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         printf("Locking session %d...\n", session->session_id);
  68         pthread_mutex_lock(&session->critter);
  69         printf("   ...got lock\n");
  70         }
  71
  72 /*
  73  * Let go of the lock.
  74  */
  75 static void unlock_session(struct wc_session *session) {
  76         printf("Unlocking.\n");
  77         pthread_mutex_unlock(&session->critter);
  78         }
  79
  80 /*
  81  * Remove a session context from the list
  82  */
  83 void remove_session(struct wc_session *TheSession, int do_lock) {
  84         struct wc_session *sptr;
  85
  86         printf("Removing session.\n");
  87         if (do_lock) pthread_mutex_lock(&MasterCritter);
  88
  89         if (SessionList==TheSession) {
  90                 SessionList = SessionList->next;
  91                 }
  92         else {
  93                 for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
  94                         if (sptr->next == TheSession) {
  95                                 sptr->next = TheSession->next;
  96                                 }
  97                         }
  98                 }
  99
 100         close(TheSession->inpipe[1]);
 101         close(TheSession->outpipe[0]);
 102         if (do_lock) unlock_session(TheSession);
 103         free(TheSession);
 104
 105         pthread_mutex_unlock(&MasterCritter);
 106         }
 107
 108
 109
 110
 111 void do_housekeeping(void) {
 112         struct wc_session *sptr;
 113
 114         pthread_mutex_lock(&MasterCritter);
 115
 116         /* Kill idle sessions */
 117         for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 118                 if ((time(NULL) - (sptr->lastreq)) > (time_t)WEBCIT_TIMEOUT) {
 119                         kill(sptr->webcit_pid, 15);
 120                         }
 121                 }
 122
 123         /* Remove dead sessions */
 124         for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 125                 if (kill(sptr->webcit_pid, 0)) {
 126                         remove_session(sptr, 0);
 127                         }
 128                 }
 129
 130         pthread_mutex_unlock(&MasterCritter);
 131         }
 132
 133
 134 /*
 135  * Wake up occasionally and clean house
 136  */
 137 void housekeeping_loop(void) {
 138         while(1) {
 139                 sleep(HOUSEKEEPING);
 140                 do_housekeeping();
 141                 }
 142         }
 143
 144
 145
 146
 147
 148 int GenerateSessionID(void) {
 149         return getpid();
 150         }
 151
 152
 153 void gets0(int fd, char buf[]) {
 154
 155         buf[0] = 0;
 156         do {
 157                 buf[strlen(buf)+1] = 0;
 158                 read(fd, &buf[strlen(buf)], 1);
 159                 } while (buf[strlen(buf)-1] >= 32);
 160         buf[strlen(buf)-1] = 0;
 161         }
 162
 163 /*
 164  * Collapse multiple cookies on one line
 165  */
 166 void req_gets(int sock, char *buf, char *hold) {
 167         int a;
 168
 169         if (strlen(hold)==0) {
 170                 client_gets(sock, buf);
 171                 }
 172         else {
 173                 strcpy(buf, hold);
 174                 }
 175         strcpy(hold, "");
 176
 177         if (!strncasecmp(buf, "Cookie: ", 8)) {
 178                 for (a=0; a<strlen(buf); ++a) if (buf[a]==';') {
 179                         sprintf(hold, "Cookie: %s", &buf[a+1]);
 180                         buf[a]=0;
 181                         while (isspace(hold[8])) strcpy(&hold[8], &hold[9]);
 182                         return;
 183                         }
 184                 }
 185         }
 186
 187 /*
 188  * lingering_close() a`la Apache. see
 189  * http://www.apache.org/docs/misc/fin_wait_2.html for rationale
 190  */
 191
 192 static int lingering_close(int fd) {
 193         char buf[256];
 194         int i;
 195         fd_set set;
 196         struct timeval tv, start;
 197
 198         gettimeofday(&start, NULL);
 199         shutdown(fd, 1);
 200         do {
 201                 do {
 202                         gettimeofday(&tv, NULL);
 203                         tv.tv_sec = SLEEPING - (tv.tv_sec - start.tv_sec);
 204                         tv.tv_usec = start.tv_usec - tv.tv_usec;
 205                         if (tv.tv_usec < 0) {
 206                                 tv.tv_sec--;
 207                                 tv.tv_usec += 1000000;
 208                                 }
 209
 210                         FD_ZERO(&set);
 211                         FD_SET(fd, &set);
 212                         i = select(fd + 1, &set, NULL, NULL, &tv);
 213                         } while (i == -1 && errno == EINTR);
 214
 215                 if (i <= 0)
 216                         break;
 217
 218                 i = read(fd, buf, sizeof buf);
 219                 } while (i != 0 && (i != -1 || errno == EINTR));
 220
 221         return close(fd);
 222         }
 223
 224 /*
 225  * This loop gets called once for every HTTP connection made to WebCit.
 226  */
 227 void *context_loop(int sock) {
 228         char (*req)[256];
 229         char buf[256], hold[256];
 230         char browser_host[256];
 231         int num_lines = 0;
 232         int a;
 233         int f;
 234         int desired_session = 0;
 235         char str_session[256];
 236         struct wc_session *sptr;
 237         struct wc_session *TheSession;
 238         int ContentLength;
 239         int CloseSession = 0;
 240
 241         if ((req = malloc((long)sizeof(char[256][256]))) == NULL) {
 242                 sprintf(buf, "Can't malloc buffers; dropping connection.\n");
 243                 fprintf(stderr, "%s", buf);
 244                 write(sock, buf, strlen(buf));
 245                 close (sock);
 246                 pthread_exit(NULL);
 247                 }
 248
 249         bzero(req, sizeof(char[256][256]));     /* clear it out */
 250
 251         printf("Reading request from socket %d\n", sock);
 252
 253         /*
 254          * Find out what it is that the web browser is asking for
 255          */
 256         ContentLength = 0;
 257         do {
 258                 req_gets(sock, buf, hold);
 259                 if (!strncasecmp(buf, "Cookie: webcit=", 15)) {
 260                         cookie_to_stuff(&buf[15], &desired_session, NULL, NULL, NULL, NULL);
 261                         }
 262                 if (!strncasecmp(buf, "Content-length: ", 16)) {
 263                         ContentLength = atoi(&buf[16]);
 264                         }
 265                 strcpy(&req[num_lines++][0], buf);
 266                 } while(strlen(buf)>0);
 267
 268         /*
 269          * See if there's an existing session open with the desired ID
 270          */
 271         TheSession = NULL;
 272         if (desired_session != 0) {
 273                 pthread_mutex_lock(&MasterCritter);
 274                 for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 275                         if (sptr->session_id == desired_session) {
 276                                 TheSession = sptr;
 277                                 lock_session(TheSession);
 278                                 }
 279                         }
 280                 pthread_mutex_unlock(&MasterCritter);
 281                 }
 282
 283         /*
 284          * Before we trumpet to the universe that the session we're looking
 285          * for actually exists, check first to make sure it's still there.
 286          */
 287         if (TheSession != NULL) {
 288                 if (kill(TheSession->webcit_pid, 0)) {
 289                         printf("   Session is *DEAD* !!\n");
 290                         remove_session(TheSession, 1);
 291                         TheSession = NULL;
 292                         }
 293                 }
 294
 295         /*
 296          * Create a new session if we have to
 297          */
 298         if (TheSession == NULL) {
 299                 printf("Creating a new session\n");
 300                 locate_host(browser_host, sock);
 301                 pthread_mutex_lock(&MasterCritter);
 302                 TheSession = (struct wc_session *)
 303                         malloc(sizeof(struct wc_session));
 304                 TheSession->session_id = GenerateSessionID();
 305                 pipe(TheSession->inpipe);
 306                 pipe(TheSession->outpipe);
 307                 pthread_mutex_init(&TheSession->critter, NULL);
 308                 lock_session(TheSession);
 309                 TheSession->next = SessionList;
 310                 SessionList = TheSession;
 311                 pthread_mutex_unlock(&MasterCritter);
 312                 sprintf(str_session, "%d", TheSession->session_id);
 313                 f = fork();
 314                 if (f > 0) TheSession->webcit_pid = f;
 315
 316                 fflush(stdout); fflush(stdin);
 317                 if (f==0) {
 318
 319                         /* Hook stdio to the ends of the pipe we're using */
 320                         dup2(TheSession->inpipe[0], 0);
 321                         dup2(TheSession->outpipe[1], 1);
 322
 323                         /* Close the ends of the pipes that we're not using */
 324                         close(TheSession->inpipe[1]);
 325                         close(TheSession->outpipe[0]);
 326
 327                         /* Close the HTTP socket in this pid; don't need it */
 328                         close(sock);
 329
 330                         /* Run the actual WebCit session */
 331                         execlp("./webcit", "webcit", str_session, defaulthost,
 332                                defaultport, browser_host, NULL);
 333
 334                         /* Simple page to display if exec fails */
 335                         printf("HTTP/1.0 404 WebCit Failure\n\n");
 336                         printf("Server: %s\n", SERVER);
 337                         printf("X-WebCit-Session: close\n");
 338                         printf("Content-type: text/html\n");
 339                         printf("Content-length: 76\n");
 340                         printf("\n");
 341                         printf("<HTML><HEAD><TITLE>Error</TITLE></HEAD><BODY>\n");
 342                         printf("execlp() failed: %s</BODY></HTML>\n", strerror(errno));
 343                         exit(0);
 344                         }
 345                 else {
 346                         /* Close the ends of the pipes that we're not using */
 347                         close(TheSession->inpipe[0]);
 348                         close(TheSession->outpipe[1]);
 349                         }
 350                 }
 351
 352         /*
 353          * Send the request to the appropriate session...
 354          */
 355         TheSession->lastreq = time(NULL);
 356         printf("   Writing %d lines of command\n", num_lines);
 357         printf("%s\n", &req[0][0]);
 358         for (a=0; a<num_lines; ++a) {
 359                 write(TheSession->inpipe[1], &req[a][0], strlen(&req[a][0]));
 360                 write(TheSession->inpipe[1], "\n", 1);
 361                 }
 362         printf("   Writing %d bytes of content\n", ContentLength);
 363         while (ContentLength > 0) {
 364                 a = ContentLength;
 365                 if (a > sizeof buf) a = sizeof buf;
 366                 if (!client_read(sock, buf, a)) goto end;
 367                 if (write(TheSession->inpipe[1], buf, a) != a) goto end;
 368                 ContentLength -= a;
 369                 }
 370
 371         /*
 372          * ...and get the response.
 373          */
 374         printf("   Reading response\n");
 375         ContentLength = 0;
 376         do {
 377                 gets0(TheSession->outpipe[0], buf);
 378                 write(sock, buf, strlen(buf));
 379                 write(sock, "\n", 1);
 380                 if (!strncasecmp(buf, "Content-length: ", 16))
 381                         ContentLength = atoi(&buf[16]);
 382                 if (!strcasecmp(buf, "X-WebCit-Session: close")) {
 383                         CloseSession = 1;
 384                         }
 385                 } while (strlen(buf) > 0);
 386
 387         printf("   Reading %d bytes of content\n", ContentLength);
 388         while(ContentLength--) {
 389                 read(TheSession->outpipe[0], buf, 1);
 390                 write(sock, buf, 1);
 391                 }
 392
 393         /*
 394          * If the last response included a "close session" directive,
 395          * remove the context now.
 396          */
 397         if (CloseSession) {
 398                 remove_session(TheSession, 1);
 399                 }
 400         else {
 401 end:            unlock_session(TheSession);
 402                 }
 403         free(req);
 404
 405
 406         /*
 407          * Now our HTTP connection is done.  It would be relatively easy
 408          * to support HTTP/1.1 "persistent" connections by looping back to
 409          * the top of this function.  For now, we'll just close.
 410          */
 411         printf("   Closing socket %d ... ret=%d\n", sock,
 412                lingering_close(sock));
 413
 414         /*
 415          * The thread handling this HTTP connection is now finished.
 416          */
 417         pthread_exit(NULL);
 418         }