Re: [HELP] (bug?) Saving a buffer without any conversion?

[Kim F. Storm]

Kenichi Handa <address@hidden> writes:

> In article <address@hidden>, Mario Lang <address@hidden> writes:
> > We're receiving binary content via a network process.  After the
> > transfer is complete, this buffer should be saved to a file.
> 
> > The effect I'm having is that we receive 1372422 bytes via the process
> > filter function STRING argument, and after insertion into a buffer,
> > we have a buffer with buffer-size 1372422, but after calling (save-buffer)
> > we get this:
> 
> > -rw-r--r--    1 root     root      1865264 Jan 13 18:35 blah28.mp3
> 
> > I'm using:
> 
> >       (set-process-coding-system proc 'binary 'binary)
> >       (set-buffer-file-coding-system 'no-conversion t)
> 
> address@hidden (Kim F. Storm) writes:
> > I have looked at Mario's data before sending it to emacs and after
> > emacs has written it to a file.
> 
> > It seems that every byte in the range 0xa0 .. 0xff that were in the
> > original file is prefixed with an 0x81 byte in the file containing the
> > received data.  To me, that looks like the internal multi-byte
> > representation for the binary data.
> 
> No.  0x81 means that 0xA0..0xFF are decoded as Latin-1
> chars.  That's why raw-text and no-conversion write out 0x81
> as is to a file.  And that means that somehow:
>       (set-process-coding-system proc 'binary 'binary)
> didn't take effect.  When did you execute this function?  It
> should be before accepting any data from the process
> (usually just after start-process or open-network-stream).
> 

Mario's code is using open-network-stream, and the set-process-... things are
done immediately after creating the process (IIRC).

He uses a process filter to "insert" the received strings to the
buffer like this [approximately]:

        (defun filter (proc string)
          (with-current-buffer (process-buffer proc)
            (insert string)))


Here is a small, selfcontained test case.  

If you eval the following form, wait a few seconds, the result is
        "BUFFER=10 FILE=20"
meaning that the temp.out buffer is 10 "bytes", but the written
file is 20 "bytes".

Adding the "set-buffer-multibyte" line produces the right result.


(let (proc proc2)
  (if (get-buffer "temp.out")
      (kill-buffer "temp.out"))

  (save-excursion
    (set-buffer (get-buffer-create "temp.out"))
    (set-buffer-file-coding-system 'binary)
    (erase-buffer)
;;    (set-buffer-multibyte nil)
    )

  (setq proc (make-network-process
              :server t
              :name "temp"
              :buffer "temp.out"
              :service 2000
              :sentinel nil
              :filter (lambda (proc string)
                        (with-current-buffer (get-buffer "temp.out")
                          (insert string)))
              :coding 'binary))

  (setq proc2 (make-network-process
               :name "temp2"
               :buffer nil
               :service 2000
               :host 'local
               :coding 'binary))

  (sleep-for 1)
  (process-send-string proc2 (make-string 10 255))
  (sleep-for 1)
  (delete-process proc2)

  (save-excursion
    (set-buffer (get-buffer "temp.out"))
    (let (require-final-newline)
      (delete-file "/tmp/temp.out")
      (write-file "/tmp/temp.out")))

  (sleep-for 1)
  (delete-process proc)

  (format "BUFFER=%d FILE=%d" (buffer-size (get-buffer "temp.out"))
          (nth 7 (file-attributes "/tmp/temp.out")))
)



-- 
Kim F. Storm <address@hidden> http://www.cua.dk