http: Add "if" option to the "match" object

This feature allows users to specify conditions to check if one
route is matched. It is used the same way as the "if" option in
the access log.

Example:

    {
        "match": {
            "if": "`${headers['User-Agent'].split('/')[0] == 'curl'}`"
        },
        "action": {
            "return": 204
        }
    }

src/nxt_conf_validation.c

@@ -696,6 +696,10 @@ static nxt_conf_vldt_object_t  nxt_conf_vldt_match_members[] = {
         .type       = NXT_CONF_VLDT_OBJECT | NXT_CONF_VLDT_ARRAY,
         .validator  = nxt_conf_vldt_match_patterns_sets,
         .u.string   = "cookies"
+    }, {
+        .name       = nxt_string("if"),
+        .type       = NXT_CONF_VLDT_STRING,
+        .validator  = nxt_conf_vldt_if,
     },
 
     NXT_CONF_VLDT_END

src/nxt_http_route.c

@@ -51,6 +51,7 @@ typedef struct {
     nxt_conf_value_t               *query;
     nxt_conf_value_t               *source;
     nxt_conf_value_t               *destination;
+    nxt_conf_value_t               *condition;
 } nxt_http_route_match_conf_t;
 
 
@@ -138,6 +139,7 @@ typedef union {
 
 typedef struct {
     uint32_t                       items;
+    nxt_tstr_cond_t                condition;
     nxt_http_action_t              action;
     nxt_http_route_test_t          test[];
 } nxt_http_route_match_t;
@@ -350,6 +352,12 @@ static nxt_conf_map_t  nxt_http_route_match_conf[] = {
         NXT_CONF_MAP_PTR,
         offsetof(nxt_http_route_match_conf_t, destination),
     },
+
+    {
+        nxt_string("if"),
+        NXT_CONF_MAP_PTR,
+        offsetof(nxt_http_route_match_conf_t, condition),
+    },
 };
 
 
@@ -397,14 +405,17 @@ nxt_http_route_match_create(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
     uint32_t                     n;
     nxt_mp_t                     *mp;
     nxt_int_t                    ret;
-    nxt_conf_value_t             *match_conf, *action_conf;
+    nxt_str_t                    str;
+    nxt_conf_value_t             *match_conf, *action_conf, *condition;
+    nxt_router_conf_t            *rtcf;
     nxt_http_route_test_t        *test;
     nxt_http_route_rule_t        *rule;
     nxt_http_route_table_t       *table;
     nxt_http_route_match_t       *match;
     nxt_http_route_addr_rule_t   *addr_rule;
     nxt_http_route_match_conf_t  mtcf;
 
+    static const nxt_str_t  if_path = nxt_string("/if");
     static const nxt_str_t  match_path = nxt_string("/match");
     static const nxt_str_t  action_path = nxt_string("/action");
 
@@ -413,9 +424,21 @@ nxt_http_route_match_create(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
     n = (match_conf != NULL) ? nxt_conf_object_members_count(match_conf) : 0;
     size = sizeof(nxt_http_route_match_t) + n * sizeof(nxt_http_route_test_t *);
 
-    mp = tmcf->router_conf->mem_pool;
+    rtcf = tmcf->router_conf;
+    mp = rtcf->mem_pool;
+
+    condition = NULL;
+
+    if (match_conf != NULL) {
+        condition = nxt_conf_get_path(match_conf, &if_path);
+
+        if (condition != NULL) {
+            n--;
+            size -= sizeof(nxt_http_route_test_t *);
+        }
+    }
 
-    match = nxt_mp_alloc(mp, size);
+    match = nxt_mp_zalloc(mp, size);
     if (nxt_slow_path(match == NULL)) {
         return NULL;
     }
@@ -432,7 +455,7 @@ nxt_http_route_match_create(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
         return NULL;
     }
 
-    if (n == 0) {
+    if (n == 0 && condition == NULL) {
         return match;
     }
 
@@ -445,6 +468,15 @@ nxt_http_route_match_create(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
         return NULL;
     }
 
+    if (condition != NULL) {
+        nxt_conf_get_string(condition, &str);
+
+        ret = nxt_tstr_cond_compile(rtcf->tstr_state, &str, &match->condition);
+        if (nxt_slow_path(ret != NXT_OK)) {
+            return NULL;
+        }
+    }
+
     test = &match->test[0];
 
     if (mtcf.scheme != NULL) {
@@ -1596,6 +1628,12 @@ nxt_http_route_match(nxt_task_t *task, nxt_http_request_t *r,
     nxt_int_t              ret;
     nxt_http_route_test_t  *test, *end;
 
+    ret = nxt_http_cond_value(task, r, &match->condition);
+    if (ret <= 0) {
+        /* 0 => NULL, -1 => NXT_HTTP_ACTION_ERROR. */
+        return (nxt_http_action_t *) (intptr_t) ret;
+    }
+
     test = &match->test[0];
     end = test + match->items;