Graceful fallback to gzip if zstd is not present

README.md

@@ -6,11 +6,9 @@ Snappy reMarkable screen sharing over SSH.
 
 On your **host** machine:
 - Any POSIX-shell (e.g. bash)
-- [zstd](http://www.zstd.net/)
 - ffmpeg (with ffplay)
 - ssh
 
-On your **reMarkable**:
+On your **reMarkable** it is recommended to install [zstd](https://zstd.net) (`opkg install zstd` if you have [entware](https://github.com/evidlo/remarkable_entware) installed.) to have a smoother experience (sub-second latency). However, if you don't have it installed `reStream` will fall back to `gzip` which is installed by default.
-- zstd (`opkg install zstd`)
+
-- netcat (`opkg install netcat`)
+
-- coreutils-head (`opkg install coreutils-head`)

reStream.sh

@@ -1,40 +1,44 @@
 #!/bin/sh
-set -eo pipefail
-
 ssh_host="mohowzeg.usb"
 landscape=true
 
-bin_head="/opt/bin/head"
-bin_zstd="/opt/bin/zstd"
-bin_ncat="/opt/bin/netcat"
 width=1408
 height=1872
 bytes_per_pixel=2
+loop_wait="true"
+loglevel="info"
+
 
 if ! ssh "$ssh_host" true; then
     echo "$ssh_host unreachable"
     exit 1
 fi
 
-for prog in $bin_head $bin_zstd $bin_ncat; do
+# Gracefully degrade to gzip if zstd is not present
-    if ! ssh "$ssh_host" "[ -f $prog ]"; then
+if ssh "$ssh_host" "[ -f /opt/bin/zstd ]"; then
-        echo "Program $prog is not present on $ssh_host."
+    compress="/opt/bin/zstd"
-        exit 1
+    decompress="zstd -d"
-    fi
+else
-done
+    compress="gzip"
+    decompress="gzip -d"
+fi
 
 
 window_bytes="$(($width*$height*$bytes_per_pixel))"
-landscape_param="$($landscape && echo '-vf transpose=1')"
+orientation_param="$($landscape && echo '-vf transpose=1')"
-read_loop="while $bin_head -c $window_bytes /dev/fb0; do sleep .03; done | $bin_zstd"
+head_fb0="dd if=/dev/fb0 count=1 bs=$window_bytes 2>/dev/null"
+read_loop="while $head_fb0; do $loop_wait; done | $compress"
+
+
+set -e
 
 ssh  "$ssh_host" "$read_loop" \
-    | zstd -d \
+    | $decompress \
-    | pv - \
     | ffplay -vcodec rawvideo \
-             -loglevel error \
+             -loglevel "$loglevel" \
              -f rawvideo \
              -pixel_format gray16le \
              -video_size "$width,$height" \
              $landscape_param \
              -i -
+