goMarkableStream

README

goMarkableStream

I use this toy project to stream my remarkable 2 (firmware 2.5) on my laptop using the local wifi.

video that shows some features

Note: click on the video to take a screenshot. The screenshot is a png file with transparent background.

Quick start

You need ssh access to your remarkable

Download two files from the release page:

• the server "Linux/Armv7" for your remarkable
• the client for your laptop according to the couple OS/arch

or build it yourself if you have the go toolchain installed on your machine.

The server

Copy the server on the remarkable and start it.

scp goMarkableStreamServer.arm remarkable:
ssh remarkable './goMarkableStreamServer.arm'

Note: The processus is fault tolerant and should resume automatically on sleep/wakup or network failure; therefore, you can, normally, launch the processus in background (with nohup)

The client

• Start the client: RK_SERVER_ADDR=ip.of.remarkable:2000 ./goMarkableClient

• Point your browser to http://localhost:8080/

Configuration

It is possible to tweak the configuration via environment variables:

Server

Env var	Default	Descri[ption
RK_SERVER_BIND_ADDR	:2000	the TCP listen address

Client

Env var	Default	Descri[ption
RK_CLIENT_BIND_ADDR	:8080	the TCP listen address
RK_SERVER_ADDR	remarkabke:2000	the address of the remarkable
RK_CLIENT_AUTOROTATE	true	activate autorotate (see below)
RK_CLIENT_PAPER_TEXTURE	null	a path to a texture
RK_CLIENT_COLORIZE	false	try to colorize the highliter

Features

Auto-rotate

The client tries to locate the location of the top level switch on the picture (the round one) and rotate the picture accordingly. This experimental behavior can be disabled by env variables in the client.

Note: the browser does not like the switch of the rotation; the reload of the page solves the problem

Texture

There is an experimental texture feature that reads a texture file and use is as a background in the output. The texture does not apply to the screenshot. The texture must have this format:

> identify textures/oldpaper.png
textures/oldpaper.png PNG 1872x1404 1872x1404+0+0 8-bit Gray 256c 886691B 0.010u 0:00.001

Example:

RK_CLIENT_PAPER_TEXTURE=./textures/oldpaper.png goMarkableClient

Colorize

This option can be activated with the RK_CLIENT_COLORIZE=true env variable. This tries to set the highlighter in yellow in the video stream.

Caution This is CPU intensive.

Screenshot

The server is exposing a screenshot endpoint. You can grab a screenshot by clicking on the video stream, or by using tools such as curl:

ex:

❯ curl -o /tmp/screenshot.png http://localhost:8080/screenshot
❯ file /tmp/screenshot.png
/tmp/screenshot.png: PNG image data, 1404 x 1872, 8-bit/color RGBA, non-interlaced

Raw picture

the /raw endpoind exposes the raw picture without any treatment. It is possible to pipe the result into a thrid party tool such as imageMagick for example.

This generates a pdf from the screen

curl http://localhost:8080/raw | convert -depth 8 -size 1404x1872+0 gray:- shot.pdf

How it works?

Full explanation

I wrote a blog post that explains all the wiring. Otherwise a summary is written here.

The server loop

• The server gets the address of the framebuffer in the memory space of the xochitl
• The server launches a "ticketing system" to avoid congestion. The ticketing system is a channel that gets an event every 200ms.
• Then it exposes a gRPC function (with TLS and mutual authentication).
• The gRPC function waits for a "ticket" on the channel, and then grabs the data from the framebuffer.
• It packs the data into an image message encoded in protobuf and sends it to the consumer

The client loop

• The client creates an MJPEG stream and serves it over HTTP on the provided address
• The client dial server and sends its certificate, and add the compression header.
• Then it triggers a goroutine to get the image in a for loop.
• The image is then encoded into JPEG format and added to the MJPEG stream.

Security

The communication is using TLS. The client and the server owns an embedded certificate chain (with the CA). There are performing mutual authentication. A new certificate chain is generated per build. Therefore, if you want restrict the access to your server to your client only, you must rebuild the tool yourself.

Manual build

Note: you need go > 1.16beta to build the tool because of the embedding mechanism for the certificate.

To build the tool manually, the easiest way is to use goreleaser:

goreleaser --snapshot --skip-publish --rm-dist

To build the services manually:

go generate ./... # This generates the certificates
cd server && GOOS=linux GOARCH=arm GOARM=7 go build -o goStreamServer.arm
cd client && go build -o goStreamClient

Tipping

If you plan to buy a reMarkable 2, you can use my referal program link. It will provide a discount for you and also for me.

Acknowledgement

All the people in the reStream projet and specially @ddvk and @raisjn