Added a "fallback" option to be used with the "share" action.

It allows proceeding to another action if a file isn't available.

An example:

    {
        "share": "/data/www/",

        "fallback": {
            "pass": "applications/php"
        }
    }

In the example above, an attempt is made first to serve a request with
a file from the "/data/www/" directory.  If there's no such file, the
request is passed to the "php" application.

Fallback actions may be nested:

    {
        "share": "/data/www/",

        "fallback": {
            "share": "/data/cache/",

            "fallback": {
                "proxy": "http://127.0.0.1:9000"
            }
        }
    }

4 files changed, 68 insertions, 23 deletions

diff --git a/src/nxt_conf_validation.c b/src/nxt_conf_validation.c
index 4282f46b..8189cd44 100644
--- a/src/nxt_conf_validation.c
+++ b/src/nxt_conf_validation.c
@@ -339,6 +339,11 @@ static nxt_conf_vldt_object_t  nxt_conf_vldt_share_action_members[] = {
       NULL,
       NULL },
 
+    { nxt_string("fallback"),
+      NXT_CONF_VLDT_OBJECT,
+      &nxt_conf_vldt_action,
+      NULL },
+
     NXT_CONF_VLDT_END
 };
 
diff --git a/src/nxt_http.h b/src/nxt_http.h
index 030d77a7..67c7645b 100644
--- a/src/nxt_http.h
+++ b/src/nxt_http.h
@@ -189,6 +189,7 @@ struct nxt_http_action_s {
         nxt_http_route_t            *route;
         nxt_http_upstream_t         *upstream;
         nxt_app_t                   *application;
+        nxt_http_action_t           *fallback;
     } u;
 
     nxt_str_t                       name;
diff --git a/src/nxt_http_route.c b/src/nxt_http_route.c
index ef9593b7..6fce895e 100644
--- a/src/nxt_http_route.c
+++ b/src/nxt_http_route.c
@@ -43,6 +43,7 @@ typedef struct {
     nxt_conf_value_t               *pass;
     nxt_conf_value_t               *share;
     nxt_conf_value_t               *proxy;
+    nxt_conf_value_t               *fallback;
 } nxt_http_route_action_conf_t;
 
 
@@ -175,7 +176,7 @@ static nxt_http_route_t *nxt_http_route_create(nxt_task_t *task,
 static nxt_http_route_match_t *nxt_http_route_match_create(nxt_task_t *task,
     nxt_router_temp_conf_t *tmcf, nxt_conf_value_t *cv);
 static nxt_int_t nxt_http_route_action_create(nxt_router_temp_conf_t *tmcf,
-    nxt_conf_value_t *cv, nxt_http_route_match_t *match);
+    nxt_conf_value_t *cv, nxt_http_action_t *action);
 static nxt_http_route_table_t *nxt_http_route_table_create(nxt_task_t *task,
     nxt_mp_t *mp, nxt_conf_value_t *table_cv, nxt_http_route_object_t object,
     nxt_bool_t case_sensitive);
@@ -407,7 +408,7 @@ 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;
+    nxt_conf_value_t             *match_conf, *action_conf;
     nxt_http_route_test_t        *test;
     nxt_http_route_rule_t        *rule;
     nxt_http_route_table_t       *table;
@@ -416,6 +417,7 @@ nxt_http_route_match_create(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
     nxt_http_route_match_conf_t  mtcf;
 
     static nxt_str_t  match_path = nxt_string("/match");
+    static nxt_str_t  action_path = nxt_string("/action");
 
     match_conf = nxt_conf_get_path(cv, &match_path);
 
@@ -433,7 +435,12 @@ nxt_http_route_match_create(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
     match->action.handler = NULL;
     match->items = n;
 
-    ret = nxt_http_route_action_create(tmcf, cv, match);
+    action_conf = nxt_conf_get_path(cv, &action_path);
+    if (nxt_slow_path(action_conf == NULL)) {
+        return NULL;
+    }
+
+    ret = nxt_http_route_action_create(tmcf, action_conf, &match->action);
     if (nxt_slow_path(ret != NXT_OK)) {
         return NULL;
     }
@@ -579,30 +586,27 @@ static nxt_conf_map_t  nxt_http_route_action_conf[] = {
         NXT_CONF_MAP_PTR,
         offsetof(nxt_http_route_action_conf_t, proxy)
     },
+    {
+        nxt_string("fallback"),
+        NXT_CONF_MAP_PTR,
+        offsetof(nxt_http_route_action_conf_t, fallback)
+    },
 };
 
 
 static nxt_int_t
 nxt_http_route_action_create(nxt_router_temp_conf_t *tmcf, nxt_conf_value_t *cv,
-    nxt_http_route_match_t *match)
+    nxt_http_action_t *action)
 {
     nxt_mp_t                      *mp;
     nxt_int_t                     ret;
     nxt_str_t                     name, *string;
-    nxt_conf_value_t              *conf, *action_conf;
+    nxt_conf_value_t              *conf;
     nxt_http_route_action_conf_t  accf;
 
-    static nxt_str_t  action_path = nxt_string("/action");
-
-    action_conf = nxt_conf_get_path(cv, &action_path);
-    if (action_conf == NULL) {
-        return NXT_ERROR;
-    }
-
     nxt_memzero(&accf, sizeof(accf));
 
-    ret = nxt_conf_map_object(tmcf->mem_pool,
-                              action_conf, nxt_http_route_action_conf,
+    ret = nxt_conf_map_object(tmcf->mem_pool, cv, nxt_http_route_action_conf,
                               nxt_nitems(nxt_http_route_action_conf), &accf);
     if (ret != NXT_OK) {
         return ret;
@@ -612,7 +616,7 @@ nxt_http_route_action_create(nxt_router_temp_conf_t *tmcf, nxt_conf_value_t *cv,
 
     if (accf.share != NULL) {
         conf = accf.share;
-        match->action.handler = nxt_http_static_handler;
+        action->handler = nxt_http_static_handler;
 
     } else if (accf.proxy != NULL) {
         conf = accf.proxy;
@@ -622,13 +626,23 @@ nxt_http_route_action_create(nxt_router_temp_conf_t *tmcf, nxt_conf_value_t *cv,
 
     mp = tmcf->router_conf->mem_pool;
 
-    string = nxt_str_dup(mp, &match->action.name, &name);
+    string = nxt_str_dup(mp, &action->name, &name);
     if (nxt_slow_path(string == NULL)) {
         return NXT_ERROR;
     }
 
+    if (accf.fallback != NULL) {
+        action->u.fallback = nxt_mp_zalloc(mp, sizeof(nxt_http_action_t));
+        if (nxt_slow_path(action->u.fallback == NULL)) {
+            return NXT_ERROR;
+        }
+
+        return nxt_http_route_action_create(tmcf, accf.fallback,
+                                            action->u.fallback);
+    }
+
     if (accf.proxy != NULL) {
-        return nxt_http_proxy_create(mp, &match->action);
+        return nxt_http_proxy_create(mp, action);
     }
 
     return NXT_OK;
@@ -1043,18 +1057,13 @@ static void
 nxt_http_route_resolve(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
     nxt_http_route_t *route)
 {
-    nxt_http_action_t       *action;
     nxt_http_route_match_t  **match, **end;
 
     match = &route->match[0];
     end = match + route->items;
 
     while (match < end) {
-        action = &(*match)->action;
-
-        if (action->handler == NULL) {
-            nxt_http_action_resolve(task, tmcf, &(*match)->action);
-        }
+        nxt_http_action_resolve(task, tmcf, &(*match)->action);
 
         match++;
     }
@@ -1067,6 +1076,16 @@ nxt_http_action_resolve(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
 {
     nxt_str_t  name;
 
+    if (action->handler != NULL) {
+        if (action->handler == nxt_http_static_handler
+            && action->u.fallback != NULL)
+        {
+            nxt_http_action_resolve(task, tmcf, action->u.fallback);
+        }
+
+        return;
+    }
+
     name = action->name;
 
     if (nxt_str_start(&name, "applications/", 13)) {
@@ -1201,6 +1220,13 @@ nxt_http_action_cleanup(nxt_task_t *task, nxt_http_action_t *action)
 {
     if (action->handler == nxt_http_application_handler) {
         nxt_router_app_use(task, action->u.application, -1);
+        return;
+    }
+
+    if (action->handler == nxt_http_static_handler
+        && action->u.fallback != NULL)
+    {
+        nxt_http_action_cleanup(task, action->u.fallback);
     }
 }
 
diff --git a/src/nxt_http_static.c b/src/nxt_http_static.c
index 44132859..46ae57a7 100644
--- a/src/nxt_http_static.c
+++ b/src/nxt_http_static.c
@@ -49,6 +49,10 @@ nxt_http_static_handler(nxt_task_t *task, nxt_http_request_t *r,
     if (nxt_slow_path(!nxt_str_eq(r->method, "GET", 3))) {
 
         if (!nxt_str_eq(r->method, "HEAD", 4)) {
+            if (action->u.fallback != NULL) {
+                return action->u.fallback;
+            }
+
             nxt_http_request_error(task, r, NXT_HTTP_METHOD_NOT_ALLOWED);
             return NULL;
         }
@@ -123,6 +127,10 @@ nxt_http_static_handler(nxt_task_t *task, nxt_http_request_t *r,
             break;
         }
 
+        if (level == NXT_LOG_ERR && action->u.fallback != NULL) {
+            return action->u.fallback;
+        }
+
         if (status != NXT_HTTP_NOT_FOUND) {
             nxt_log(task, level, "open(\"%FN\") failed %E", f->name, f->error);
         }
@@ -222,8 +230,13 @@ nxt_http_static_handler(nxt_task_t *task, nxt_http_request_t *r,
         nxt_file_close(task, f);
 
         if (nxt_slow_path(!nxt_is_dir(&fi))) {
+            if (action->u.fallback != NULL) {
+                return action->u.fallback;
+            }
+
             nxt_log(task, NXT_LOG_ERR, "\"%FN\" is not a regular file",
                     f->name);
+
             nxt_http_request_error(task, r, NXT_HTTP_NOT_FOUND);
             return NULL;
         }