MINOR: sample: add a rand() sample fetch to return a sample.

Sometimes it can be useful to generate a random value, at least
for debugging purposes, but also to take routing decisions or to
pass such a value to a backend server.

doc/configuration.txt

@@ -9570,6 +9570,13 @@ queue([<backend>]) : integer
   possible action could be to reject new users but still accept old ones. See
   also the "avg_queue", "be_conn", and "be_sess_rate" fetches.
 
+rand([<range>]) : integer
+  Returns a random integer value within a range of <range> possible values,
+  starting at zero. If the range is not specified, it defaults to 2^32, which
+  gives numbers between 0 and 4294967295. It can be useful to pass some values
+  needed to take some routing decisions for example, or just for debugging
+  purposes. This random must not be used for security purposes.
+
 srv_conn([<backend>/]<server>) : integer
   Returns an integer value corresponding to the number of currently established
   connections on the designated server, possibly including the connection being

src/haproxy.c

@@ -523,6 +523,8 @@ void init(int argc, char **argv)
 	tv_update_date(-1,-1);
 	start_date = now;
 
+	srandom(now_ms - getpid());
+
 	/* Get the numeric timezone. */
 	get_localtime(start_date.tv_sec, &curtime);
 	strftime(localtimezone, 6, "%z", &curtime);

src/sample.c

@@ -1189,6 +1189,24 @@ smp_fetch_date(struct proxy *px, struct session *s, void *l7, unsigned int opt,
 	return 1;
 }
 
+/* generate a random 32-bit integer for whatever purpose, with an optional
+ * range specified in argument.
+ */
+static int
+smp_fetch_rand(struct proxy *px, struct session *s, void *l7, unsigned int opt,
+               const struct arg *args, struct sample *smp, const char *kw)
+{
+	smp->data.uint = random();
+
+	/* reduce if needed. Don't do a modulo, use all bits! */
+	if (args && args[0].type == ARGT_UINT)
+		smp->data.uint = ((uint64_t)smp->data.uint * args[0].data.uint) >> 32;
+
+	smp->type = SMP_T_UINT;
+	smp->flags |= SMP_F_VOL_TEST | SMP_F_MAY_CHANGE;
+	return 1;
+}
+
 /* Note: must not be declared <const> as its list will be overwritten.
  * Note: fetches that may return multiple types must be declared as the lowest
  * common denominator, the type that can be casted into all other ones. For
@@ -1199,6 +1217,7 @@ static struct sample_fetch_kw_list smp_kws = {ILH, {
 	{ "always_true",  smp_fetch_true,  0,            NULL, SMP_T_BOOL, SMP_USE_INTRN },
 	{ "env",          smp_fetch_env,   ARG1(1,STR),  NULL, SMP_T_CSTR, SMP_USE_INTRN },
 	{ "date",         smp_fetch_date,  ARG1(0,SINT), NULL, SMP_T_UINT, SMP_USE_INTRN },
+	{ "rand",         smp_fetch_rand,  ARG1(0,UINT), NULL, SMP_T_UINT, SMP_USE_INTRN },
 	{ /* END */ },
 }};