From d1fc0ff84894bba24f827a81597717e9f69b6c06 Mon Sep 17 00:00:00 2001
From: Adam Dickmeiss <adam@indexdata.dk>
Date: Fri, 26 Jan 1996 09:02:20 +0000
Subject: [PATCH] Open of client FIFO called with O_NDELAY when reconnecting
 to shell in order to prevent serious lock if previous shell
 died without unlinking client FIFO.

---
 www/wcgi.c   |   39 ++++++++++++++++++++++++++++++++++-----
 www/wproto.c |    8 ++++++--
 2 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/www/wcgi.c b/www/wcgi.c
index 540d23b..f6ae643 100644
--- a/www/wcgi.c
+++ b/www/wcgi.c
@@ -41,7 +41,12 @@
  * USE OR PERFORMANCE OF THIS SOFTWARE.
  *
  * $Log: wcgi.c,v $
- * Revision 1.14  1996/01/12 13:08:06  adam
+ * Revision 1.15  1996/01/26 09:02:20  adam
+ * Open of client FIFO called with O_NDELAY when reconnecting to shell
+ * in order to prevent serious lock if previous shell died without
+ * unlinking client FIFO.
+ *
+ * Revision 1.14  1996/01/12  13:08:06  adam
  * CGI script passes name of lock file to the shell. The server will not close
  * the response FIFO until this file becomes unlocked. This method handles
  * cancel operations much better.
@@ -190,12 +195,14 @@ int main()
     gw_log_session (getpid());
     gw_log (GW_LOG_STAT, prog, "Europagate www cgi server");
 
+    /* Create fifo directory if it doesn't exist already */
     sprintf(tmp, "%s/%s", FIFOROOT, FIFODIR);
     if (access(tmp, R_OK|W_OK) < 0 && mkdir(tmp, 0777) < 0)
     {
     	gw_log (GW_LOG_FATAL|GW_LOG_ERRNO, prog, "Failed to create %s", tmp);
     	fatal("Internal error in server.");
     }
+    /* Delete server FIFO if it does exist */
     sprintf(serverp, "%s/srv%d", tmp, getpid());
     if (access(serverp, R_OK|W_OK) == 0)
     {
@@ -208,16 +215,20 @@ int main()
 	else
 	    gw_log (GW_LOG_WARN, prog, "Removed stale server fifo.");
     }
+    /* Make server FIFO */
     if (mkfifo(serverp, 0666 | S_IFIFO) < 0)
     {
     	gw_log (GW_LOG_FATAL|GW_LOG_ERRNO, prog, "mkfifo(%s)", serverp);
 	fatal("Internal error in server.");
     }
+    /* The httpd server must pass PATH_INFO */
     if (!(path_info = getenv("PATH_INFO")))
     {
     	gw_log (GW_LOG_FATAL, prog, "Must set PATH_INFO.");
     	fatal("Internal error in server.");
     }
+    /* Create lock file that ensures the server (shell) doesn't */
+    /* terminate before we have read the whole response */
     sprintf (serverf, "%s/srf%d", tmp, getpid ());
     gw_log (GW_LOG_DEBUG, prog, "open w %s", serverf);
     serverf_fd = open (serverf, O_WRONLY|O_CREAT|O_TRUNC, 0666);
@@ -235,6 +246,8 @@ int main()
         area.l_len = 0L;
         fcntl (serverf_fd, F_SETLK, &area);
     }
+    /* Read first part of path_info. Either it is a numeric session id */
+    /* or it is the name of a backend shell. */
     operation = ++path_info;
     while (*path_info && *path_info != '/')
     	path_info++;
@@ -247,14 +260,17 @@ int main()
         exit (1);
     }
     gw_log (GW_LOG_DEBUG, prog, "www.db ok");
+    /* Is operation a backend shell (new session) ? */
     if ((gw_id = atoi(operation)) <= 0)
     {
         int r;
         char gw_id_str[16];
 
+        /* Get new unique id */
         gw_id = gw_db_seq_no (gw_db);
         sprintf (gw_id_str, "%d", gw_id);
-        
+       
+        /* Spawn backend shell (server) */ 
     	spawn(operation, gw_id);
         r = gw_db_insert (gw_db, gw_id_str, strlen(gw_id_str)+1,
                           operation, strlen(operation)+1);
@@ -276,10 +292,23 @@ int main()
 	    fatal("Internal error in server");
 	}
     	gw_log (GW_LOG_DEBUG, prog, "Synchronized");
+        sprintf(clientp, "%s/clt%d", tmp, gw_id);
+        gw_log (GW_LOG_DEBUG, prog, "open w %s", clientp);
+        lineout = open (clientp, O_WRONLY);
+    }
+    else /* A session is continued */
+    {
+        sprintf(clientp, "%s/clt%d", tmp, gw_id);
+        gw_log (GW_LOG_DEBUG, prog, "open w|n %s", clientp);
+        /* Open the FIFO in O_NDELAY-mode: This prevents blocking */
+        /* even though the shell died without unlinking the FIFO */
+        /* On the other hand, if the shell is running, it will never */
+        /* close this FIFO */
+        lineout = open (clientp, O_WRONLY|O_NDELAY);
     }
-    sprintf(clientp, "%s/clt%d", tmp, gw_id);
-    gw_log (GW_LOG_DEBUG, prog, "open w %s", clientp);
-    if ((lineout = open(clientp, O_WRONLY)) < 0)
+    /* If open of clientp failed, the shell is not running, so we */
+    /* invoke it again */
+    if (lineout < 0)
     {
         char gw_id_str[16];
         void *sprog;
diff --git a/www/wproto.c b/www/wproto.c
index a90223e..03b04d5 100644
--- a/www/wproto.c
+++ b/www/wproto.c
@@ -41,7 +41,12 @@
  * USE OR PERFORMANCE OF THIS SOFTWARE.
  *
  * $Log: wproto.c,v $
- * Revision 1.16  1996/01/24 10:13:56  adam
+ * Revision 1.17  1996/01/26 09:02:22  adam
+ * Open of client FIFO called with O_NDELAY when reconnecting to shell
+ * in order to prevent serious lock if previous shell died without
+ * unlinking client FIFO.
+ *
+ * Revision 1.16  1996/01/24  10:13:56  adam
  * Bug fix: in function wo_write realloc is used only when memory is already
  * allocated with malloc.
  *
@@ -363,7 +368,6 @@ int wproto_process(WCLIENT wc, int timeout)
             unlink (wc->wf_serverp);
 	    return 0;
 	}
-        /* determine handle (fifo or user) */
 	if (read(wc->linein, &toread, sizeof(toread)) < sizeof(toread))
 	{
 	    gw_log (GW_LOG_FATAL|GW_LOG_ERRNO, mod, "wp_proc:len read failed");
-- 
1.7.10.4