emacs: Return unibyte strings for binary part data

Unibyte strings are meant for representing binary data.  In practice,
using unibyte versus multibyte strings affects *almost* nothing.  It
does happen to matter if we use the binary data in an image descriptor
(which is, helpfully, not documented anywhere and getting it wrong
results in opaque errors like "Not a PNG image: <giant binary spew
that is, in fact, a PNG image>").

diff --git a/emacs/notmuch-lib.el b/emacs/notmuch-lib.el
index a0a95d8f28c27df0ad240b1bde0929bd3ea1729e..31547253cc0c120686fec975998393fec427b8cf 100644 (file)
--- a/emacs/notmuch-lib.el
+++ b/emacs/notmuch-lib.el
@@ -530,7 +530,7 @@ the given type."
    parts))
 
 (defun notmuch-get-bodypart-binary (msg part process-crypto)
    parts))
 
 (defun notmuch-get-bodypart-binary (msg part process-crypto)

-  "Return the unprocessed content of PART in MSG.
+  "Return the unprocessed content of PART in MSG as a unibyte string.

 
 This returns the \"raw\" content of the given part after content
 transfer decoding, but with no further processing (see the
 
 This returns the \"raw\" content of the given part after content
 transfer decoding, but with no further processing (see the


@@ -541,6 +541,16 @@ this does no charset conversion."
                ,@(when process-crypto '("--decrypt"))
                ,(notmuch-id-to-query (plist-get msg :id)))))
     (with-temp-buffer
                ,@(when process-crypto '("--decrypt"))
                ,(notmuch-id-to-query (plist-get msg :id)))))
     (with-temp-buffer

+      ;; Emacs internally uses a UTF-8-like multibyte string
+      ;; representation by default (regardless of the coding system,
+      ;; which only affects how it goes from outside data to this
+      ;; internal representation).  This *almost* never matters.
+      ;; Annoyingly, it does matter if we use this data in an image
+      ;; descriptor, since Emacs will use its internal data buffer
+      ;; directly and this multibyte representation corrupts binary
+      ;; image formats.  Since the caller is asking for binary data, a
+      ;; unibyte string is a more appropriate representation anyway.
+      (set-buffer-multibyte nil)

       (let ((coding-system-for-read 'no-conversion))
        (apply #'call-process notmuch-command nil '(t nil) nil args)
        (buffer-string)))))
       (let ((coding-system-for-read 'no-conversion))
        (apply #'call-process notmuch-command nil '(t nil) nil args)
        (buffer-string)))))