epg: Improve error handling

* epa.el (epa-error-buffer): New variable.
(epa-display-error): New function.
(epa-decrypt-file, epa-verify-file, epa-verify-region)
(epa-delete-keys, epa-import-keys): Display output sent to stderr.
(epa-sign-file, epa-sign-region, epa-encrypt-region)
(epa-export-keys, epa-insert-keys): Display output sent to stderr.
Use setf instead of epg-context-set-*.
* epa-file.el (epa-file-insert-file-contents): Use
epa-display-error instead of epa-display-info.  Mimic the behavior
of jka-compr when decryption program is not found.
(epa-file-write-region): Use epa-display-error instead of
epa-display-info.

3 files changed, 197 insertions, 107 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index a0108305ac3..e81b3a736a7 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,18 @@
+2014-11-06  Daiki Ueno  <ueno@gnu.org>
+
+        * epa.el (epa-error-buffer): New variable.
+        (epa-display-error): New function.
+        (epa-decrypt-file, epa-verify-file, epa-verify-region)
+        (epa-delete-keys, epa-import-keys): Display output sent to stderr.
+        (epa-sign-file, epa-sign-region, epa-encrypt-region)
+        (epa-export-keys, epa-insert-keys): Display output sent to stderr.
+        Use setf instead of epg-context-set-*.
+        * epa-file.el (epa-file-insert-file-contents): Use
+        epa-display-error instead of epa-display-info.  Mimic the behavior
+        of jka-compr when decryption program is not found.
+        (epa-file-write-region): Use epa-display-error instead of
+        epa-display-info.
+
 2014-11-05  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * vc/vc.el (vc-region-history): New command.
diff --git a/lisp/epa-file.el b/lisp/epa-file.el
index 6f3bb188190..759271bc4e8 100644
--- a/lisp/epa-file.el
+++ b/lisp/epa-file.el
@@ -105,9 +105,9 @@ encryption is used."
         (insert (if enable-multibyte-characters
                     (string-to-multibyte string)
                   string))
-          (decode-coding-inserted-region
-           (point-min) (point-max)
-           (substring file 0 (string-match epa-file-name-regexp file))
+        (decode-coding-inserted-region
+         (point-min) (point-max)
+         (substring file 0 (string-match epa-file-name-regexp file))
          visit beg end replace))
     (insert (epa-file--decode-coding-string string (or coding-system-for-read
                                                        'undecided)))))
@@ -151,8 +151,17 @@ encryption is used."
           (condition-case error
               (setq string (epg-decrypt-file context local-file nil))
             (error
+             (epa-display-error context)
              (if (setq entry (assoc file epa-file-passphrase-alist))
                  (setcdr entry nil))
+             ;; If the decryption program can't be found,
+             ;; signal that as a non-file error
+             ;; so that find-file-noselect-1 won't handle it.
+             ;; Borrowed from jka-compr.el.
+             (if (and (eq (car error) 'file-error)
+                      (equal (cadr error) "Searching for program"))
+                 (error "Decryption program `%s' not found"
+                        (nth 3 error)))
              ;; Hack to prevent find-file from opening empty buffer
              ;; when decryption failed (bug#6568).  See the place
              ;; where `find-file-not-found-functions' are called in
@@ -162,11 +171,6 @@ encryption is used."
                (add-hook 'find-file-not-found-functions
                          'epa-file--find-file-not-found-function
                          nil t))
-             (if (epg-context-error-output context)
-                 (epa-display-info
-                  (concat (format "Error while executing \"%s\":\n\n"
-                                  epg-gpg-program)
-                          (epg-context-error-output context))))
              (signal 'file-error
                      (cons "Opening input file" (cdr error)))))
           (set-buffer buf) ;In case timer/filter changed/killed it (bug#16029)!
@@ -226,7 +230,7 @@ encryption is used."
      context
      (cons #'epa-progress-callback-function
            (format "Encrypting %s" file)))
-    (epg-context-set-armor context epa-armor)
+    (setf (epg-context-armor context) epa-armor)
     (condition-case error
         (setq string
               (epg-encrypt-string
@@ -260,13 +264,9 @@ If no one is selected, symmetric encryption will be performed.  "
                  (if epa-file-encrypt-to
                      (epg-list-keys context recipients)))))
       (error
+       (epa-display-error context)
        (if (setq entry (assoc file epa-file-passphrase-alist))
            (setcdr entry nil))
-       (if (epg-context-error-output context)
-           (epa-display-info
-            (concat (format "Error while executing \"%s\":\n\n"
-                            epg-gpg-program)
-                    (epg-context-error-output context))))
        (signal 'file-error (cons "Opening output file" (cdr error)))))
     (epa-file-run-real-handler
      #'write-region
diff --git a/lisp/epa.el b/lisp/epa.el
index 0c833ab84d6..6d20a190d9c 100644
--- a/lisp/epa.el
+++ b/lisp/epa.el
@@ -166,6 +166,7 @@ You should bind this variable with `let', but do not set it globally.")
 (defvar epa-key nil)
 (defvar epa-list-keys-arguments nil)
 (defvar epa-info-buffer nil)
+(defvar epa-error-buffer nil)
 (defvar epa-last-coding-system-specified nil)
 
 (defvar epa-key-list-mode-map
@@ -578,6 +579,34 @@ If SECRET is non-nil, list secret keys instead of public keys."
               (shrink-window (- (window-height) epa-info-window-height)))))
     (message "%s" info)))
 
+(defun epa-display-error (context)
+  (unless (equal (epg-context-error-output context) "")
+    (let ((buffer (get-buffer-create "*Error*")))
+      (save-selected-window
+        (unless (and epa-error-buffer (buffer-live-p epa-error-buffer))
+          (setq epa-error-buffer (generate-new-buffer "*Error*")))
+        (if (get-buffer-window epa-error-buffer)
+            (delete-window (get-buffer-window epa-error-buffer)))
+        (with-current-buffer buffer
+          (let ((inhibit-read-only t)
+                buffer-read-only)
+            (erase-buffer)
+            (insert (format
+                     (pcase (epg-context-operation context)
+                       (`decrypt "Error while decrypting with \"%s\":")
+                       (`verify "Error while verifying with \"%s\":")
+                       (`sign "Error while signing with \"%s\":")
+                       (`encrypt "Error while encrypting with \"%s\":")
+                       (`import-keys "Error while importing keys with \"%s\":")
+                       (`export-keys "Error while exporting keys with \"%s\":")
+                       (_ "Error while executing \"%s\":\n\n"))
+                     epg-gpg-program)
+                    "\n\n"
+                    (epg-context-error-output context)))
+          (epa-info-mode)
+          (goto-char (point-min)))
+        (display-buffer buffer)))))
+
 (defun epa-display-verify-result (verify-result)
   (declare (obsolete epa-display-info "23.1"))
   (epa-display-info (epg-verify-result-to-string verify-result)))
@@ -593,14 +622,14 @@ If SECRET is non-nil, list secret keys instead of public keys."
        (eq (epg-context-operation context) 'encrypt))
     (read-passwd
      (if (eq key-id 'PIN)
-        "Passphrase for PIN: "
+         "Passphrase for PIN: "
        (let ((entry (assoc key-id epg-user-id-alist)))
          (if entry
              (format "Passphrase for %s %s: " key-id (cdr entry))
            (format "Passphrase for %s: " key-id)))))))
 
 (defun epa-progress-callback-function (_context what _char current total
-                                               handback)
+                                                handback)
   (let ((prompt (or handback
                     (format "Processing %s: " what))))
     ;; According to gnupg/doc/DETAIL: a "total" of 0 indicates that
@@ -641,7 +670,11 @@ If you do not specify PLAIN-FILE, this functions prompts for the value to use."
                                         (format "Decrypting %s..."
                                                 (file-name-nondirectory decrypt-file))))
     (message "Decrypting %s..." (file-name-nondirectory decrypt-file))
-    (epg-decrypt-file context decrypt-file plain-file)
+    (condition-case error
+        (epg-decrypt-file context decrypt-file plain-file)
+      (error
+       (epa-display-error context)
+       (signal (car error) (cdr error))))
     (message "Decrypting %s...wrote %s" (file-name-nondirectory decrypt-file)
              (file-name-nondirectory plain-file))
     (if (epg-context-result-for context 'verify)
@@ -662,7 +695,11 @@ If you do not specify PLAIN-FILE, this functions prompts for the value to use."
                                         (format "Verifying %s..."
                                                 (file-name-nondirectory file))))
     (message "Verifying %s..." (file-name-nondirectory file))
-    (epg-verify-file context file plain)
+    (condition-case error
+        (epg-verify-file context file plain)
+      (error
+       (epa-display-error context)
+       (signal (car error) (cdr error))))
     (message "Verifying %s...done" (file-name-nondirectory file))
     (if (epg-context-result-for context 'verify)
         (epa-display-info (epg-verify-result-to-string
@@ -717,18 +754,22 @@ If no one is selected, default secret key is used.  "
                                  ".p7s"
                                ".p7m"))))
         (context (epg-make-context epa-protocol)))
-    (epg-context-set-armor context epa-armor)
-    (epg-context-set-textmode context epa-textmode)
-    (epg-context-set-signers context signers)
-    (epg-context-set-passphrase-callback context
-                                         #'epa-passphrase-callback-function)
-    (epg-context-set-progress-callback context
-                                       (cons
-                                        #'epa-progress-callback-function
-                                        (format "Signing %s..."
-                                                (file-name-nondirectory file))))
+    (setf (epg-context-armor context) epa-armor)
+    (setf (epg-context-textmode context) epa-textmode)
+    (setf (epg-context-signers context) signers)
+    (setf (epg-context-passphrase-callback context)
+          #'epa-passphrase-callback-function)
+    (setf (epg-context-progress-callback context)
+          (cons
+           #'epa-progress-callback-function
+           (format "Signing %s..."
+                   (file-name-nondirectory file))))
     (message "Signing %s..." (file-name-nondirectory file))
-    (epg-sign-file context file signature mode)
+    (condition-case error
+        (epg-sign-file context file signature mode)
+      (error
+       (epa-display-error context)
+       (signal (car error) (cdr error))))
     (message "Signing %s...wrote %s" (file-name-nondirectory file)
              (file-name-nondirectory signature))))
 
@@ -744,17 +785,21 @@ If no one is selected, symmetric encryption will be performed.  ")))
                                  (if epa-armor ".asc" ".gpg")
                                ".p7m")))
         (context (epg-make-context epa-protocol)))
-    (epg-context-set-armor context epa-armor)
-    (epg-context-set-textmode context epa-textmode)
-    (epg-context-set-passphrase-callback context
-                                         #'epa-passphrase-callback-function)
-    (epg-context-set-progress-callback context
-                                       (cons
-                                        #'epa-progress-callback-function
-                                        (format "Encrypting %s..."
-                                                (file-name-nondirectory file))))
+    (setf (epg-context-armor context) epa-armor)
+    (setf (epg-context-textmode context) epa-textmode)
+    (setf (epg-context-passphrase-callback context)
+          #'epa-passphrase-callback-function)
+    (setf (epg-context-progress-callback context)
+          (cons
+           #'epa-progress-callback-function
+           (format "Encrypting %s..."
+                   (file-name-nondirectory file))))
     (message "Encrypting %s..." (file-name-nondirectory file))
-    (epg-encrypt-file context file recipients cipher)
+    (condition-case error
+        (epg-encrypt-file context file recipients cipher)
+      (error
+       (epa-display-error context)
+       (signal (car error) (cdr error))))
     (message "Encrypting %s...wrote %s" (file-name-nondirectory file)
              (file-name-nondirectory cipher))))
 
@@ -785,14 +830,18 @@ For example:
   (save-excursion
     (let ((context (epg-make-context epa-protocol))
           plain)
-      (epg-context-set-passphrase-callback context
-                                           #'epa-passphrase-callback-function)
-      (epg-context-set-progress-callback context
-                                         (cons
-                                          #'epa-progress-callback-function
-                                          "Decrypting..."))
+      (setf (epg-context-passphrase-callback context)
+            #'epa-passphrase-callback-function)
+      (setf (epg-context-progress-callback context)
+            (cons
+             #'epa-progress-callback-function
+             "Decrypting..."))
       (message "Decrypting...")
-      (setq plain (epg-decrypt-string context (buffer-substring start end)))
+      (condition-case error
+          (setq plain (epg-decrypt-string context (buffer-substring start end)))
+        (error
+         (epa-display-error context)
+         (signal (car error) (cdr error))))
       (message "Decrypting...done")
       (setq plain (epa--decode-coding-string
                    plain
@@ -810,8 +859,8 @@ For example:
               (insert plain))
           (with-output-to-temp-buffer "*Temp*"
             (set-buffer standard-output)
-              (insert plain)
-              (epa-info-mode))))
+            (insert plain)
+            (epa-info-mode))))
       (if (epg-context-result-for context 'verify)
           (epa-display-info (epg-verify-result-to-string
                              (epg-context-result-for context 'verify)))))))
@@ -878,17 +927,21 @@ For example:
   (interactive "r")
   (let ((context (epg-make-context epa-protocol))
         plain)
-    (epg-context-set-progress-callback context
-                                       (cons
-                                        #'epa-progress-callback-function
-                                        "Verifying..."))
+    (setf (epg-context-progress-callback context)
+          (cons
+           #'epa-progress-callback-function
+           "Verifying..."))
     (message "Verifying...")
-    (setq plain (epg-verify-string
-                 context
-                 (epa--encode-coding-string
-                  (buffer-substring start end)
-                  (or coding-system-for-write
-                      (get-text-property start 'epa-coding-system-used)))))
+    (condition-case error
+        (setq plain (epg-verify-string
+                     context
+                     (epa--encode-coding-string
+                      (buffer-substring start end)
+                      (or coding-system-for-write
+                          (get-text-property start 'epa-coding-system-used)))))
+      (error
+       (epa-display-error context)
+       (signal (car error) (cdr error))))
     (message "Verifying...done")
     (setq plain (epa--decode-coding-string
                  plain
@@ -927,11 +980,11 @@ See the reason described in the `epa-verify-region' documentation."
                                   nil t)
           (setq cleartext-start (match-beginning 0))
           (unless (re-search-forward "^-----BEGIN PGP SIGNATURE-----$"
-                                           nil t)
+                                     nil t)
             (error "Invalid cleartext signed message"))
           (setq cleartext-end (re-search-forward
-                           "^-----END PGP SIGNATURE-----$"
-                           nil t))
+                               "^-----END PGP SIGNATURE-----$"
+                               nil t))
           (unless cleartext-end
             (error "No cleartext tail"))
           (epa-verify-region cleartext-start cleartext-end))))))
@@ -978,23 +1031,27 @@ If no one is selected, default secret key is used.  "
   (save-excursion
     (let ((context (epg-make-context epa-protocol))
           signature)
-      ;;(epg-context-set-armor context epa-armor)
-      (epg-context-set-armor context t)
-      ;;(epg-context-set-textmode context epa-textmode)
-      (epg-context-set-textmode context t)
-      (epg-context-set-signers context signers)
-      (epg-context-set-passphrase-callback context
-                                           #'epa-passphrase-callback-function)
-      (epg-context-set-progress-callback context
-                                         (cons
-                                          #'epa-progress-callback-function
-                                          "Signing..."))
+      ;;(setf (epg-context-armor context) epa-armor)
+      (setf (epg-context-armor context) t)
+      ;;(setf (epg-context-textmode context) epa-textmode)
+      (setf (epg-context-textmode context) t)
+      (setf (epg-context-signers context) signers)
+      (setf (epg-context-passphrase-callback context)
+            #'epa-passphrase-callback-function)
+      (setf (epg-context-progress-callback context)
+            (cons
+             #'epa-progress-callback-function
+             "Signing..."))
       (message "Signing...")
-      (setq signature (epg-sign-string context
-                                       (epa--encode-coding-string
-                                        (buffer-substring start end)
-                                        epa-last-coding-system-specified)
-                                       mode))
+      (condition-case error
+          (setq signature (epg-sign-string context
+                                           (epa--encode-coding-string
+                                            (buffer-substring start end)
+                                            epa-last-coding-system-specified)
+                                           mode))
+        (error
+         (epa-display-error context)
+         (signal (car error) (cdr error))))
       (message "Signing...done")
       (delete-region start end)
       (goto-char start)
@@ -1061,25 +1118,29 @@ If no one is selected, symmetric encryption will be performed.  ")
   (save-excursion
     (let ((context (epg-make-context epa-protocol))
           cipher)
-      ;;(epg-context-set-armor context epa-armor)
-      (epg-context-set-armor context t)
-      ;;(epg-context-set-textmode context epa-textmode)
-      (epg-context-set-textmode context t)
+      ;;(setf (epg-context-armor context) epa-armor)
+      (setf (epg-context-armor context) t)
+      ;;(setf (epg-context-textmode context) epa-textmode)
+      (setf (epg-context-textmode context) t)
       (if sign
-          (epg-context-set-signers context signers))
-      (epg-context-set-passphrase-callback context
-                                           #'epa-passphrase-callback-function)
-      (epg-context-set-progress-callback context
-                                         (cons
-                                          #'epa-progress-callback-function
-                                          "Encrypting..."))
+          (setf (epg-context-signers context) signers))
+      (setf (epg-context-passphrase-callback context)
+            #'epa-passphrase-callback-function)
+      (setf (epg-context-progress-callback context)
+            (cons
+             #'epa-progress-callback-function
+             "Encrypting..."))
       (message "Encrypting...")
-      (setq cipher (epg-encrypt-string context
-                                       (epa--encode-coding-string
-                                        (buffer-substring start end)
-                                        epa-last-coding-system-specified)
-                                       recipients
-                                       sign))
+      (condition-case error
+          (setq cipher (epg-encrypt-string context
+                                           (epa--encode-coding-string
+                                            (buffer-substring start end)
+                                            epa-last-coding-system-specified)
+                                           recipients
+                                           sign))
+        (error
+         (epa-display-error context)
+         (signal (car error) (cdr error))))
       (message "Encrypting...done")
       (delete-region start end)
       (goto-char start)
@@ -1105,7 +1166,11 @@ If no one is selected, symmetric encryption will be performed.  ")
            (eq (nth 1 epa-list-keys-arguments) t))))
   (let ((context (epg-make-context epa-protocol)))
     (message "Deleting...")
-    (epg-delete-keys context keys allow-secret)
+    (condition-case error
+        (epg-delete-keys context keys allow-secret)
+      (error
+       (epa-display-error context)
+       (signal (car error) (cdr error))))
     (message "Deleting...done")
     (apply #'epa--list-keys epa-list-keys-arguments)))
 
@@ -1121,6 +1186,7 @@ If no one is selected, symmetric encryption will be performed.  ")
           (epg-import-keys-from-file context file)
           (message "Importing %s...done" (file-name-nondirectory file)))
       (error
+       (epa-display-error context)
        (message "Importing %s...failed" (file-name-nondirectory file))))
     (if (epg-context-result-for context 'import)
         (epa-display-info (epg-import-result-to-string
@@ -1140,6 +1206,7 @@ If no one is selected, symmetric encryption will be performed.  ")
           (epg-import-keys-from-string context (buffer-substring start end))
           (message "Importing...done"))
       (error
+       (epa-display-error context)
        (message "Importing...failed")))
     (if (epg-context-result-for context 'import)
         (epa-display-info (epg-import-result-to-string
@@ -1188,9 +1255,13 @@ between START and END."
              (file-name-directory default-name)
              default-name)))))
   (let ((context (epg-make-context epa-protocol)))
-    (epg-context-set-armor context epa-armor)
+    (setf (epg-context-armor context) epa-armor)
     (message "Exporting to %s..." (file-name-nondirectory file))
-    (epg-export-keys-to-file context keys file)
+    (condition-case error
+        (epg-export-keys-to-file context keys file)
+      (error
+       (epa-display-error context)
+       (signal (car error) (cdr error))))
     (message "Exporting to %s...done" (file-name-nondirectory file))))
 
 ;;;###autoload
@@ -1198,12 +1269,16 @@ between START and END."
   "Insert selected KEYS after the point."
   (interactive
    (list (epa-select-keys (epg-make-context epa-protocol)
-                                "Select keys to export.
+                          "Select keys to export.
 If no one is selected, default public key is exported.  ")))
   (let ((context (epg-make-context epa-protocol)))
-    ;;(epg-context-set-armor context epa-armor)
-    (epg-context-set-armor context t)
-    (insert (epg-export-keys-to-string context keys))))
+    ;;(setf (epg-context-armor context) epa-armor)
+    (setf (epg-context-armor context) t)
+    (condition-case error
+        (insert (epg-export-keys-to-string context keys))
+      (error
+       (epa-display-error context)
+       (signal (car error) (cdr error))))))
 
 ;; (defun epa-sign-keys (keys &optional local)
 ;;   "Sign selected KEYS.
@@ -1217,12 +1292,12 @@ If no one is selected, default public key is exported.  ")))
 ;;        (error "No keys selected"))
 ;;      (list keys current-prefix-arg)))
 ;;   (let ((context (epg-make-context epa-protocol)))
-;;     (epg-context-set-passphrase-callback context
-;;                                       #'epa-passphrase-callback-function)
-;;     (epg-context-set-progress-callback context
-;;                                     (cons
-;;                                      #'epa-progress-callback-function
-;;                                      "Signing keys..."))
+;;     (setf (epg-context-passphrase-callback context)
+;;           #'epa-passphrase-callback-function)
+;;     (setf (epg-context-progress-callback context)
+;;           (cons
+;;             #'epa-progress-callback-function
+;;             "Signing keys..."))
 ;;     (message "Signing keys...")
 ;;     (epg-sign-keys context keys local)
 ;;     (message "Signing keys...done")))