All communication consists of messages that are one line of
human-readable UTF-8 text optionally followed by a single newline and
binary data.

The protocol is not a request-response one. Messages may be sent in
either direction at any time, either in response to some message, or
spontaneously. For 'tile' messages, the client may send a bunch of
tile requests without waiting for return messages. The server may send
tiles proactively (guessing what the client might need). Etc.

client -> server
================

canceltiles

    All outstanding tile messages from the client to the server are
    dropped and will not be handled. There is no guarantee of exactly
    which tile: messages might still be sent back to the client.

gettextselection mimetype=<mimeType>

    Request selection's content

invalidatetiles part=<partNumber> tileposx=<xpos> tileposy=<ypos> tilewidth=<tileWidth> tileheight=<tileHeight>

    All parameters are numbers. Makes the server remove any cached
    tiles intersecting with the given area (in twips).

key type=<type> char=<charcode> key=<keycode>

    <type> is 'input' or 'up', <charcode> and <keycode> are numbers.

load <pathname>

    Deprecated.

load url=<url> [timestamp=<time>]

    timestamp is an optional parameter.  <time> is provided in microseconds
    since the Unix epoch - midnight, January 1, 1970.

mouse type=<type> x=<x> y=<y> count=<count>

    <type> is 'buttondown', 'buttonup' or 'move', others are numbers.

requestloksession

    requests the initialization of a LOK process in an attempt to predict the user's
    interaction with the document

resetselection

saveas url=<url> format=<format> options=<options>

    <url> is a URL, encoded. <format> is also URL-encoded, i.e. spaces as %20 and it can be empty
    options are the whole rest of the line, not URL-encoded, and can be empty

selecttext type=<type> x=<x> y=<y>

    <type> is 'start', 'end' or 'reset', <x> and <y> are numbers.

selectgraphic type=<type> x=<x> y=<y>

    <type> is 'start' or 'end' <x> and <y> are numbers.

status

styles

tile part=<partNumber> width=<width> height=<height> tileposx=<xpos> tileposy=<ypos> tilewidth=<tileWidth> tileheight=<tileHeight>

    All parameters are numbers.

uno <command>

    <command> is a line of text.


server -> client
================

error: cmd=<command> kind=<kind>
<freeErrorText>

    <command> is the command part of the corresponding client->server
    message that caused the error. <kind> is some single-word
    classification

invalidate: part=<partNumber> x=<x> y=<y> width=<width> height=<height>

    All parameters are numbers. Tells the client to invalidate any
    cached tiles for the document area specified (in twips), at any
    zoom level.

    The client should handle either this message or the
    invalidatetiles: message, which has a different syntax, with
    payload directly from the LOK_CALLBACK_INVALIDATE_TILES
    callback. (The latter does not contain a part number, and as the
    protocol is asynchronous, it is unclear whether a client can be
    sure, or find out with certainty, for what part the
    invalidatetiles: message is. The invalidatetiles: message will be
    dropped soon.)

nextmessage: size=<byteSize>

    <byteSize> is the size, in bytes, of the next message, in case it
    is "large". (In practice, nextmessage: messages precede each tile:
    message). Can be ignored by clients using an API that can read
    arbitrarily large buffers from a WebSocket (like JavaScript), but
    must be handled by clients that cannot (like those using Poco
    1.6.0, like the "loadtest" program in the loolwsd sources).

status: type=<typeName> parts=<numberOfParts> current=<currentPartNumber> width=<width> height=<height> [partNames]

    <typeName> is 'text, 'spreadsheet', 'presentation', 'drawing' or 'other. Others are numbers.
    if the document has multiple parts and those have names, part names follow separated by '\n'

styles: {"styleFamily": ["styles in family"], etc. }

textselectioncontent: <content>

    Current selection's content

tile: part=<partNumber> width=<width> height=<height> tileposx=<xpos> tileposy=<ypos> tilewidth=<tileWidth> tileheight=<tileHeight>
<binaryPngImage>

    The parameters from the corresponding 'tile' command.

Each LOK_CALLBACK_FOO_BAR callback causes a corresponding message to
the client, consisting of the FOO_BAR part in lowercase, without
underscore, followed by a colon, space and the callback payload. For
instance:

invalidatecursor:

invalidatetiles: <payload>

The communication between the parent process (the one keeping open the
Websocket connections to the clients) and a child process (handling
one document through LibreOfficeKit) uses the same protocol, with
the following additions and changes:


child -> parent
===============

child <id>

    Must be the first message sent from the child to the parent. The
    parent has passed the id (a 64-bit random number) to the child
    when starting it, so this is how the child identificates itself.

curpart: part=<partNumber>

    Sent to the parent process before certain messages that the parent
    needs to act on in addition to passing them on to the client, like
    invalidatetiles:

nextmessage: size=<upperlimit>

    each tile: message sent from the child to the parent is preceded
    by a nextmessage: message that gives an upper limit on the size of
    the tile: message that will follow. (We assume it is only tile:
    messages that can be "large".) Once we depend on Poco 1.6.1, where
    one doesn't need to use a pre-allocated buffer when receiving
    WebSocket messages, this will go away.