middleclick-autoscroll 1.0.0

Middle-click autoscroll for every Chromium-based application on the system:
Electron and CEF applications, Chromium-based browsers, Flatpaks, Spotify and
Steam, plus anything installed later.

The flag goes into an Arch wrapper's <name>-flags.conf where one exists, and
into a shadowing desktop entry where it does not. Steam gets its web helper
script patched and -noverifyfiles on its launcher, because it restores its own
files otherwise. Every change is recorded so it can be taken back exactly.

src/lib/steam.sh

@@ -0,0 +1,163 @@
+# shellcheck shell=bash
+#
+# Steam.
+#
+# Steam's interface is CEF, so the feature is there - but Steam builds the
+# command line for its web helper itself and offers no way to add to it. The
+# only place to get an argument in is the shell script that starts the helper,
+# which lives inside Steam's own installation:
+#
+#   ~/.local/share/Steam/ubuntu12_64/steamwebhelper_sniper_wrap.sh
+#
+# Steam checksums that script at every start and restores it when it differs,
+# which is why the launcher gets -noverifyfiles as well. The trade-off is real
+# and belongs to the user, so this is a switch of its own rather than part of
+# the general application handling: with verification off, Steam no longer
+# repairs a damaged installation by itself.
+#
+# The file comes back on every client update, and the watcher re-applies the
+# patch when that happens.
+
+MCA_STEAM_EXEC='exec ./steamwebhelper "$@"'
+MCA_STEAM_LAUNCH_FLAG='-noverifyfiles'
+
+# Every place a Steam installation is known to live, resolved and de-duplicated
+# because ~/.steam/steam is normally a symlink into ~/.local/share.
+mca_steam_roots() {
+	local candidates=(
+		"$MCA_XDG_DATA/Steam"
+		"$HOME/.steam/steam"
+		"$HOME/.steam/root"
+		"$HOME/.steam/debian-installation"
+		"$HOME/.var/app/com.valvesoftware.Steam/.local/share/Steam"
+	)
+	local dir real
+	local -A seen=()
+
+	for dir in "${candidates[@]}"; do
+		[[ -d $dir ]] || continue
+		real="$(readlink -f -- "$dir" 2>/dev/null)" || continue
+		[[ -n ${seen[$real]+set} ]] && continue
+		seen[$real]=1
+		printf '%s\n' "$real"
+	done
+}
+
+# The script to patch inside a Steam installation. Newer clients start the
+# helper through a wrapper inside the container runtime; older ones exec it
+# from steamwebhelper.sh directly, and that one forwards its arguments too.
+mca_steam_script() {
+	local root="$1" f
+	for f in \
+		"$root/ubuntu12_64/steamwebhelper_sniper_wrap.sh" \
+		"$root/ubuntu12_64/steamwebhelper.sh"
+	do
+		[[ -f $f && -w $f ]] && { printf '%s\n' "$f"; return 0; }
+	done
+	return 1
+}
+
+mca_steam_installed() {
+	local root
+	while IFS= read -r root; do
+		mca_steam_script "$root" > /dev/null && return 0
+	done < <(mca_steam_roots)
+	return 1
+}
+
+# mca_steam_script_patched <script>
+mca_steam_script_patched() {
+	grep -q -- "$MCA_FEATURE" "$1" 2>/dev/null
+}
+
+mca_steam_patched() {
+	local root script
+	while IFS= read -r root; do
+		script="$(mca_steam_script "$root")" || continue
+		mca_steam_script_patched "$script" && return 0
+	done < <(mca_steam_roots)
+	return 1
+}
+
+# _mca_steam_exec_line <script>
+# The line number of the command that starts the web helper: the last
+# uncommented line that both names steamwebhelper and forwards "$@". Both the
+# current layout (exec ./steamwebhelper "$@" inside the container wrapper) and
+# the older one (steamwebhelper.sh handing the arguments to the runtime entry
+# point) end in exactly that.
+_mca_steam_exec_line() {
+	awk '
+		/^[[:space:]]*#/ { next }
+		/steamwebhelper/ && /"\$@"/ { n = NR }
+		END { if (n) print n }
+	' "$1" 2>/dev/null
+}
+
+# mca_steam_apply
+# Appends the flags to the line that starts the web helper. Everything else in
+# the script - setting up the container runtime, deciding whether the sandbox
+# can be used - is left alone.
+mca_steam_apply() {
+	local root script backup flags lineno found=0 out
+
+	flags="$(mca_flags)"
+
+	while IFS= read -r root; do
+		script="$(mca_steam_script "$root")" || continue
+		found=1
+
+		mca_steam_script_patched "$script" && { MCA_TOUCHED+=("$script"); continue; }
+
+		lineno="$(_mca_steam_exec_line "$script")"
+		if [[ -z $lineno ]]; then
+			# A client update changed how the helper is started. Leaving the
+			# file alone is the only safe answer: this script is what starts
+			# Steam's entire interface.
+			mca_note "$(mca_msg "Steam starts its interface in a way this version does not recognise; leaving it alone.")"
+			continue
+		fi
+
+		out="$(awk -v n="$lineno" -v f=" $flags" 'NR == n { $0 = $0 f } { print }' "$script")" || continue
+
+		backup="$(mca_backup "$script")" || continue
+		if mca_write_if_changed "$script" "$out"$'\n'; then
+			MCA_CHANGES=$(( MCA_CHANGES + 1 ))
+		fi
+		chmod +x -- "$script" 2>/dev/null || true
+		mca_ledger_add steam "$script" "$backup"
+		MCA_TOUCHED+=("$script")
+	done < <(mca_steam_roots)
+
+	(( found ))
+}
+
+# mca_steam_revert <script> <backup name>
+mca_steam_revert() {
+	local script="$1" backup="$2"
+
+	if [[ -n $backup && -f "$MCA_BACKUPDIR/$backup" ]]; then
+		if [[ -e $script ]]; then
+			cp -p -- "$MCA_BACKUPDIR/$backup" "$script" 2>/dev/null || true
+			chmod +x -- "$script" 2>/dev/null || true
+		fi
+		rm -f -- "$MCA_BACKUPDIR/$backup"
+		return 0
+	fi
+
+	# No backup to fall back on - take the flags back out of the exec line.
+	[[ -f $script ]] || return 1
+	local tmp
+	tmp="$(mktemp "${script}.XXXXXX")" || return 1
+	sed "s| $MCA_FLAG||g" "$script" > "$tmp" && mv -f "$tmp" "$script" || { rm -f "$tmp"; return 1; }
+	chmod +x -- "$script" 2>/dev/null || true
+	return 0
+}
+
+# mca_steam_desktop_apply <id> <source entry>
+# Steam restores its own files at every start unless it is told not to verify
+# them, so the launcher entry carries that switch. It goes directly after the
+# program because Steam reads its options before the steam:// argument that the
+# right-click actions pass.
+mca_steam_desktop_apply() {
+	mca_desktop_apply "$1" "$2" "$MCA_STEAM_LAUNCH_FLAG" after-program
+}