new file mode 100644
--- /dev/null
+++ b/src/http/modules/ngx_http_limit_zone_module.c
@@ -0,0 +1,444 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_http.h>
+
+
+typedef struct {
+    u_char              color;
+    u_char              len;
+    u_short             conn;
+    u_char              data[1];
+} ngx_http_limit_zone_node_t;
+
+
+typedef struct {
+    ngx_shm_zone_t     *shm_zone;
+    ngx_rbtree_node_t  *node;
+} ngx_http_limit_zone_cleanup_t;
+
+
+typedef struct {
+    ngx_rbtree_t       *rbtree;
+    ngx_int_t           index;
+    ngx_str_t           var;
+} ngx_http_limit_zone_ctx_t;
+
+
+typedef struct {
+    ngx_shm_zone_t     *shm_zone;
+    ngx_uint_t          conn;
+} ngx_http_limit_zone_conf_t;
+
+
+static void ngx_http_limit_zone_cleanup(void *data);
+
+static void *ngx_http_limit_zone_create_conf(ngx_conf_t *cf);
+static char *ngx_http_limit_zone_merge_conf(ngx_conf_t *cf, void *parent,
+    void *child);
+static char *ngx_http_limit_zone(ngx_conf_t *cf, ngx_command_t *cmd,
+    void *conf);
+static char *ngx_http_limit_conn(ngx_conf_t *cf, ngx_command_t *cmd,
+    void *conf);
+static ngx_int_t ngx_http_limit_zone_init(ngx_conf_t *cf);
+
+
+static ngx_command_t  ngx_http_limit_zone_commands[] = {
+
+    { ngx_string("limit_zone"),
+      NGX_HTTP_MAIN_CONF|NGX_CONF_TAKE3,
+      ngx_http_limit_zone,
+      0,
+      0,
+      NULL },
+
+    { ngx_string("limit_conn"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE2,
+      ngx_http_limit_conn,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      0,
+      NULL },
+
+      ngx_null_command
+};
+
+
+static ngx_http_module_t  ngx_http_limit_zone_module_ctx = {
+    NULL,                                  /* preconfiguration */
+    ngx_http_limit_zone_init,              /* postconfiguration */
+
+    NULL,                                  /* create main configuration */
+    NULL,                                  /* init main configuration */
+
+    NULL,                                  /* create server configuration */
+    NULL,                                  /* merge server configuration */
+
+    ngx_http_limit_zone_create_conf,       /* create location configration */
+    ngx_http_limit_zone_merge_conf         /* merge location configration */
+};
+
+
+ngx_module_t  ngx_http_limit_zone_module = {
+    NGX_MODULE_V1,
+    &ngx_http_limit_zone_module_ctx,       /* module context */
+    ngx_http_limit_zone_commands,          /* module directives */
+    NGX_HTTP_MODULE,                       /* module type */
+    NULL,                                  /* init master */
+    NULL,                                  /* init module */
+    NULL,                                  /* init process */
+    NULL,                                  /* init thread */
+    NULL,                                  /* exit thread */
+    NULL,                                  /* exit process */
+    NULL,                                  /* exit master */
+    NGX_MODULE_V1_PADDING
+};
+
+
+static ngx_int_t
+ngx_http_limit_zone_handler(ngx_http_request_t *r)
+{
+    size_t                          len, n;
+    uint32_t                        hash;
+    ngx_slab_pool_t                *shpool;
+    ngx_rbtree_node_t              *node, *sentinel;
+    ngx_pool_cleanup_t             *cln;
+    ngx_http_variable_value_t      *vv;
+    ngx_http_limit_zone_ctx_t      *ctx;
+    ngx_http_limit_zone_node_t     *lz;
+    ngx_http_limit_zone_conf_t     *lzcf;
+    ngx_http_limit_zone_cleanup_t  *lzcln;
+
+    if (r->main->limit_zone_set) {
+        return NGX_DECLINED;
+    }
+
+    lzcf = ngx_http_get_module_loc_conf(r, ngx_http_limit_zone_module);
+
+    if (lzcf->shm_zone == NULL) {
+        return NGX_DECLINED;
+    }
+
+    ctx = lzcf->shm_zone->data;
+
+    vv = ngx_http_get_indexed_variable(r, ctx->index);
+
+    if (vv == NULL || vv->not_found) {
+        return NGX_DECLINED;
+    }
+
+    r->limit_zone_set = 1;
+
+    len = vv->len;
+
+    hash = ngx_crc32_short(vv->data, len);
+
+    cln = ngx_pool_cleanup_add(r->pool, sizeof(ngx_http_limit_zone_cleanup_t));
+    if (cln == NULL) {
+        return NGX_HTTP_INTERNAL_SERVER_ERROR;
+    }
+
+    shpool = (ngx_slab_pool_t *) lzcf->shm_zone->shm.addr;
+
+    ngx_shmtx_lock(&shpool->mutex);
+
+    node = ctx->rbtree->root;
+    sentinel = ctx->rbtree->sentinel;
+
+    while (node != sentinel) {
+
+        if (hash < node->key) {
+            node = node->left;
+            continue;
+        }
+
+        if (hash > node->key) {
+            node = node->right;
+            continue;
+        }
+
+        if (hash == node->key ){
+            lz = (ngx_http_limit_zone_node_t *) &node->color;
+
+            if (len == (size_t) lz->len
+                && ngx_strncmp(lz->data, vv->data, len) == 0)
+            {
+                if ((ngx_uint_t) lz->conn < lzcf->conn) {
+                    lz->conn++;
+                    goto done;
+                }
+
+                ngx_shmtx_unlock(&shpool->mutex);
+
+                return NGX_HTTP_SERVICE_UNAVAILABLE;
+            }
+        }
+    }
+
+    n = offsetof(ngx_rbtree_node_t, color)
+        + offsetof(ngx_http_limit_zone_node_t, data)
+        + len;
+
+    node = ngx_slab_alloc_locked(shpool, n);
+    if (node == NULL) {
+        ngx_shmtx_unlock(&shpool->mutex);
+        return NGX_HTTP_SERVICE_UNAVAILABLE;
+    }
+
+    lz = (ngx_http_limit_zone_node_t *) &node->color;
+
+    node->key = hash;
+    lz->len = (u_char) len;
+    lz->conn = 1;
+    ngx_memcpy(lz->data, vv->data, len);
+
+    ngx_rbtree_insert(ctx->rbtree, node);
+
+done:
+
+    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                   "limit zone: %08XD %d", node->key, lz->conn);
+
+    ngx_shmtx_unlock(&shpool->mutex);
+
+    cln->handler = ngx_http_limit_zone_cleanup;
+    lzcln = cln->data;
+
+    lzcln->shm_zone = lzcf->shm_zone;
+    lzcln->node = node;
+
+    return NGX_DECLINED;
+}
+
+
+static void
+ngx_http_limit_zone_cleanup(void *data)
+{
+    ngx_http_limit_zone_cleanup_t  *lzcln = data;
+
+    ngx_slab_pool_t             *shpool;
+    ngx_rbtree_node_t           *node;
+    ngx_http_limit_zone_ctx_t   *ctx;
+    ngx_http_limit_zone_node_t  *lz;
+
+    ctx = lzcln->shm_zone->data;
+    shpool = (ngx_slab_pool_t *) lzcln->shm_zone->shm.addr;
+    node = lzcln->node;
+    lz = (ngx_http_limit_zone_node_t *) &node->color;
+
+    ngx_shmtx_lock(&shpool->mutex);
+
+    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, lzcln->shm_zone->shm.log, 0,
+                   "limit zone cleanup: %08XD %d", node->key, lz->conn);
+
+    lz->conn--;
+
+    if (lz->conn == 0) {
+        ngx_rbtree_delete(ctx->rbtree, node);
+        ngx_slab_free_locked(shpool, node);
+    }
+
+    ngx_shmtx_unlock(&shpool->mutex);
+}
+
+
+static ngx_int_t
+ngx_http_limit_zone_init_zone(ngx_shm_zone_t *shm_zone, void *data)
+{
+    ngx_http_limit_zone_ctx_t  *octx = data;
+
+    ngx_slab_pool_t            *shpool;
+    ngx_rbtree_node_t          *sentinel;
+    ngx_http_limit_zone_ctx_t  *ctx;
+
+    ctx = shm_zone->data;
+
+    if (octx) {
+        if (ngx_strcmp(ctx->var.data, octx->var.data) != 0) {
+            ngx_log_error(NGX_LOG_EMERG, shm_zone->shm.log, 0,
+                          "limit_zone \"%V\" use the \"%V\" variable "
+                          "while previously it used the \"%V\" variable",
+                          &shm_zone->name, &ctx->var, &octx->var);
+            return NGX_ERROR;
+        }
+
+        ctx->rbtree = octx->rbtree;
+
+        return NGX_OK;
+    }
+
+    shpool = (ngx_slab_pool_t *) shm_zone->shm.addr;
+
+    ctx->rbtree = ngx_slab_alloc(shpool, sizeof(ngx_rbtree_t));
+    if (ctx->rbtree == NULL) {
+        return NGX_ERROR;
+    }
+
+    sentinel = ngx_slab_alloc(shpool, sizeof(ngx_rbtree_node_t));
+    if (sentinel == NULL) {
+        return NGX_ERROR;
+    }
+
+    ngx_rbtree_sentinel_init(sentinel);
+
+    ctx->rbtree->root = sentinel;
+    ctx->rbtree->sentinel = sentinel;
+    ctx->rbtree->insert = ngx_rbtree_insert_value;
+
+    return NGX_OK;
+}
+
+
+static void *
+ngx_http_limit_zone_create_conf(ngx_conf_t *cf)
+{
+    ngx_http_limit_zone_conf_t  *conf;
+
+    conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_limit_zone_conf_t));
+    if (conf == NULL) {
+        return NGX_CONF_ERROR;
+    }
+
+    /*
+     * set by ngx_pcalloc():
+     *
+     *     conf->shm_zone = NULL;
+     *     conf->conn = 0;
+     */
+
+    return conf;
+}
+
+
+static char *
+ngx_http_limit_zone_merge_conf(ngx_conf_t *cf, void *parent, void *child)
+{
+    ngx_http_limit_zone_conf_t *prev = parent;
+    ngx_http_limit_zone_conf_t *conf = child;
+
+    if (conf->shm_zone == NULL) {
+        *conf = *prev;
+    }
+
+    return NGX_CONF_OK;
+}
+
+
+static char *
+ngx_http_limit_zone(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
+{
+    ssize_t                     n;
+    ngx_str_t                  *value;
+    ngx_shm_zone_t             *shm_zone;
+    ngx_http_limit_zone_ctx_t  *ctx;
+
+    value = cf->args->elts;
+
+    if (value[2].data[0] != '$') {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "invalid variable name \"%V\"", &value[2]);
+        return NGX_CONF_ERROR;
+    }
+
+    value[2].len--;
+    value[2].data++;
+
+    ctx = ngx_pcalloc(cf->pool, sizeof(ngx_http_limit_zone_ctx_t));
+    if (ctx == NULL) {
+        return NGX_CONF_ERROR;
+    }
+
+    ctx->index = ngx_http_get_variable_index(cf, &value[2]);
+    if (ctx->index == NGX_ERROR) {
+        return NGX_CONF_ERROR;
+    }
+
+    ctx->var = value[2];
+
+    n = ngx_parse_size(&value[3]);
+
+    if (n == NGX_ERROR) {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "invalid size of limit_zone \"%V\"", &value[3]);
+        return NGX_CONF_ERROR;
+    }
+
+    if (n < (ngx_int_t) (8 * ngx_pagesize)) {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "limit_zone \"%V\" is too small", &value[1]);
+        return NGX_CONF_ERROR;
+    }
+
+
+    shm_zone = ngx_shared_memory_add(cf, &value[1], n,
+                                     &ngx_http_limit_zone_module);
+    if (shm_zone == NULL) {
+        return NGX_CONF_ERROR;
+    }
+
+    if (shm_zone->data) {
+        ctx = shm_zone->data;
+
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                        "limit_zone \"%V\" is already bound to variable \"%V\"",
+                        &value[1], &ctx->var);
+        return NGX_CONF_ERROR;
+    }
+
+    shm_zone->init = ngx_http_limit_zone_init_zone;
+    shm_zone->data = ctx;
+
+    return NGX_CONF_OK;
+}
+
+
+static char *
+ngx_http_limit_conn(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
+{
+    ngx_http_limit_zone_conf_t  *lzcf = conf;
+
+    ngx_int_t   n;
+    ngx_str_t  *value;
+
+    value = cf->args->elts;
+
+    lzcf->shm_zone = ngx_shared_memory_add(cf, &value[1], 0,
+                                           &ngx_http_limit_zone_module);
+    if (lzcf->shm_zone == NULL) {
+        return NGX_CONF_ERROR;
+    }
+
+    n = ngx_atoi(value[2].data, value[2].len);
+    if (n <= 0) {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "invalid number of connections \"%V\"", &value[2]);
+        return NGX_CONF_ERROR;
+    }
+
+    lzcf->conn = n;
+
+    return NGX_CONF_OK;
+}
+
+
+static ngx_int_t
+ngx_http_limit_zone_init(ngx_conf_t *cf)
+{
+    ngx_http_handler_pt        *h;
+    ngx_http_core_main_conf_t  *cmcf;
+
+    cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);
+
+    h = ngx_array_push(&cmcf->phases[NGX_HTTP_PREACCESS_PHASE].handlers);
+    if (h == NULL) {
+        return NGX_ERROR;
+    }
+
+    *h = ngx_http_limit_zone_handler;
+
+    return NGX_OK;
+}