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         };
  52
  53 struct wc_session *SessionList = NULL;
  54 extern const char *defaulthost;
  55 extern const char *defaultport;
  56
  57 /* Only one thread may manipulate SessionList at a time... */
  58 pthread_mutex_t MasterCritter;
  59
  60 int GenerateSessionID(void) {
  61         return getpid();
  62         }
  63
  64
  65 void gets0(int fd, char buf[]) {
  66
  67         buf[0] = 0;
  68         do {
  69                 buf[strlen(buf)+1] = 0;
  70                 read(fd, &buf[strlen(buf)], 1);
  71                 } while (buf[strlen(buf)-1] >= 32);
  72         buf[strlen(buf)-1] = 0;
  73         }
  74
  75 /*
  76  * Collapse multiple cookies on one line
  77  */
  78 void req_gets(int sock, char *buf, char *hold) {
  79         int a;
  80
  81         if (strlen(hold)==0) {
  82                 client_gets(sock, buf);
  83                 }
  84         else {
  85                 strcpy(buf, hold);
  86                 }
  87         strcpy(hold, "");
  88
  89         if (!strncasecmp(buf, "Cookie: ", 8)) {
  90                 for (a=0; a<strlen(buf); ++a) if (buf[a]==';') {
  91                         sprintf(hold, "Cookie: %s", &buf[a+1]);
  92                         buf[a]=0;
  93                         while (isspace(hold[8])) strcpy(&hold[8], &hold[9]);
  94                         return;
  95                         }
  96                 }
  97         }
  98
  99 /*
 100  * Grab a lock on the session, so other threads don't try to access
 101  * the pipes at the same time.
 102  */
 103 static void lock_session(struct wc_session *session) {
 104         printf("Locking session %d...\n", session->session_id);
 105         pthread_mutex_lock(&session->critter);
 106         printf("   ...got lock\n");
 107         }
 108
 109 /*
 110  * Let go of the lock.
 111  */
 112 static void unlock_session(struct wc_session *session) {
 113         printf("Unlocking.\n");
 114         pthread_mutex_unlock(&session->critter);
 115         }
 116
 117 /*
 118  * lingering_close() a`la Apache. see
 119  * http://www.apache.org/docs/misc/fin_wait_2.html for rationale
 120  */
 121
 122 static int lingering_close(int fd) {
 123         char buf[256];
 124         int i;
 125         fd_set set;
 126         struct timeval tv, start;
 127
 128         gettimeofday(&start, NULL);
 129         shutdown(fd, 1);
 130         do {
 131                 do {
 132                         gettimeofday(&tv, NULL);
 133                         tv.tv_sec = SLEEPING - (tv.tv_sec - start.tv_sec);
 134                         tv.tv_usec = start.tv_usec - tv.tv_usec;
 135                         if (tv.tv_usec < 0) {
 136                                 tv.tv_sec--;
 137                                 tv.tv_usec += 1000000;
 138                                 }
 139
 140                         FD_ZERO(&set);
 141                         FD_SET(fd, &set);
 142                         i = select(fd + 1, &set, NULL, NULL, &tv);
 143                         } while (i == -1 && errno == EINTR);
 144
 145                 if (i <= 0)
 146                         break;
 147
 148                 i = read(fd, buf, sizeof buf);
 149                 } while (i != 0 && (i != -1 || errno == EINTR));
 150
 151         return close(fd);
 152         }
 153
 154 /*
 155  * Remove a session context from the list
 156  */
 157 void remove_session(struct wc_session *TheSession) {
 158         struct wc_session *sptr;
 159
 160         printf("Removing session.\n");
 161         pthread_mutex_lock(&MasterCritter);
 162
 163         if (SessionList==TheSession) {
 164                 SessionList = SessionList->next;
 165                 }
 166         else {
 167                 for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 168                         if (sptr->next == TheSession) {
 169                                 sptr->next = TheSession->next;
 170                                 }
 171                         }
 172                 }
 173
 174         close(TheSession->inpipe[1]);
 175         close(TheSession->outpipe[0]);
 176         unlock_session(TheSession);
 177         free(TheSession);
 178
 179         pthread_mutex_unlock(&MasterCritter);
 180         }
 181
 182 /*
 183  * This loop gets called once for every HTTP connection made to WebCit.
 184  */
 185 void *context_loop(int sock) {
 186         char (*req)[256];
 187         char buf[256], hold[256];
 188         int num_lines = 0;
 189         int a;
 190         int f;
 191         int desired_session = 0;
 192         char str_session[256];
 193         struct wc_session *sptr;
 194         struct wc_session *TheSession;
 195         int ContentLength;
 196         int CloseSession = 0;
 197
 198         if ((req = malloc((long)sizeof(char[256][256]))) == NULL) {
 199                 sprintf(buf, "Can't malloc buffers; dropping connection.\n");
 200                 fprintf(stderr, "%s", buf);
 201                 write(sock, buf, strlen(buf));
 202                 close (sock);
 203                 pthread_exit(NULL);
 204                 }
 205
 206         printf("Reading request from socket %d\n", sock);
 207
 208         /*
 209          * Find out what it is that the web browser is asking for
 210          */
 211         ContentLength = 0;
 212         do {
 213                 req_gets(sock, buf, hold);
 214                 if (!strncasecmp(buf, "Cookie: wc_session=", 19)) {
 215                         desired_session = atoi(&buf[19]);
 216                         }
 217                 if (!strncasecmp(buf, "Content-length: ", 16)) {
 218                         ContentLength = atoi(&buf[16]);
 219                         }
 220                 strcpy(&req[num_lines++][0], buf);
 221                 } while(strlen(buf)>0);
 222
 223         /*
 224          * See if there's an existing session open with the desired ID
 225          */
 226         TheSession = NULL;
 227         if (desired_session != 0) {
 228                 pthread_mutex_lock(&MasterCritter);
 229                 for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 230                         if (sptr->session_id == desired_session) {
 231                                 TheSession = sptr;
 232                                 lock_session(TheSession);
 233                                 }
 234                         }
 235                 pthread_mutex_unlock(&MasterCritter);
 236                 }
 237
 238         /*
 239          * Before we trumpet to the universe that the session we're looking
 240          * for actually exists, check first to make sure it's still there.
 241          */
 242         if (TheSession != NULL) {
 243                 if (kill(TheSession->webcit_pid, 0)) {
 244                         printf("   Session is *DEAD* !!\n");
 245                         remove_session(TheSession);
 246                         TheSession = NULL;
 247                         }
 248                 }
 249
 250         /*
 251          * Create a new session if we have to
 252          */
 253         if (TheSession == NULL) {
 254                 printf("Creating a new session\n");
 255                 pthread_mutex_lock(&MasterCritter);
 256                 TheSession = (struct wc_session *)
 257                         malloc(sizeof(struct wc_session));
 258                 TheSession->session_id = GenerateSessionID();
 259                 pipe(TheSession->inpipe);
 260                 pipe(TheSession->outpipe);
 261                 pthread_mutex_init(&TheSession->critter, NULL);
 262                 lock_session(TheSession);
 263                 TheSession->next = SessionList;
 264                 SessionList = TheSession;
 265                 pthread_mutex_unlock(&MasterCritter);
 266                 sprintf(str_session, "%d", TheSession->session_id);
 267                 f = fork();
 268                 if (f > 0) TheSession->webcit_pid = f;
 269
 270                 fflush(stdout); fflush(stdin);
 271                 if (f==0) {
 272
 273                         /* Hook stdio to the ends of the pipe we're using */
 274                         dup2(TheSession->inpipe[0], 0);
 275                         dup2(TheSession->outpipe[1], 1);
 276
 277                         /* Close the ends of the pipes that we're not using */
 278                         close(TheSession->inpipe[1]);
 279                         close(TheSession->outpipe[0]);
 280
 281                         /* Close the HTTP socket in this pid; don't need it */
 282                         close(sock);
 283
 284                         /* Run the actual WebCit session */
 285                         execlp("./webcit", "webcit", str_session, defaulthost,
 286                                defaultport, NULL);
 287
 288                         /* Simple page to display if exec fails */
 289                         printf("HTTP/1.0 404 WebCit Failure\n\n");
 290                         printf("Server: %s\n", SERVER);
 291                         printf("X-WebCit-Session: close\n");
 292                         printf("Content-type: text/html\n");
 293                         printf("Content-length: 76\n");
 294                         printf("\n");
 295                         printf("<HTML><HEAD><TITLE>Error</TITLE></HEAD>\n");
 296                         printf("<BODY BACKGROUND=\"/image&name=background\" TEXT=\"#000000\" LINK=\"#004400\">execlp() failed</BODY></HTML>\n");
 297                         exit(0);
 298                         }
 299                 else {
 300                         /* Close the ends of the pipes that we're not using */
 301                         close(TheSession->inpipe[0]);
 302                         close(TheSession->outpipe[1]);
 303                         }
 304                 }
 305
 306         /*
 307          * Send the request to the appropriate session...
 308          */
 309         printf("   Writing %d lines of command\n", num_lines);
 310         printf("%s\n", &req[0][0]);
 311         for (a=0; a<num_lines; ++a) {
 312                 write(TheSession->inpipe[1], &req[a][0], strlen(&req[a][0]));
 313                 write(TheSession->inpipe[1], "\n", 1);
 314                 }
 315         printf("   Writing %d bytes of content\n", ContentLength);
 316         while (ContentLength > 0) {
 317                 a = ContentLength;
 318                 if (a > sizeof buf) a = sizeof buf;
 319                 if (!client_read(sock, buf, a)) goto end;
 320                 if (write(TheSession->inpipe[1], buf, a) != a) goto end;
 321                 ContentLength -= a;
 322                 }
 323
 324         /*
 325          * ...and get the response.
 326          */
 327         printf("   Reading response\n");
 328         ContentLength = 0;
 329         do {
 330                 gets0(TheSession->outpipe[0], buf);
 331                 write(sock, buf, strlen(buf));
 332                 write(sock, "\n", 1);
 333                 if (!strncasecmp(buf, "Content-length: ", 16))
 334                         ContentLength = atoi(&buf[16]);
 335                 if (!strcasecmp(buf, "X-WebCit-Session: close")) {
 336                         CloseSession = 1;
 337                         }
 338                 } while (strlen(buf) > 0);
 339
 340         printf("   Reading %d bytes of content\n", ContentLength);
 341         while(ContentLength--) {
 342                 read(TheSession->outpipe[0], buf, 1);
 343                 write(sock, buf, 1);
 344                 }
 345
 346         /*
 347          * If the last response included a "close session" directive,
 348          * remove the context now.
 349          */
 350         if (CloseSession) {
 351                 remove_session(TheSession);
 352                 }
 353         else {
 354 end:            unlock_session(TheSession);
 355                 }
 356         free(req);
 357
 358
 359         /*
 360          * Now our HTTP connection is done.  It would be relatively easy
 361          * to support HTTP/1.1 "persistent" connections by looping back to
 362          * the top of this function.  For now, we'll just close.
 363          */
 364         printf("   Remember, the pid is %d\n", TheSession->webcit_pid);
 365         printf("   Closing socket %d ... ret=%d\n", sock,
 366                lingering_close(sock));
 367
 368         /*
 369          * The thread handling this HTTP connection is now finished.
 370          */
 371         pthread_exit(NULL);
 372         }