gri3-wm/docs/i3bar-protocol

i3bar input protocol
====================
Michael Stapelberg <michael@i3wm.org>
August 2012

This document explains the protocol in which i3bar expects its input. It
provides support for colors, urgency, shortening and easy manipulation.

== Rationale for chosing JSON

Before describing the protocol, let’s cover why JSON is a building block of
this protocol.

1. Other bar display programs such as dzen2 or xmobar are using in-band
   signaling: they recognize certain sequences (like ^fg(#330000) in your input
   text). We would like to avoid that and separate information from
   meta-information. By information, we mean the actual output, like the IP
   address of your ethernet adapter and by meta-information, we mean in which
   color it should be displayed right now.
2. It is easy to write a simple script which manipulates part(s) of the input.
   Each block of information (like a block for the disk space indicator, a block
   for the current IP address, etc.) can be identified specifically and modified
   in whichever way you like.
3. It remains easy to write a simple script which just suffixes (or prefixes) a
   status line input, because tools like i3status will output their JSON in
   such a way that each line array will be terminated by a newline. Therefore,
   you are not required to use a streaming JSON parser, but you can use any
   JSON parser and write your script in any programming language. In fact, you
   can decide to not bother with the JSON parsing at all and just inject your
   output at a specific position (beginning or end).
4. Relying on JSON does not introduce any new dependencies. In fact, the IPC
   interface of i3 also uses JSON, therefore i3bar already depends on JSON.

The only point against using JSON is computational complexity. If that really
bothers you, just use the plain text input format (which i3bar will continue to
support).

== The protocol

The first message of the protocol is a header block, which contains (at least)
the version of the protocol to be used. In case there are significant changes
(not only additions), the version will be incremented. i3bar will still
understand the old protocol version, but in order to use the new one, you need
to provide the correct version. The header block is terminated by a newline and
consists of a single JSON hash:

*Minimal example*:
------------------------------
{ "version": 1 }
------------------------------

*All features example*:
------------------------------
{ "version": 1, "stop_signal": 10, "cont_signal": 12 }
------------------------------

(Note that before i3 v4.3 the precise format had to be +{"version":1}+,
byte-for-byte.)

What follows is an infinite array (so it should be parsed by a streaming JSON
parser, but as described above you can go for a simpler solution), whose
elements are one array per status line. A status line is one unit of
information which should be displayed at a time. i3bar will not display any
input until the status line is complete. In each status line, every block will
be represented by a JSON hash:

*Example*:
------
[

 [
  {
   "full_text": "E: 10.0.0.1 (1000 Mbit/s)",
   "color": "#00ff00"
  },
  {
   "full_text": "2012-01-05 20:00:01"
  }
 ],

 [
  {
   "full_text": "E: 10.0.0.1 (1000 Mbit/s)",
   "color": "#00ff00"
  },
  {
   "full_text": "2012-01-05 20:00:02"
  }
 ],
 …
------

Please note that this example was pretty printed for human consumption.
i3status and others will output single statuslines in one line, separated by
\n.

You can find an example of a shell script which can be used as your
+status_command+ in the bar configuration at
http://code.stapelberg.de/git/i3/tree/contrib/trivial-bar-script.sh?h=next

=== Header in detail

version::
	The version number (as an integer) of the i3bar protocol you will use.
stop_signal::
	Specify to i3bar the signal (as an integer) to send to stop your
	processing.
	The default value (if none is specified) is SIGSTOP.
cont_signal::
	Specify to i3bar the signal (as an integer)to send to continue your
	processing.
	The default value (if none is specified) is SIGCONT.

=== Blocks in detail

full_text::
	The most simple block you can think of is one which just includes the
	only required key, the +full_text+ key. i3bar will display the string
	value and that’s it.
short_text::
	Where appropriate, the +short_text+ (string) entry should also be
	provided. It will be used in case the status line needs to be shortened
	because it uses more space than your screen provides. For example, when
	displaying an IPv6 address, the prefix is usually (!) more relevant
	than the suffix, because the latter stays constant when using autoconf,
	while the prefix changes. When displaying the date, the time is more
	important than the date (it is more likely that you know which day it
	is than what time it is).
color::
	To make the current state of the information easy to spot, colors can
	be used. For example, the wireless block could be displayed in red
	(using the +color+ (string) entry) if the card is not associated with
	any network and in green or yellow (depending on the signal strength)
	when it is associated.
	Colors are specified in hex (like in HTML), starting with a leading
	hash sign. For example, +#ff0000+ means red.
min_width::
	The minimum width (in pixels) of the block. If the content of the
	+full_text+ key take less space than the specified min_width, the block
	will be padded to the left and/or the right side, according to the +align+
	key. This is useful when you want to prevent the whole status line to shift
	when value take more or less space between each iteration.
        The value can also be a string. In this case, the width of the text given
        by +min_width+ determines the minimum width of the block. This is useful
        when you want to set a sensible minimum width regardless of which font you
        are using, and at what particular size.
align::
	Align text on the +center+ (default), +right+ or +left+ of the block, when
	the minimum width of the latter, specified by the +min_width+ key, is not
	reached.
name and instance::
	Every block should have a unique +name+ (string) entry so that it can
	be easily identified in scripts which process the output. i3bar
	completely ignores the name and instance fields. Make sure to also
	specify an +instance+ (string) entry where appropriate. For example,
	the user can have multiple disk space blocks for multiple mount points.
urgent::
	A boolean which specifies whether the current value is urgent. Examples
	are battery charge values below 1 percent or no more available disk
	space (for non-root users). The presentation of urgency is up to i3bar.
separator::
	A boolean which specifies whether a separator line should be drawn
	after this block. The default is true, meaning the separator line will
	be drawn. Note that if you disable the separator line, there will still
	be a gap after the block, unless you also use +separator_block_width+.
separator_block_width::
	The amount of pixels to leave blank after the block. In the middle of
	this gap, a separator line will be drawn unless +separator+ is
	disabled. Normally, you want to set this to an odd value (the default
	is 9 pixels), since the separator line is drawn in the middle.

If you want to put in your own entries into a block, prefix the key with an
underscore (_). i3bar will ignore all keys it doesn’t understand, and prefixing
them with an underscore makes it clear in every script that they are not part
of the i3bar protocol.

*Example*:
------------------------------------------
{
 "full_text": "E: 10.0.0.1 (1000 Mbit/s)",
 "_ethernet_vendor": "Intel"
}
------------------------------------------

In the following example, the longest (widest) possible value of the block is
used to set the minimum width:

------------------------------------------
{
 "full_text": "CPU 4%",
 "min_width": "CPU 100%",
 "align": "left"
}
------------------------------------------

An example of a block which uses all possible entries follows:

*Example*:
------------------------------------------
{
 "full_text": "E: 10.0.0.1 (1000 Mbit/s)",
 "short_text": "10.0.0.1",
 "color": "#00ff00",
 "min_width": 300,
 "align": "right",
 "urgent": false,
 "name": "ethernet",
 "instance": "eth0",
 "separator": true,
 "separator_block_width": 9
}
------------------------------------------