From 4ffb5c69bdf5a8437b689cee010d02d08c988cbe Mon Sep 17 00:00:00 2001
From: Brendan Abolivier <babolivier@matrix.org>
Date: Wed, 3 Jun 2020 15:24:20 +0200
Subject: [PATCH 1/3] Check if the localpart is reserved for guests earlier in
 the registration flow

---
 changelog.d/7625.misc        |  1 +
 synapse/handlers/register.py | 18 +++++++++---------
 2 files changed, 10 insertions(+), 9 deletions(-)
 create mode 100644 changelog.d/7625.misc

diff --git a/changelog.d/7625.misc b/changelog.d/7625.misc
new file mode 100644
index 000000000000..6a8fc7eeb318
--- /dev/null
+++ b/changelog.d/7625.misc
@@ -0,0 +1 @@
+Check if the localpart is reserved for guests users earlier in the registration flow, as well as when responding to requests on `/register/available`.
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index a6178e74a19b..d2c1712f00b0 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -128,6 +128,15 @@ def check_username(self, localpart, guest_access_token=None, assigned_user_id=No
                     errcode=Codes.FORBIDDEN,
                 )
 
+        if guest_access_token is not None:
+            try:
+                int(localpart)
+                raise SynapseError(
+                    400, "Numeric user IDs are reserved for guest users."
+                )
+            except ValueError:
+                pass
+
     @defer.inlineCallbacks
     def register_user(
         self,
@@ -170,15 +179,6 @@ def register_user(
 
             was_guest = guest_access_token is not None
 
-            if not was_guest:
-                try:
-                    int(localpart)
-                    raise SynapseError(
-                        400, "Numeric user IDs are reserved for guest users."
-                    )
-                except ValueError:
-                    pass
-
             user = UserID(localpart, self.hs.hostname)
             user_id = user.to_string()
 

From 5922eb0978cda542146236e6bbd74a057d456c48 Mon Sep 17 00:00:00 2001
From: Brendan Abolivier <babolivier@matrix.org>
Date: Wed, 3 Jun 2020 16:13:40 +0200
Subject: [PATCH 2/3] Update synapse/handlers/register.py

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
---
 synapse/handlers/register.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index d2c1712f00b0..55a03e53ead4 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -128,7 +128,7 @@ def check_username(self, localpart, guest_access_token=None, assigned_user_id=No
                     errcode=Codes.FORBIDDEN,
                 )
 
-        if guest_access_token is not None:
+        if guest_access_token is None:
             try:
                 int(localpart)
                 raise SynapseError(

From 69dc75266f15e134f39b24f873a322f6f6e9cb7a Mon Sep 17 00:00:00 2001
From: Brendan Abolivier <babolivier@matrix.org>
Date: Wed, 3 Jun 2020 16:21:50 +0200
Subject: [PATCH 3/3] Update changelog.d/7625.misc

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
---
 changelog.d/7625.misc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/changelog.d/7625.misc b/changelog.d/7625.misc
index 6a8fc7eeb318..4c61d8d99f15 100644
--- a/changelog.d/7625.misc
+++ b/changelog.d/7625.misc
@@ -1 +1 @@
-Check if the localpart is reserved for guests users earlier in the registration flow, as well as when responding to requests on `/register/available`.
+Check if the localpart of a Matrix ID is reserved for guest users earlier in the registration flow, as well as when responding to requests to `/register/available`.