[[!img notmuch-logo.png alt="Notmuch logo" class="left"]]
#Using notmuch remotely#

##Why?##
It is hard to keep nomuch tags in sync across multiple instances of
notmuch, on multiple computers. Though you can do this with "notmuch
dump" and "notmuch restore", it is often preferable to be able to use
notmuch on a remote computer as if it were present on a local
computer.

The following guidelines show how I have accomplished this. It isn't
perfect, but it works pretty well, and allows me to access notmuch on
my home computer, using only an emacs client on my netbook or work
computer, a trivial shell script, a few settings in my .emacs, and
ssh.

Note that this is all something of a hack, and future versions of
notmuch will likely make all of these steps much more
transparent. I'll note particularly which things should become
unneccessary with future version. At the moment though, this does
work, and might enable some of you to use notmuch away from your
primary computer.

##What you will need##
You will need to have the following items in place:

1.  a working notmuch on one computer (let's call that computer
"server"). The notmuch should be at least version 0.2.
2.  a working notmuch emacs interface on another computer (let's call
that computer "client")
3.   password-free login (public key authentication) from client to
server. [Here](http://sial.org/howto/openssh/publickey-auth/) is a
good page on how to set it up.
4.   a reasonably fast connection. (This isn't really *neccessary*, but
if your connection is too slow, this won't be very pleasant to use,
and certainly won't seem transparent.)

##Write a wrapper shell script##
Now we will need to write a simple shell script that does two things:

1.  replaces the call to the notmuch binary with a call to notmuch
over ssh.
2.  offers, via the "--get" option, a utility for downloading raw
message text over scp (this is necessary for attachments) and
caching for future use.

Note that this shell script also pauses briefly after every message
entries. This is currently necessary so that the emacs process-filter
doesn't chop off messages. It's an obvious hack, and hopefully won't
be necessary in the furture.

    #!/usr/bin/env bash
    SSH_BIN="/path/to/ssh/on/client"
    USER="user_name"
    SSH_HOST="server_name"
    NOTMUCH_REMOTE_BIN="/path/to/notmuch/on/server"
    CACHE=${HOME}/.notmuch-cache.d

    notmuch_run ()
    {
        if [ $1 = "search" ]; then
    	OUT=$($SSH_BIN $USER@$SSH_HOST $NOTMUCH_REMOTE_BIN $@)
    	echo "$OUT" | while read line; do
    	    echo "$line";
    	    sleep 0.1;
    	done
        else
    	$SSH_BIN $USER@$SSH_HOST $NOTMUCH_REMOTE_BIN $@
        fi
    }
    
    check_for_file_name ()
    {
        [ -f "${CACHE}/${1}" ]
    }
    
    fetch_file ()
    {
        FILE_DIR="${CACHE}/$(dirname ${1})"
        [ -d "${FILE_DIR}" ] || mkdir -p "${FILE_DIR}"
        scp ${SSH_HOST}:${1} "${FILE_DIR}" > /dev/null 2>&1
        retcode="${?}"
        if [ "${retcode}" -ne "0" ]; then
    	echo "Failed to fetch file" 1>&2
    	exit ${retcode}
        fi
    }
    
    notmuch_get ()
    {
        [ -d "${CACHE}" ] || mkdir -p "${CACHE}"
     
        check_for_file_name || 
        fetch_file ${1} && 
        printf "${CACHE}/${1}\n"
    }
    
    if [ ${1} = "--get" ]; then
        notmuch_get $2
    else
        notmuch_run $@
    fi
    	
Save this to a file, "remote-notmuch.sh", in your path.

Now you can run "remote-notmuch.sh new". You can call the script
anything you like. If you don't have a notmuch instance on your client
computer, you can even call it "notmuch" and have totally transparent
usage. (Since I run "new" from an emacs keybinding, I've never
bothered with this renaming.)

##Configure your emacs client##

Add the following to your .emacs (this is on your client machine):

    (setq notmuch-command "/path/to/your/remote-notmuch.sh")

Now add the following, to overwrite the way in which notmuch gets raw
message text. 

    (defun notmuch-show-get-filename ()
      (let* ((orig-filename (notmuch-show-get-prop :filename))
 	     (retvalue (shell-command-to-string (concat 
 	     				     notmuch-command
 					     " --get "
 					     orig-filename))))
        (replace-regexp-in-string "\n" "" retvalue)))

This will will use the "--get" option of the above
script. Note that it only has to do this for attachments or for
viewing the raw file, and only the first time. After that, it is
cached.

##A tip to speed things up##
If you have openssh >= 0.4, you can make use of the "ControlMaster"
feature. This allows you to reuse an existing connection. Therefore
if you keep a connection open, you won't have to authenticate every
time.

Add the following to your ~/.ssh/config file:

    Host server_name 
    ControlMaster auto
    ControlPath ~/.ssh/master-%r@%h:%p
    
You can also se the Host to "*", if you want to use it for all
connections. I usually have an interactive ssh connection to my home
computer open, so I don't need to do anything more. But if not, you
can always run:

    ssh -Nf server_name

which will open up a background connection, which you can then reuse
for all of your notmuch commands.

##Problems##
Some things won't work perfectly, and there might be some unexpected
mismatches between normal usage and this sort of usage. If you're
using this approach and run into any problems, please feel free to
list them here. And, of course, if you improve on any of these
approaches, please do edit this page and let people know!