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 "webcit.h"
  38 #include "webserver.h"
  39
  40 /*
  41  * We keep one of these around for each active session
  42  */
  43 struct wc_session {
  44         struct wc_session *next;        /* Next session in list */
  45         int session_id;                 /* Session ID */
  46         int inpipe[2];                  /* Data from webserver to session */
  47         int outpipe[2];                 /* Data from session to webserver */
  48         pthread_mutex_t critter;        /* Critical section uses pipes */
  49         };
  50
  51 struct wc_session *SessionList = NULL;
  52
  53 /* Only one thread may manipulate SessionList at a time... */
  54 pthread_mutex_t MasterCritter;
  55
  56 int GenerateSessionID(void) {
  57         return getpid();
  58         }
  59
  60
  61 void gets0(int fd, char buf[]) {
  62
  63         buf[0] = 0;
  64         do {
  65                 buf[strlen(buf)+1] = 0;
  66                 read(fd, &buf[strlen(buf)], 1);
  67                 } while (buf[strlen(buf)-1] >= 32);
  68         buf[strlen(buf)-1] = 0;
  69         }
  70
  71 /*
  72  * Collapse multiple cookies on one line
  73  */
  74 void req_gets(int sock, char *buf, char *hold) {
  75         int a;
  76
  77         if (strlen(hold)==0) {
  78                 client_gets(sock, buf);
  79                 }
  80         else {
  81                 strcpy(buf, hold);
  82                 }
  83         strcpy(hold, "");
  84
  85         if (!strncasecmp(buf, "Cookie: ", 8)) {
  86                 for (a=0; a<strlen(buf); ++a) if (buf[a]==';') {
  87                         sprintf(hold, "Cookie: %s", &buf[a+1]);
  88                         buf[a]=0;
  89                         while (isspace(hold[8])) strcpy(&hold[8], &hold[9]);
  90                         return;
  91                         }
  92                 }
  93         }
  94
  95 /*
  96  * Grab a lock on the session, so other threads don't try to access
  97  * the pipes at the same time.
  98  */
  99 static void lock_session(struct wc_session *session) {
 100         printf("Locking session %d...\n", session->session_id);
 101         pthread_mutex_lock(&session->critter);
 102         printf("   ...got lock\n");
 103         }
 104
 105 /*
 106  * Let go of the lock.
 107  */
 108 static void unlock_session(struct wc_session *session) {
 109         printf("Unlocking.\n");
 110         pthread_mutex_unlock(&session->critter);
 111         }
 112
 113 /*
 114  * lingering_close() a`la Apache. see
 115  * http://www.apache.org/docs/misc/fin_wait_2.html for rationale
 116  */
 117
 118 static int lingering_close(int fd) {
 119         char buf[256];
 120         int i;
 121         fd_set set;
 122         struct timeval tv, start;
 123
 124         gettimeofday(&start, NULL);
 125         shutdown(fd, 1);
 126         do {
 127                 do {
 128                         gettimeofday(&tv, NULL);
 129                         tv.tv_sec = SLEEPING - (tv.tv_sec - start.tv_sec);
 130                         tv.tv_usec = start.tv_usec - tv.tv_usec;
 131                         if (tv.tv_usec < 0) {
 132                                 tv.tv_sec--;
 133                                 tv.tv_usec += 1000000;
 134                                 }
 135
 136                         FD_ZERO(&set);
 137                         FD_SET(fd, &set);
 138                         i = select(fd + 1, &set, NULL, NULL, &tv);
 139                         } while (i == -1 && errno == EINTR);
 140
 141                 if (i <= 0)
 142                         break;
 143
 144                 i = read(fd, buf, sizeof buf);
 145                 } while (i != 0 && (i != -1 || errno == EINTR));
 146
 147         return close(fd);
 148         }
 149
 150 extern const char *defaulthost;
 151 extern const char *defaultport;
 152
 153 /*
 154  * This loop gets called once for every HTTP connection made to WebCit.
 155  */
 156 void *context_loop(int sock) {
 157         char (*req)[256];
 158         char buf[256], hold[256];
 159         int num_lines = 0;
 160         int a;
 161         int f;
 162         int desired_session = 0;
 163         char str_session[256];
 164         struct wc_session *sptr;
 165         struct wc_session *TheSession;
 166         int ContentLength;
 167         int CloseSession = 0;
 168
 169         if ((req = malloc((long)sizeof(char[256][256]))) == NULL) {
 170                 sprintf(buf, "Can't malloc buffers; dropping connection.\n");
 171                 fprintf(stderr, "%s", buf);
 172                 write(sock, buf, strlen(buf));
 173                 close (sock);
 174                 pthread_exit(NULL);
 175                 }
 176
 177         printf("Reading request from socket %d\n", sock);
 178
 179         /*
 180          * Find out what it is that the web browser is asking for
 181          */
 182         ContentLength = 0;
 183         do {
 184                 req_gets(sock, buf, hold);
 185                 if (!strncasecmp(buf, "Cookie: wc_session=", 19)) {
 186                         desired_session = atoi(&buf[19]);
 187                         }
 188                 if (!strncasecmp(buf, "Content-length: ", 16)) {
 189                         ContentLength = atoi(&buf[16]);
 190                         }
 191                 strcpy(&req[num_lines++][0], buf);
 192                 } while(strlen(buf)>0);
 193
 194         /*
 195          * See if there's an existing session open with the desired ID
 196          */
 197         TheSession = NULL;
 198         if (desired_session != 0) {
 199                 pthread_mutex_lock(&MasterCritter);
 200                 for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 201                         if (sptr->session_id == desired_session) {
 202                                 TheSession = sptr;
 203                                 lock_session(TheSession);
 204                                 }
 205                         }
 206                 pthread_mutex_unlock(&MasterCritter);
 207                 }
 208
 209         /*
 210          * Create a new session if we have to
 211          */
 212         if (TheSession == NULL) {
 213                 printf("Creating a new session\n");
 214                 pthread_mutex_lock(&MasterCritter);
 215                 TheSession = (struct wc_session *)
 216                         malloc(sizeof(struct wc_session));
 217                 TheSession->session_id = GenerateSessionID();
 218                 pipe(TheSession->inpipe);
 219                 pipe(TheSession->outpipe);
 220                 pthread_mutex_init(&TheSession->critter, NULL);
 221                 lock_session(TheSession);
 222                 TheSession->next = SessionList;
 223                 SessionList = TheSession;
 224                 pthread_mutex_unlock(&MasterCritter);
 225                 sprintf(str_session, "%d", TheSession->session_id);
 226                 f = fork();
 227                 fflush(stdout); fflush(stdin);
 228                 if (f==0) {
 229                         dup2(TheSession->inpipe[0], 0);
 230                         dup2(TheSession->outpipe[1], 1);
 231                         /* Close the ends of the pipes that we're not using */
 232                         close(TheSession->inpipe[1]);
 233                         close(TheSession->outpipe[0]);
 234                         close(sock);
 235                         execlp("./webcit", "webcit", str_session, defaulthost,
 236                                defaultport, NULL);
 237                         printf("HTTP/1.0 404 WebCit Failure\n\n");
 238                         printf("Server: %s\n", SERVER);
 239                         printf("Content-type: text/html\n");
 240                         printf("Content-length: 76\n");
 241                         printf("\n");
 242                         printf("<HTML><HEAD><TITLE>Error</TITLE></HEAD>\n");
 243                         printf("<BODY BACKGROUND=\"/image&name=background\" TEXT=\"#000000\" LINK=\"#004400\">execlp() failed</BODY></HTML>\n");
 244                         exit(0);
 245                         }
 246                 /* Close the ends of the pipes that we're not using */
 247                 close(TheSession->inpipe[0]);
 248                 close(TheSession->outpipe[1]);
 249                 }
 250
 251         /*
 252          * Send the request to the appropriate session...
 253          */
 254         printf("   Writing %d lines of command\n", num_lines);
 255         printf("%s\n", &req[0][0]);
 256         for (a=0; a<num_lines; ++a) {
 257                 write(TheSession->inpipe[1], &req[a][0], strlen(&req[a][0]));
 258                 write(TheSession->inpipe[1], "\n", 1);
 259                 }
 260         printf("   Writing %d bytes of content\n", ContentLength);
 261         while (ContentLength > 0) {
 262                 a = ContentLength;
 263                 if (a > sizeof buf) a = sizeof buf;
 264                 if (!client_read(sock, buf, a)) goto end;
 265                 if (write(TheSession->inpipe[1], buf, a) != a) goto end;
 266                 ContentLength -= a;
 267                 }
 268
 269         /*
 270          * ...and get the response.
 271          */
 272         printf("   Reading response\n");
 273         ContentLength = 0;
 274         do {
 275                 gets0(TheSession->outpipe[0], buf);
 276                 write(sock, buf, strlen(buf));
 277                 write(sock, "\n", 1);
 278                 if (!strncasecmp(buf, "Content-length: ", 16))
 279                         ContentLength = atoi(&buf[16]);
 280                 if (!strcasecmp(buf, "X-WebCit-Session: close")) {
 281                         CloseSession = 1;
 282                         }
 283                 } while (strlen(buf) > 0);
 284
 285         printf("   Reading %d bytes of content\n", ContentLength);
 286         while(ContentLength--) {
 287                 read(TheSession->outpipe[0], buf, 1);
 288                 write(sock, buf, 1);
 289                 }
 290
 291         /*
 292          * If the last response included a "close session" directive,
 293          * remove the context now.
 294          */
 295         if (CloseSession) {
 296                 printf("Removing session.\n");
 297                 pthread_mutex_lock(&MasterCritter);
 298
 299                 if (SessionList==TheSession) {
 300                         SessionList = SessionList->next;
 301                         }
 302                 else {
 303                         for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 304                                 if (sptr->next == TheSession) {
 305                                         sptr->next = TheSession->next;
 306                                         }
 307                                 }
 308                         }
 309
 310                 close(TheSession->inpipe[1]);
 311                 close(TheSession->outpipe[0]);
 312                 unlock_session(TheSession);
 313                 free(TheSession);
 314
 315                 pthread_mutex_unlock(&MasterCritter);
 316                 }
 317         else {
 318         end:
 319                 unlock_session(TheSession);
 320                 }
 321         free(req);
 322
 323
 324         /*
 325          * Now our HTTP connection is done.  It would be relatively easy
 326          * to support HTTP/1.1 "persistent" connections by looping back to
 327          * the top of this function.  For now, we'll just close.
 328          */
 329         printf("   Closing socket %d ... ret=%d\n", sock,
 330                lingering_close(sock));
 331
 332         /*
 333          * The thread handling this HTTP connection is now finished.
 334          */
 335         pthread_exit(NULL);
 336         }