text: 
  /*
   * Copyright (C) Igor Sysoev
   */
  
  #include <ngx_config.h>
  #include <ngx_core.h>
  #include <ngx_http.h>
  
  
  static char *ngx_http_empty_gif(ngx_conf_t *cf, ngx_command_t *cmd,
      void *conf);
  
  static ngx_command_t  ngx_http_empty_gif_commands[] = {
  
      { ngx_string("empty_gif"),
        NGX_HTTP_LOC_CONF|NGX_CONF_NOARGS,
        ngx_http_empty_gif,
        0,
        0,
        NULL },
  
        ngx_null_command
  };
  
  
  /* the minimal single pixel transparent GIF, 43 bytes */
  
  static u_char  ngx_empty_gif[] = {
  
      'G', 'I', 'F', '8', '9', 'a',  /* header                                 */
  
                                     /* logical screen descriptor              */
      0x01, 0x00,                    /* logical screen width                   */
      0x01, 0x00,                    /* logical screen height                  */
      0x80,                          /* global 1-bit color table               */
      0x01,                          /* background color #1                    */
      0x00,                          /* no aspect ratio                        */
  
                                     /* global color table                     */
      0x00, 0x00, 0x00,              /* #0: black                              */
      0xff, 0xff, 0xff,              /* #1: white                              */
  
                                     /* graphic control extension              */
      0x21,                          /* extension introducer                   */
      0xf9,                          /* graphic control label                  */
      0x04,                          /* block size                             */
      0x01,                          /* transparent color is given,            */
                                     /*     no disposal specified,             */
                                     /*     user input is not expected         */
      0x00, 0x00,                    /* delay time                             */
      0x01,                          /* transparent color #1                   */
      0x00,                          /* block terminator                       */
  
                                     /* image descriptor                       */
      0x2c,                          /* image separator                        */
      0x00, 0x00,                    /* image left position                    */
      0x00, 0x00,                    /* image top position                     */
      0x01, 0x00,                    /* image width                            */
      0x01, 0x00,                    /* image height                           */
      0x00,                          /* no local color table, no interlaced    */
  
                                     /* table based image data                 */
      0x02,                          /* LZW minimum code size,                 */
                                     /*     must be at least 2-bit             */
      0x02,                          /* block size                             */
      0x4c, 0x01,                    /* compressed bytes 01_001_100, 0000000_1 */
                                     /* 100: clear code                        */
                                     /* 001: 1                                 */
                                     /* 101: end of information code           */
      0x00,                          /* block terminator                       */
  
      0x3B                           /* trailer                                */
  };
  
  
  static ngx_http_module_t  ngx_http_empty_gif_module_ctx = {
      NULL,                          /* preconfiguration */
      NULL,                          /* postconfiguration */
  
      NULL,                          /* create main configuration */
      NULL,                          /* init main configuration */
  
      NULL,                          /* create server configuration */
      NULL,                          /* merge server configuration */
  
      NULL,                          /* create location configuration */
      NULL                           /* merge location configuration */
  };
  
  
  ngx_module_t  ngx_http_empty_gif_module = {
      NGX_MODULE_V1,
      &ngx_http_empty_gif_module_ctx, /* module context */
      ngx_http_empty_gif_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_empty_gif_handler(ngx_http_request_t *r)
  {
      ngx_int_t     rc;
      ngx_buf_t    *b;
      ngx_chain_t   out;
  
      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;
      }
  
      r->headers_out.content_type_len = sizeof("image/gif") - 1;
      ngx_str_set(&r->headers_out.content_type, "image/gif");
  
      if (r->method == NGX_HTTP_HEAD) {
          r->headers_out.status = NGX_HTTP_OK;
          r->headers_out.content_length_n = sizeof(ngx_empty_gif);
          r->headers_out.last_modified_time = 23349600;
  
          return ngx_http_send_header(r);
      }
  
      b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
      if (b == NULL) {
          return NGX_HTTP_INTERNAL_SERVER_ERROR;
      }
  
      out.buf = b;
      out.next = NULL;
  
      b->pos = ngx_empty_gif;
      b->last = ngx_empty_gif + sizeof(ngx_empty_gif);
      b->memory = 1;
      b->last_buf = 1;
  
      r->headers_out.status = NGX_HTTP_OK;
      r->headers_out.content_length_n = sizeof(ngx_empty_gif);
      r->headers_out.last_modified_time = 23349600;
  
      rc = ngx_http_send_header(r);
  
      if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
          return rc;
      }
  
      return ngx_http_output_filter(r, &out);
  }
  
  
  static char *
  ngx_http_empty_gif(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
  {
      ngx_http_core_loc_conf_t  *clcf;
  
      clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);
      clcf->handler = ngx_http_empty_gif_handler;
  
      return NGX_CONF_OK;
  }
  