add sha256sum check

bin/install

@@ -1,13 +1,49 @@
 #!/bin/sh
+
+checkShasum ()
+{
+  local archive_file_name="${1}"
+  local authentic_checksum="${2}"
+
+  if $(command -v sha256sum >/dev/null 2>&1); then
+	sha256sum \
+		-c <<<"$authentic_checksum $archive_file_name"
+  elif $(command -v shasum >/dev/null 2>&1); then
+    shasum \
+      -a 256 \
+      -c <<<"$authentic_checksum $archive_file_name"
+  else
+    echo "sha256sum or shasum is not available for use" >&2
+    return 1
+  fi
+}
+
+
 # instructions taken straight from https://gradle.org/install/#manually
 if [ "$ASDF_INSTALL_TYPE" = "ref" ]
 then
+	echo "start clone $ASDF_INSTALL_VERSION"
 	git clone "$ASDF_INSTALL_VERSION" "$ASDF_INSTALL_PATH"
 else
+	echo "start install $ASDF_INSTALL_VERSION"
 	mkdir -p "$ASDF_INSTALL_PATH"
 	cd "$ASDF_INSTALL_PATH" || exit 1
 	curl -OJL https://services.gradle.org/distributions/gradle-${ASDF_INSTALL_VERSION}-bin.zip
+	curl -OJL https://services.gradle.org/distributions/gradle-${ASDF_INSTALL_VERSION}-bin.zip.sha256
+
+	archive_file_name=$PWD/gradle-${ASDF_INSTALL_VERSION}-bin.zip
+	authentic_checksum_file=$archive_file_name.sha256
+	authentic_checksum=$(cat $authentic_checksum_file)
+
+	echo 'start check sha256sum'
+	if ! checkShasum "$archive_file_name" "$authentic_checksum"; then
+        echo "Authenticity of package archive can not be assured. Exiting." >&2
+        exit 1
+    fi
+
 	unzip gradle-${ASDF_INSTALL_VERSION}-bin.zip
 	rm gradle-${ASDF_INSTALL_VERSION}-bin.zip
 	mv gradle-${ASDF_INSTALL_VERSION}/* .
+	rm -rf gradle-${ASDF_INSTALL_VERSION}
+	rm $authentic_checksum_file
 fi