From 2b467d0b61ff094a305c2c92f0cec6ca04b5d16d Mon Sep 17 00:00:00 2001
From: Patrick Cloke <clokep@users.noreply.github.com>
Date: Mon, 18 Jan 2021 10:21:42 -0500
Subject: [PATCH] Properly raise an exception when the body exceeds the max
 size. (#9145)

...instead of just creating the exception object and doing nothing with it.
---
 changelog.d/9145.bugfix                | 1 +
 synapse/http/client.py                 | 2 +-
 synapse/http/matrixfederationclient.py | 2 +-
 3 files changed, 3 insertions(+), 2 deletions(-)
 create mode 100644 changelog.d/9145.bugfix

diff --git a/changelog.d/9145.bugfix b/changelog.d/9145.bugfix
new file mode 100644
index 0000000000..947cf1dc25
--- /dev/null
+++ b/changelog.d/9145.bugfix
@@ -0,0 +1 @@
+Fix "UnboundLocalError: local variable 'length' referenced before assignment" errors when the response body exceeds the expected size. This bug was introduced in v1.25.0.
diff --git a/synapse/http/client.py b/synapse/http/client.py
index df498c8645..37ccf5ab98 100644
--- a/synapse/http/client.py
+++ b/synapse/http/client.py
@@ -724,7 +724,7 @@ class SimpleHttpClient:
                 read_body_with_max_size(response, output_stream, max_size)
             )
         except BodyExceededMaxSize:
-            SynapseError(
+            raise SynapseError(
                 502,
                 "Requested file is too large > %r bytes" % (max_size,),
                 Codes.TOO_LARGE,
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index b7103d6541..19293bf673 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -996,7 +996,7 @@ class MatrixFederationHttpClient:
             logger.warning(
                 "{%s} [%s] %s", request.txn_id, request.destination, msg,
             )
-            SynapseError(502, msg, Codes.TOO_LARGE)
+            raise SynapseError(502, msg, Codes.TOO_LARGE)
         except Exception as e:
             logger.warning(
                 "{%s} [%s] Error reading response: %s",
-- 
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