Make check for compression programs more robust in Tramp

* lisp/net/tramp-sh.el (tramp-inline-compress-start-size):
Revert change of init value.  We fix this differently.
(tramp-find-inline-compress): Check also the output of the
processes, not only the return code.

1 files changed, 30 insertions, 23 deletions

diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 63c1bf48f51..bebe2c2d334 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -38,14 +38,13 @@
 (defvar vc-hg-program)
 
 ;;;###tramp-autoload
-(defcustom tramp-inline-compress-start-size
-  (unless (memq system-type '(windows-nt)) 4096)
+(defcustom tramp-inline-compress-start-size 4096
   "The minimum size of compressing where inline transfer.
-When inline transfer, compress transferred data of file
-whose size is this value or above (up to `tramp-copy-size-limit').
+When inline transfer, compress transferred data of file whose
+size is this value or above (up to `tramp-copy-size-limit' for
+out-of-band methods).
 If it is nil, no compression at all will be applied."
   :group 'tramp
-  :version "26.3"
   :type '(choice (const nil) integer))
 
 ;;;###tramp-autoload
@@ -4557,30 +4556,38 @@ Goes through the list `tramp-inline-compress-commands'."
            vec 5
            "Checking local compress commands `%s', `%s' for sanity"
            compress decompress)
-          (unless
-              (zerop
-               (tramp-call-local-coding-command
-                (format
-                 "echo %s | %s | %s" magic
-                 ;; Windows shells need the program file name after
-                 ;; the pipe symbol be quoted if they use forward
-                 ;; slashes as directory separators.
-                 (mapconcat
-                  #'tramp-unquote-shell-quote-argument
-                  (split-string compress) " ")
-                 (mapconcat
-                  #'tramp-unquote-shell-quote-argument
-                  (split-string decompress) " "))
-                nil nil))
-            (throw 'next nil))
-          (tramp-message
+          (with-temp-buffer
+            (unless
+                (and
+                 (zerop
+                  (tramp-call-local-coding-command
+                   (format
+                    "echo %s | %s | %s" magic
+                    ;; Windows shells need the program file name after
+                    ;; the pipe symbol be quoted if they use forward
+                    ;; slashes as directory separators.
+                    (mapconcat
+                     #'tramp-unquote-shell-quote-argument
+                     (split-string compress) " ")
+                    (mapconcat
+                     #'tramp-unquote-shell-quote-argument
+                     (split-string decompress) " "))
+                   nil t))
+                 (string-match
+                  (concat "^" (regexp-quote magic) "$") (buffer-string)))
+              (throw 'next nil)))
+          (tramp-message
            vec 5
            "Checking remote compress commands `%s', `%s' for sanity"
            compress decompress)
           (unless (tramp-send-command-and-check
                    vec (format "echo %s | %s | %s" magic compress decompress) t)
             (throw 'next nil))
-          (setq found t)))
+  (with-current-buffer (tramp-get-buffer vec)
+    (goto-char (point-min))
+    (unless (looking-at (regexp-quote magic))
+      (throw 'next nil)))
+  (setq found t)))
 
       ;; Did we find something?
       (if found