 ms → ~0.6 ms. It works, but every client with a large result set has to discover and re-implement it.

3. The per-operation floor is execute_sync, not HTTP

Same worker, same connection, 200 iterations:

HTTP framing is ~7% of the floor; marshalling the operation onto IDA's main thread is the other ~93%. The worker runs IDA's own kernwin.serve(), so this is plausibly IDA's dispatch latency rather than anything you control — but it is worth documenting, because it sets a hard 2 ms per-operation budget that shapes how a client must be designed.

It did not hurt us (our call volume is 1–8 per user action; 4 calls to build a 1060-block graph), but a client that makes one call per row or per symbol will be 20–100x slower than an in-process one and the authors will not know why.

Suggested fixes: document the floor; and consider a batch endpoint — accept [{op, args}, ...] and dispatch them within a single execute_sync — which would let chatty clients amortise it without redesigning around it.

4. Loader switches on an existing database are a FATAL, not an error

Opening a target that already has an .i64, while passing spawn-only options, kills the worker:

FATAL ERROR: @0:636[]
Switch '-b400' can be used only when loading a new file

The client sees only:

IDAConnectionError: idalib worker launcher <pid> exited with status 1

This is easy to hit and hard to diagnose: it is the natural second run of anything that opens a raw blob (processor=/image_base=/file_type= are recorded in the database the first run produced). Our test suite hit it as a crash five minutes into a run.

Suggested fixes

• In DatabaseHandle.open(), when the resolved IDB already exists and new_database is not set, either ignore the spawn-only options or raise a typed error naming them — before handing them to IDA.
• Propagate the worker's fatal text into the client exception. The message already exists on the worker's stderr; losing it turns a one-line fix into a bisect.

Our workaround: the client checks whether the expected IDB exists and drops processor/image_base/file_type when it does.

5. Deleting or replacing an IDB under a live lease fails silently

A suite that did "delete the .i64, reopen the same path" (safe when it owned a private worker) now races the previous worker's lease grace. The reopen produced a handle that never became usable, with no error — just a database with no listing, and every wait timing out.

Suggested fixes

• Detect that the IDB backing a registered instance has been removed or replaced and fail loudly (the registry already holds idb_key).
• Expose a public "wait until this database is released" primitive. We needed one and ended up reaching into registry.REGISTRY_DIR and FileLock to build it, which is not an API we should be depending on.
• Document the lease-grace window as part of the lifecycle contract.

6. No close-without-save, and no rollback

A managed worker saves when its final lease closes. A GUI handle leaves GUI state as-is. Neither gives a client a way to say "discard what I did".

ida-tui had a "discard & quit" that we could not port; it is now "leave as-is & quit", and we cannot honestly promise the user their edits are not persisted.

Suggested fixes: a close policy on a lease the client created (close(save=False)), or a transaction/rollback API, or a documented disposable-copy pattern that clients can follow.

7. No change notification for shared databases

The lease reports liveness, not mutations. If a GUI user or another Code Mode client renames or retypes while we are attached, our materialised caches (name generation, decompilation, listing pages) are silently stale. Our own edits invalidate correctly; someone else's cannot.

Suggested fix — cheap and sufficient: a monotonic database revision counter, bumped on any mutating operation and exposed on /health (and ideally on the lease event stream). Clients can then invalidate by comparing one integer. A full change feed would be better but is much more work; the counter alone would make shared editing safe for every caching client.

8. Package exports and API surface stability

ida_codemode/__init__.py exports nothing, so a library consumer must import from submodules:

from ida_codemode.client   import DatabaseHandle, ClientError, RemoteError, InstanceDisconnectedError
from ida_codemode.registry import REGISTRY_DIR, FileLock, RegistryEntry, canonical_path, idb_key, scan_instances
from ida_codemode.resolver import IdbBusy, expected_idb_path

Some of those are clearly internals (FileLock, REGISTRY_DIR) that we only touch because no public equivalent exists (see §5).

Suggested fix: export DatabaseHandle and the public exception types from the package root, and mark the intended-public registry helpers explicitly. It also makes "what is API and what is internal" answerable, which right now it is not.

9. A testing note: DatabaseHandle.open()'s 30 keyword-only options

The port we started from called open(..., loading_address=...). The real parameter is image_base. Every connect() would have raised TypeError on the first call, and its contract tests passed anyway, because a hand-written fake handle accepts **kwargs.

Not a library bug — but with 30 keyword-only options it is a very easy mistake, and it is invisible to exactly the offline tests people write.

Suggested fix: ship py.typed and/or a Protocol for the handle, so a fake can be checked against the real signature and a typo is caught statically. (We added a test asserting our kwargs are a subset of inspect.signature(DatabaseHandle.open).parameters, which is a poor substitute.)

Priority, from a client author's view

Items 1 and 2 together were the difference between "the port is 35x slower than the private worker it replaced" and "the port is within 2x, and faster on several operations". Both are in the runtime, not in client code — which is why they are worth fixing centrally rather than leaving each client to rediscover.

Happy to supply the benchmark harness (it is backend-agnostic and runs against both our old worker and Code Mode), or to test a patch.