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ngx_http_empty_gif_module.c
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1 
2 /*
3  * Copyright (C) Igor Sysoev
4  * Copyright (C) Nginx, Inc.
5  */
6 
7 #include <ngx_config.h>
8 #include <ngx_core.h>
9 #include <ngx_http.h>
10 
11 
12 static char *ngx_http_empty_gif(ngx_conf_t *cf, ngx_command_t *cmd,
13  void *conf);
14 
15 static ngx_command_t ngx_http_empty_gif_commands[] = {
16 
17  { ngx_string("empty_gif"),
18  NGX_HTTP_LOC_CONF|NGX_CONF_NOARGS,
19  ngx_http_empty_gif,
20  0,
21  0,
22  NULL },
23 
24  ngx_null_command
25 };
26 
27 
28 /* the minimal single pixel transparent GIF, 43 bytes */
29 
30 static u_char ngx_empty_gif[] = {
31 
32  'G', 'I', 'F', '8', '9', 'a', /* header */
33 
34  /* logical screen descriptor */
35  0x01, 0x00, /* logical screen width */
36  0x01, 0x00, /* logical screen height */
37  0x80, /* global 1-bit color table */
38  0x01, /* background color #1 */
39  0x00, /* no aspect ratio */
40 
41  /* global color table */
42  0x00, 0x00, 0x00, /* #0: black */
43  0xff, 0xff, 0xff, /* #1: white */
44 
45  /* graphic control extension */
46  0x21, /* extension introducer */
47  0xf9, /* graphic control label */
48  0x04, /* block size */
49  0x01, /* transparent color is given, */
50  /* no disposal specified, */
51  /* user input is not expected */
52  0x00, 0x00, /* delay time */
53  0x01, /* transparent color #1 */
54  0x00, /* block terminator */
55 
56  /* image descriptor */
57  0x2c, /* image separator */
58  0x00, 0x00, /* image left position */
59  0x00, 0x00, /* image top position */
60  0x01, 0x00, /* image width */
61  0x01, 0x00, /* image height */
62  0x00, /* no local color table, no interlaced */
63 
64  /* table based image data */
65  0x02, /* LZW minimum code size, */
66  /* must be at least 2-bit */
67  0x02, /* block size */
68  0x4c, 0x01, /* compressed bytes 01_001_100, 0000000_1 */
69  /* 100: clear code */
70  /* 001: 1 */
71  /* 101: end of information code */
72  0x00, /* block terminator */
73 
74  0x3B /* trailer */
75 };
76 
77 
78 static ngx_http_module_t ngx_http_empty_gif_module_ctx = {
79  NULL, /* preconfiguration */
80  NULL, /* postconfiguration */
81 
82  NULL, /* create main configuration */
83  NULL, /* init main configuration */
84 
85  NULL, /* create server configuration */
86  NULL, /* merge server configuration */
87 
88  NULL, /* create location configuration */
89  NULL /* merge location configuration */
90 };
91 
92 
93 ngx_module_t ngx_http_empty_gif_module = {
94  NGX_MODULE_V1,
95  &ngx_http_empty_gif_module_ctx, /* module context */
96  ngx_http_empty_gif_commands, /* module directives */
97  NGX_HTTP_MODULE, /* module type */
98  NULL, /* init master */
99  NULL, /* init module */
100  NULL, /* init process */
101  NULL, /* init thread */
102  NULL, /* exit thread */
103  NULL, /* exit process */
104  NULL, /* exit master */
105  NGX_MODULE_V1_PADDING
106 };
107 
108 
109 static ngx_str_t ngx_http_gif_type = ngx_string("image/gif");
110 
111 
112 static ngx_int_t
113 ngx_http_empty_gif_handler(ngx_http_request_t *r)
114 {
115  ngx_http_complex_value_t cv;
116 
117  if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD))) {
118  return NGX_HTTP_NOT_ALLOWED;
119  }
120 
121  ngx_memzero(&cv, sizeof(ngx_http_complex_value_t));
122 
123  cv.value.len = sizeof(ngx_empty_gif);
124  cv.value.data = ngx_empty_gif;
125  r->headers_out.last_modified_time = 23349600;
126 
127  return ngx_http_send_response(r, NGX_HTTP_OK, &ngx_http_gif_type, &cv);
128 }
129 
130 
131 static char *
132 ngx_http_empty_gif(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
133 {
134  ngx_http_core_loc_conf_t *clcf;
135 
136  clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);
137  clcf->handler = ngx_http_empty_gif_handler;
138 
139  return NGX_CONF_OK;
140 }
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