[PATCH 19.07] mbedtls: add config option to compile with hkdf

[Etan Kissling]

This adds a config option to allow compiling with HKDF algorithm support
to support applications that require this feature.

Backport from master.

Signed-off-by: Etan Kissling <etan_kissling at apple.com>
---
 package/libs/mbedtls/Makefile | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/package/libs/mbedtls/Makefile b/package/libs/mbedtls/Makefile
index 04033b1e47..ea8df0783c 100644
--- a/package/libs/mbedtls/Makefile
+++ b/package/libs/mbedtls/Makefile
@@ -20,7 +20,9 @@ PKG_BUILD_PARALLEL:=1
 PKG_LICENSE:=GPL-2.0+
 PKG_CPE_ID:=cpe:/a:arm:mbed_tls
 
-PKG_CONFIG_DEPENDS:=CONFIG_LIBMBEDTLS_DEBUG_C
+PKG_CONFIG_DEPENDS := \
+	CONFIG_LIBMBEDTLS_DEBUG_C \
+	CONFIG_LIBMBEDTLS_HKDF_C
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
@@ -56,6 +58,14 @@ config LIBMBEDTLS_DEBUG_C
 	 by around 60 KiB (for an ARMv5 platform).
 
 	 Usually, you don't need this, so don't select this if you're unsure.
+
+config LIBMBEDTLS_HKDF_C
+	depends on PACKAGE_libmbedtls
+	bool "Enable the HKDF algorithm (RFC 5869)"
+	default n
+	help
+	 This option adds support for the Hashed Message Authentication Code
+	 (HMAC)-based key derivation function (HKDF).
 endef
 
 define Package/mbedtls-util
@@ -96,6 +106,13 @@ define Build/Configure
 	     END { exit(rc) }' $(PKG_BUILD_DIR)/include/mbedtls/config.h \
 	     >$(PKG_BUILD_DIR)/include/mbedtls/config.h.new && \
 	mv $(PKG_BUILD_DIR)/include/mbedtls/config.h.new $(PKG_BUILD_DIR)/include/mbedtls/config.h
+
+	awk 'BEGIN { rc = 1 } \
+	     /#define MBEDTLS_HKDF_C/ { $$$$0 = "$(if $(CONFIG_LIBMBEDTLS_HKDF_C),,// )#define MBEDTLS_HKDF_C"; rc = 0 } \
+	     { print } \
+	     END { exit(rc) }' $(PKG_BUILD_DIR)/include/mbedtls/config.h \
+	     >$(PKG_BUILD_DIR)/include/mbedtls/config.h.new && \
+	mv $(PKG_BUILD_DIR)/include/mbedtls/config.h.new $(PKG_BUILD_DIR)/include/mbedtls/config.h
 endef
 
 define Build/InstallDev
-- 
2.21.1 (Apple Git-122.3)