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 int GenerateSessionID() {
  42         return getpid();
  43         }
  44
  45
  46 void gets0(int fd, char buf[]) {
  47
  48         buf[0] = 0;
  49         do {
  50                 buf[strlen(buf)+1] = 0;
  51                 read(fd, &buf[strlen(buf)], 1);
  52                 } while (buf[strlen(buf)-1] >= 32);
  53         buf[strlen(buf)-1] = 0;
  54         }
  55
  56 /*
  57  * Collapse multiple cookies on one line
  58  */
  59 void req_gets(int sock, char *buf, char *hold) {
  60         int a;
  61
  62         if (strlen(hold)==0) {
  63                 client_gets(sock, buf);
  64                 }
  65         else {
  66                 strcpy(buf, hold);
  67                 }
  68         strcpy(hold, "");
  69
  70         if (!strncasecmp(buf, "Cookie: ", 8)) {
  71                 for (a=0; a<strlen(buf); ++a) if (buf[a]==';') {
  72                         sprintf(hold, "Cookie: %s", &buf[a+1]);
  73                         buf[a]=0;
  74                         while (isspace(hold[8])) strcpy(&hold[8], &hold[9]);
  75                         return;
  76                         }
  77                 }
  78         }
  79
  80
  81 /*
  82  * This loop gets called once for every HTTP connection made to WebCit.
  83  */
  84 void *context_loop(int sock) {
  85         char req[256][256];
  86         char buf[256], hold[256];
  87         int num_lines = 0;
  88         int a;
  89         int f;
  90         int desired_session = 0;
  91         char str_session[256];
  92         struct wc_session *sptr;
  93         struct wc_session *TheSession;
  94         int ContentLength;
  95
  96         printf("Reading request from socket %d\n", sock);
  97
  98         /*
  99          * Find out what it is that the web browser is asking for
 100          */
 101         ContentLength = 0;
 102         do {
 103                 req_gets(sock, buf, hold);
 104                 if (!strncasecmp(buf, "Cookie: wc_session=", 19)) {
 105                         desired_session = atoi(&buf[19]);
 106                         }
 107                 if (!strncasecmp(buf, "Content-length: ", 16)) {
 108                         ContentLength = atoi(&buf[16]);
 109                         }
 110                 strcpy(&req[num_lines++][0], buf);
 111                 } while(strlen(buf)>0);
 112
 113         /*
 114          * See if there's an existing session open with the desired ID
 115          */
 116         TheSession = NULL;
 117         if (desired_session != 0) {
 118                 for (sptr=SessionList; sptr!=NULL; sptr=sptr->next) {
 119                         if (sptr->session_id == desired_session) {
 120                                 TheSession = sptr;
 121                                 }
 122                         }
 123                 }
 124
 125         /*
 126          * Create a new session if we have to
 127          */
 128         if (TheSession == NULL) {
 129                 printf("Creating a new session\n");
 130                 TheSession = (struct wc_session *)
 131                         malloc(sizeof(struct wc_session));
 132                 TheSession->session_id = GenerateSessionID();
 133                 pipe(TheSession->inpipe);
 134                 pipe(TheSession->outpipe);
 135                 pthread_mutex_init(&TheSession->critter, NULL);
 136                 TheSession->next = SessionList;
 137                 SessionList = TheSession;
 138                 sprintf(str_session, "%d", TheSession->session_id);
 139                 f = fork();
 140                 fflush(stdout); fflush(stdin);
 141                 if (f==0) {
 142                         dup2(TheSession->inpipe[0], 0);
 143                         dup2(TheSession->outpipe[1], 1);
 144                         execlp("./webcit", "webcit", str_session, NULL);
 145                         printf("HTTP/1.0 404 WebCit Failure\n\n");
 146                         printf("Server: %s\n", SERVER);
 147                         printf("Content-type: text/html\n");
 148                         printf("Content-length: 76\n");
 149                         printf("\n");
 150                         printf("<HTML><HEAD><TITLE>Error</TITLE></HEAD>\n");
 151                         printf("<BODY>execlp() failed</BODY></HTML>\n");
 152                         exit(0);
 153                         }
 154                 }
 155
 156         /*
 157          * Grab a lock on the session, so other threads don't try to access
 158          * the pipes at the same time.
 159          */
 160         printf("Locking session %d...\n", TheSession->session_id);
 161         pthread_mutex_lock(&TheSession->critter);
 162         printf("   ...got lock\n");
 163
 164         /*
 165          * Send the request to the appropriate session...
 166          */
 167         printf("   Writing %d lines of command\n", num_lines);
 168         printf("%s\n", &req[0][0]);
 169         for (a=0; a<num_lines; ++a) {
 170                 write(TheSession->inpipe[1], &req[a][0], strlen(&req[a][0]));
 171                 write(TheSession->inpipe[1], "\n", 1);
 172                 }
 173         printf("   Writing %d bytes of content\n", ContentLength);
 174         while (ContentLength--) {
 175                 read(sock, buf, 1);
 176                 write(TheSession->inpipe[1], buf, 1);
 177                 }
 178
 179         /*
 180          * ...and get the response.
 181          */
 182         printf("   Reading response\n");
 183         ContentLength = 0;
 184         do {
 185                 gets0(TheSession->outpipe[0], buf);
 186                 write(sock, buf, strlen(buf));
 187                 write(sock, "\n", 1);
 188                 if (!strncasecmp(buf, "Content-length: ", 16))
 189                         ContentLength = atoi(&buf[16]);
 190                 } while (strlen(buf) > 0);
 191
 192         printf("   Reading %d bytes of content\n");
 193         while(ContentLength--) {
 194                 read(TheSession->outpipe[0], buf, 1);
 195                 write(sock, buf, 1);
 196                 }
 197
 198         /*
 199          * Now our HTTP connection is done.  It would be relatively easy
 200          * to support HTTP/1.1 "persistent" connections by looping back to
 201          * the top of this function.  For now, we'll just close.
 202          */
 203         printf("   Closing socket\n");
 204         close(sock);
 205
 206         /*
 207          * Let go of the lock
 208          */
 209         printf("Unlocking.\n");
 210         pthread_mutex_unlock(&TheSession->critter);
 211
 212         /*
 213          * The thread handling this HTTP connection is now finished.
 214          */
 215         pthread_exit(NULL);
 216         }