tang: Add package into tree

Tang is lightweight server for binding data to network presence.
---
Tang's source: https://github.com/latchset/tang

Maintainer: @Tiboris

Compile tested: (mips, TL-WR842N, 17.01.4, r3560-79f57e422d)

**Tang requires a few other software libraries:**

1. libhttp-parser
2. xinetd's socket activation
3. jose >= 8

**Two new files compared to tang upstream:**
- tangdx : configuration file for xinetd
- tangdw : wrapper for tangd service
	- puts timestamp when service activated, and
	- redirects stderr to log file in /var/log/

**Removed systemd requirement**

Signed-off-by: Tibor Dudlák <tdudlak@redhat.com>

utils/tang/Makefile

@@ -0,0 +1,68 @@
+#
+# Author: Tibor Dudlák
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=tang
+PKG_VERSION:=6
+PKG_RELEASE:=1
+
+PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
+PKG_SOURCE_URL:=https://github.com/latchset/$(PKG_NAME)/releases/download/v$(PKG_VERSION)/
+PKG_HASH:=1df78b48a52d2ca05656555cfe52bd4427c884f5a54a2c5e37a7b39da9e155e3
+
+PKG_INSTALL:=1
+PKG_BUILD_PARALLEL:=1
+
+PKG_FIXUP:=autoreconf
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/tang
+  SECTION:=utils
+  TITLE:=tang v$(PKG_VERSION) - daemon for binding data to the presence of a third party
+  DEPENDS:=+libhttp-parser +xinetd +jose +bash
+  URL:=https://github.com/latchset/tang
+  MAINTAINER:=Tibor Dudlák <tibor.dudlak@gmail.com>
+endef
+
+define Package/tang/description
+	Tang is a small daemon for binding data to the presence of a third party.
+endef
+
+define Package/tang/conffiles
+/etc/xinetd.d/tangdx
+/usr/share/tang/db/
+endef
+
+define Package/tang/install
+	$(INSTALL_DIR)	$(1)/usr/libexec
+	$(INSTALL_DIR)	$(1)/etc/xinetd.d/
+	$(INSTALL_BIN)	$(PKG_INSTALL_DIR)/usr/lib/tangd*	$(1)/usr/libexec/
+	$(INSTALL_BIN)	./files/tangdw				$(1)/usr/libexec/
+	$(CP)		./files/tangdx				$(1)/etc/xinetd.d/
+endef
+
+define Package/tang/postinst
+#!/bin/sh
+if [ -z "$${IPKG_INSTROOT}" ]; then
+	mkdir -p /usr/share/tang/db && mkdir -p /usr/share/tang/cache
+	KEYS=$(find /usr/share/tang/db/ -name "*.jw*" -maxdepth 1 | wc -l)
+	if [ "${KEYS}" = "0" ]; then # if db is empty generate new key pair
+		/usr/libexec/tangd-keygen /usr/share/tang/db/
+	elif [ "${KEYS}" = "1" ]; then # having 1 key should not happen
+		(>&2 echo "Please check the Tang's keys in /usr/share/tang/db \
+and regenate cache using /usr/libexec/tangd-update script.")
+	else
+		/usr/libexec/tangd-update /usr/share/tang/db/ /usr/share/tang/cache/
+	fi
+	(cat /etc/services | grep -E "tangd.*8888\/tcp") > /dev/null \
+		|| echo -e "tangd\t\t8888/tcp" >> /etc/services
+fi
+endef
+
+$(eval $(call BuildPackage,tang))