[libmicrohttpd] [PATCH] Add support for using a monotonic clock for timeouts

[Mike Crowe]

Change various uses of time(NULL) to new MHD_monotonic_time() function to
make timeouts immune to the system real time clock changing. Leave one call
to time(2) which continues to use the real time for the HTTP Date: header.

If clock_gettime does not support CLOCK_MONOTONIC then fall through to
calling time(NULL) instead. This will be problematic if clock_gettime
sometimes fails and sometimes succeeds but that shouldn't happen.

The autoconf magic was lifted from
http://lists.gnu.org/archive/html/autoconf/2010-08/msg00035.html
---
 configure.ac                  |    3 +++
 src/daemon/connection.c       |    6 +++---
 src/daemon/connection_https.c |    4 ++--
 src/daemon/daemon.c           |    7 +++----
 src/daemon/digestauth.c       |    4 ++--
 src/daemon/internal.c         |   10 ++++++++++
 src/daemon/internal.h         |    6 ++++++
 7 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/configure.ac b/configure.ac
index 41d5472..7b47278 100644
--- a/configure.ac
+++ b/configure.ac
@@ -190,6 +190,9 @@ 
AC_CHECK_HEADERS([plibc.h],our_private_plibc_h=0,our_private_plibc_h=1)
 AM_CONDITIONAL(USE_PRIVATE_PLIBC_H, test x$our_private_plibc_h = x1)    
 
 AC_CHECK_FUNCS(memmem)
+AC_SEARCH_LIBS([clock_gettime], [rt], [
+                               AC_DEFINE(HAVE_CLOCK_GETTIME, 1, [Have 
clock_gettime])
+])
 
 # IPv6
 AC_MSG_CHECKING(for IPv6)
diff --git a/src/daemon/connection.c b/src/daemon/connection.c
index acc4839..13c465b 100644
--- a/src/daemon/connection.c
+++ b/src/daemon/connection.c
@@ -1786,7 +1786,7 @@ parse_connection_headers (struct MHD_Connection 
*connection)
 int
 MHD_connection_handle_read (struct MHD_Connection *connection)
 {
-  connection->last_activity = time (NULL);
+  connection->last_activity = MHD_monotonic_time();
   if (connection->state == MHD_CONNECTION_CLOSED)
     return MHD_YES;
   /* make sure "read" has a reasonable number of bytes
@@ -1851,7 +1851,7 @@ MHD_connection_handle_write (struct MHD_Connection 
*connection)
 {
   struct MHD_Response *response;
   int ret;
-  connection->last_activity = time (NULL);
+  connection->last_activity = MHD_monotonic_time();
   while (1)
     {
 #if DEBUG_STATES
@@ -2372,7 +2372,7 @@ MHD_connection_handle_idle (struct MHD_Connection 
*connection)
     }
   timeout = connection->connection_timeout;
   if ( (timeout != 0) &&
-       (timeout <= (time (NULL) - connection->last_activity)) )
+       (timeout <= (MHD_monotonic_time() - connection->last_activity)) )
     {
       MHD_connection_close (connection, 
MHD_REQUEST_TERMINATED_TIMEOUT_REACHED);
       return MHD_YES;
diff --git a/src/daemon/connection_https.c b/src/daemon/connection_https.c
index 1330c3a..539b8de 100644
--- a/src/daemon/connection_https.c
+++ b/src/daemon/connection_https.c
@@ -47,7 +47,7 @@ run_tls_handshake (struct MHD_Connection *connection)
 {
   int ret;
 
-  connection->last_activity = time (NULL);
+  connection->last_activity = MHD_monotonic_time();
   if (connection->state == MHD_TLS_CONNECTION_INIT)
     {
       ret = gnutls_handshake (connection->tls_session);
@@ -138,7 +138,7 @@ MHD_tls_connection_handle_idle (struct MHD_Connection 
*connection)
             __FUNCTION__, MHD_state_to_string (connection->state));
 #endif
   timeout = connection->connection_timeout;
-  if ( (timeout != 0) && (time (NULL) - timeout > connection->last_activity))
+  if ( (timeout != 0) && (MHD_monotonic_time() - timeout > 
connection->last_activity))
     MHD_connection_close (connection,
                          MHD_REQUEST_TERMINATED_TIMEOUT_REACHED);
   switch (connection->state)
diff --git a/src/daemon/daemon.c b/src/daemon/daemon.c
index 29d7ced..451bb39 100644
--- a/src/daemon/daemon.c
+++ b/src/daemon/daemon.c
@@ -546,7 +546,6 @@ MHD_get_fdset (struct MHD_Daemon *daemon,
   return MHD_YES;
 }
 
-
 /**
  * Main function of the thread that handles an individual
  * connection when MHD_USE_THREAD_PER_CONNECTION is set.
@@ -578,7 +577,7 @@ MHD_handle_connection (void *data)
       tvp = NULL;
       if (timeout > 0)
        {
-         now = time (NULL);
+         now = MHD_monotonic_time();
          if (now - con->last_activity > timeout)
            tv.tv_sec = 0;
          else
@@ -938,7 +937,7 @@ MHD_add_connection (struct MHD_Daemon *daemon,
   connection->addr_len = addrlen;
   connection->socket_fd = client_socket;
   connection->daemon = daemon;
-  connection->last_activity = time (NULL);
+  connection->last_activity = MHD_monotonic_time();
 
   /* set default connection handlers  */
   MHD_set_http_callbacks_ (connection);
@@ -1252,7 +1251,7 @@ MHD_get_timeout (struct MHD_Daemon *daemon,
     }
   if (!have_timeout)
     return MHD_NO;
-  now = time (NULL);
+  now = MHD_monotonic_time();
   if (earliest_deadline < now)
     *timeout = 0;
   else
diff --git a/src/daemon/digestauth.c b/src/daemon/digestauth.c
index 1e976bb..1f9547c 100644
--- a/src/daemon/digestauth.c
+++ b/src/daemon/digestauth.c
@@ -619,7 +619,7 @@ MHD_digest_auth_check(struct MHD_Connection *connection,
       
     /* 8 = 4 hexadecimal numbers for the timestamp */  
     nonce_time = strtoul(nonce + len - 8, (char **)NULL, 16);  
-    t = (uint32_t) time(NULL);    
+    t = (uint32_t) MHD_monotonic_time();    
     /*
      * First level vetting for the nonce validity if the timestamp
      * attached to the nonce exceeds `nonce_timeout' then the nonce is
@@ -751,7 +751,7 @@ MHD_queue_auth_fail_response(struct MHD_Connection 
*connection,
   char nonce[HASH_MD5_HEX_LEN + 9];
 
   /* Generating the server nonce */  
-  calculate_nonce ((uint32_t) time(NULL),
+  calculate_nonce ((uint32_t) MHD_monotonic_time(),
                   connection->method,
                   connection->daemon->digest_auth_random,
                   connection->daemon->digest_auth_rand_size,
diff --git a/src/daemon/internal.c b/src/daemon/internal.c
index 3b0a544..453634e 100644
--- a/src/daemon/internal.c
+++ b/src/daemon/internal.c
@@ -157,4 +157,14 @@ MHD_http_unescape (void *cls,
   return wpos - val; /* = strlen(val) */
 }
 
+time_t MHD_monotonic_time(void)
+{
+#ifdef HAVE_CLOCK_GETTIME
+    struct timespec ts;
+    if (clock_gettime(CLOCK_MONOTONIC, &ts) == 0)
+       return ts.tv_sec;
+#endif
+    return time(NULL);
+}
+
 /* end of internal.c */
diff --git a/src/daemon/internal.h b/src/daemon/internal.h
index 6e15af2..15900f1 100644
--- a/src/daemon/internal.h
+++ b/src/daemon/internal.h
@@ -1057,5 +1057,11 @@ struct MHD_Daemon
   (element)->next = NULL; \
   (element)->prev = NULL; } while (0)
 
+/**
+ * Equivalent to time(NULL) but tries to use some sort of monotonic
+ * clock that isn't affected by someone setting the system real time
+ * clock.
+ */
+time_t MHD_monotonic_time(void);
 
 #endif
-- 
1.7.10