Download files uploaded to a Slack instance using data from a Slack JSON export file.

download_slack_files.sh

#!/bin/bash
#
# Parses Slack JSON exports for files and downloads them.
#
# Requires 'jq' (https://stedolan.github.io/jq/) and 'httpie' (https://httpie.org/).
#

##
# Checks for a single dependency.
#
# @param string DEP The function name to check.
##
function check_dep() {
	local DEP="${1}"
	local HAS_DEP

	[ -z "${DEP}" ] && printf "No function name given to check.\n" && exit 0

	printf "Checking for %s...\n" "${DEP}"

	HAS_DEP="$(
		type "${DEP}" >/dev/null 2>&1
		echo $?
	)"

	if [ "${HAS_DEP}" -eq 1 ]; then
		printf "%s not found.\n" "${DEP}"
		exit 1
	else
		printf "%s found. Continuing...\n" "${DEP}"
	fi

	echo '----------------'
	printf '\n'
}

##
# Checks the dependencies used for the script.
##
function check_deps() {
	declare -A deps
    deps["jq"]="https://stedolan.github.io/jq/"
    deps["http"]="https://httpie.org/"

	for dep in "${!deps[@]}"; do
        check_dep "${dep}"
        if [ "$?" -eq 1 ]; then
            printf "%s missing. Download from %s and install before continuing.\n" "${dep}" "${deps[$dep]}"
        fi
    done
}

##
# Parses the Slack export JSON for uploaded files and downloads them to the current directory.
#
# @param string source_file Path to the Slack export JSON file.
##
function main() {
	local source_file="${1}"
	local link_count=0
	declare links=()

	local output_path # @todo Make this a parameter and configure it for httpie's --continue flag.
	local session_file
	local file_hash

	check_deps

	if [[ ! -f "${source_file}" ]]; then
		printf "%s not found.\nPlease check the filename and try again.\n" "${source_file}"
		exit 0
	else
		printf "Parsing %s for files to download...\n" "${source_file}"
	fi

	# Parse the JSON using jq, combining them into a list of URLs for uploaded files.
	while read -r url; do
		links+=("${url}")
	done < <(
		jq -rc '.[]?.subtype="file_share" |
	[.[]?.files[]?.url_private_download] |
	unique |
	.[]' \
			"${source_file}"
	)

	link_count="${#links[@]}"

	if [[ "${link_count}" -gt 0 ]]; then
		output_path="$(pwd)" # @todo make this a variable parameter.
		file_hash="$(md5 -q "${source_file}")"
		session_file="${output_path}/httpie-session-${file_hash}.json"

		# this doesn't do anything yet, since we're alreay starting in an existing directory
		mkdir -p "${output_path}"

		printf "Downloading %d files to %s\nusing httpie session from %s\n" "$link_count" "${output_path}" "${session_file}"
		echo '----------------'
		printf '\n'

		for link in "${links[@]}"; do
			printf "\nTrying %s\n" "${link}"

			if http --check-status --ignore-stdin --timeout=2.5 HEAD "${link}" &>/dev/null; then
				http --session "${session_file}" --ignore-stdin -xbd "${link}"
			else
				case $? in
				2) printf 'Request timed out!\n\n' ;;
				3) printf 'Unexpected HTTP 3xx Redirection!\n\n' ;;
				4) printf 'HTTP 4xx Client Error!\n\n' ;;
				5) printf 'HTTP 5xx Server Error!\n\n' ;;
				6) printf 'Exceeded --max-redirects=<n> redirects!\n\n' ;;
				*) printf 'Other Error!\n\n' ;;
				esac
			fi
		done
	else
		printf 'Nothing found to download.\n\n'
	fi
}

main "$@"