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Clarify code that chooses a thread ID to include in a receipt (#3797)
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* Extract threadIdForReceipt function from sendReceipt

* Tests for threadIdForReceipt

* Correct test of threadIdForReceipt to expect main for redaction of threaded

* Expand and comment implementation of threadIdForReceipt
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@andybalaam
andybalaam authored Oct 16, 2023
1 parent 5d233f3 commit 5595e84
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198 changes: 197 additions & 1 deletion spec/unit/read-receipt.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ import MockHttpBackend from "matrix-mock-request";

import { MAIN_ROOM_TIMELINE, ReceiptType, WrappedReceipt } from "../../src/@types/read_receipts";
import { MatrixClient } from "../../src/client";
import { EventType, MatrixEvent, Room } from "../../src/matrix";
import { EventType, MatrixEvent, RelationType, Room, threadIdForReceipt } from "../../src/matrix";
import { synthesizeReceipt } from "../../src/models/read-receipt";
import { encodeUri } from "../../src/utils";
import * as utils from "../test-utils/test-utils";
Expand Down Expand Up @@ -258,4 +258,200 @@ describe("Read receipt", () => {
expect(room.getEventReadUpTo(userId)).toBe(mainTimelineReceipt.eventId);
});
});

describe("Determining the right thread ID for a receipt", () => {
it("provides the thread root ID for a normal threaded message", () => {
const event = utils.mkEvent({
event: true,
type: EventType.RoomMessage,
user: "@bob:matrix.org",
room: "!roomx",
content: {
"body": "Hello from a thread",
"m.relates_to": {
"event_id": "$thread1",
"m.in_reply_to": {
event_id: "$thread1",
},
"rel_type": "m.thread",
},
},
});

expect(threadIdForReceipt(event)).toEqual("$thread1");
});

it("provides 'main' for a non-thread message", () => {
const event = utils.mkEvent({
event: true,
type: EventType.RoomMessage,
user: "@bob:matrix.org",
room: "!roomx",
content: { body: "Hello" },
});

expect(threadIdForReceipt(event)).toEqual("main");
});

it("provides 'main' for a thread root", () => {
const event = utils.mkEvent({
event: true,
type: EventType.RoomMessage,
user: "@bob:matrix.org",
room: "!roomx",
content: { body: "Hello" },
});
// Set thread ID to this event's ID, meaning this is the thread root
event.setThreadId(event.getId());

expect(threadIdForReceipt(event)).toEqual("main");
});

it("provides 'main' for a reaction to a thread root", () => {
const event = utils.mkEvent({
event: true,
type: EventType.Reaction,
user: "@bob:matrix.org",
room: "!roomx",
content: {
"m.relates_to": {
rel_type: RelationType.Annotation,
event_id: "$thread1",
key: Math.random().toString(),
},
},
});

// Set thread Id, meaning this looks like it's in the thread (this
// happens for relations like this, so that they appear in the
// thread's timeline).
event.setThreadId("$thread1");

// But because it's a reaction to the thread root, it's in main
expect(threadIdForReceipt(event)).toEqual("main");
});

it("provides the thread ID for a reaction to a threaded message", () => {
const event = utils.mkEvent({
event: true,
type: EventType.Reaction,
user: "@bob:matrix.org",
room: "!roomx",
content: {
"m.relates_to": {
rel_type: RelationType.Annotation,
event_id: "$withinthread2",
key: Math.random().toString(),
},
},
});

// Set thread Id, to say this message is in the thread. This happens
// when the message arrived and is classified.
event.setThreadId("$thread1");

// It's in the thread because it refers to something else, not the
// thread root
expect(threadIdForReceipt(event)).toEqual("$thread1");
});

it("(suprisingly?) provides 'main' for a redaction of a threaded message", () => {
const event = utils.mkEvent({
event: true,
type: EventType.RoomRedaction,
content: {
reason: "Spamming",
},
redacts: "$withinthread2",
room: "!roomx",
user: "@bob:matrix.org",
});

// Set thread Id, to say this message is in the thread.
event.setThreadId("$thread1");

// Because redacting a message removes all its m.relations, the
// message is no longer in the thread, so we must send a receipt for
// it in the main timeline.
//
// This is surprising, but it follows the spec (at least up to
// current latest room version, 11). In fact, the event should no
// longer have a thread ID set on it, so this testcase should not
// come up. (At time of writing, this is not the case though - it
// does still have threadId set.)
expect(threadIdForReceipt(event)).toEqual("main");
});

it("provides the thread ID for an edit of a threaded message", () => {
const event = utils.mkEvent({
event: true,
type: EventType.RoomRedaction,
content: {
"body": "Edited!",
"m.new_content": {
body: "Edited!",
},
"m.relates_to": {
rel_type: RelationType.Replace,
event_id: "$withinthread2",
},
},
room: "!roomx",
user: "@bob:matrix.org",
});

// Set thread Id, to say this message is in the thread.
event.setThreadId("$thread1");

// It's in the thread, because it redacts something inside the
// thread (not the thread root)
expect(threadIdForReceipt(event)).toEqual("$thread1");
});

it("provides 'main' for an edit of a thread root", () => {
const event = utils.mkEvent({
event: true,
type: EventType.RoomRedaction,
content: {
"body": "Edited!",
"m.new_content": {
body: "Edited!",
},
"m.relates_to": {
rel_type: RelationType.Replace,
event_id: "$thread1",
},
},
room: "!roomx",
user: "@bob:matrix.org",
});

// Set thread Id, to say this message is in the thread.
event.setThreadId("$thread1");

// It's in the thread, because it redacts something inside the
// thread (not the thread root)
expect(threadIdForReceipt(event)).toEqual("main");
});

it("provides 'main' for a redaction of the thread root", () => {
const event = utils.mkEvent({
event: true,
type: EventType.RoomRedaction,
content: {
reason: "Spamming",
},
redacts: "$thread1",
room: "!roomx",
user: "@bob:matrix.org",
});

// Set thread Id, to say this message is in the thread.
event.setThreadId("$thread1");

// It's in the thread, because it redacts something inside the
// thread (not the thread root)
expect(threadIdForReceipt(event)).toEqual("main");
});
});
});
85 changes: 68 additions & 17 deletions src/client.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -5157,24 +5157,12 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
$eventId: event.getId()!,
});

if (!unthreaded && this.supportsThreads()) {
// XXX: the spec currently says a threaded read receipt can be sent for the root of a thread,
// but in practice this isn't possible and the spec needs updating.
const isThread =
!!event.threadRootId &&
// A thread cannot be just a thread root and a thread root can only be read in the main timeline
!event.isThreadRoot &&
// Similarly non-thread relations upon the thread root (reactions, edits) should also be for the main timeline.
event.isRelation() &&
(event.isRelation(THREAD_RELATION_TYPE.name) || event.relationEventId !== event.threadRootId);
body = {
...body,
// Only thread replies should define a specific thread. Thread roots can only be read in the main timeline.
thread_id: isThread ? event.threadRootId : MAIN_ROOM_TIMELINE,
};
}
// Unless we're explicitly making an unthreaded receipt or we don't
// support threads, include the `thread_id` property in the body.
const shouldAddThreadId = !unthreaded && this.supportsThreads();
const fullBody = shouldAddThreadId ? { ...body, thread_id: threadIdForReceipt(event) } : body;

const promise = this.http.authedRequest<{}>(Method.Post, path, undefined, body || {});
const promise = this.http.authedRequest<{}>(Method.Post, path, undefined, fullBody || {});

const room = this.getRoom(event.getRoomId());
if (room && this.credentials.userId) {
Expand Down Expand Up @@ -9925,3 +9913,66 @@ export function fixNotificationCountOnDecryption(cli: MatrixClient, event: Matri
}
}
}

/**
* Given an event, figure out the thread ID we should use for it in a receipt.
*
* This will either be "main", or event.threadRootId. For the thread root, or
* e.g. reactions to the thread root, this will be main. For events inside the
* thread, or e.g. reactions to them, this will be event.threadRootId.
*
* (Exported for test.)
*/
export function threadIdForReceipt(event: MatrixEvent): string {
return inMainTimelineForReceipt(event) ? MAIN_ROOM_TIMELINE : event.threadRootId!;
}

/**
* a) True for non-threaded messages, thread roots and non-thread relations to thread roots.
* b) False for messages with thread relations to the thread root.
* c) False for messages with any kind of relation to a message from case b.
*
* Note: true for redactions of messages that are in threads. Redacted messages
* are not really in threads (because their relations are gone), so if they look
* like they are in threads, that is a sign of a bug elsewhere. (At time of
* writing, this bug definitely exists - messages are not moved to another
* thread when they are redacted.)
*
* @returns true if this event is considered to be in the main timeline as far
* as receipts are concerned.
*/
function inMainTimelineForReceipt(event: MatrixEvent): boolean {
if (!event.threadRootId) {
// Not in a thread: then it is in the main timeline
return true;
}

if (event.isThreadRoot) {
// Thread roots are in the main timeline. Note: the spec is ambiguous (or
// wrong) on this - see
// https://github.com/matrix-org/matrix-spec-proposals/pull/4037
return true;
}

if (!event.isRelation()) {
// If it's not related to anything, it can't be related via a chain of
// relations to a thread root.
//
// Note: this is a bug, because how does it have a threadRootId if it is
// neither a thread root, nor related to one?
logger.warn(`Event is not a relation or a thread root, but still has a threadRootId! id=${event.getId()}`);
return true;
}

if (event.isRelation(THREAD_RELATION_TYPE.name)) {
// It's a message in a thread - definitely not in the main timeline.
return false;
}

const isRelatedToRoot = event.relationEventId === event.threadRootId;

// If it's related to the thread root (and we already know it's not a thread
// relation) then it's in the main timeline. If it's related to something
// else, then it's in the thread (because it has a thread ID).
return isRelatedToRoot;
}

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