Grabs an image from a system-image-server channel for a given device with a given tag

fetch-and-prepare-image-version.sh

#!/bin/bash

set -e

# Fetches and prepares a certain tag from system server
# First argument: Channel, like '16.04/arm64/android9/stable'
# Second argument: Device, like 'yggdrasil'
# Third argument: Destination directory
# Fourth argument: Image tag, like 'OTA-16'
# The files created in the destination directory can be pushed to /cache/recovery/ on an Ubuntu Touch device.
# Once the files are in place, booting UBports recovery will cause installation to begin.

URL='https://system-image.ubports.com'

CHANNEL="$1"
DEVICE="$2"
OUTPUT="$3"
TAG="$4"

mkdir -p "$OUTPUT" || true

download_file_and_asc() {
    wget "$1" -P "$2"
    wget "$1.asc" -P "$2"
}

# Gets the latest image from the system-image server
latest_image=$(wget -qO- "${URL}/${CHANNEL}/${DEVICE}/index.json" | jq ".images |  map(select(.type == \"full\")) | sort_by(.version) | map(select(.version_detail | contains(\"${TAG}\"))) | .[-1]")

# Gets a list of files to download
files=$(echo "${latest_image}" | jq --raw-output '.files[].path')

# Downloads master and signing keyrings
download_file_and_asc "${URL}/gpg/image-signing.tar.xz" "$OUTPUT"
download_file_and_asc "${URL}/gpg/image-master.tar.xz" "$OUTPUT"

# Start to generate ubuntu_command file
echo '# Generated by fetch-and-prepare-image-version' > "$OUTPUT/ubuntu_command"

cat << EOF >> "$OUTPUT/ubuntu_command"
format system
load_keyring image-master.tar.xz image-master.tar.xz.asc
load_keyring image-signing.tar.xz image-signing.tar.xz.asc
mount system
EOF

# Download and fill ubuntu_command
for file_path in ${files}; do
    file=$(basename ${file_path})
    download_file_and_asc "${URL}/${file_path}" "$OUTPUT"
    echo "update $file $file.asc" >> "$OUTPUT/ubuntu_command"
done

# End ubuntu_command
echo 'unmount system' >> "$OUTPUT/ubuntu_command"