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Devtools: send error replies instead of ignoring messages (#37686)

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Client messages, which are always requests, are dispatched to Actor
instances one at a time via Actor::handle_message. Each request must be
paired with exactly one reply from the same actor the request was sent
to, where a reply is a message with no type (if a message from the
server has a type, it’s a notification, not a reply).

Failing to reply to a request will almost always permanently break that
actor, because either the client gets stuck waiting for a reply, or the
client receives the reply for a subsequent request as if it was the
reply for the current request. If an actor fails to reply to a request,
we want the dispatcher (ActorRegistry::handle_message) to send an error
of type `unrecognizedPacketType`, to keep the conversation for that
actor in sync. Since replies come in all shapes and sizes, we want to
allow Actor types to send replies without having to return them to the
dispatcher.

This patch adds a wrapper type around a client stream that guarantees
request/reply invariants. It allows the dispatcher to check if a valid
reply was sent, and guarantees that if the actor tries to send a reply,
it’s actually a valid reply (see ClientRequest::is_valid_reply). It does
not currently guarantee anything about messages sent via the TcpStream
released via ClientRequest::try_clone_stream or the return value of
ClientRequest::reply. We also send `unrecognizedPacketType`,
`missingParameter`, `badParameterType`, and `noSuchActor` messages per
the
[protocol](https://firefox-source-docs.mozilla.org/devtools/backend/protocol.html#error-packets)
[docs](https://firefox-source-docs.mozilla.org/devtools/backend/protocol.html#packets).

Testing: automated tests all pass, and manual testing looks ok
Fixes: #37683 and at least six bugs, plus one with a different root
cause, plus three with zero impact

---------

Signed-off-by: atbrakhi <atbrakhi@igalia.com>
Signed-off-by: Delan Azabani <dazabani@igalia.com>
Co-authored-by: delan azabani <dazabani@igalia.com>
Co-authored-by: Simon Wülker <simon.wuelker@arcor.de>
Co-authored-by: the6p4c <me@doggirl.gay>
This commit is contained in:
atbrakhi 2025-07-07 14:40:44 +02:00 • committed by GitHub
parent fcb2a4cd95
commit 71d97bd935
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36 changed files with 661 additions and 637 deletions
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6
components/devtools/lib.rs
View file

@ -28,7 +28,7 @@ use devtools_traits::{
};
use embedder_traits::{AllowOrDeny, EmbedderMsg, EmbedderProxy};
use ipc_channel::ipc::{self, IpcSender};
use log::trace;
use log::{trace, warn};
use resource::{ResourceArrayType, ResourceAvailable};
use serde::Serialize;
use servo_rand::RngCore;
@ -646,8 +646,8 @@ fn allow_devtools_client(stream: &mut TcpStream, embedder: &EmbedderProxy, token
fn handle_client(actors: Arc<Mutex<ActorRegistry>>, mut stream: TcpStream, stream_id: StreamId) {
log::info!("Connection established to {}", stream.peer_addr().unwrap());
let msg = actors.lock().unwrap().find::<RootActor>("root").encodable();
if let Err(e) = stream.write_json_packet(&msg) {
log::warn!("Error writing response: {:?}", e);
if let Err(error) = stream.write_json_packet(&msg) {
warn!("Failed to send initial packet from root actor: {error:?}");
return;
}