add option in configure to use shared libraries

Makefile.am

@@ -1,4 +1,8 @@
+if USE_SYSTEM_SHARED_LIB
+SUBDIRS = libcork libipset src
+else
 SUBDIRS = libsodium libcork libipset libudns libev src
+endif
 
 ACLOCAL_AMFLAGS = -I m4
 man_MANS = man/shadowsocks-libev.8 man/ss-server.1 man/ss-local.1 man/ss-redir.1\

configure.ac

@@ -19,6 +19,18 @@ AC_DISABLE_STATIC
 AC_DISABLE_SHARED
 LT_INIT([dlopen])
 
+dnl Checks for using shared libraries from system
+AC_ARG_ENABLE(
+  [system-shared-lib],
+  AS_HELP_STRING([--enable-system-shared-lib], [build against shared libraries when possible]),
+  [
+    case "${enableval}" in
+      yes) enable_system_shared_lib=true ;;
+      no) enable_system_shared_lib=false ;;
+      *) AC_MSG_ERROR([bad value ${enableval} for --enable-system-shared-lib]) ;;
+    esac], [enable_system_shared_lib=false])
+AM_CONDITIONAL([USE_SYSTEM_SHARED_LIB], [test x$enable_system_shared_lib = xtrue])
+
 dnl Checks for crypto library
 AC_ARG_WITH(
   [crypto-library],

src/Makefile.am

@@ -2,17 +2,23 @@ VERSION_INFO = 1:0:0
 
 AM_CFLAGS = -g -O2 -Wall -Werror -Wno-deprecated-declarations -fno-strict-aliasing -std=gnu99 -D_GNU_SOURCE
 AM_CFLAGS += $(PTHREAD_CFLAGS)
+if !USE_SYSTEM_SHARED_LIB
 AM_CFLAGS += -I$(top_srcdir)/libev
 AM_CFLAGS += -I$(top_srcdir)/libudns
+AM_CFLAGS += -I$(top_srcdir)/libsodium/src/libsodium/include
+endif
 AM_CFLAGS += -I$(top_srcdir)/libipset/include
 AM_CFLAGS += -I$(top_srcdir)/libcork/include
-AM_CFLAGS += -I$(top_srcdir)/libsodium/src/libsodium/include
 
-SS_COMMON_LIBS = $(top_builddir)/libev/libev.la \
-				 $(top_builddir)/libipset/libipset.la \
-				 $(top_builddir)/libcork/libcork.la \
-				 $(top_builddir)/libsodium/src/libsodium/libsodium.la \
-				 $(INET_NTOP_LIB)
+SS_COMMON_LIBS = $(top_builddir)/libipset/libipset.la \
+                 $(top_builddir)/libcork/libcork.la \
+                 $(INET_NTOP_LIB)
+if USE_SYSTEM_SHARED_LIB
+SS_COMMON_LIBS += -lev -lsodium -lm
+else
+SS_COMMON_LIBS += $(top_builddir)/libev/libev.la \
+                  $(top_builddir)/libsodium/src/libsodium/libsodium.la
+endif
 
 bin_PROGRAMS = ss-local ss-tunnel
 if !BUILD_WINCOMPAT
@@ -61,9 +67,15 @@ ss_local_LDADD = $(SS_COMMON_LIBS)
 ss_tunnel_LDADD = $(SS_COMMON_LIBS)
 ss_server_LDADD = $(SS_COMMON_LIBS)
 ss_manager_LDADD = $(SS_COMMON_LIBS)
+if USE_SYSTEM_SHARED_LIB
+ss_local_LDADD += -ludns
+ss_tunnel_LDADD += -ludns
+ss_server_LDADD += -ludns
+else
 ss_local_LDADD += $(top_builddir)/libudns/libudns.la
 ss_tunnel_LDADD += $(top_builddir)/libudns/libudns.la
 ss_server_LDADD += $(top_builddir)/libudns/libudns.la
+endif
 
 ss_local_CFLAGS = $(AM_CFLAGS) -DUDPRELAY_LOCAL
 ss_tunnel_CFLAGS = $(AM_CFLAGS) -DUDPRELAY_LOCAL -DUDPRELAY_TUNNEL
@@ -87,8 +99,12 @@ ss_redir_SOURCES = utils.c \
                    redir.c
 ss_redir_CFLAGS = $(AM_CFLAGS) -DUDPRELAY_REDIR -DUDPRELAY_LOCAL
 ss_redir_LDADD = $(SS_COMMON_LIBS)
+if USE_SYSTEM_SHARED_LIB
+ss_redir_LDADD += -ludns
+else
 ss_redir_LDADD += $(top_builddir)/libudns/libudns.la
 endif
+endif
 
 lib_LTLIBRARIES = libshadowsocks.la
 libshadowsocks_la_SOURCES = $(ss_local_SOURCES)