BUG/MAJOR: tcp: fix a possible busy spinning loop in content track-sc*
As a consequence of various recent changes on the sample conversion,
a corner case has emerged where it is possible to wait forever for a
sample in track-sc*.
The issue is caused by the fact that functions relying on sample_process()
don't all exactly work the same regarding the SMP_F_MAY_CHANGE flag and
the output result. Here it was possible to wait forever for an output
sample from stktable_fetch_key() without checking the SMP_OPT_FINAL flag.
As a result, if the client connects and closes without sending the data
and haproxy expects a sample which is capable of coming, it will ignore
this impossible case and will continue to wait.
This change adds control for SMP_OPT_FINAL before waiting for extra data.
The various relevant functions have been better documented regarding their
output values.
This fix must be backported to 1.5 since it appeared there.
diff --git a/src/proto_tcp.c b/src/proto_tcp.c
index 9778856..72dc92b 100644
--- a/src/proto_tcp.c
+++ b/src/proto_tcp.c
@@ -1048,8 +1048,8 @@
t = rule->act_prm.trk_ctr.table.t;
key = stktable_fetch_key(t, s->be, s, &s->txn, SMP_OPT_DIR_REQ | partial, rule->act_prm.trk_ctr.expr, &smp);
- if (smp.flags & SMP_F_MAY_CHANGE)
- goto missing_data;
+ if ((smp.flags & SMP_F_MAY_CHANGE) && !(partial & SMP_OPT_FINAL))
+ goto missing_data; /* key might appear later */
if (key && (ts = stktable_get_entry(t, key))) {
session_track_stkctr(&s->stkctr[tcp_trk_idx(rule->action)], t, ts);
diff --git a/src/sample.c b/src/sample.c
index 99acb5a..3343739 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -930,6 +930,18 @@
* Note: the fetch functions are required to properly set the return type. The
* conversion functions must do so too. However the cast functions do not need
* to since they're made to cast mutiple types according to what is required.
+ *
+ * The caller may indicate in <opt> if it considers the result final or not.
+ * The caller needs to check the SMP_F_MAY_CHANGE flag in p->flags to verify
+ * if the result is stable or not, according to the following table :
+ *
+ * return MAY_CHANGE FINAL Meaning for the sample
+ * NULL 0 * Not present and will never be (eg: header)
+ * NULL 1 0 Not present yet, could change (eg: POST param)
+ * NULL 1 1 Not present yet, will not change anymore
+ * smp 0 * Present and will not change (eg: header)
+ * smp 1 0 Present, may change (eg: request length)
+ * smp 1 1 Present, last known value (eg: request length)
*/
struct sample *sample_process(struct proxy *px, struct session *l4, void *l7,
unsigned int opt,
@@ -1187,7 +1199,16 @@
* and <opt> does not contain SMP_OPT_FINAL, then the sample is returned as-is
* with its SMP_F_MAY_CHANGE flag so that the caller can check it and decide to
* take actions (eg: wait longer). If a sample could not be found or could not
- * be converted, NULL is returned.
+ * be converted, NULL is returned. The caller MUST NOT use the sample if the
+ * SMP_F_MAY_CHANGE flag is present, as it is used only as a hint that there is
+ * still hope to get it after waiting longer, and is not converted to string.
+ * The possible output combinations are the following :
+ *
+ * return MAY_CHANGE FINAL Meaning for the sample
+ * NULL * * Not present and will never be (eg: header)
+ * smp 0 * Final value converted (eg: header)
+ * smp 1 0 Not present yet, may appear later (eg: header)
+ * smp 1 1 never happens (either flag is cleared on output)
*/
struct sample *sample_fetch_string(struct proxy *px, struct session *l4, void *l7,
unsigned int opt, struct sample_expr *expr)
diff --git a/src/stick_table.c b/src/stick_table.c
index 1226591..32fd60a 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -669,7 +669,16 @@
* no key could be extracted, or a pointer to the converted result stored in
* static_table_key in format <table_type>. If <smp> is not NULL, it will be reset
* and its flags will be initialized so that the caller gets a copy of the input
- * sample, and knows why it was not accepted (eg: SMP_F_MAY_CHANGE is present).
+ * sample, and knows why it was not accepted (eg: SMP_F_MAY_CHANGE is present
+ * without SMP_OPT_FINAL). The output will be usable like this :
+ *
+ * return MAY_CHANGE FINAL Meaning for the sample
+ * NULL 0 * Not present and will never be (eg: header)
+ * NULL 1 0 Not present or unstable, could change (eg: req_len)
+ * NULL 1 1 Not present, will not change anymore
+ * smp 0 * Present and will not change (eg: header)
+ * smp 1 0 not possible
+ * smp 1 1 Present, last known value (eg: request length)
*/
struct stktable_key *stktable_fetch_key(struct stktable *t, struct proxy *px, struct session *l4, void *l7,
unsigned int opt, struct sample_expr *expr, struct sample *smp)