MINOR: haproxy: Add -cc argument

This patch adds the `-cc` (check condition) argument to evaluate conditions on
startup and return the result as the exit code.

As an example this can be used to easily check HAProxy's version in scripts:

    haproxy -cc 'version_atleast(2.4)'

This resolves GitHub issue #1246.

Co-authored-by: Tim Duesterhus <tim@bastelstu.be>

doc/configuration.txt

@@ -802,6 +802,9 @@ Comments may be placed on the same line if needed after a '#', they will be
 ignored. The directives are tokenized like other configuration directives, and
 as such it is possible to use environment variables in conditions.
 
+Conditions can also be evaluated on startup with the -cc parameter.
+See "3. Starting HAProxy" in the management doc.
+
 The conditions are currently limited to:
 
   - an empty string, always returns "false"

doc/management.txt

@@ -195,6 +195,10 @@ list of options is :
     to bind. The exit status is zero if everything is OK, or non-zero if an
     error is encountered. Presence of warnings will be reported if any.
 
+  -cc : evaluates a condition as used within a conditional block of the
+    configuration. The exit status is zero if the condition is true, 1 if the
+    condition is false or 2 if an error is encountered.
+
   -d : enable debug mode. This disables daemon mode, forces the process to stay
     in foreground and to show incoming and outgoing events. It must never be
     used in an init script.

include/haproxy/cfgparse.h

@@ -126,6 +126,7 @@ void free_email_alert(struct proxy *p);
 const char *cfg_find_best_match(const char *word, const struct list *list, int section, const char **extra);
 int warnifnotcap(struct proxy *proxy, int cap, const char *file, int line, const char *arg, const char *hint);
 int failifnotcap(struct proxy *proxy, int cap, const char *file, int line, const char *arg, const char *hint);
+int cfg_eval_condition(char **args, char **err, const char **errptr);
 
 /* simplified way to define a section parser */
 #define REGISTER_CONFIG_SECTION(name, parse, post)                            \

include/haproxy/global-t.h

@@ -38,6 +38,7 @@
 #define	MODE_MWORKER_WAIT	0x100    /* Master Worker wait mode */
 #define	MODE_ZERO_WARNING       0x200    /* warnings cause a failure */
 #define	MODE_DIAG	0x400   /* extra warnings */
+#define	MODE_CHECK_CONDITION	0x800    /* -cc mode */
 
 /* list of last checks to perform, depending on config options */
 #define LSTCHK_CAP_BIND	0x00000001	/* check that we can bind to any port */

reg-tests/startup/check_condition.vtc

@@ -0,0 +1,13 @@
+varnishtest "Tests the -cc argument"
+
+#REQUIRE_VERSION=2.5
+feature cmd "$HAPROXY_PROGRAM -cc 'version_atleast(2.5-dev0)'"
+
+shell {
+    $HAPROXY_PROGRAM -cc "version_atleast(2.4)"
+    ! $HAPROXY_PROGRAM -cc "version_atleast(1024)"
+
+    $HAPROXY_PROGRAM -cc "streq(foo,'foo')"
+    $HAPROXY_PROGRAM -cc "streq(\"foo bar\",'foo bar')"
+    ! $HAPROXY_PROGRAM -cc "streq(foo,bar)"
+} -run

src/cfgparse.c

@@ -1736,7 +1736,7 @@ static const struct cond_pred_kw *cfg_lookup_cond_pred(const char *str)
  * and only in this case), 0 if the condition is false, 1 if it's true. If
  * <errptr> is not NULL, it's set to the first invalid character on error.
  */
-static int cfg_eval_condition(char **args, char **err, const char **errptr)
+int cfg_eval_condition(char **args, char **err, const char **errptr)
 {
 	const struct cond_pred_kw *cond_pred = NULL;
 	const char *end_ptr;

src/haproxy.c

@@ -570,6 +570,7 @@ static void usage(char *name)
 #endif
 		"        -q quiet mode : don't display messages\n"
 		"        -c check mode : only check config files and exit\n"
+		"        -cc check condition : evaluate a condition and exit\n"
 		"        -n sets the maximum total # of connections (uses ulimit -n)\n"
 		"        -m limits the usable amount of memory (in MB)\n"
 		"        -N sets the default, per-proxy maximum # of connections (%d)\n"
@@ -1464,6 +1465,7 @@ static void init(int argc, char **argv)
 	struct proxy *px;
 	struct post_check_fct *pcf;
 	int ideal_maxconn;
+	char *check_condition = NULL;
 
 	global.mode = MODE_STARTING;
 	old_argv = copy_argv(argc, argv);
@@ -1619,6 +1621,12 @@ static void init(int argc, char **argv)
 				global.tune.options |= GTUNE_RESOLVE_DONTFAIL;
 			else if (*flag == 'd')
 				arg_mode |= MODE_DEBUG;
+			else if (*flag == 'c' && flag[1] == 'c') {
+				arg_mode |= MODE_CHECK_CONDITION;
+				argv++;
+				argc--;
+				check_condition = *argv;
+			}
 			else if (*flag == 'c')
 				arg_mode |= MODE_CHECK;
 			else if (*flag == 'D')
@@ -1752,7 +1760,7 @@ static void init(int argc, char **argv)
 
 	global.mode |= (arg_mode & (MODE_DAEMON | MODE_MWORKER | MODE_FOREGROUND | MODE_VERBOSE
 				    | MODE_QUIET | MODE_CHECK | MODE_DEBUG | MODE_ZERO_WARNING
-				    | MODE_DIAG));
+				    | MODE_DIAG | MODE_CHECK_CONDITION));
 
 	if (getenv("HAPROXY_MWORKER_WAIT_ONLY")) {
 		unsetenv("HAPROXY_MWORKER_WAIT_ONLY");
@@ -1787,6 +1795,58 @@ static void init(int argc, char **argv)
 
 	usermsgs_clr("config");
 
+	if (global.mode & MODE_CHECK_CONDITION) {
+		int result;
+
+		uint32_t err;
+		const char *errptr;
+		char *errmsg = NULL;
+
+		char *args[MAX_LINE_ARGS+1];
+		int arg = sizeof(args) / sizeof(*args);
+		size_t outlen = strlen(check_condition) + 1;
+
+		err = parse_line(check_condition, check_condition, &outlen, args, &arg,
+		                 PARSE_OPT_DQUOTE | PARSE_OPT_SQUOTE | PARSE_OPT_BKSLASH,
+		                 &errptr);
+
+		if (err & PARSE_ERR_QUOTE) {
+			ha_alert("Syntax Error in condition: Unmatched quote.\n");
+			exit(2);
+		}
+
+		if (err & PARSE_ERR_HEX) {
+			ha_alert("Syntax Error in condition: Truncated or invalid hexadecimal sequence.\n");
+			exit(2);
+		}
+
+		if (err & (PARSE_ERR_TOOLARGE|PARSE_ERR_OVERLAP)) {
+			ha_alert("Error in condition: Line too long.\n");
+			exit(2);
+		}
+
+		if (err & PARSE_ERR_TOOMANY) {
+			ha_alert("Error in condition: Too many words.\n");
+			exit(2);
+		}
+
+		if (err) {
+			ha_alert("Unhandled error in condition, please report this to the developers.\n");
+			exit(2);
+		}
+
+		result = cfg_eval_condition(args, &errmsg, &errptr);
+
+		if (result < 0) {
+			if (errmsg)
+				ha_alert("Failed to evaluate condition: %s\n", errmsg);
+
+			exit(2);
+		}
+
+		exit(result ? 0 : 1);
+	}
+
 	/* in wait mode, we don't try to read the configuration files */
 	if (!(global.mode & MODE_MWORKER_WAIT)) {
 		char *env_cfgfiles = NULL;