Add a NODELAY option

Add a new option SSH_OPTIONS_NODELAY to enable or disable the
Nagle Algorithm (TCP_NODELAY) on the session socket.

Improved performance can be achieved for some applications like
sftp servers by enabling SSH_OPTIONS_NODELAY as typically, the
next request won't arrive until the server replies, which are
typically small writes.

Signed-off-by: Alberto Aguirre <albaguirre@gmail.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/libssh.h

@@ -355,7 +355,8 @@ enum ssh_options_e {
   SSH_OPTIONS_PUBKEY_AUTH,
   SSH_OPTIONS_KBDINT_AUTH,
   SSH_OPTIONS_GSSAPI_AUTH,
-  SSH_OPTIONS_GLOBAL_KNOWNHOSTS
+  SSH_OPTIONS_GLOBAL_KNOWNHOSTS,
+  SSH_OPTIONS_NODELAY,
 };
 
 enum {

include/libssh/session.h

@@ -205,6 +205,7 @@ struct ssh_session_struct {
         char *gss_client_identity;
         int gss_delegate_creds;
         int flags;
+        int nodelay;
     } opts;
     /* counters */
     ssh_counter socket_counter;

src/connect.c

@@ -74,6 +74,7 @@
 #include <sys/socket.h>
 #include <sys/select.h>
 #include <netinet/in.h>
+#include <netinet/tcp.h>
 
 #endif /* _WIN32 */
 
@@ -216,6 +217,12 @@ static int ssh_connect_ai_timeout(ssh_session session, const char *host,
   return s;
 }
 
+static int set_tcp_nodelay(socket_t socket)
+{
+    int opt = 1;
+    return setsockopt(socket, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof(opt));
+}
+
 /**
  * @internal
  *
@@ -387,6 +394,18 @@ socket_t ssh_connect_host_nonblocking(ssh_session session, const char *host,
         continue;
     }
 
+    if (session->opts.nodelay) {
+        /* For winsock, socket options are only effective before connect */
+        rc = set_tcp_nodelay(s);
+        if (rc < 0) {
+            ssh_set_error(session, SSH_FATAL,
+                "Failed to set TCP_NODELAY on socket: %s", strerror(errno));
+            ssh_connect_socket_close(s);
+            s = -1;
+            continue;
+        }
+    }
+
     errno = 0;
     rc = connect(s, itr->ai_addr, itr->ai_addrlen);
     if (rc == -1 && (errno != 0) && (errno != EINPROGRESS)) {

src/options.c

@@ -408,6 +408,10 @@ int ssh_options_set_algo(ssh_session session,
  *                Currently without effect (ssh_userauth_auto_pubkey doesn't use
  *                gssapi authentication).
  *
+ *              - SSH_OPTIONS_NODELAY
+ *                Set it to disable Nagle's Algorithm (TCP_NODELAY) on the
+ *                session socket. (int, 0=false)
+ *
  * @param  value The value to set. This is a generic pointer and the
  *               datatype which is used should be set according to the
  *               type set.
@@ -938,7 +942,15 @@ int ssh_options_set(ssh_session session, enum ssh_options_e type,
                 }
             }
             break;
-
+        case SSH_OPTIONS_NODELAY:
+            if (value == NULL) {
+                ssh_set_error_invalid(session);
+                return -1;
+            } else {
+                int *x = (int *) value;
+                session->opts.nodelay = (*x & 0xff) > 0 ? 1 : 0;
+            }
+            break;
         default:
             ssh_set_error(session, SSH_REQUEST_DENIED, "Unknown ssh option %d", type);
             return -1;

src/session.c

@@ -107,6 +107,7 @@ ssh_session ssh_new(void) {
     session->opts.fd = -1;
     session->opts.ssh2 = 1;
     session->opts.compressionlevel=7;
+    session->opts.nodelay = 0;
 #ifdef WITH_SSH1
     session->opts.ssh1 = 1;
 #else