Detect ssh 'ControlMaster' argument automatically in some cases.

* net/tramp.el (tramp-detect-ssh-controlmaster): New defun.
(tramp-default-method): Use it.

2 files changed, 30 insertions, 10 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index d7c32848543..dd14ff9e77c 100755
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,9 +1,18 @@
+2010-04-22  Noah Lavine  <noah549@gmail.com>  (tiny change)
+
+        Detect ssh 'ControlMaster' argument automatically in some cases.
+
+        * net/tramp.el (tramp-detect-ssh-controlmaster): New defun.
+        (tramp-default-method): Use it.
+
 2010-04-22  Michael Albinus  <michael.albinus@gmx.de>
 
         * net/tramp.el (tramp-handle-copy-file): Add new optional
         parameter `preserve-selinux-context'.
         (tramp-file-name-for-operation): Add `set-file-selinux-context'.
 
+2010-04-22  Michael Albinus  <michael.albinus@gmx.de>
+
         * net/tramp.el (tramp-completion-handle-file-name-all-completions):
         Ensure, that non remote files are still checked.  Oops.
 
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 6959879e677..af5d526bfc6 100755
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -723,6 +723,16 @@ started on the local host.  You should specify a remote host
 `localhost' or the name of the local host.  Another host name is
 useful only in combination with `tramp-default-proxies-alist'.")
 
+(defun tramp-detect-ssh-controlmaster ()
+  "Call ssh to detect whether it supports the ControlMaster argument.
+This function may return nil when the argument is supported, but
+shouldn't return t when it isn't."
+  (ignore-errors
+    (with-temp-buffer
+      (call-process "ssh" nil t nil "-o" "ControlMaster")
+      (goto-char (point-min))
+      (search-forward-regexp "Missing ControlMaster argument" nil t))))
+
 (defcustom tramp-default-method
   ;; An external copy method seems to be preferred, because it is much
   ;; more performant for large files, and it hasn't too serious delays
@@ -730,9 +740,8 @@ useful only in combination with `tramp-default-proxies-alist'.")
   ;; permanent password queries.  Either a password agent like
   ;; "ssh-agent" or "Pageant" shall run, or the optional
   ;; password-cache.el or auth-sources.el packages shall be active for
-  ;; password caching.  "scpc" would be another good choice because of
-  ;; the "ControlMaster" option, but this is a more modern alternative
-  ;; in OpenSSH 4, which cannot be taken as default.
+  ;; password caching.  "scpc" is chosen if we detect that the user is
+  ;; running OpenSSH 4.0 or newer.
   (cond
    ;; PuTTY is installed.
    ((executable-find "pscp")
@@ -744,13 +753,15 @@ useful only in combination with `tramp-default-proxies-alist'.")
       "plink"))
    ;; There is an ssh installation.
    ((executable-find "scp")
-    (if (or (fboundp 'password-read)
-            (fboundp 'auth-source-user-or-password)
-            ;; ssh-agent is running.
-            (getenv "SSH_AUTH_SOCK")
-            (getenv "SSH_AGENT_PID"))
-        "scp"
-      "ssh"))
+    (cond
+     ((tramp-detect-ssh-controlmaster) "scpc")
+     ((or (fboundp 'password-read)
+          (fboundp 'auth-source-user-or-password)
+          ;; ssh-agent is running.
+          (getenv "SSH_AUTH_SOCK")
+          (getenv "SSH_AGENT_PID"))
+      "scp")
+     (t "ssh")))
    ;; Fallback.
    (t "ftp"))
   "*Default method to use for transferring files.