systemd: replace vendored files with libsystemd (beanstalkd#577)

Fixes beanstalkd#501

Makefile

@@ -8,6 +8,7 @@ LDLIBS?=
 
 OS?=$(shell uname | tr 'A-Z' 'a-z')
 INSTALL?=install
+PKG_CONFIG?=pkg-config
 
 ifeq ($(OS),sunos)
 override LDFLAGS += -lxnet -lsocket -lnsl
@@ -26,7 +27,6 @@ OFILES=\
 	net.o\
 	primes.o\
 	prot.o\
-	sd-daemon.o\
 	serv.o\
 	time.o\
 	tube.o\
@@ -43,12 +43,26 @@ TOFILES=\
 
 HFILES=\
 	dat.h\
-	sd-daemon.h\
 
 ifeq ($(OS),linux)
    LDLIBS+=-lrt
 endif
 
+# systemd support can be configured via USE_SYSTEMD:
+#        no: disabled
+#       yes: enabled, build fails if libsystemd is not found
+# otherwise: enabled if libsystemd is found
+ifneq ($(USE_SYSTEMD),no)
+ifeq ($(shell $(PKG_CONFIG) --exists libsystemd && echo $$?),0)
+	LDLIBS+=$(shell $(PKG_CONFIG) --libs libsystemd)
+	CPPFLAGS+=-DHAVE_LIBSYSTEMD
+else
+ifeq ($(USE_SYSTEMD),yes)
+$(error USE_SYSTEMD is set to "$(USE_SYSTEMD)", but $(PKG_CONFIG) cannot find libsystemd)
+endif
+endif
+endif
+
 CLEANFILES=\
 	vers.c\
 	$(wildcard *.gc*)

net.c

@@ -1,5 +1,4 @@
 #include "dat.h"
-#include "sd-daemon.h"
 #include <netdb.h>
 #include <stdio.h>
 #include <unistd.h>
@@ -12,6 +11,10 @@
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 
+#ifdef HAVE_LIBSYSTEMD
+#include <systemd/sd-daemon.h>
+#endif
+
 static int
 set_nonblocking(int fd)
 {
@@ -211,6 +214,7 @@ make_unix_socket(char *path)
 int
 make_server_socket(char *host, char *port)
 {
+#ifdef HAVE_LIBSYSTEMD
     int fd = -1, r;
 
     /* See if we got a listen fd from systemd. If so, all socket options etc
@@ -247,6 +251,7 @@ make_server_socket(char *host, char *port)
         }
         return fd;
     }
+#endif
 
     if (host && !strncmp(host, "unix:", 5)) {
         return make_unix_socket(&host[5]);