emacs: Create an API for fetching parts as undecoded binary

The new function, `notmuch-get-bodypart-binary', replaces
`notmuch-get-bodypart-internal'.  Whereas the old function was really
meant for internal use in `notmuch-get-bodypart-content', it was used
in a few other places.  Since the difference between
`notmuch-get-bodypart-content' and `notmuch-get-bodypart-internal' was
unclear, these other uses were always confusing and potentially
inconsistent.  The new call clearly requests the part as undecoded
binary.

This is step 1 of 2 in separating `notmuch-get-bodypart-content' into
two APIs for retrieving either undecoded binary or decoded text.

emacs/notmuch-lib.el

@@ -529,25 +529,25 @@ the given type."
    (lambda (part) (notmuch-match-content-type (plist-get part :content-type) type))
    parts))
 
-;; Helper for parts which are generally not included in the default
+(defun notmuch-get-bodypart-binary (msg part process-crypto)
-;; SEXP output.
+  "Return the unprocessed content of PART in MSG.
-(defun notmuch-get-bodypart-internal (query part-number process-crypto)
+
-  (let ((args '("show" "--format=raw"))
+This returns the \"raw\" content of the given part after content
-	(part-arg (format "--part=%s" part-number)))
+transfer decoding, but with no further processing (see the
-    (setq args (append args (list part-arg)))
+discussion of --format=raw in man notmuch-show).  In particular,
-    (if process-crypto
+this does no charset conversion."
-	(setq args (append args '("--decrypt"))))
+  (let ((args `("show" "--format=raw"
-    (setq args (append args (list query)))
+		,(format "--part=%d" (plist-get part :id))
+		,@(when process-crypto '("--decrypt"))
+		,(notmuch-id-to-query (plist-get msg :id)))))
     (with-temp-buffer
       (let ((coding-system-for-read 'no-conversion))
-	(progn
+	(apply #'call-process notmuch-command nil '(t nil) nil args)
-	  (apply 'call-process (append (list notmuch-command nil (list t nil) nil) args))
+	(buffer-string)))))
-	  (buffer-string))))))
 
 (defun notmuch-get-bodypart-content (msg part process-crypto)
   (or (plist-get part :content)
-      (notmuch-get-bodypart-internal (notmuch-id-to-query (plist-get msg :id))
+      (notmuch-get-bodypart-binary msg part process-crypto)))
-				     (plist-get part :id) process-crypto)))
 
 ;; Workaround: The call to `mm-display-part' below triggers a bug in
 ;; Emacs 24 if it attempts to use the shr renderer to display an HTML

emacs/notmuch-show.el

@@ -579,16 +579,14 @@ message at DEPTH in the current thread."
 	(let* ((msg (nth 1 matching-part))
 	       (part (nth 2 matching-part))
 	       (content (nth 3 matching-part))
-	       (message-id (plist-get msg :id))
-	       (part-number (plist-get part :id))
 	       (content-type (plist-get part :content-type)))
 	  ;; If we don't already have the content, get it and cache
 	  ;; it, as some messages reference the same cid: part many
 	  ;; times (hundreds!), which results in many calls to
 	  ;; `notmuch part'.
 	  (unless content
-	    (setq content (notmuch-get-bodypart-internal (notmuch-id-to-query message-id)
+	    (setq content (notmuch-get-bodypart-binary
-							      part-number notmuch-show-process-crypto))
+			   msg part notmuch-show-process-crypto))
 	    (with-current-buffer w3m-current-buffer
 	      (notmuch-show-w3m-cid-store-internal url msg part content)))
 	  (insert content)
@@ -2162,15 +2160,14 @@ omit --in-reply-to=<Message-Id>."
 
 ;; Interactive part functions and their helpers
 
-(defun notmuch-show-generate-part-buffer (message-id nth)
+(defun notmuch-show-generate-part-buffer (msg part)
   "Return a temporary buffer containing the specified part's content."
   (let ((buf (generate-new-buffer " *notmuch-part*"))
 	(process-crypto notmuch-show-process-crypto))
     (with-current-buffer buf
-      (setq notmuch-show-process-crypto process-crypto)
+      ;; This is always used in the content of mm handles, which
-      ;; Always acquires the part via `notmuch part', even if it is
+      ;; expect undecoded, binary part content.
-      ;; available in the SEXP output.
+      (insert (notmuch-get-bodypart-binary msg part process-crypto)))
-      (insert (notmuch-get-bodypart-internal message-id nth notmuch-show-process-crypto)))
     buf))
 
 (defun notmuch-show-current-part-handle ()
@@ -2178,10 +2175,9 @@ omit --in-reply-to=<Message-Id>."
 
 This creates a temporary buffer for the part's content; the
 caller is responsible for killing this buffer as appropriate."
-  (let* ((part (notmuch-show-get-part-properties))
+  (let* ((msg (notmuch-show-get-message-properties))
-	 (message-id (notmuch-show-get-message-id))
+	 (part (notmuch-show-get-part-properties))
-	 (nth (plist-get part :id))
+	 (buf (notmuch-show-generate-part-buffer msg part))
-	 (buf (notmuch-show-generate-part-buffer message-id nth))
 	 (computed-type (plist-get part :computed-type))
 	 (filename (plist-get part :filename))
 	 (disposition (if filename `(attachment (filename . ,filename)))))