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MINOR: session: document explicitely that session_add_conn() is safe

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A set of recent patches have simplified management of backend connection
attached to sessions. The API is now stricter to prevent any misuse.

One of this change is the addition of a BUG_ON() in session_add_conn(),
which ensures that a connection is not attached to a session if its
<owner> field points to another entry.

On older haproxy releases, this assertion could not be enforced due to
NTLM as a connection is turned as private during its transfer. When
using a true multiplexed protocol on the backend side, the connection
could be assigned in turn to several sessions. However, NTLM is now only
applied for HTTP/1.1 as it does not make sense if the connection is
already shared.

To better clarify this situation, extend the comment on BUG_ON() inside
session_add_conn().
This commit is contained in:
Amaury Denoyelle 2025-08-13 18:13:10 +02:00
parent b3ce464435
commit d0df41fd22
1 changed files with 9 additions and 1 deletions
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10
include/haproxy/session.h
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@ -187,7 +187,15 @@ static inline int session_add_conn(struct session *sess, struct connection *conn
/* Connection target is used to index it in the session. Only BE conns are expected in session list. */
BUG_ON(!conn->target || objt_listener(conn->target));
/* A connection cannot be attached already to another session. */
/* A connection cannot be attached already to another session.
*
* This is safe as BE connections are flagged as private immediately
* after being created during connect_server(). The only potential
* issue would be if a connection is turned private later on during its
* lifetime. Currently, this happens only on NTLM headers detection,
* however this case is only implemented with HTTP/1.1 which cannot
* multiplex several streams on the same connection.
*/
BUG_ON(conn->owner && conn->owner != sess);
/* Already attach to the session */