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