Cache file model contents in a buffer

* jupyter-rest-api.el (jupyter-api-content-buffer): New function.
(jupyter-api-insert-model-content): Use it.

* jupyter-tramp.el (jupyter-tramp-file-local-copy): Use it.

jupyter-rest-api.el

@@ -1012,6 +1012,32 @@ otherwise nil."
   "Return non-nil if MODEL corresponds to Jupyter notebook JSON."
   (equal (plist-get model :type) "notebook"))
 
+;; TODO: Replace the :content key with the buffer? It is redundant to have both
+;; a string and a buffer holding the contents.
+(defun jupyter-api-content-buffer (model)
+  "Return a buffer holding MODEL's content.
+If MODEL's content is binary, the returned buffer will hold the
+decoded content.
+
+The returned buffer will be a single-byte buffer, i.e. will not
+contain any multibyte characters.
+
+Note, the returned buffer will be killed when MODEL is garbage
+collected."
+  (cl-assert (member (plist-get model :format) '("text" "base64")))
+  (unless (bufferp (plist-get model :_buffer))
+    (let ((buffer (generate-new-buffer " *jupyter-api-model-content*")))
+      (with-current-buffer buffer
+        ;; NOTE: Order of insertion matters here
+        (insert (or (plist-get model :content) ""))
+        (set-buffer-multibyte nil)
+        (plist-put model :_buffer (current-buffer))
+        (plist-put model :_finalizer (make-finalizer
+                                      (lambda () (kill-buffer buffer))))
+        (when (jupyter-api-binary-content-p model)
+          (base64-decode-region (point-min) (point-max))))))
+  (plist-get model :_buffer))
+
 (defun jupyter-api-insert-model-content (model &optional replace beg end)
   "Insert the content of MODEL into the current buffer.
 If REPLACE is non-nil, replace the contents of the current buffer
@@ -1019,21 +1045,13 @@ using `replace-buffer-contents'. BEG and END are byte offsets
 into the content of MODEL, only insert the portion of MODEL's
 contents bounded by BEG and END. BEG and END default to
 `point-min' and `point-max' respectively."
-  (cl-assert (not (equal (plist-get model :type) "directory")))
-  (let ((source (generate-new-buffer " *temp*")))
-    (unwind-protect
-        (progn
+  (let ((source (jupyter-api-content-buffer model)))
     (with-current-buffer source
-            (set-buffer-multibyte nil)
-            (insert (or (plist-get model :content) ""))
-            (when (jupyter-api-binary-content-p model)
-              ;; TODO: Cache the result of decoding?
-              (base64-decode-region (point-min) (point-max)))
+      (widen)
       (when (or beg end)
         (narrow-to-region (or beg (point-min)) (or end (point-max)))))
     (if replace (replace-buffer-contents source)
-            (insert-buffer-substring source)))
-      (and (buffer-live-p source) (kill-buffer source)))))
+      (insert-buffer-substring source))))
 
 (provide 'jupyter-rest-api)
 

jupyter-tramp.el

@@ -748,17 +748,18 @@ the server. For any other file, call ORIG, which is the function
     ;; Ensure we grab a fresh model since the cached version may be out of
     ;; sync with the server.
     (jupyter-tramp-flush-file-properties v localname)
-    (let* ((model (jupyter-tramp-get-file-model filename))
-           (content (plist-get model :content)))
+    (let ((model (jupyter-tramp-get-file-model filename)))
+      (when (jupyter-api-notebook-p model)
+        (error "Notebooks not supported yet"))
+      (let ((coding-system-for-write
+             (if (jupyter-api-binary-content-p model)
+                 'no-conversion
+               'utf-8-auto)))
         (tramp-run-real-handler
          'make-temp-file
          (list "jupyter-tramp." nil (file-name-extension filename t)
-             (cond
-              ((jupyter-api-binary-content-p model)
-               (base64-decode-string content))
-              ((jupyter-api-notebook-p model)
-               (error "Notebooks not supported yet"))
-              (t content)))))))
+               (with-current-buffer (jupyter-api-content-buffer model)
+                 (buffer-string))))))))
 
 ;;; File/directory attributes
 

test/jupyter-tramp-test.el

@@ -77,7 +77,7 @@
     (let* ((tfile (make-temp-file "file-local-copy"))
            (jpyfile (expand-file-name (file-name-nondirectory tfile) "/jpy::/")))
       (unwind-protect
-          (let ((contents (jupyter-new-uuid)))
+          (let ((contents (concat "αβ" (jupyter-new-uuid) "λ")))
             (with-temp-file tfile
               (insert contents))
             (let ((lfile (file-local-copy jpyfile)))
@@ -293,6 +293,8 @@
             (ert-info ("Basic write")
               (write-region "foo" nil jpyfile)
               (should (equal (file-contents) "foo"))
+              (write-region "foλo" nil jpyfile)
+              (should (equal (file-contents) "foλo"))
               (with-temp-buffer
                 (insert "foo")
                 (write-region nil nil jpyfile)