Debian Bug 764251: Set the build timestamp to a deterministic time

CHANGES

@@ -97,6 +97,10 @@ porting:
 	broke cross compiling. The particular check gets reverted.
 	Thanks to Ross Burton and Danomi Manchego for reporting this issue.
 
+	Debian Bug#764251: Set the build timestamp to a deterministic time:
+	support external BUILD_DATE env var to allow to build reproducable
+	binaries
+
 testing:
 	Do not distribute testcert.conf with socat source but generate it
 	(and new testcert6.conf) during test.sh run.

config.h.in

@@ -584,4 +584,6 @@
 
 #undef WITH_MSGLEVEL
 
+#define BUILD_DATE __DATE__ " " __TIME__
+
 #endif /* !defined(__config_h_included) */

configure.in

@@ -1863,4 +1863,11 @@ if test -n "$WITH_FIPS"; then
 fi
 AC_SUBST(FIPSLD_CC)
 
+# allow BUILD_DATE to be externally set for build reproducibility
+if test "$BUILD_DATE"; then
+  AC_DEFINE_UNQUOTED(BUILD_DATE, ["$BUILD_DATE"])
+else
+  AC_DEFINE(BUILD_DATE, [__DATE__" "__TIME__])
+fi
+
 AC_OUTPUT(Makefile)

socat.c

@@ -70,7 +70,7 @@ static int socat_newchild(void);
 static const char socatversion[] =
 #include "./VERSION"
       ;
-static const char timestamp[] = __DATE__" "__TIME__;
+static const char timestamp[] = BUILD_DATE;
 
 const char copyright_socat[] = "socat by Gerhard Rieger - see www.dest-unreach.org";
 #if WITH_OPENSSL