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 #include <unistd.h>
  15 #include <stdio.h>
  16 #include <fcntl.h>
  17 #include <signal.h>
  18 #include <sys/types.h>
  19 #include <sys/wait.h>
  20 #include <sys/socket.h>
  21 #include <sys/time.h>
  22 #include <limits.h>
  23 #include <netinet/in.h>
  24 #include <netdb.h>
  25 #include <string.h>
  26 #include <errno.h>
  27 #include <stdarg.h>
  28 #include <pthread.h>
  29 #include "webcit.h"
  30 #include "webserver.h"
  31
  32 /*
  33  * We keep one of these around for each active session
  34  */
  35 struct wc_session {
  36         struct wc_session *next;        /* Next session in list */
  37         int session_id;                 /* Session ID */
  38         int inpipe[2];                  /* Data from webserver to session */
  39         int outpipe[2];                 /* Data from session to webserver */
  40         pthread_mutex_t critter;        /* Critical section uses pipes */
  41         };
  42
  43 struct wc_session *SessionList = NULL;
  44
  45 /* Only one thread may manipulate SessionList at a time... */
  46 pthread_mutex_t MasterCritter;
  47
  48 int GenerateSessionID() {
  49         return getpid();
  50         }
  51
  52
  53 void gets0(int fd, char buf[]) {
  54
  55         buf[0] = 0;
  56         do {
  57                 buf[strlen(buf)+1] = 0;
  58                 read(fd, &buf[strlen(buf)], 1);
  59                 } while (buf[strlen(buf)-1] >= 32);
  60         buf[strlen(buf)-1] = 0;
  61         }
  62
  63 /*
  64  * Collapse multiple cookies on one line
  65  */
  66 void req_gets(int sock, char *buf, char *hold) {
  67         int a;
  68
  69         if (strlen(hold)==0) {
  70                 client_gets(sock, buf);
  71                 }
  72         else {
  73                 strcpy(buf, hold);
  74                 }
  75         strcpy(hold, "");
  76
  77         if (!strncasecmp(buf, "Cookie: ", 8)) {
  78                 for (a=0; a<strlen(buf); ++a) if (buf[a]==';') {
  79                         sprintf(hold, "Cookie: %s", &buf[a+1]);
  80                         buf[a]=0;
  81                         while (isspace(hold[8])) strcpy(&hold[8], &hold[9]);
  82                         return;
  83                         }
  84                 }
  85         }
  86
  87 /*
  88  * Grab a lock on the session, so other threads don't try to access
  89  * the pipes at the same time.
  90  */
  91 static void lock_session(struct wc_session *session) {
  92         printf("Locking session %d...\n", session->session_id);
  93         pthread_mutex_lock(&session->critter);
  94         printf("   ...got lock\n");
  95         }
  96
  97 /*
  98  * Let go of the lock.
  99  */
 100 static void unlock_session(struct wc_session *session) {
 101         printf("Unlocking.\n");
 102         pthread_mutex_unlock(&session->critter);
 103         }
 104
 105 extern const char *defaulthost;
 106 extern const char *defaultport;
 107
 108 /*
 109  * This loop gets called once for every HTTP connection made to WebCit.
 110  */
 111 void *context_loop(int sock) {
 112         char (*req)[256];
 113         char buf[256], hold[256];
 114         int num_lines = 0;
 115         int a;
 116         int f;
 117         int desired_session = 0;
 118         char str_session[256];
 119         struct wc_session *sptr;
 120         struct wc_session *TheSession;
 121         int ContentLength;
 122         int CloseSession = 0;
 123
 124         if ((req = malloc(sizeof(char[256][256]))) == NULL) {
 125                 printf("Can't malloc buffers; dropping connection.\n");
 126                 close (sock);
 127                 return NULL;
 128                 }
 129
 130         printf("Reading request from socket %d\n", sock);
 131
 132         /*
 133          * Find out what it is that the web browser is asking for
 134          */
 135         ContentLength = 0;
 136         do {
 137                 req_gets(sock, buf, hold);
 138                 if (!strncasecmp(buf, "Cookie: wc_session=", 19)) {
 139                         desired_session = atoi(&buf[19]);
 140                         }
 141                 if (!strncasecmp(buf, "Content-length: ", 16)) {
 142                         ContentLength = atoi(&buf[16]);
 143                         }
 144                 strcpy(&req[num_lines++][0], buf);
 145                 } while(strlen(buf)>0);
 146
 147         /*
 148          * See if there's an existing session open with the desired ID
 149          */
 150         TheSession = NULL;
 151         if (desired_session != 0) {
 152                 pthread_mutex_lock(&MasterCritter);
 153                 for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 154                         if (sptr->session_id == desired_session) {
 155                                 TheSession = sptr;
 156                                 lock_session(TheSession);
 157                                 }
 158                         }
 159                 pthread_mutex_unlock(&MasterCritter);
 160                 }
 161
 162         /*
 163          * Create a new session if we have to
 164          */
 165         if (TheSession == NULL) {
 166                 printf("Creating a new session\n");
 167                 pthread_mutex_lock(&MasterCritter);
 168                 TheSession = (struct wc_session *)
 169                         malloc(sizeof(struct wc_session));
 170                 TheSession->session_id = GenerateSessionID();
 171                 pipe(TheSession->inpipe);
 172                 pipe(TheSession->outpipe);
 173                 pthread_mutex_init(&TheSession->critter, NULL);
 174                 lock_session(TheSession);
 175                 TheSession->next = SessionList;
 176                 SessionList = TheSession;
 177                 pthread_mutex_unlock(&MasterCritter);
 178                 sprintf(str_session, "%d", TheSession->session_id);
 179                 f = fork();
 180                 fflush(stdout); fflush(stdin);
 181                 if (f==0) {
 182                         dup2(TheSession->inpipe[0], 0);
 183                         dup2(TheSession->outpipe[1], 1);
 184                         /* Close the ends of the pipes that we're not using */
 185                         close(TheSession->inpipe[1]);
 186                         close(TheSession->outpipe[0]);
 187                         execlp("./webcit", "webcit", str_session, defaulthost,
 188                                defaultport, NULL);
 189                         printf("HTTP/1.0 404 WebCit Failure\n\n");
 190                         printf("Server: %s\n", SERVER);
 191                         printf("Content-type: text/html\n");
 192                         printf("Content-length: 76\n");
 193                         printf("\n");
 194                         printf("<HTML><HEAD><TITLE>Error</TITLE></HEAD>\n");
 195                         printf("<BODY>execlp() failed</BODY></HTML>\n");
 196                         exit(0);
 197                         }
 198                 /* Close the ends of the pipes that we're not using */
 199                 close(TheSession->inpipe[0]);
 200                 close(TheSession->outpipe[1]);
 201                 }
 202
 203         /*
 204          * Send the request to the appropriate session...
 205          */
 206         printf("   Writing %d lines of command\n", num_lines);
 207         printf("%s\n", &req[0][0]);
 208         for (a=0; a<num_lines; ++a) {
 209                 write(TheSession->inpipe[1], &req[a][0], strlen(&req[a][0]));
 210                 write(TheSession->inpipe[1], "\n", 1);
 211                 }
 212         printf("   Writing %d bytes of content\n", ContentLength);
 213         while (ContentLength--) {
 214                 read(sock, buf, 1);
 215                 write(TheSession->inpipe[1], buf, 1);
 216                 }
 217
 218         /*
 219          * ...and get the response.
 220          */
 221         printf("   Reading response\n");
 222         ContentLength = 0;
 223         do {
 224                 gets0(TheSession->outpipe[0], buf);
 225                 write(sock, buf, strlen(buf));
 226                 write(sock, "\n", 1);
 227                 if (!strncasecmp(buf, "Content-length: ", 16))
 228                         ContentLength = atoi(&buf[16]);
 229                 if (!strcasecmp(buf, "X-WebCit-Session: close")) {
 230                         CloseSession = 1;
 231                         }
 232                 } while (strlen(buf) > 0);
 233
 234         printf("   Reading %d bytes of content\n", ContentLength);
 235         while(ContentLength--) {
 236                 read(TheSession->outpipe[0], buf, 1);
 237                 write(sock, buf, 1);
 238                 }
 239
 240         /*
 241          * Now our HTTP connection is done.  It would be relatively easy
 242          * to support HTTP/1.1 "persistent" connections by looping back to
 243          * the top of this function.  For now, we'll just close.
 244          */
 245         printf("   Closing socket\n");
 246         close(sock);
 247
 248         unlock_session(TheSession);
 249
 250         /*
 251          * If the last response included a "close session" directive,
 252          * remove the context now.
 253          */
 254         if (CloseSession) {
 255                 printf("Removing session.\n");
 256                 pthread_mutex_lock(&MasterCritter);
 257
 258                 lock_session(TheSession);
 259
 260                 if (SessionList==TheSession) {
 261                         SessionList = SessionList->next;
 262                         }
 263                 else {
 264                         for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 265                                 if (sptr->next == TheSession) {
 266                                         sptr->next = TheSession->next;
 267                                         }
 268                                 }
 269                         }
 270
 271                 close(TheSession->inpipe[1]);
 272                 close(TheSession->outpipe[0]);
 273                 unlock_session(TheSession);
 274                 free(TheSession);
 275
 276                 pthread_mutex_unlock(&MasterCritter);
 277                 }
 278
 279         free(req);
 280
 281         /*
 282          * The thread handling this HTTP connection is now finished.
 283          */
 284         return NULL;
 285         }