From ec64c3e88d14e9b1d14c093b91b82817c7ede424 Mon Sep 17 00:00:00 2001
From: Kegan Dougal <7190048+kegsay@users.noreply.github.com>
Date: Fri, 12 Sep 2025 09:54:20 +0100
Subject: [PATCH] Ensure we `/send` PDUs which pass canonical JSON checks
 (#18641)

### Pull Request Checklist

Fixes https://github.com/element-hq/synapse/issues/18554

Looks like this was missed when it was
[implemented](https://github.com/element-hq/synapse/commit/2277df2a1eb685f85040ef98fa21d41aa4cdd389).

<!-- Please read
https://element-hq.github.io/synapse/latest/development/contributing_guide.html
before submitting your pull request -->

* [x] Pull request is based on the develop branch
* [x] Pull request includes a [changelog
file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog).
The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
  - Use markdown where necessary, mostly for `code blocks`.
  - End with either a period (.) or an exclamation mark (!).
  - Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by
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* [x] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct (run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

---------

Co-authored-by: reivilibre <oliverw@element.io>
---
 changelog.d/18641.bugfix                         | 1 +
 synapse/federation/sender/transaction_manager.py | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)
 create mode 100644 changelog.d/18641.bugfix

diff --git a/changelog.d/18641.bugfix b/changelog.d/18641.bugfix
new file mode 100644
index 0000000000..8f2a2e3d8b
--- /dev/null
+++ b/changelog.d/18641.bugfix
@@ -0,0 +1 @@
+Ensure all PDUs sent via `/send` pass canonical JSON checks.
diff --git a/synapse/federation/sender/transaction_manager.py b/synapse/federation/sender/transaction_manager.py
index 63ed13c6fa..050982c499 100644
--- a/synapse/federation/sender/transaction_manager.py
+++ b/synapse/federation/sender/transaction_manager.py
@@ -26,7 +26,7 @@ from synapse.api.constants import EduTypes
 from synapse.api.errors import HttpResponseException
 from synapse.events import EventBase
 from synapse.federation.persistence import TransactionActions
-from synapse.federation.units import Edu, Transaction
+from synapse.federation.units import Edu, Transaction, serialize_and_filter_pdus
 from synapse.logging.opentracing import (
     extract_text_map,
     set_tag,
@@ -119,7 +119,7 @@ class TransactionManager:
                 transaction_id=txn_id,
                 origin=self.server_name,
                 destination=destination,
-                pdus=[p.get_pdu_json() for p in pdus],
+                pdus=serialize_and_filter_pdus(pdus),
                 edus=[edu.get_dict() for edu in edus],
             )