new file mode 100644
--- /dev/null
+++ b/src/http/modules/ngx_http_limit_req_module.c
@@ -0,0 +1,794 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_http.h>
+
+
+typedef struct {
+    u_char              color;
+    u_char              dummy;
+    u_short             len;
+    ngx_queue_t         queue;
+    ngx_msec_t          last;
+    float               rate;
+    u_char              data[1];
+} ngx_http_limit_req_node_t;
+
+
+typedef struct {
+    ngx_rbtree_t       *rbtree;
+    ngx_queue_t        *queue;
+    ngx_slab_pool_t    *shpool;
+    float               rate;
+    ngx_int_t           index;
+    ngx_str_t           var;
+} ngx_http_limit_req_ctx_t;
+
+
+typedef struct {
+    ngx_shm_zone_t     *shm_zone;
+    float               burst;
+    ngx_msec_t          delay;
+} ngx_http_limit_req_conf_t;
+
+
+static void ngx_http_limit_req_delay(ngx_http_request_t *r);
+static ngx_int_t ngx_http_limit_req_lookup(ngx_http_limit_req_conf_t *lzcf,
+    ngx_uint_t hash, u_char *data, size_t len, ngx_http_limit_req_node_t **lzp);
+static void ngx_http_limit_req_expire(ngx_http_limit_req_ctx_t *ctx,
+    ngx_uint_t n);
+
+static void *ngx_http_limit_req_create_conf(ngx_conf_t *cf);
+static char *ngx_http_limit_req_merge_conf(ngx_conf_t *cf, void *parent,
+    void *child);
+static char *ngx_http_limit_req_zone(ngx_conf_t *cf, ngx_command_t *cmd,
+    void *conf);
+static char *ngx_http_limit_req(ngx_conf_t *cf, ngx_command_t *cmd,
+    void *conf);
+static ngx_int_t ngx_http_limit_req_init(ngx_conf_t *cf);
+
+
+static ngx_command_t  ngx_http_limit_req_commands[] = {
+
+    { ngx_string("limit_req_zone"),
+      NGX_HTTP_MAIN_CONF|NGX_CONF_TAKE3,
+      ngx_http_limit_req_zone,
+      0,
+      0,
+      NULL },
+
+    { ngx_string("limit_req"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE123,
+      ngx_http_limit_req,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      0,
+      NULL },
+
+      ngx_null_command
+};
+
+
+static ngx_http_module_t  ngx_http_limit_req_module_ctx = {
+    NULL,                                  /* preconfiguration */
+    ngx_http_limit_req_init,               /* postconfiguration */
+
+    NULL,                                  /* create main configuration */
+    NULL,                                  /* init main configuration */
+
+    NULL,                                  /* create server configuration */
+    NULL,                                  /* merge server configuration */
+
+    ngx_http_limit_req_create_conf,        /* create location configration */
+    ngx_http_limit_req_merge_conf          /* merge location configration */
+};
+
+
+ngx_module_t  ngx_http_limit_req_module = {
+    NGX_MODULE_V1,
+    &ngx_http_limit_req_module_ctx,        /* module context */
+    ngx_http_limit_req_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_req_handler(ngx_http_request_t *r)
+{
+    float                       rate;
+    size_t                      len, n;
+    uint32_t                    hash;
+    ngx_int_t                   rc;
+    ngx_time_t                 *tp;
+    ngx_rbtree_node_t          *node;
+    ngx_http_variable_value_t  *vv;
+    ngx_http_limit_req_ctx_t   *ctx;
+    ngx_http_limit_req_node_t  *lz;
+    ngx_http_limit_req_conf_t  *lzcf;
+
+    if (r->main->limit_req_set) {
+        return NGX_DECLINED;
+    }
+
+    lzcf = ngx_http_get_module_loc_conf(r, ngx_http_limit_req_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;
+    }
+
+    len = vv->len;
+
+    if (len == 0) {
+        return NGX_DECLINED;
+    }
+
+    if (len > 65535) {
+        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
+                      "the value of the \"%V\" variable "
+                      "is more than 65535 bytes: \"%v\"",
+                      &ctx->var, vv);
+        return NGX_DECLINED;
+    }
+
+    r->main->limit_req_set = 1;
+
+    hash = ngx_crc32_short(vv->data, len);
+
+    ngx_shmtx_lock(&ctx->shpool->mutex);
+
+    ngx_http_limit_req_expire(ctx, 1);
+
+    rc = ngx_http_limit_req_lookup(lzcf, hash, vv->data, len, &lz);
+
+    if (lz) {
+        ngx_queue_remove(&lz->queue);
+
+        ngx_queue_insert_head(ctx->queue, &lz->queue);
+
+        rate = lz->rate;
+
+    } else {
+        rate = 0.0;
+    }
+
+    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                  "limit_req: %i %.3f", rc, rate);
+
+    if (rc == NGX_BUSY) {
+        ngx_shmtx_unlock(&ctx->shpool->mutex);
+
+        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
+                      "limiting requests, %.3f r/s", rate);
+
+        return NGX_HTTP_SERVICE_UNAVAILABLE;
+    }
+
+    if (rc == NGX_AGAIN) {
+        ngx_shmtx_unlock(&ctx->shpool->mutex);
+
+        if (lzcf->delay) {
+            ngx_log_error(NGX_LOG_WARN, r->connection->log, 0,
+                          "delaying requests, %.3f r/s", rate);
+
+            if (ngx_handle_read_event(r->connection->read, 0) != NGX_OK) {
+                return NGX_HTTP_INTERNAL_SERVER_ERROR;
+            }
+
+            r->read_event_handler = ngx_http_test_reading;
+            r->write_event_handler = ngx_http_limit_req_delay;
+            ngx_add_timer(r->connection->write, lzcf->delay);
+
+            return NGX_AGAIN;
+        }
+
+        return NGX_DECLINED;
+    }
+
+    if (rc == NGX_OK) {
+        goto done;
+    }
+
+    /* rc == NGX_DECLINED */
+
+    n = offsetof(ngx_rbtree_node_t, color)
+        + offsetof(ngx_http_limit_req_node_t, data)
+        + len;
+
+    node = ngx_slab_alloc_locked(ctx->shpool, n);
+    if (node == NULL) {
+
+        ngx_http_limit_req_expire(ctx, 0);
+
+        node = ngx_slab_alloc_locked(ctx->shpool, n);
+        if (node == NULL) {
+            ngx_shmtx_unlock(&ctx->shpool->mutex);
+            return NGX_HTTP_SERVICE_UNAVAILABLE;
+        }
+    }
+
+    lz = (ngx_http_limit_req_node_t *) &node->color;
+
+    node->key = hash;
+    lz->len = (u_char) len;
+
+    tp = ngx_timeofday();
+    lz->last = (ngx_msec_t) (tp->sec * 1000 + tp->msec);
+
+    lz->rate = 0.0;
+    ngx_memcpy(lz->data, vv->data, len);
+
+    ngx_rbtree_insert(ctx->rbtree, node);
+
+    ngx_queue_insert_head(ctx->queue, &lz->queue);
+
+done:
+
+    ngx_shmtx_unlock(&ctx->shpool->mutex);
+
+    return NGX_DECLINED;
+}
+
+
+static void
+ngx_http_limit_req_delay(ngx_http_request_t *r)
+{
+    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                  "limit_req delay");
+
+    if (ngx_handle_read_event(r->connection->read, 0) != NGX_OK) {
+        ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
+        return;
+    }
+
+    r->read_event_handler = ngx_http_block_reading;
+    r->write_event_handler = ngx_http_core_run_phases;
+
+    ngx_http_core_run_phases(r);
+}
+
+
+static void
+ngx_http_limit_req_rbtree_insert_value(ngx_rbtree_node_t *temp,
+    ngx_rbtree_node_t *node, ngx_rbtree_node_t *sentinel)
+{
+    ngx_rbtree_node_t          **p;
+    ngx_http_limit_req_node_t   *lzn, *lznt;
+
+    for ( ;; ) {
+
+        if (node->key < temp->key) {
+
+            p = &temp->left;
+
+        } else if (node->key > temp->key) {
+
+            p = &temp->right;
+
+        } else { /* node->key == temp->key */
+
+            lzn = (ngx_http_limit_req_node_t *) &node->color;
+            lznt = (ngx_http_limit_req_node_t *) &temp->color;
+
+            p = (ngx_memn2cmp(lzn->data, lznt->data, lzn->len, lznt->len) < 0)
+                ? &temp->left : &temp->right;
+        }
+
+        if (*p == sentinel) {
+            break;
+        }
+
+        temp = *p;
+    }
+
+    *p = node;
+    node->parent = temp;
+    node->left = sentinel;
+    node->right = sentinel;
+    ngx_rbt_red(node);
+}
+
+
+static ngx_int_t
+ngx_http_limit_req_lookup(ngx_http_limit_req_conf_t *lzcf, ngx_uint_t hash,
+    u_char *data, size_t len, ngx_http_limit_req_node_t **lzp)
+{
+    ngx_int_t                   rc;
+    ngx_time_t                 *tp;
+    ngx_msec_t                  now;
+    ngx_msec_int_t              ms;
+    ngx_rbtree_node_t          *node, *sentinel;
+    ngx_http_limit_req_ctx_t   *ctx;
+    ngx_http_limit_req_node_t  *lz;
+
+    ctx = lzcf->shm_zone->data;
+
+    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;
+        }
+
+        /* hash == node->key */
+
+        do {
+            lz = (ngx_http_limit_req_node_t *) &node->color;
+
+            rc = ngx_memn2cmp(data, lz->data, len, (size_t) lz->len);
+
+            if (rc == 0) {
+
+                tp = ngx_timeofday();
+
+                now = (ngx_msec_t) (tp->sec * 1000 + tp->msec);
+                ms = (ngx_msec_int_t) (now - lz->last);
+
+                lz->rate = lz->rate - ctx->rate * ngx_abs(ms) / 1000 + 1;
+
+                if (lz->rate < 0.0) {
+                    lz->rate = 0.0;
+                }
+
+                lz->last = now;
+
+                *lzp = lz;
+
+                if (lz->rate > lzcf->burst) {
+                    return NGX_BUSY;
+                }
+
+                if (lz->rate > ctx->rate) {
+                    return NGX_AGAIN;
+                }
+
+                return NGX_OK;
+            }
+
+            node = (rc < 0) ? node->left : node->right;
+
+        } while (node != sentinel && hash == node->key);
+
+        break;
+    }
+
+    *lzp = NULL;
+
+    return NGX_DECLINED;
+}
+
+
+static void
+ngx_http_limit_req_expire(ngx_http_limit_req_ctx_t *ctx, ngx_uint_t n)
+{
+    float                       rate;
+    ngx_time_t                 *tp;
+    ngx_msec_t                  now;
+    ngx_queue_t                *q;
+    ngx_msec_int_t              ms;
+    ngx_rbtree_node_t          *node;
+    ngx_http_limit_req_node_t  *lz;
+
+    tp = ngx_timeofday();
+
+    now = (ngx_msec_t) (tp->sec * 1000 + tp->msec);
+
+    /*
+     * n == 1 deletes one or two zero rate entries
+     * n == 0 deletes oldest entry by force
+     *        and one or two zero rate entries
+     */
+
+    while (n < 3) {
+
+        if (ngx_queue_empty(ctx->queue)) {
+            return;
+        }
+
+        q = ngx_queue_last(ctx->queue);
+
+        lz = ngx_queue_data(q, ngx_http_limit_req_node_t, queue);
+
+        if (n++ != 0) {
+
+            ms = (ngx_msec_int_t) (now - lz->last);
+            ms = ngx_abs(ms);
+
+            if (ms < 60000) {
+                return;
+            }
+
+            rate = lz->rate - ctx->rate * ms / 1000;
+
+            if (rate > 0.0) {
+                return;
+            }
+        }
+
+        ngx_queue_remove(q);
+
+        node = (ngx_rbtree_node_t *)
+                   ((u_char *) lz - offsetof(ngx_rbtree_node_t, color));
+
+        ngx_rbtree_delete(ctx->rbtree, node);
+
+        ngx_slab_free_locked(ctx->shpool, node);
+    }
+}
+
+
+static ngx_int_t
+ngx_http_limit_req_init_zone(ngx_shm_zone_t *shm_zone, void *data)
+{
+    ngx_http_limit_req_ctx_t  *octx = data;
+
+    ngx_rbtree_node_t         *sentinel;
+    ngx_http_limit_req_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_req \"%V\" uses the \"%V\" variable "
+                          "while previously it used the \"%V\" variable",
+                          &shm_zone->name, &ctx->var, &octx->var);
+            return NGX_ERROR;
+        }
+
+        ctx->rbtree = octx->rbtree;
+        ctx->queue = octx->queue;
+        ctx->shpool = octx->shpool;
+
+        return NGX_OK;
+    }
+
+    ctx->shpool = (ngx_slab_pool_t *) shm_zone->shm.addr;
+
+    ctx->rbtree = ngx_slab_alloc(ctx->shpool, sizeof(ngx_rbtree_t));
+    if (ctx->rbtree == NULL) {
+        return NGX_ERROR;
+    }
+
+    sentinel = ngx_slab_alloc(ctx->shpool, sizeof(ngx_rbtree_node_t));
+    if (sentinel == NULL) {
+        return NGX_ERROR;
+    }
+
+    ngx_rbtree_init(ctx->rbtree, sentinel,
+                    ngx_http_limit_req_rbtree_insert_value);
+
+    ctx->queue = ngx_slab_alloc(ctx->shpool, sizeof(ngx_queue_t));
+    if (ctx->queue == NULL) {
+        return NGX_ERROR;
+    }
+
+    ngx_queue_init(ctx->queue);
+
+    return NGX_OK;
+}
+
+
+static void *
+ngx_http_limit_req_create_conf(ngx_conf_t *cf)
+{
+    ngx_http_limit_req_conf_t  *conf;
+
+    conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_limit_req_conf_t));
+    if (conf == NULL) {
+        return NGX_CONF_ERROR;
+    }
+
+    /*
+     * set by ngx_pcalloc():
+     *
+     *     conf->shm_zone = NULL;
+     *     conf->burst = 0.0;
+     *     conf->delay = 0;
+     */
+
+    return conf;
+}
+
+
+static char *
+ngx_http_limit_req_merge_conf(ngx_conf_t *cf, void *parent, void *child)
+{
+    ngx_http_limit_req_conf_t *prev = parent;
+    ngx_http_limit_req_conf_t *conf = child;
+
+    if (conf->shm_zone == NULL) {
+        *conf = *prev;
+    }
+
+    return NGX_CONF_OK;
+}
+
+
+static char *
+ngx_http_limit_req_zone(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
+{
+    u_char                    *p;
+    size_t                     size, len;
+    ngx_str_t                 *value, name, s;
+    ngx_int_t                  rate, scale;
+    ngx_uint_t                 i;
+    ngx_shm_zone_t            *shm_zone;
+    ngx_http_limit_req_ctx_t  *ctx;
+
+    value = cf->args->elts;
+
+    ctx = NULL;
+    size = 0;
+    rate = 1;
+    scale = 1;
+    name.len = 0;
+
+    for (i = 1; i < cf->args->nelts; i++) {
+
+        if (ngx_strncmp(value[i].data, "zone=", 5) == 0) {
+
+            name.data = value[i].data + 5;
+
+            p = (u_char *) ngx_strchr(name.data, ':');
+
+            if (p) {
+                name.len = p - name.data;
+
+                p++;
+
+                s.len = value[i].data + value[i].len - p;
+                s.data = p;
+
+                size = ngx_parse_size(&s);
+                if (size > 8191) {
+                    continue;
+                }
+            }
+
+            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                               "invalid zone size \"%V\"", &value[i]);
+            return NGX_CONF_ERROR;
+        }
+
+        if (ngx_strncmp(value[i].data, "rate=", 5) == 0) {
+
+            len = value[i].len;
+            p = value[i].data + len - 3;
+
+            if (ngx_strncmp(p, "r/s", 3) == 0) {
+                scale = 1;
+                len -= 3;
+
+            } else if (ngx_strncmp(p, "r/m", 3) == 0) {
+                scale = 60;
+                len -= 3;
+            }
+
+            rate = ngx_atoi(value[i].data + 5, len - 5);
+            if (rate <= NGX_ERROR) {
+                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                                   "invalid rate \"%V\"", &value[i]);
+                return NGX_CONF_ERROR;
+            }
+
+            continue;
+        }
+
+        if (value[i].data[0] == '$') {
+
+            value[i].len--;
+            value[i].data++;
+
+            ctx = ngx_pcalloc(cf->pool, sizeof(ngx_http_limit_req_ctx_t));
+            if (ctx == NULL) {
+                return NGX_CONF_ERROR;
+            }
+
+            ctx->index = ngx_http_get_variable_index(cf, &value[i]);
+            if (ctx->index == NGX_ERROR) {
+                return NGX_CONF_ERROR;
+            }
+
+            ctx->var = value[i];
+
+            continue;
+        }
+
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "invalid parameter \"%V\"", &value[i]);
+        return NGX_CONF_ERROR;
+    }
+
+    if (name.len == 0 || size == 0) {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "\"%V\" must have \"zone\" parameter",
+                           &cmd->name);
+        return NGX_CONF_ERROR;
+    }
+
+    if (ctx == NULL) {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "no variable is defined for limit_req_zone \"%V\"",
+                           &cmd->name);
+        return NGX_CONF_ERROR;
+    }
+
+    ctx->rate = (float) rate / scale;
+
+    shm_zone = ngx_shared_memory_add(cf, &name, size,
+                                     &ngx_http_limit_req_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_req_zone \"%V\" is already bound to variable \"%V\"",
+                   &value[1], &ctx->var);
+        return NGX_CONF_ERROR;
+    }
+
+    shm_zone->init = ngx_http_limit_req_init_zone;
+    shm_zone->data = ctx;
+
+    return NGX_CONF_OK;
+}
+
+
+static char *
+ngx_http_limit_req(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
+{
+    ngx_http_limit_req_conf_t  *lzcf = conf;
+
+    u_char                    *p;
+    size_t                     len;
+    ngx_int_t                  burst, scale, delay;
+    ngx_str_t                 *value, s;
+    ngx_uint_t                 i;
+    ngx_http_limit_req_ctx_t  *ctx;
+
+    if (lzcf->shm_zone) {
+        return "is duplicate";
+    }
+
+    value = cf->args->elts;
+
+    burst = 0;
+    scale = 1;
+    delay = 0;
+
+    for (i = 1; i < cf->args->nelts; i++) {
+
+        if (ngx_strncmp(value[i].data, "zone=", 5) == 0) {
+
+            s.len = value[i].len - 5;
+            s.data = value[i].data + 5;
+
+            lzcf->shm_zone = ngx_shared_memory_add(cf, &s, 0,
+                                                   &ngx_http_limit_req_module);
+            if (lzcf->shm_zone == NULL) {
+                return NGX_CONF_ERROR;
+            }
+
+            continue;
+        }
+
+        if (ngx_strncmp(value[i].data, "burst=", 6) == 0) {
+
+            len = value[i].len;
+            p = value[i].data + len - 3;
+
+            if (ngx_strncmp(p, "r/s", 3) == 0) {
+                scale = 1;
+                len -= 3;
+
+            } else if (ngx_strncmp(p, "r/m", 3) == 0) {
+                scale = 60;
+                len -= 3;
+            }
+
+            burst = ngx_atoi(value[i].data + 6, len - 6);
+            if (burst <= 0) {
+                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                                   "invalid burst rate \"%V\"", &value[i]);
+                return NGX_CONF_ERROR;
+            }
+
+            continue;
+        }
+
+        if (ngx_strncmp(value[i].data, "delay=", 6) == 0) {
+
+            s.len = value[i].len - 6;
+            s.data = value[i].data + 6;
+
+            delay = ngx_parse_time(&s, 0);
+            if (delay < 0) {
+                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                                 "invalid clean_time value \"%V\"", &value[i]);
+                return NGX_CONF_ERROR;
+            }
+
+            continue;
+        }
+
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "invalid parameter \"%V\"", &value[i]);
+        return NGX_CONF_ERROR;
+    }
+
+    if (lzcf->shm_zone == NULL) {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "\"%V\" must have \"zone\" parameter",
+                           &cmd->name);
+        return NGX_CONF_ERROR;
+    }
+
+    if (lzcf->shm_zone->data == NULL) {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "unknown limit_req_zone \"%V\"",
+                           &lzcf->shm_zone->name);
+        return NGX_CONF_ERROR;
+    }
+
+    if (burst) {
+        lzcf->burst = (float) burst / scale;
+
+    } else {
+        ctx = lzcf->shm_zone->data;
+        lzcf->burst = ctx->rate;
+    }
+
+    lzcf->delay = (ngx_msec_t) delay;
+
+    return NGX_CONF_OK;
+}
+
+
+static ngx_int_t
+ngx_http_limit_req_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_req_handler;
+
+    return NGX_OK;
+}