ngx_http_memcached_hash_module.c

/*
 * ngx_http_memcached_hash_hash_module.c
 *
 * Works exactly as ngx_http_memcached, except that it hashes the key
 * with SHA256 before attempting to retrieve it. This gaurantees that
 * nginx caching works with keys longer than the allowable memcache 
 * key length.
 *
 * This module will never URI Escape the memcached key (since it is
 * hashable as-is).
 *
 * Based on work Copyright (C) Igor Sysoev
 * 
 */

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

#include <ngx_sha1.h>

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


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


static ngx_int_t ngx_http_memcached_hash_create_request(ngx_http_request_t *r);
static ngx_int_t ngx_http_memcached_hash_reinit_request(ngx_http_request_t *r);
static ngx_int_t ngx_http_memcached_hash_process_header(ngx_http_request_t *r);
static ngx_int_t ngx_http_memcached_hash_filter_init(void *data);
static ngx_int_t ngx_http_memcached_hash_filter(void *data, ssize_t bytes);
static void ngx_http_memcached_hash_abort_request(ngx_http_request_t *r);
static void ngx_http_memcached_hash_finalize_request(ngx_http_request_t *r,
    ngx_int_t rc);

static void *ngx_http_memcached_hash_create_loc_conf(ngx_conf_t *cf);
static char *ngx_http_memcached_hash_merge_loc_conf(ngx_conf_t *cf,
    void *parent, void *child);

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

static u_char*
ngx_http_memcached_hash_sha256_hash(u_char *result, const u_char *key, 
    size_t key_length);

static ngx_conf_bitmask_t  ngx_http_memcached_hash_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_hash_commands[] = {

    { ngx_string("memcached_hash_pass"),
      NGX_HTTP_LOC_CONF|NGX_HTTP_LIF_CONF|NGX_CONF_TAKE1,
      ngx_http_memcached_hash_pass,
      NGX_HTTP_LOC_CONF_OFFSET,
      0,
      NULL },

    { ngx_string("memcached_hash_bind"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_http_upstream_bind_set_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_memcached_hash_loc_conf_t, upstream.local),
      NULL },

    { ngx_string("memcached_hash_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_hash_loc_conf_t, upstream.connect_timeout),
      NULL },

    { ngx_string("memcached_hash_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_hash_loc_conf_t, upstream.send_timeout),
      NULL },

    { ngx_string("memcached_hash_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_hash_loc_conf_t, upstream.buffer_size),
      NULL },

    { ngx_string("memcached_hash_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_hash_loc_conf_t, upstream.read_timeout),
      NULL },
      
    { ngx_string("memcached_hash_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_hash_loc_conf_t, gzip_flag),
      NULL },

    { ngx_string("memcached_hash_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_hash_loc_conf_t, upstream.next_upstream),
      &ngx_http_memcached_hash_next_upstream_masks },

      ngx_null_command
};


static ngx_http_module_t  ngx_http_memcached_hash_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_hash_create_loc_conf,    /* create location configration */
    ngx_http_memcached_hash_merge_loc_conf      /* merge location configration */
};


ngx_module_t  ngx_http_memcached_hash_module = {
    NGX_MODULE_V1,
    &ngx_http_memcached_hash_module_ctx,        /* module context */
    ngx_http_memcached_hash_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_hash_key = ngx_string("memcached_hash_key");


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


static ngx_int_t
ngx_http_memcached_hash_handler(ngx_http_request_t *r)
{
    ngx_int_t                       rc;
    ngx_http_upstream_t            *u;
    ngx_http_memcached_hash_ctx_t       *ctx;
    ngx_http_memcached_hash_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_hash_module;

    mlcf = ngx_http_get_module_loc_conf(r, ngx_http_memcached_hash_module);

    u->conf = &mlcf->upstream;

    u->create_request = ngx_http_memcached_hash_create_request;
    u->reinit_request = ngx_http_memcached_hash_reinit_request;
    u->process_header = ngx_http_memcached_hash_process_header;
    u->abort_request = ngx_http_memcached_hash_abort_request;
    u->finalize_request = ngx_http_memcached_hash_finalize_request;

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

    ctx->rest = NGX_HTTP_MEMCACHED_HASH_END;
    ctx->request = r;

    ngx_http_set_ctx(r, ctx, ngx_http_memcached_hash_module);

    u->input_filter_init = ngx_http_memcached_hash_filter_init;
    u->input_filter = ngx_http_memcached_hash_filter;
    u->input_filter_ctx = ctx;

    r->main->count++;

    ngx_http_upstream_init(r);

    return NGX_DONE;
}


static ngx_int_t
ngx_http_memcached_hash_create_request(ngx_http_request_t *r)
{
    size_t                          len;
    ngx_buf_t                      *b;
    ngx_chain_t                    *cl;
    ngx_http_memcached_hash_ctx_t       *ctx;
    ngx_http_variable_value_t      *vv;
    ngx_http_memcached_hash_loc_conf_t  *mlcf;

    mlcf = ngx_http_get_module_loc_conf(r, ngx_http_memcached_hash_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_hash_key\" variable is not set");
        return NGX_ERROR;
    }

    len = sizeof("get ") - 1 + 64 + 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_hash_module);

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

    b->last = ngx_http_memcached_hash_sha256_hash(b->last, vv->data, vv->len);

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

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "http memcached hash request: \"%v\" \"%V\"", vv, &ctx->key);

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

    return NGX_OK;
}


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


static ngx_int_t
ngx_http_memcached_hash_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_hash_ctx_t       *ctx;
    ngx_http_memcached_hash_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:

    *p = '\0';

    line.len = p - u->buffer.pos - 1;
    line.data = u->buffer.pos;

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

    p = u->buffer.pos;

    ctx = ngx_http_get_module_ctx(r, ngx_http_memcached_hash_module);
    mlcf = ngx_http_get_module_loc_conf(r, ngx_http_memcached_hash_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;
            h->key.len = sizeof("Content-Encoding") - 1;
            h->key.data = (u_char *) "Content-Encoding";
            h->value.len = sizeof("gzip") - 1;
            h->value.data = (u_char *) "gzip";
    
            r->headers_out.content_encoding = h;
        }

    length:

        start = p;
        
        while (*p && *p++ != CR) { /* void */ }

        r->headers_out.content_length_n = ngx_atoof(start, p - start - 1);
        if (r->headers_out.content_length_n == -1) {
            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 + 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.status_n = 404;
        u->state->status = 404;

        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_hash_filter_init(void *data)
{
    ngx_http_memcached_hash_ctx_t  *ctx = data;

    ngx_http_upstream_t  *u;

    u = ctx->request->upstream;

    u->length += NGX_HTTP_MEMCACHED_HASH_END;

    return NGX_OK;
}


static ngx_int_t
ngx_http_memcached_hash_filter(void *data, ssize_t bytes)
{
    ngx_http_memcached_hash_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 == ctx->rest) {

        if (ngx_strncmp(b->last,
                   ngx_http_memcached_hash_end + NGX_HTTP_MEMCACHED_HASH_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;

        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:%z rest:%z",
                   bytes, b->last - b->pos, u->length, ctx->rest);

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

    last += u->length - NGX_HTTP_MEMCACHED_HASH_END;

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

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

    return NGX_OK;
}


static void
ngx_http_memcached_hash_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_hash_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_hash_create_loc_conf(ngx_conf_t *cf)
{
    ngx_http_memcached_hash_loc_conf_t  *conf;

    conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_memcached_hash_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.uri = { 0, NULL };
     *     conf->upstream.location = NULL;
     */

    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.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->index = NGX_CONF_UNSET;
    conf->gzip_flag = NGX_CONF_UNSET_UINT;
    
    return conf;
}


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

    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_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_hash_pass(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_memcached_hash_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_hash_handler;

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

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

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

    return NGX_CONF_OK;
}

static u_char*
ngx_http_memcached_hash_sha256_hash(u_char *result, const u_char *key, size_t key_length)
{
    SHA256_CTX sha256;
    u_char hash[SHA256_DIGEST_LENGTH];

    SHA256_Init(&sha256);
    SHA256_Update(&sha256, key, key_length);
    SHA256_Final(hash, &sha256);

    result = ngx_hex_dump(result, hash, SHA256_DIGEST_LENGTH);

    return result;
}