sngrep: use pkg-config to discover OpenSSL to fix static linking

Building sngrep with OpenSSL support in static linking configurations
currently fails due to undefined symbols in the OpenSSL library. It's
the usual problem with using AC_CHECK_LIB() to discover libraries
instead of the pkg-config based PKG_CHECK_MODULES().

Therefore, this commit introduces a patch that switches to using
pkg-config to discover OpenSSL. A preliminary patch is needed, without
which appending to LIBS/CFLAGS doesn't work. Both patches have been
submitted upstream.

Fixes:

  http://autobuild.buildroot.net/results/911143de823b2c749ac0a59dfa06adb6ddd3de50/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/sngrep/0001-src-Makefile.am-don-t-use-VPATH.patch

@@ -0,0 +1,43 @@
+From b6dcae8ec4334e2436cfa19a8052c3473f57a586 Mon Sep 17 00:00:00 2001
+From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Date: Sat, 4 Mar 2017 15:02:43 +0100
+Subject: [PATCH 1/2] src/Makefile.am: don't use VPATH
+
+VPATH is a mechanism used to allow out-of-tree build, not to use source
+code from a different directory. For this purpose, one should simply use
+the "subdir-objects" AUTOMAKE_OPTIONS, and reference the source code of
+the sub-directory in the <prog>_SOURCES variable.
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Upstream-status: https://github.com/irontec/sngrep/pull/176
+---
+ src/Makefile.am | 10 +++++-----
+ 1 file changed, 5 insertions(+), 5 deletions(-)
+
+diff --git a/src/Makefile.am b/src/Makefile.am
+index 931ee06..961f4a0 100644
+--- a/src/Makefile.am
++++ b/src/Makefile.am
+@@ -1,5 +1,5 @@
++AUTOMAKE_OPTIONS=subdir-objects
+ bin_PROGRAMS=sngrep
+-VPATH=curses
+ sngrep_SOURCES=capture.c
+ if USE_EEP
+ sngrep_SOURCES+=capture_eep.c
+@@ -12,8 +12,8 @@ sngrep_SOURCES+=capture_openssl.c
+ endif
+ sngrep_SOURCES+=address.c packet.c sip.c sip_call.c sip_msg.c sip_attr.c main.c
+ sngrep_SOURCES+=option.c group.c filter.c keybinding.c media.c setting.c rtp.c
+-sngrep_SOURCES+=util.c hash.c vector.c ui_panel.c scrollbar.c
+-sngrep_SOURCES+=ui_manager.c ui_call_list.c ui_call_flow.c ui_call_raw.c
+-sngrep_SOURCES+=ui_stats.c ui_filter.c ui_save.c ui_msg_diff.c
+-sngrep_SOURCES+=ui_column_select.c ui_settings.c
++sngrep_SOURCES+=util.c hash.c vector.c curses/ui_panel.c curses/scrollbar.c
++sngrep_SOURCES+=curses/ui_manager.c curses/ui_call_list.c curses/ui_call_flow.c curses/ui_call_raw.c
++sngrep_SOURCES+=curses/ui_stats.c curses/ui_filter.c curses/ui_save.c curses/ui_msg_diff.c
++sngrep_SOURCES+=curses/ui_column_select.c curses/ui_settings.c
+ 
+-- 
+2.7.4
+

package/sngrep/0002-configure.ac-switch-to-pkg-config-to-find-openssl.patch

@@ -0,0 +1,75 @@
+From 22b08ab1a45eb3773b3c90dc37a31a7574520daa Mon Sep 17 00:00:00 2001
+From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Date: Sat, 4 Mar 2017 14:56:53 +0100
+Subject: [PATCH 2/2] configure.ac: switch to pkg-config to find openssl
+
+Using AC_CHECK_LIB() doesn't work properly for static linking, because
+it doesn't return information on transitive dependencies of
+libraries. For example, if library A internally uses library B, then
+with dynamic linking, doing -lA is sufficient. However, with static
+linking, one must do -lA -lB, and AC_CHECK_LIB() will only give the -lA
+information. This for example causes a build failure when building
+sngrep statically with openssl enabled:
+
+checking for SSL_new in -lssl... no
+configure: error:  You need to have libssl installed to compile sngrep
+
+due to undefined symbols in the OpenSSL library.
+
+The proper solution for this is to discover the library using
+pkg-config, because pkg-config properly returns the list of necessary
+libraries, as it understands the concept of "list of libraries needed
+when dynamic linking" and "list of libraries needed for static linking".
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Upstream-status: https://github.com/irontec/sngrep/pull/176
+---
+ configure.ac    | 9 +--------
+ src/Makefile.am | 4 ++++
+ 2 files changed, 5 insertions(+), 8 deletions(-)
+
+diff --git a/configure.ac b/configure.ac
+index 42e00e9..9f8e6d2 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -129,14 +129,7 @@ AS_IF([test "x$WITH_OPENSSL" == "xyes"], [
+ 	AS_IF([test "x$WITH_GNUTLS" == "xyes"], [
+ 	    AC_MSG_ERROR([ GnuTLS and OpenSSL can not be enabled at the same time ])
+ 	], [])
+-
+-	AC_CHECK_LIB([ssl], [SSL_new], [], [
+-	    AC_MSG_ERROR([ You need to have libssl installed to compile sngrep])
+-	])
+-
+-	AC_CHECK_LIB([crypto], [EVP_get_cipherbyname], [], [
+-	    AC_MSG_ERROR([ You need to have libcrypto installed to compile sngrep])
+-	])
++	PKG_CHECK_MODULES([SSL], [libssl libcrypto])
+ 	AC_DEFINE([WITH_OPENSSL],[],[Compile With Openssl compatibility])
+ ], [])
+ 
+diff --git a/src/Makefile.am b/src/Makefile.am
+index 961f4a0..3a471b7 100644
+--- a/src/Makefile.am
++++ b/src/Makefile.am
+@@ -1,6 +1,8 @@
+ AUTOMAKE_OPTIONS=subdir-objects
+ bin_PROGRAMS=sngrep
+ sngrep_SOURCES=capture.c
++sngrep_CFLAGS=
++sngrep_LDADD=
+ if USE_EEP
+ sngrep_SOURCES+=capture_eep.c
+ endif
+@@ -9,6 +11,8 @@ sngrep_SOURCES+=capture_gnutls.c
+ endif
+ if WITH_OPENSSL
+ sngrep_SOURCES+=capture_openssl.c
++sngrep_CFLAGS+=$(SSL_CFLAGS)
++sngrep_LDADD+=$(SSL_LIBS)
+ endif
+ sngrep_SOURCES+=address.c packet.c sip.c sip_call.c sip_msg.c sip_attr.c main.c
+ sngrep_SOURCES+=option.c group.c filter.c keybinding.c media.c setting.c rtp.c
+-- 
+2.7.4
+

package/sngrep/sngrep.mk

@@ -9,7 +9,7 @@ SNGREP_SITE = $(call github,irontec,sngrep,$(SNGREP_VERSION))
 SNGREP_LICENSE = GPLv3+
 SNGREP_LICENSE_FILES = LICENSE
 SNGREP_AUTORECONF = YES
-SNGREP_DEPENDENCIES = libpcap ncurses
+SNGREP_DEPENDENCIES = libpcap ncurses host-pkgconf
 
 SNGREP_CONF_ENV += \
 	$(if $(BR2_STATIC_LIBS),LIBS="`$(STAGING_DIR)/usr/bin/pcap-config --static --libs`")