Limit number of GnuTLS handshakes per connection.

* gnutls.c (gnutls_log_function2i): Convenience log function.
(emacs_gnutls_read): Use new log functions,
`gnutls_handshakes_tried' process member, and
`GNUTLS_EMACS_HANDSHAKES_LIMIT' to limit the number of handshake
attempts per process (connection).

* gnutls.h: Add `GNUTLS_EMACS_HANDSHAKES_LIMIT' upper limit.  Add
convenience `GNUTLS_LOG2i' macro.

* process.c (make_process):
* process.h: Add integer `gnutls_handshakes_tried' member to
process struct.

5 files changed, 50 insertions, 2 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 7c3dd115c5b..f7889d99335 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,18 @@
+2012-04-09  Teodor Zlatanov  <tzz@lifelogs.com>
+
+        * process.c (make_process):
+        * process.h: Add integer `gnutls_handshakes_tried' member to
+        process struct.
+
+        * gnutls.h: Add `GNUTLS_EMACS_HANDSHAKES_LIMIT' upper limit.  Add
+        convenience `GNUTLS_LOG2i' macro.
+
+        * gnutls.c (gnutls_log_function2i): Convenience log function.
+        (emacs_gnutls_read): Use new log functions,
+        `gnutls_handshakes_tried' process member, and
+        `GNUTLS_EMACS_HANDSHAKES_LIMIT' to limit the number of handshake
+        attempts per process (connection).
+
 2012-04-09  Chong Yidong  <cyd@gnu.org>
 
         * eval.c (Fuser_variable_p, user_variable_p_eh)
diff --git a/src/gnutls.c b/src/gnutls.c
index 6b5cb47001b..70eea3b0b89 100644
--- a/src/gnutls.c
+++ b/src/gnutls.c
@@ -247,18 +247,27 @@ init_gnutls_functions (Lisp_Object libraries)
 #endif /* !WINDOWSNT */
 
 
+/* Function to log a simple message.  */
 static void
 gnutls_log_function (int level, const char* string)
 {
   message ("gnutls.c: [%d] %s", level, string);
 }
 
+/* Function to log a message and a string.  */
 static void
 gnutls_log_function2 (int level, const char* string, const char* extra)
 {
   message ("gnutls.c: [%d] %s %s", level, string, extra);
 }
 
+/* Function to log a message and an integer.  */
+static void
+gnutls_log_function2i (int level, const char* string, int extra)
+{
+  message ("gnutls.c: [%d] %s %d", level, string, extra);
+}
+
 static int
 emacs_gnutls_handshake (struct Lisp_Process *proc)
 {
@@ -399,10 +408,25 @@ emacs_gnutls_read (struct Lisp_Process *proc, char *buf, EMACS_INT nbyte)
   ssize_t rtnval;
   gnutls_session_t state = proc->gnutls_state;
 
+  int log_level = proc->gnutls_log_level;
+
   if (proc->gnutls_initstage != GNUTLS_STAGE_READY)
     {
-      emacs_gnutls_handshake (proc);
-      return -1;
+      /* If the handshake count is under the limit, try the handshake
+         again and increment the handshake count.  This count is kept
+         per process (connection), not globally.  */
+      if (proc->gnutls_handshakes_tried < GNUTLS_EMACS_HANDSHAKES_LIMIT)
+        {
+          proc->gnutls_handshakes_tried++;
+          emacs_gnutls_handshake (proc);
+          GNUTLS_LOG2i (5, log_level, "Retried handshake", 
+                        proc->gnutls_handshakes_tried);
+          return -1;
+        }
+
+      GNUTLS_LOG (2, log_level, "Giving up on handshake; resetting retries");
+      proc->gnutls_handshakes_tried = 0;
+      return 0;
     }
   rtnval = fn_gnutls_record_recv (state, buf, nbyte);
   if (rtnval >= 0)
diff --git a/src/gnutls.h b/src/gnutls.h
index 474da77aec5..37b9a2eb4df 100644
--- a/src/gnutls.h
+++ b/src/gnutls.h
@@ -23,6 +23,9 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <gnutls/gnutls.h>
 #include <gnutls/x509.h>
 
+/* This limits the attempts to handshake per process (connection).  */
+#define GNUTLS_EMACS_HANDSHAKES_LIMIT 100
+
 typedef enum
 {
   /* Initialization stages.  */
@@ -53,6 +56,8 @@ typedef enum
 
 #define GNUTLS_LOG2(level, max, string, extra) do { if (level <= max) { gnutls_log_function2 (level, "(Emacs) " string, extra); } } while (0)
 
+#define GNUTLS_LOG2i(level, max, string, extra) do { if (level <= max) { gnutls_log_function2i (level, "(Emacs) " string, extra); } } while (0)
+
 extern EMACS_INT
 emacs_gnutls_write (struct Lisp_Process *proc, const char *buf, EMACS_INT nbyte);
 extern EMACS_INT
diff --git a/src/process.c b/src/process.c
index f2f33a9eafc..dc43191ebef 100644
--- a/src/process.c
+++ b/src/process.c
@@ -640,7 +640,10 @@ make_process (Lisp_Object name)
 
 #ifdef HAVE_GNUTLS
   p->gnutls_initstage = GNUTLS_STAGE_EMPTY;
+  /* Default log level.  */
   p->gnutls_log_level = 0;
+  /* GnuTLS handshakes attempted for this connection.  */
+  p->gnutls_handshakes_tried = 0;
   p->gnutls_p = 0;
   p->gnutls_state = NULL;
   p->gnutls_x509_cred = NULL;
diff --git a/src/process.h b/src/process.h
index 9efde261386..3eb94cb196b 100644
--- a/src/process.h
+++ b/src/process.h
@@ -134,6 +134,7 @@ struct Lisp_Process
     gnutls_certificate_client_credentials gnutls_x509_cred;
     gnutls_anon_client_credentials_t gnutls_anon_cred;
     int gnutls_log_level;
+    int gnutls_handshakes_tried;
     int gnutls_p;
 #endif
 };