1 // This file is part of the Civetweb project, http://code.google.com/p/civetweb
2 // It implements an online chat server. For more details,
3 // see the documentation on the project web site.
4 // To test the application,
5 // 1. type "make" in the directory where this file lives
6 // 2. point your browser to http://127.0.0.1:8081
7
8 #include <stdio.h>
9 #include <stdlib.h>
10 #include <assert.h>
11 #include <string.h>
12 #include <time.h>
13 #include <stdarg.h>
14 #include <pthread.h>
15
16 #include "civetweb.h"
17
18 #define MAX_USER_LEN 20
19 #define MAX_MESSAGE_LEN 100
20 #define MAX_MESSAGES 5
21 #define MAX_SESSIONS 2
22 #define SESSION_TTL 120
23
24 static const char *authorize_url = "/authorize";
25 static const char *login_url = "/login.html";
26 static const char *ajax_reply_start =
27 "HTTP/1.1 200 OK\r\n"
28 "Cache: no-cache\r\n"
29 "Content-Type: application/x-javascript\r\n"
30 "\r\n";
31
32 // Describes single message sent to a chat. If user is empty (0 length),
33 // the message is then originated from the server itself.
34 struct message {
35 long id; // Message ID
36 char user[MAX_USER_LEN]; // User that have sent the message
37 char text[MAX_MESSAGE_LEN]; // Message text
38 time_t timestamp; // Message timestamp, UTC
39 };
40
41 // Describes web session.
42 struct session {
43 char session_id[33]; // Session ID, must be unique
44 char random[20]; // Random data used for extra user validation
45 char user[MAX_USER_LEN]; // Authenticated user
46 time_t expire; // Expiration timestamp, UTC
47 };
48
49 static struct message messages[MAX_MESSAGES]; // Ringbuffer for messages
50 static struct session sessions[MAX_SESSIONS]; // Current sessions
51 static long last_message_id;
52
53 // Protects messages, sessions, last_message_id
54 static pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;
55
56 // Get session object for the connection. Caller must hold the lock.
get_session(const struct mg_connection * conn)57 static struct session *get_session(const struct mg_connection *conn)
58 {
59 int i;
60 const char *cookie = mg_get_header(conn, "Cookie");
61 char session_id[33];
62 time_t now = time(NULL);
63 mg_get_cookie(cookie, "session", session_id, sizeof(session_id));
64 for (i = 0; i < MAX_SESSIONS; i++) {
65 if (sessions[i].expire != 0 &&
66 sessions[i].expire > now &&
67 strcmp(sessions[i].session_id, session_id) == 0) {
68 break;
69 }
70 }
71 return i == MAX_SESSIONS ? NULL : &sessions[i];
72 }
73
get_qsvar(const struct mg_request_info * request_info,const char * name,char * dst,size_t dst_len)74 static void get_qsvar(const struct mg_request_info *request_info,
75 const char *name, char *dst, size_t dst_len)
76 {
77 const char *qs = request_info->query_string;
78 mg_get_var(qs, strlen(qs == NULL ? "" : qs), name, dst, dst_len);
79 }
80
81 // Get a get of messages with IDs greater than last_id and transform them
82 // into a JSON string. Return that string to the caller. The string is
83 // dynamically allocated, caller must free it. If there are no messages,
84 // NULL is returned.
messages_to_json(long last_id)85 static char *messages_to_json(long last_id)
86 {
87 const struct message *message;
88 int max_msgs, len;
89 char buf[sizeof(messages)]; // Large enough to hold all messages
90
91 // Read-lock the ringbuffer. Loop over all messages, making a JSON string.
92 pthread_rwlock_rdlock(&rwlock);
93 len = 0;
94 max_msgs = sizeof(messages) / sizeof(messages[0]);
95 // If client is too far behind, return all messages.
96 if (last_message_id - last_id > max_msgs) {
97 last_id = last_message_id - max_msgs;
98 }
99 for (; last_id < last_message_id; last_id++) {
100 message = &messages[last_id % max_msgs];
101 if (message->timestamp == 0) {
102 break;
103 }
104 // buf is allocated on stack and hopefully is large enough to hold all
105 // messages (it may be too small if the ringbuffer is full and all
106 // messages are large. in this case asserts will trigger).
107 len += snprintf(buf + len, sizeof(buf) - len,
108 "{user: '%s', text: '%s', timestamp: %lu, id: %ld},",
109 message->user, message->text, message->timestamp, message->id);
110 assert(len > 0);
111 assert((size_t) len < sizeof(buf));
112 }
113 pthread_rwlock_unlock(&rwlock);
114
115 return len == 0 ? NULL : strdup(buf);
116 }
117
118 // If "callback" param is present in query string, this is JSONP call.
119 // Return 1 in this case, or 0 if "callback" is not specified.
120 // Wrap an output in Javascript function call.
handle_jsonp(struct mg_connection * conn,const struct mg_request_info * request_info)121 static int handle_jsonp(struct mg_connection *conn,
122 const struct mg_request_info *request_info)
123 {
124 char cb[64];
125
126 get_qsvar(request_info, "callback", cb, sizeof(cb));
127 if (cb[0] != '\0') {
128 mg_printf(conn, "%s(", cb);
129 }
130
131 return cb[0] == '\0' ? 0 : 1;
132 }
133
134 // A handler for the /ajax/get_messages endpoint.
135 // Return a list of messages with ID greater than requested.
ajax_get_messages(struct mg_connection * conn,const struct mg_request_info * request_info)136 static void ajax_get_messages(struct mg_connection *conn,
137 const struct mg_request_info *request_info)
138 {
139 char last_id[32], *json;
140 int is_jsonp;
141
142 mg_printf(conn, "%s", ajax_reply_start);
143 is_jsonp = handle_jsonp(conn, request_info);
144
145 get_qsvar(request_info, "last_id", last_id, sizeof(last_id));
146 if ((json = messages_to_json(strtoul(last_id, NULL, 10))) != NULL) {
147 mg_printf(conn, "[%s]", json);
148 free(json);
149 }
150
151 if (is_jsonp) {
152 mg_printf(conn, "%s", ")");
153 }
154 }
155
156 // Allocate new message. Caller must hold the lock.
new_message(void)157 static struct message *new_message(void)
158 {
159 static int size = sizeof(messages) / sizeof(messages[0]);
160 struct message *message = &messages[last_message_id % size];
161 message->id = last_message_id++;
162 message->timestamp = time(0);
163 return message;
164 }
165
my_strlcpy(char * dst,const char * src,size_t len)166 static void my_strlcpy(char *dst, const char *src, size_t len)
167 {
168 strncpy(dst, src, len);
169 dst[len - 1] = '\0';
170 }
171
172 // A handler for the /ajax/send_message endpoint.
ajax_send_message(struct mg_connection * conn,const struct mg_request_info * request_info)173 static void ajax_send_message(struct mg_connection *conn,
174 const struct mg_request_info *request_info)
175 {
176 struct message *message;
177 struct session *session;
178 char text[sizeof(message->text) - 1];
179 int is_jsonp;
180
181 mg_printf(conn, "%s", ajax_reply_start);
182 is_jsonp = handle_jsonp(conn, request_info);
183
184 get_qsvar(request_info, "text", text, sizeof(text));
185 if (text[0] != '\0') {
186 // We have a message to store. Write-lock the ringbuffer,
187 // grab the next message and copy data into it.
188 pthread_rwlock_wrlock(&rwlock);
189 message = new_message();
190 // TODO(lsm): JSON-encode all text strings
191 session = get_session(conn);
192 assert(session != NULL);
193 my_strlcpy(message->text, text, sizeof(text));
194 my_strlcpy(message->user, session->user, sizeof(message->user));
195 pthread_rwlock_unlock(&rwlock);
196 }
197
198 mg_printf(conn, "%s", text[0] == '\0' ? "false" : "true");
199
200 if (is_jsonp) {
201 mg_printf(conn, "%s", ")");
202 }
203 }
204
205 // Redirect user to the login form. In the cookie, store the original URL
206 // we came from, so that after the authorization we could redirect back.
redirect_to_login(struct mg_connection * conn,const struct mg_request_info * request_info)207 static void redirect_to_login(struct mg_connection *conn,
208 const struct mg_request_info *request_info)
209 {
210 mg_printf(conn, "HTTP/1.1 302 Found\r\n"
211 "Set-Cookie: original_url=%s\r\n"
212 "Location: %s\r\n\r\n",
213 request_info->uri, login_url);
214 }
215
216 // Return 1 if username/password is allowed, 0 otherwise.
check_password(const char * user,const char * password)217 static int check_password(const char *user, const char *password)
218 {
219 // In production environment we should ask an authentication system
220 // to authenticate the user.
221 // Here however we do trivial check that user and password are not empty
222 return (user[0] && password[0]);
223 }
224
225 // Allocate new session object
new_session(void)226 static struct session *new_session(void)
227 {
228 int i;
229 time_t now = time(NULL);
230 pthread_rwlock_wrlock(&rwlock);
231 for (i = 0; i < MAX_SESSIONS; i++) {
232 if (sessions[i].expire == 0 || sessions[i].expire < now) {
233 sessions[i].expire = time(0) + SESSION_TTL;
234 break;
235 }
236 }
237 pthread_rwlock_unlock(&rwlock);
238 return i == MAX_SESSIONS ? NULL : &sessions[i];
239 }
240
241 // Generate session ID. buf must be 33 bytes in size.
242 // Note that it is easy to steal session cookies by sniffing traffic.
243 // This is why all communication must be SSL-ed.
generate_session_id(char * buf,const char * random,const char * user)244 static void generate_session_id(char *buf, const char *random,
245 const char *user)
246 {
247 mg_md5(buf, random, user, NULL);
248 }
249
send_server_message(const char * fmt,...)250 static void send_server_message(const char *fmt, ...)
251 {
252 va_list ap;
253 struct message *message;
254
255 pthread_rwlock_wrlock(&rwlock);
256 message = new_message();
257 message->user[0] = '\0'; // Empty user indicates server message
258 va_start(ap, fmt);
259 vsnprintf(message->text, sizeof(message->text), fmt, ap);
260 va_end(ap);
261
262 pthread_rwlock_unlock(&rwlock);
263 }
264
265 // A handler for the /authorize endpoint.
266 // Login page form sends user name and password to this endpoint.
authorize(struct mg_connection * conn,const struct mg_request_info * request_info)267 static void authorize(struct mg_connection *conn,
268 const struct mg_request_info *request_info)
269 {
270 char user[MAX_USER_LEN], password[MAX_USER_LEN];
271 struct session *session;
272
273 // Fetch user name and password.
274 get_qsvar(request_info, "user", user, sizeof(user));
275 get_qsvar(request_info, "password", password, sizeof(password));
276
277 if (check_password(user, password) && (session = new_session()) != NULL) {
278 // Authentication success:
279 // 1. create new session
280 // 2. set session ID token in the cookie
281 // 3. remove original_url from the cookie - not needed anymore
282 // 4. redirect client back to the original URL
283 //
284 // The most secure way is to stay HTTPS all the time. However, just to
285 // show the technique, we redirect to HTTP after the successful
286 // authentication. The danger of doing this is that session cookie can
287 // be stolen and an attacker may impersonate the user.
288 // Secure application must use HTTPS all the time.
289 my_strlcpy(session->user, user, sizeof(session->user));
290 snprintf(session->random, sizeof(session->random), "%d", rand());
291 generate_session_id(session->session_id, session->random, session->user);
292 send_server_message("<%s> joined", session->user);
293 mg_printf(conn, "HTTP/1.1 302 Found\r\n"
294 "Set-Cookie: session=%s; max-age=3600; http-only\r\n" // Session ID
295 "Set-Cookie: user=%s\r\n" // Set user, needed by Javascript code
296 "Set-Cookie: original_url=/; max-age=0\r\n" // Delete original_url
297 "Location: /\r\n\r\n",
298 session->session_id, session->user);
299 } else {
300 // Authentication failure, redirect to login.
301 redirect_to_login(conn, request_info);
302 }
303 }
304
305 // Return 1 if request is authorized, 0 otherwise.
is_authorized(const struct mg_connection * conn,const struct mg_request_info * request_info)306 static int is_authorized(const struct mg_connection *conn,
307 const struct mg_request_info *request_info)
308 {
309 struct session *session;
310 char valid_id[33];
311 int authorized = 0;
312
313 // Always authorize accesses to login page and to authorize URI
314 if (!strcmp(request_info->uri, login_url) ||
315 !strcmp(request_info->uri, authorize_url)) {
316 return 1;
317 }
318
319 pthread_rwlock_rdlock(&rwlock);
320 if ((session = get_session(conn)) != NULL) {
321 generate_session_id(valid_id, session->random, session->user);
322 if (strcmp(valid_id, session->session_id) == 0) {
323 session->expire = time(0) + SESSION_TTL;
324 authorized = 1;
325 }
326 }
327 pthread_rwlock_unlock(&rwlock);
328
329 return authorized;
330 }
331
redirect_to_ssl(struct mg_connection * conn,const struct mg_request_info * request_info)332 static void redirect_to_ssl(struct mg_connection *conn,
333 const struct mg_request_info *request_info)
334 {
335 const char *p, *host = mg_get_header(conn, "Host");
336 if (host != NULL && (p = strchr(host, ':')) != NULL) {
337 mg_printf(conn, "HTTP/1.1 302 Found\r\n"
338 "Location: https://%.*s:8082/%s:8082\r\n\r\n",
339 (int) (p - host), host, request_info->uri);
340 } else {
341 mg_printf(conn, "%s", "HTTP/1.1 500 Error\r\n\r\nHost: header is not set");
342 }
343 }
344
begin_request_handler(struct mg_connection * conn)345 static int begin_request_handler(struct mg_connection *conn)
346 {
347 const struct mg_request_info *request_info = mg_get_request_info(conn);
348 int processed = 1;
349
350 if (!request_info->is_ssl) {
351 redirect_to_ssl(conn, request_info);
352 } else if (!is_authorized(conn, request_info)) {
353 redirect_to_login(conn, request_info);
354 } else if (strcmp(request_info->uri, authorize_url) == 0) {
355 authorize(conn, request_info);
356 } else if (strcmp(request_info->uri, "/ajax/get_messages") == 0) {
357 ajax_get_messages(conn, request_info);
358 } else if (strcmp(request_info->uri, "/ajax/send_message") == 0) {
359 ajax_send_message(conn, request_info);
360 } else {
361 // No suitable handler found, mark as not processed. Civetweb will
362 // try to serve the request.
363 processed = 0;
364 }
365 return processed;
366 }
367
368 static const char *options[] = {
369 "document_root", "html",
370 "listening_ports", "8081,8082s",
371 "ssl_certificate", "ssl_cert.pem",
372 "num_threads", "5",
373 NULL
374 };
375
main(void)376 int main(void)
377 {
378 struct mg_callbacks callbacks;
379 struct mg_context *ctx;
380
381 // Initialize random number generator. It will be used later on for
382 // the session identifier creation.
383 srand((unsigned) time(0));
384
385 // Setup and start Civetweb
386 memset(&callbacks, 0, sizeof(callbacks));
387 callbacks.begin_request = begin_request_handler;
388 if ((ctx = mg_start(&callbacks, NULL, options)) == NULL) {
389 printf("%s\n", "Cannot start chat server, fatal exit");
390 exit(EXIT_FAILURE);
391 }
392
393 // Wait until enter is pressed, then exit
394 printf("Chat server started on ports %s, press enter to quit.\n",
395 mg_get_option(ctx, "listening_ports"));
396 getchar();
397 mg_stop(ctx);
398 printf("%s\n", "Chat server stopped.");
399
400 return EXIT_SUCCESS;
401 }
402
403 // vim:ts=2:sw=2:et
404