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view src/http/modules/ngx_http_memcached_module.c @ 7281:bd6563e81cea

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Limit req: improved handling of negative times. Negative times can appear since workers only update time on an event loop iteration start. If a worker was blocked for a long time during an event loop iteration, it is possible that another worker already updated the time stored in the node. As such, time since last update of the node (ms) will be negative. Previous code used ngx_abs(ms) in the calculations. That is, negative times were effectively treated as positive ones. As a result, it was not possible to maintain high request rates, where the same node can be updated multiple times from during an event loop iteration. In particular, this affected setups with many SSL handshakes, see http://mailman.nginx.org/pipermail/nginx/2018-May/056291.html. Fix is to only update the last update time stored in the node if the new time is larger than previously stored one. If a future time is stored in the node, we preserve this time as is. To prevent breaking things on platforms without monotonic time available if system time is updated backwards, a safety limit of 60 seconds is used. If the time stored in the node is more than 60 seconds in the future, we assume that the time was changed backwards and update lr->last to the current time.
author Maxim Dounin <mdounin@mdounin.ru>
date Wed, 30 May 2018 15:40:34 +0300
parents 06cf0c4b8618
children 45e513c3540d
line wrap: on
line source


/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>


typedef struct {
    ngx_http_upstream_conf_t   upstream;
    ngx_int_t                  index;
    ngx_uint_t                 gzip_flag;
} ngx_http_memcached_loc_conf_t;


typedef struct {
    size_t                     rest;
    ngx_http_request_t        *request;
    ngx_str_t                  key;
} ngx_http_memcached_ctx_t;


static ngx_int_t ngx_http_memcached_create_request(ngx_http_request_t *r);
static ngx_int_t ngx_http_memcached_reinit_request(ngx_http_request_t *r);
static ngx_int_t ngx_http_memcached_process_header(ngx_http_request_t *r);
static ngx_int_t ngx_http_memcached_filter_init(void *data);
static ngx_int_t ngx_http_memcached_filter(void *data, ssize_t bytes);
static void ngx_http_memcached_abort_request(ngx_http_request_t *r);
static void ngx_http_memcached_finalize_request(ngx_http_request_t *r,
    ngx_int_t rc);

static void *ngx_http_memcached_create_loc_conf(ngx_conf_t *cf);
static char *ngx_http_memcached_merge_loc_conf(ngx_conf_t *cf,
    void *parent, void *child);

static char *ngx_http_memcached_pass(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);


static ngx_conf_bitmask_t  ngx_http_memcached_next_upstream_masks[] = {
    { ngx_string("error"), NGX_HTTP_UPSTREAM_FT_ERROR },
    { ngx_string("timeout"), NGX_HTTP_UPSTREAM_FT_TIMEOUT },
    { ngx_string("invalid_response"), NGX_HTTP_UPSTREAM_FT_INVALID_HEADER },
    { ngx_string("not_found"), NGX_HTTP_UPSTREAM_FT_HTTP_404 },
    { ngx_string("off"), NGX_HTTP_UPSTREAM_FT_OFF },
    { ngx_null_string, 0 }
};


static ngx_command_t  ngx_http_memcached_commands[] = {

    { ngx_string("memcached_pass"),
      NGX_HTTP_LOC_CONF|NGX_HTTP_LIF_CONF|NGX_CONF_TAKE1,
      ngx_http_memcached_pass,
      NGX_HTTP_LOC_CONF_OFFSET,
      0,
      NULL },

    { ngx_string("memcached_bind"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE12,
      ngx_http_upstream_bind_set_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, upstream.local),
      NULL },

    { ngx_string("memcached_connect_timeout"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_msec_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, upstream.connect_timeout),
      NULL },

    { ngx_string("memcached_send_timeout"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_msec_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, upstream.send_timeout),
      NULL },

    { ngx_string("memcached_buffer_size"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_size_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, upstream.buffer_size),
      NULL },

    { ngx_string("memcached_read_timeout"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_msec_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, upstream.read_timeout),
      NULL },

    { ngx_string("memcached_next_upstream"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_1MORE,
      ngx_conf_set_bitmask_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, upstream.next_upstream),
      &ngx_http_memcached_next_upstream_masks },

    { ngx_string("memcached_next_upstream_tries"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_num_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, upstream.next_upstream_tries),
      NULL },

    { ngx_string("memcached_next_upstream_timeout"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_msec_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, upstream.next_upstream_timeout),
      NULL },

    { ngx_string("memcached_gzip_flag"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_num_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_loc_conf_t, gzip_flag),
      NULL },

      ngx_null_command
};


static ngx_http_module_t  ngx_http_memcached_module_ctx = {
    NULL,                                  /* preconfiguration */
    NULL,                                  /* postconfiguration */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    NULL,                                  /* create server configuration */
    NULL,                                  /* merge server configuration */

    ngx_http_memcached_create_loc_conf,    /* create location configuration */
    ngx_http_memcached_merge_loc_conf      /* merge location configuration */
};


ngx_module_t  ngx_http_memcached_module = {
    NGX_MODULE_V1,
    &ngx_http_memcached_module_ctx,        /* module context */
    ngx_http_memcached_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_str_t  ngx_http_memcached_key = ngx_string("memcached_key");


#define NGX_HTTP_MEMCACHED_END   (sizeof(ngx_http_memcached_end) - 1)
static u_char  ngx_http_memcached_end[] = CRLF "END" CRLF;


static ngx_int_t
ngx_http_memcached_handler(ngx_http_request_t *r)
{
    ngx_int_t                       rc;
    ngx_http_upstream_t            *u;
    ngx_http_memcached_ctx_t       *ctx;
    ngx_http_memcached_loc_conf_t  *mlcf;

    if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD))) {
        return NGX_HTTP_NOT_ALLOWED;
    }

    rc = ngx_http_discard_request_body(r);

    if (rc != NGX_OK) {
        return rc;
    }

    if (ngx_http_set_content_type(r) != NGX_OK) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    if (ngx_http_upstream_create(r) != NGX_OK) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    u = r->upstream;

    ngx_str_set(&u->schema, "memcached://");
    u->output.tag = (ngx_buf_tag_t) &ngx_http_memcached_module;

    mlcf = ngx_http_get_module_loc_conf(r, ngx_http_memcached_module);

    u->conf = &mlcf->upstream;

    u->create_request = ngx_http_memcached_create_request;
    u->reinit_request = ngx_http_memcached_reinit_request;
    u->process_header = ngx_http_memcached_process_header;
    u->abort_request = ngx_http_memcached_abort_request;
    u->finalize_request = ngx_http_memcached_finalize_request;

    ctx = ngx_palloc(r->pool, sizeof(ngx_http_memcached_ctx_t));
    if (ctx == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    ctx->request = r;

    ngx_http_set_ctx(r, ctx, ngx_http_memcached_module);

    u->input_filter_init = ngx_http_memcached_filter_init;
    u->input_filter = ngx_http_memcached_filter;
    u->input_filter_ctx = ctx;

    r->main->count++;

    ngx_http_upstream_init(r);

    return NGX_DONE;
}


static ngx_int_t
ngx_http_memcached_create_request(ngx_http_request_t *r)
{
    size_t                          len;
    uintptr_t                       escape;
    ngx_buf_t                      *b;
    ngx_chain_t                    *cl;
    ngx_http_memcached_ctx_t       *ctx;
    ngx_http_variable_value_t      *vv;
    ngx_http_memcached_loc_conf_t  *mlcf;

    mlcf = ngx_http_get_module_loc_conf(r, ngx_http_memcached_module);

    vv = ngx_http_get_indexed_variable(r, mlcf->index);

    if (vv == NULL || vv->not_found || vv->len == 0) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                      "the \"$memcached_key\" variable is not set");
        return NGX_ERROR;
    }

    escape = 2 * ngx_escape_uri(NULL, vv->data, vv->len, NGX_ESCAPE_MEMCACHED);

    len = sizeof("get ") - 1 + vv->len + escape + sizeof(CRLF) - 1;

    b = ngx_create_temp_buf(r->pool, len);
    if (b == NULL) {
        return NGX_ERROR;
    }

    cl = ngx_alloc_chain_link(r->pool);
    if (cl == NULL) {
        return NGX_ERROR;
    }

    cl->buf = b;
    cl->next = NULL;

    r->upstream->request_bufs = cl;

    *b->last++ = 'g'; *b->last++ = 'e'; *b->last++ = 't'; *b->last++ = ' ';

    ctx = ngx_http_get_module_ctx(r, ngx_http_memcached_module);

    ctx->key.data = b->last;

    if (escape == 0) {
        b->last = ngx_copy(b->last, vv->data, vv->len);

    } else {
        b->last = (u_char *) ngx_escape_uri(b->last, vv->data, vv->len,
                                            NGX_ESCAPE_MEMCACHED);
    }

    ctx->key.len = b->last - ctx->key.data;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "http memcached request: \"%V\"", &ctx->key);

    *b->last++ = CR; *b->last++ = LF;

    return NGX_OK;
}


static ngx_int_t
ngx_http_memcached_reinit_request(ngx_http_request_t *r)
{
    return NGX_OK;
}


static ngx_int_t
ngx_http_memcached_process_header(ngx_http_request_t *r)
{
    u_char                         *p, *start;
    ngx_str_t                       line;
    ngx_uint_t                      flags;
    ngx_table_elt_t                *h;
    ngx_http_upstream_t            *u;
    ngx_http_memcached_ctx_t       *ctx;
    ngx_http_memcached_loc_conf_t  *mlcf;

    u = r->upstream;

    for (p = u->buffer.pos; p < u->buffer.last; p++) {
        if (*p == LF) {
            goto found;
        }
    }

    return NGX_AGAIN;

found:

    line.data = u->buffer.pos;
    line.len = p - u->buffer.pos;

    if (line.len == 0 || *(p - 1) != CR) {
        goto no_valid;
    }

    *p = '\0';
    line.len--;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "memcached: \"%V\"", &line);

    p = u->buffer.pos;

    ctx = ngx_http_get_module_ctx(r, ngx_http_memcached_module);
    mlcf = ngx_http_get_module_loc_conf(r, ngx_http_memcached_module);

    if (ngx_strncmp(p, "VALUE ", sizeof("VALUE ") - 1) == 0) {

        p += sizeof("VALUE ") - 1;

        if (ngx_strncmp(p, ctx->key.data, ctx->key.len) != 0) {
            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                          "memcached sent invalid key in response \"%V\" "
                          "for key \"%V\"",
                          &line, &ctx->key);

            return NGX_HTTP_UPSTREAM_INVALID_HEADER;
        }

        p += ctx->key.len;

        if (*p++ != ' ') {
            goto no_valid;
        }

        /* flags */

        start = p;

        while (*p) {
            if (*p++ == ' ') {
                if (mlcf->gzip_flag) {
                    goto flags;
                } else {
                    goto length;
                }
            }
        }

        goto no_valid;

    flags:

        flags = ngx_atoi(start, p - start - 1);

        if (flags == (ngx_uint_t) NGX_ERROR) {
            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                          "memcached sent invalid flags in response \"%V\" "
                          "for key \"%V\"",
                          &line, &ctx->key);
            return NGX_HTTP_UPSTREAM_INVALID_HEADER;
        }

        if (flags & mlcf->gzip_flag) {
            h = ngx_list_push(&r->headers_out.headers);
            if (h == NULL) {
                return NGX_ERROR;
            }

            h->hash = 1;
            ngx_str_set(&h->key, "Content-Encoding");
            ngx_str_set(&h->value, "gzip");
            r->headers_out.content_encoding = h;
        }

    length:

        start = p;
        p = line.data + line.len;

        u->headers_in.content_length_n = ngx_atoof(start, p - start);
        if (u->headers_in.content_length_n == NGX_ERROR) {
            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                          "memcached sent invalid length in response \"%V\" "
                          "for key \"%V\"",
                          &line, &ctx->key);
            return NGX_HTTP_UPSTREAM_INVALID_HEADER;
        }

        u->headers_in.status_n = 200;
        u->state->status = 200;
        u->buffer.pos = p + sizeof(CRLF) - 1;

        return NGX_OK;
    }

    if (ngx_strcmp(p, "END\x0d") == 0) {
        ngx_log_error(NGX_LOG_INFO, r->connection->log, 0,
                      "key: \"%V\" was not found by memcached", &ctx->key);

        u->headers_in.content_length_n = 0;
        u->headers_in.status_n = 404;
        u->state->status = 404;
        u->buffer.pos = p + sizeof("END" CRLF) - 1;
        u->keepalive = 1;

        return NGX_OK;
    }

no_valid:

    ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                  "memcached sent invalid response: \"%V\"", &line);

    return NGX_HTTP_UPSTREAM_INVALID_HEADER;
}


static ngx_int_t
ngx_http_memcached_filter_init(void *data)
{
    ngx_http_memcached_ctx_t  *ctx = data;

    ngx_http_upstream_t  *u;

    u = ctx->request->upstream;

    if (u->headers_in.status_n != 404) {
        u->length = u->headers_in.content_length_n + NGX_HTTP_MEMCACHED_END;
        ctx->rest = NGX_HTTP_MEMCACHED_END;

    } else {
        u->length = 0;
    }

    return NGX_OK;
}


static ngx_int_t
ngx_http_memcached_filter(void *data, ssize_t bytes)
{
    ngx_http_memcached_ctx_t  *ctx = data;

    u_char               *last;
    ngx_buf_t            *b;
    ngx_chain_t          *cl, **ll;
    ngx_http_upstream_t  *u;

    u = ctx->request->upstream;
    b = &u->buffer;

    if (u->length == (ssize_t) ctx->rest) {

        if (ngx_strncmp(b->last,
                   ngx_http_memcached_end + NGX_HTTP_MEMCACHED_END - ctx->rest,
                   bytes)
            != 0)
        {
            ngx_log_error(NGX_LOG_ERR, ctx->request->connection->log, 0,
                          "memcached sent invalid trailer");

            u->length = 0;
            ctx->rest = 0;

            return NGX_OK;
        }

        u->length -= bytes;
        ctx->rest -= bytes;

        if (u->length == 0) {
            u->keepalive = 1;
        }

        return NGX_OK;
    }

    for (cl = u->out_bufs, ll = &u->out_bufs; cl; cl = cl->next) {
        ll = &cl->next;
    }

    cl = ngx_chain_get_free_buf(ctx->request->pool, &u->free_bufs);
    if (cl == NULL) {
        return NGX_ERROR;
    }

    cl->buf->flush = 1;
    cl->buf->memory = 1;

    *ll = cl;

    last = b->last;
    cl->buf->pos = last;
    b->last += bytes;
    cl->buf->last = b->last;
    cl->buf->tag = u->output.tag;

    ngx_log_debug4(NGX_LOG_DEBUG_HTTP, ctx->request->connection->log, 0,
                   "memcached filter bytes:%z size:%z length:%O rest:%z",
                   bytes, b->last - b->pos, u->length, ctx->rest);

    if (bytes <= (ssize_t) (u->length - NGX_HTTP_MEMCACHED_END)) {
        u->length -= bytes;
        return NGX_OK;
    }

    last += (size_t) (u->length - NGX_HTTP_MEMCACHED_END);

    if (ngx_strncmp(last, ngx_http_memcached_end, b->last - last) != 0) {
        ngx_log_error(NGX_LOG_ERR, ctx->request->connection->log, 0,
                      "memcached sent invalid trailer");

        b->last = last;
        cl->buf->last = last;
        u->length = 0;
        ctx->rest = 0;

        return NGX_OK;
    }

    ctx->rest -= b->last - last;
    b->last = last;
    cl->buf->last = last;
    u->length = ctx->rest;

    if (u->length == 0) {
        u->keepalive = 1;
    }

    return NGX_OK;
}


static void
ngx_http_memcached_abort_request(ngx_http_request_t *r)
{
    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "abort http memcached request");
    return;
}


static void
ngx_http_memcached_finalize_request(ngx_http_request_t *r, ngx_int_t rc)
{
    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "finalize http memcached request");
    return;
}


static void *
ngx_http_memcached_create_loc_conf(ngx_conf_t *cf)
{
    ngx_http_memcached_loc_conf_t  *conf;

    conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_memcached_loc_conf_t));
    if (conf == NULL) {
        return NULL;
    }

    /*
     * set by ngx_pcalloc():
     *
     *     conf->upstream.bufs.num = 0;
     *     conf->upstream.next_upstream = 0;
     *     conf->upstream.temp_path = NULL;
     */

    conf->upstream.local = NGX_CONF_UNSET_PTR;
    conf->upstream.next_upstream_tries = NGX_CONF_UNSET_UINT;
    conf->upstream.connect_timeout = NGX_CONF_UNSET_MSEC;
    conf->upstream.send_timeout = NGX_CONF_UNSET_MSEC;
    conf->upstream.read_timeout = NGX_CONF_UNSET_MSEC;
    conf->upstream.next_upstream_timeout = NGX_CONF_UNSET_MSEC;

    conf->upstream.buffer_size = NGX_CONF_UNSET_SIZE;

    /* the hardcoded values */
    conf->upstream.cyclic_temp_file = 0;
    conf->upstream.buffering = 0;
    conf->upstream.ignore_client_abort = 0;
    conf->upstream.send_lowat = 0;
    conf->upstream.bufs.num = 0;
    conf->upstream.busy_buffers_size = 0;
    conf->upstream.max_temp_file_size = 0;
    conf->upstream.temp_file_write_size = 0;
    conf->upstream.intercept_errors = 1;
    conf->upstream.intercept_404 = 1;
    conf->upstream.pass_request_headers = 0;
    conf->upstream.pass_request_body = 0;
    conf->upstream.force_ranges = 1;

    conf->index = NGX_CONF_UNSET;
    conf->gzip_flag = NGX_CONF_UNSET_UINT;

    return conf;
}


static char *
ngx_http_memcached_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_http_memcached_loc_conf_t *prev = parent;
    ngx_http_memcached_loc_conf_t *conf = child;

    ngx_conf_merge_ptr_value(conf->upstream.local,
                              prev->upstream.local, NULL);

    ngx_conf_merge_uint_value(conf->upstream.next_upstream_tries,
                              prev->upstream.next_upstream_tries, 0);

    ngx_conf_merge_msec_value(conf->upstream.connect_timeout,
                              prev->upstream.connect_timeout, 60000);

    ngx_conf_merge_msec_value(conf->upstream.send_timeout,
                              prev->upstream.send_timeout, 60000);

    ngx_conf_merge_msec_value(conf->upstream.read_timeout,
                              prev->upstream.read_timeout, 60000);

    ngx_conf_merge_msec_value(conf->upstream.next_upstream_timeout,
                              prev->upstream.next_upstream_timeout, 0);

    ngx_conf_merge_size_value(conf->upstream.buffer_size,
                              prev->upstream.buffer_size,
                              (size_t) ngx_pagesize);

    ngx_conf_merge_bitmask_value(conf->upstream.next_upstream,
                              prev->upstream.next_upstream,
                              (NGX_CONF_BITMASK_SET
                               |NGX_HTTP_UPSTREAM_FT_ERROR
                               |NGX_HTTP_UPSTREAM_FT_TIMEOUT));

    if (conf->upstream.next_upstream & NGX_HTTP_UPSTREAM_FT_OFF) {
        conf->upstream.next_upstream = NGX_CONF_BITMASK_SET
                                       |NGX_HTTP_UPSTREAM_FT_OFF;
    }

    if (conf->upstream.upstream == NULL) {
        conf->upstream.upstream = prev->upstream.upstream;
    }

    if (conf->index == NGX_CONF_UNSET) {
        conf->index = prev->index;
    }

    ngx_conf_merge_uint_value(conf->gzip_flag, prev->gzip_flag, 0);

    return NGX_CONF_OK;
}


static char *
ngx_http_memcached_pass(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_memcached_loc_conf_t *mlcf = conf;

    ngx_str_t                 *value;
    ngx_url_t                  u;
    ngx_http_core_loc_conf_t  *clcf;

    if (mlcf->upstream.upstream) {
        return "is duplicate";
    }

    value = cf->args->elts;

    ngx_memzero(&u, sizeof(ngx_url_t));

    u.url = value[1];
    u.no_resolve = 1;

    mlcf->upstream.upstream = ngx_http_upstream_add(cf, &u, 0);
    if (mlcf->upstream.upstream == NULL) {
        return NGX_CONF_ERROR;
    }

    clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);

    clcf->handler = ngx_http_memcached_handler;

    if (clcf->name.data[clcf->name.len - 1] == '/') {
        clcf->auto_redirect = 1;
    }

    mlcf->index = ngx_http_get_variable_index(cf, &ngx_http_memcached_key);

    if (mlcf->index == NGX_ERROR) {
        return NGX_CONF_ERROR;
    }

    return NGX_CONF_OK;
}