MINOR: vars: add a "set-var-fmt" directive to the global section

Just like the set-var-fmt action for tcp/http rules, the set-var-fmt
directive in global sections allows to pre-set process-wide variables
using a format string instead of a sample expression. This is often
more convenient when it is required to concatenate multiple fields,
or when emitting just one word.

doc/configuration.txt

@@ -1750,7 +1750,7 @@ set-var <var-name> <expr>
   'set-var' action in TCP or HTTP rules except that the expression is evaluated
   at configuration parsing time and that the variable is instantly set. The
   sample fetch functions and converters permitted in the expression are only
-  those using internal data, typically 'int(value)' or 'str(value)'. It's is
+  those using internal data, typically 'int(value)' or 'str(value)'. It is
   possible to reference previously allocated variables as well. These variables
   will then be readable (and modifiable) from the regular rule sets.
 
@@ -1760,6 +1760,23 @@ set-var <var-name> <expr>
           set-var proc.prio int(100)
           set-var proc.threshold int(200),sub(proc.prio)
 
+set-var-fmt <var-name> <fmt>
+  Sets the process-wide variable '<var-name>' to the string resulting from the
+  evaluation of the log-format <fmt>. The variable '<var-name>' may only be a
+  process-wide variable (using the 'proc.' prefix). It works exactly like the
+  'set-var-fmt' action in TCP or HTTP rules except that the expression is
+  evaluated at configuration parsing time and that the variable is instantly
+  set. The sample fetch functions and converters permitted in the expression
+  are only those using internal data, typically 'int(value)' or 'str(value)'.
+  It is possible to reference previously allocated variables as well. These
+  variables will then be readable (and modifiable) from the regular rule sets.
+  Please see section 8.2.4 for details on the log-format syntax.
+
+  Example:
+      global
+          set-var-fmt proc.current_state "primary"
+          set-var-fmt proc.bootid        "%pid|%t"
+
 setenv <name> <value>
   Sets environment variable <name> to value <value>. If the variable exists, it
   is overwritten. The changes immediately take effect so that the next line in

reg-tests/sample_fetches/vars.vtc

@@ -10,7 +10,7 @@ haproxy h1 -conf {
         set-var proc.str1  str("this is")
         set-var proc.str2  str("a string")
         set-var proc.str   var(proc.str1)
-        set-var proc.str   str(""),concat("",proc.str," a string")
+        set-var-fmt proc.str "%[var(proc.str)] a string"
         set-var proc.uuid  uuid()
 
     defaults

src/vars.c

@@ -12,6 +12,7 @@
 #include <haproxy/list.h>
 #include <haproxy/log.h>
 #include <haproxy/sample.h>
+#include <haproxy/session.h>
 #include <haproxy/stream-t.h>
 #include <haproxy/tcp_rules.h>
 #include <haproxy/tcpcheck.h>
@@ -894,6 +895,7 @@ static enum act_parse_ret parse_store(const char **args, int *arg, struct proxy
  * expression that are parsed, processed, and released on the fly so that we
  * respect the real set-var syntax. These directives take the following format:
  *    set-var <name> <expression>
+ *    set-var-fmt <name> <fmt>
  * Note that parse_store() expects "set-var(name) <expression>" so we have to
  * temporarily replace the keyword here.
  */
@@ -910,21 +912,29 @@ static int vars_parse_global_set_var(char **args, int section_type, struct proxy
 		.arg.vars.scope = SCOPE_PROC,
 		.from = ACT_F_CFG_PARSER,
 	};
+	enum obj_type objt = OBJ_TYPE_NONE;
+	struct session *sess = NULL;
 	enum act_parse_ret p_ret;
 	char *old_arg1;
 	char *tmp_arg1;
 	int arg = 2; // variable name
 	int ret = -1;
+	int use_fmt = 0;
 
 	LIST_INIT(&px.conf.args.list);
 
+	use_fmt = strcmp(args[0], "set-var-fmt") == 0;
+
 	if (!*args[1] || !*args[2]) {
-		memprintf(err, "'%s' requires a process-wide variable name ('proc.<name>') and a sample expression.", args[0]);
+		if (use_fmt)
+			memprintf(err, "'%s' requires a process-wide variable name ('proc.<name>') and a format string.", args[0]);
+		else
+			memprintf(err, "'%s' requires a process-wide variable name ('proc.<name>') and a sample expression.", args[0]);
 		goto end;
 	}
 
 	tmp_arg1 = NULL;
-	if (!memprintf(&tmp_arg1, "set-var(%s)", args[1]))
+	if (!memprintf(&tmp_arg1, "set-var%s(%s)", use_fmt ? "-fmt" : "", args[1]))
 		goto end;
 
 	/* parse_store() will always return a message in <err> on error */
@@ -946,8 +956,16 @@ static int vars_parse_global_set_var(char **args, int section_type, struct proxy
 		goto end;
 	}
 
-	action_store(&rule, &px, NULL, NULL, 0);
+	if (use_fmt && !(sess = session_new(&px, NULL, &objt))) {
+		release_sample_expr(rule.arg.vars.expr);
+		memprintf(err, "'%s': out of memory when trying to set variable '%s' in the global section.", args[0], args[1]);
+		goto end;
+	}
+
+	action_store(&rule, &px, sess, NULL, 0);
 	release_sample_expr(rule.arg.vars.expr);
+	if (sess)
+		session_free(sess);
 
 	ret = 0;
  end:
@@ -1205,6 +1223,7 @@ INITCALL1(STG_REGISTER, http_after_res_keywords_register, &http_after_res_kws);
 
 static struct cfg_kw_list cfg_kws = {{ },{
 	{ CFG_GLOBAL, "set-var",              vars_parse_global_set_var },
+	{ CFG_GLOBAL, "set-var-fmt",          vars_parse_global_set_var },
 	{ CFG_GLOBAL, "tune.vars.global-max-size", vars_max_size_global },
 	{ CFG_GLOBAL, "tune.vars.proc-max-size",   vars_max_size_proc   },
 	{ CFG_GLOBAL, "tune.vars.sess-max-size",   vars_max_size_sess   },