webcit/context_loop.c

   1 /*
   2  * context_loop.c
   3  *
   4  * This is the other half of the webserver.  It handles the task of hooking
   5  * up HTTP requests with the session they belong to, using HTTP cookies to
   6  * keep track of things.  If the HTTP request doesn't belong to any currently
   7  * active session, a new session is spawned.
   8  *
   9  * $Id$
  10  */
  11
  12 #include <ctype.h>
  13 #include <stdlib.h>
  14 #ifdef HAVE_UNISTD_H
  15 #include <unistd.h>
  16 #endif
  17 #include <stdio.h>
  18 #ifdef HAVE_FCNTL_H
  19 #include <fcntl.h>
  20 #endif
  21 #include <signal.h>
  22 #include <sys/types.h>
  23 #include <sys/wait.h>
  24 #include <sys/socket.h>
  25 #ifdef HAVE_SYS_TIME_H
  26 #include <sys/time.h>
  27 #endif
  28 #ifdef HAVE_LIMITS_H
  29 #include <limits.h>
  30 #endif
  31 #include <netinet/in.h>
  32 #include <netdb.h>
  33 #include <string.h>
  34 #include <errno.h>
  35 #include <stdarg.h>
  36 #include <pthread.h>
  37 #include <signal.h>
  38 #include "webcit.h"
  39 #include "webserver.h"
  40
  41 /*
  42  * We keep one of these around for each active session
  43  */
  44 struct wc_session {
  45         struct wc_session *next;        /* Next session in list */
  46         int session_id;         /* Session ID */
  47         pid_t webcit_pid;       /* PID of the webcit process */
  48         int inpipe[2];          /* Data from webserver to session */
  49         int outpipe[2];         /* Data from session to webserver */
  50         pthread_mutex_t critter;        /* Critical section uses pipes */
  51         time_t lastreq;         /* Timestamp of most recent http */
  52 };
  53
  54 struct wc_session *SessionList = NULL;
  55 extern const char *defaulthost;
  56 extern const char *defaultport;
  57
  58 /* Only one thread may manipulate SessionList at a time... */
  59 pthread_mutex_t MasterCritter;
  60
  61
  62 /*
  63  * Grab a lock on the session, so other threads don't try to access
  64  * the pipes at the same time.
  65  */
  66 static void lock_session(struct wc_session *session)
  67 {
  68         printf("Locking session %d...\n", session->session_id);
  69         pthread_mutex_lock(&session->critter);
  70         printf("   ...got lock\n");
  71 }
  72
  73 /*
  74  * Let go of the lock.
  75  */
  76 static void unlock_session(struct wc_session *session)
  77 {
  78         printf("Unlocking.\n");
  79         pthread_mutex_unlock(&session->critter);
  80 }
  81
  82 /*
  83  * Remove a session context from the list
  84  */
  85 void remove_session(struct wc_session *TheSession, int do_lock)
  86 {
  87         struct wc_session *sptr;
  88
  89         printf("Removing session.\n");
  90         if (do_lock)
  91                 pthread_mutex_lock(&MasterCritter);
  92
  93         if (SessionList == TheSession) {
  94                 SessionList = SessionList->next;
  95         } else {
  96                 for (sptr = SessionList; sptr != NULL; sptr = sptr->next) {
  97                         if (sptr->next == TheSession) {
  98                                 sptr->next = TheSession->next;
  99                         }
 100                 }
 101         }
 102
 103         close(TheSession->inpipe[1]);
 104         close(TheSession->outpipe[0]);
 105         if (do_lock)
 106                 unlock_session(TheSession);
 107         free(TheSession);
 108
 109         pthread_mutex_unlock(&MasterCritter);
 110 }
 111
 112
 113
 114
 115 void do_housekeeping(void)
 116 {
 117         struct wc_session *sptr;
 118
 119         pthread_mutex_lock(&MasterCritter);
 120
 121         /* Kill idle sessions */
 122         for (sptr = SessionList; sptr != NULL; sptr = sptr->next) {
 123                 if ((time(NULL) - (sptr->lastreq)) > (time_t) WEBCIT_TIMEOUT) {
 124                         kill(sptr->webcit_pid, 15);
 125                 }
 126         }
 127
 128         /* Remove dead sessions */
 129         for (sptr = SessionList; sptr != NULL; sptr = sptr->next) {
 130                 if (kill(sptr->webcit_pid, 0)) {
 131                         remove_session(sptr, 0);
 132                 }
 133         }
 134
 135         pthread_mutex_unlock(&MasterCritter);
 136 }
 137
 138
 139 /*
 140  * Wake up occasionally and clean house
 141  */
 142 void housekeeping_loop(void)
 143 {
 144         while (1) {
 145                 sleep(HOUSEKEEPING);
 146                 do_housekeeping();
 147         }
 148 }
 149
 150
 151
 152
 153
 154 int GenerateSessionID(void)
 155 {
 156         return getpid();
 157 }
 158
 159
 160 void gets0(int fd, char buf[])
 161 {
 162
 163         buf[0] = 0;
 164         do {
 165                 buf[strlen(buf) + 1] = 0;
 166                 read(fd, &buf[strlen(buf)], 1);
 167         } while (buf[strlen(buf) - 1] >= 32);
 168         buf[strlen(buf) - 1] = 0;
 169 }
 170
 171 /*
 172  * Collapse multiple cookies on one line
 173  */
 174 void req_gets(int sock, char *buf, char *hold)
 175 {
 176         int a;
 177
 178         if (strlen(hold) == 0) {
 179                 client_gets(sock, buf);
 180         } else {
 181                 strcpy(buf, hold);
 182         }
 183         strcpy(hold, "");
 184
 185         if (!strncasecmp(buf, "Cookie: ", 8)) {
 186                 for (a = 0; a < strlen(buf); ++a)
 187                         if (buf[a] == ';') {
 188                                 sprintf(hold, "Cookie: %s", &buf[a + 1]);
 189                                 buf[a] = 0;
 190                                 while (isspace(hold[8]))
 191                                         strcpy(&hold[8], &hold[9]);
 192                                 return;
 193                         }
 194         }
 195 }
 196
 197 /*
 198  * lingering_close() a`la Apache. see
 199  * http://www.apache.org/docs/misc/fin_wait_2.html for rationale
 200  */
 201
 202 static int lingering_close(int fd)
 203 {
 204         char buf[256];
 205         int i;
 206         fd_set set;
 207         struct timeval tv, start;
 208
 209         gettimeofday(&start, NULL);
 210         shutdown(fd, 1);
 211         do {
 212                 do {
 213                         gettimeofday(&tv, NULL);
 214                         tv.tv_sec = SLEEPING - (tv.tv_sec - start.tv_sec);
 215                         tv.tv_usec = start.tv_usec - tv.tv_usec;
 216                         if (tv.tv_usec < 0) {
 217                                 tv.tv_sec--;
 218                                 tv.tv_usec += 1000000;
 219                         }
 220                         FD_ZERO(&set);
 221                         FD_SET(fd, &set);
 222                         i = select(fd + 1, &set, NULL, NULL, &tv);
 223                 } while (i == -1 && errno == EINTR);
 224
 225                 if (i <= 0)
 226                         break;
 227
 228                 i = read(fd, buf, sizeof buf);
 229         } while (i != 0 && (i != -1 || errno == EINTR));
 230
 231         return close(fd);
 232 }
 233
 234 /*
 235  * This loop gets called once for every HTTP connection made to WebCit.
 236  */
 237 void *context_loop(int sock)
 238 {
 239         char (*req)[256];
 240         char buf[256], hold[256];
 241         char browser_host[256];
 242         char browser[256];
 243         int num_lines = 0;
 244         int a;
 245         int f;
 246         int desired_session = 0;
 247         int got_cookie = 0;
 248         char str_session[256];
 249         struct wc_session *sptr;
 250         struct wc_session *TheSession;
 251         int ContentLength;
 252         int CloseSession = 0;
 253
 254         if ((req = malloc((long) sizeof(char[256][256]))) == NULL) {
 255                 sprintf(buf, "Can't malloc buffers; dropping connection.\n");
 256                 fprintf(stderr, "%s", buf);
 257                 write(sock, buf, strlen(buf));
 258                 close(sock);
 259                 pthread_exit(NULL);
 260         }
 261         bzero(req, sizeof(char[256][256]));     /* clear it out */
 262         strcpy(browser, "unknown");
 263
 264         printf("Reading request from socket %d\n", sock);
 265
 266         /*
 267          * Find out what it is that the web browser is asking for
 268          */
 269         ContentLength = 0;
 270         do {
 271                 req_gets(sock, buf, hold);
 272                 if (!strncasecmp(buf, "Cookie: webcit=", 15)) {
 273                         cookie_to_stuff(&buf[15], &desired_session,
 274                                 NULL, NULL, NULL);
 275                         got_cookie = 1;
 276                 }
 277                 else if (!strncasecmp(buf, "Content-length: ", 16)) {
 278                         ContentLength = atoi(&buf[16]);
 279                 }
 280                 else if (!strncasecmp(buf, "User-agent: ", 12)) {
 281                         strcpy(browser, &buf[12]);
 282                 }
 283                 strcpy(&req[num_lines++][0], buf);
 284         } while (strlen(buf) > 0);
 285
 286
 287         /*
 288          * If requesting a non-root page, there should already be a cookie
 289          * set.  If there isn't, the client browser has cookies turned off
 290          * (or doesn't support them) and we have to barf & bail.
 291          */
 292         strcpy(buf, &req[0][0]);
 293         if (!strncasecmp(buf, "GET ", 4)) strcpy(buf, &buf[4]);
 294         else if (!strncasecmp(buf, "HEAD ", 5)) strcpy(buf, &buf[5]);
 295         if (buf[1]==' ') buf[1]=0;
 296         if ( (strcmp(buf, "/")) && (got_cookie == 0)) {
 297                 strcpy(&req[0][0], "GET /static/nocookies.html HTTP/1.0");
 298         }
 299
 300
 301         /*
 302          * See if there's an existing session open with the desired ID
 303          */
 304         TheSession = NULL;
 305         if (desired_session != 0) {
 306                 pthread_mutex_lock(&MasterCritter);
 307                 for (sptr = SessionList; sptr != NULL; sptr = sptr->next) {
 308                         if (sptr->session_id == desired_session) {
 309                                 TheSession = sptr;
 310                                 lock_session(TheSession);
 311                         }
 312                 }
 313                 pthread_mutex_unlock(&MasterCritter);
 314         }
 315         /*
 316          * Before we trumpet to the universe that the session we're looking
 317          * for actually exists, check first to make sure it's still there.
 318          */
 319         if (TheSession != NULL) {
 320                 if (kill(TheSession->webcit_pid, 0)) {
 321                         printf("   Session is *DEAD* !!\n");
 322                         remove_session(TheSession, 1);
 323                         TheSession = NULL;
 324                 }
 325         }
 326         /*
 327          * Create a new session if we have to
 328          */
 329         if (TheSession == NULL) {
 330                 printf("Creating a new session\n");
 331                 locate_host(browser_host, sock);
 332                 pthread_mutex_lock(&MasterCritter);
 333                 TheSession = (struct wc_session *)
 334                     malloc(sizeof(struct wc_session));
 335                 TheSession->session_id = GenerateSessionID();
 336                 pipe(TheSession->inpipe);
 337                 pipe(TheSession->outpipe);
 338                 pthread_mutex_init(&TheSession->critter, NULL);
 339                 lock_session(TheSession);
 340                 TheSession->next = SessionList;
 341                 SessionList = TheSession;
 342                 pthread_mutex_unlock(&MasterCritter);
 343                 sprintf(str_session, "%d", TheSession->session_id);
 344                 f = fork();
 345                 if (f > 0)
 346                         TheSession->webcit_pid = f;
 347
 348                 fflush(stdout);
 349                 fflush(stdin);
 350                 if (f == 0) {
 351
 352                         /* Hook stdio to the ends of the pipe we're using */
 353                         dup2(TheSession->inpipe[0], 0);
 354                         dup2(TheSession->outpipe[1], 1);
 355
 356                         /* Close the ends of the pipes that we're not using */
 357                         close(TheSession->inpipe[1]);
 358                         close(TheSession->outpipe[0]);
 359
 360                         /* Close the HTTP socket in this pid; don't need it */
 361                         close(sock);
 362
 363                         /* Run the actual WebCit session */
 364                         execlp("./webcit", "webcit", str_session, defaulthost,
 365                                defaultport, browser_host, browser, NULL);
 366
 367                         /* Simple page to display if exec fails */
 368                         printf("HTTP/1.0 404 WebCit Failure\n\n");
 369                         printf("Server: %s\n", SERVER);
 370                         printf("X-WebCit-Session: close\n");
 371                         printf("Content-type: text/html\n");
 372                         printf("Content-length: 76\n");
 373                         printf("\n");
 374                         printf("<HTML><HEAD><TITLE>Error</TITLE></HEAD><BODY>\n");
 375                         printf("execlp() failed: %s</BODY></HTML>\n", strerror(errno));
 376                         exit(0);
 377                 } else {
 378                         /* Close the ends of the pipes that we're not using */
 379                         close(TheSession->inpipe[0]);
 380                         close(TheSession->outpipe[1]);
 381                 }
 382         }
 383         /*
 384          * Send the request to the appropriate session...
 385          */
 386         TheSession->lastreq = time(NULL);
 387         printf("   Writing %d lines of command\n", num_lines);
 388         printf("%s\n", &req[0][0]);
 389         for (a = 0; a < num_lines; ++a) {
 390                 write(TheSession->inpipe[1], &req[a][0], strlen(&req[a][0]));
 391                 write(TheSession->inpipe[1], "\n", 1);
 392         }
 393         printf("   Writing %d bytes of content\n", ContentLength);
 394         while (ContentLength > 0) {
 395                 a = ContentLength;
 396                 if (a > sizeof buf)
 397                         a = sizeof buf;
 398                 if (!client_read(sock, buf, a))
 399                         goto end;
 400                 if (write(TheSession->inpipe[1], buf, a) != a)
 401                         goto end;
 402                 ContentLength -= a;
 403         }
 404
 405         /*
 406          * ...and get the response.
 407          */
 408         printf("   Reading response\n");
 409         ContentLength = 0;
 410         do {
 411                 gets0(TheSession->outpipe[0], buf);
 412                 write(sock, buf, strlen(buf));
 413                 write(sock, "\n", 1);
 414                 if (!strncasecmp(buf, "Content-length: ", 16))
 415                         ContentLength = atoi(&buf[16]);
 416                 if (!strcasecmp(buf, "X-WebCit-Session: close")) {
 417                         CloseSession = 1;
 418                 }
 419         } while (strlen(buf) > 0);
 420
 421         printf("   Reading %d bytes of content\n", ContentLength);
 422
 423         while (ContentLength--) {
 424                 read(TheSession->outpipe[0], buf, 1);
 425                 write(sock, buf, 1);
 426         }
 427
 428         /*
 429          * If the last response included a "close session" directive,
 430          * remove the context now.
 431          */
 432         if (CloseSession) {
 433                 remove_session(TheSession, 1);
 434         } else {
 435 end:            unlock_session(TheSession);
 436         }
 437         free(req);
 438
 439
 440         /*
 441          * Now our HTTP connection is done.  It would be relatively easy
 442          * to support HTTP/1.1 "persistent" connections by looping back to
 443          * the top of this function.  For now, we'll just close.
 444          */
 445         printf("   Closing socket %d ... ret=%d\n", sock,
 446                lingering_close(sock));
 447
 448         /*
 449          * The thread handling this HTTP connection is now finished.
 450          * Instead of calling pthread_exit(), just return. It does the same
 451          * thing, and supresses a compiler warning.
 452          */
 453         return NULL;
 454 }