embed SOURCE_DATE_EPOCH for psl_compiled_time() to make build reproducible.

debian/changelog

@@ -2,6 +2,8 @@ libpsl (0.7.1-1) unstable; urgency=medium
 
   * New upstream release.
   * switch from autotools-dev to dh_autoreconf
+  * embed SOURCE_DATE_EPOCH for psl_compiled_time() to make build
+    reproducible.
 
  -- Daniel Kahn Gillmor <dkg@fifthhorseman.net>  Thu, 09 Jul 2015 10:06:59 -0400
 

debian/patches/0002-Embed-_psl_compile_time-derived-from-SOURCE_DATE_EPO.patch

@@ -0,0 +1,50 @@
+From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
+Date: Sun, 12 Jul 2015 15:50:47 -0400
+Subject: Embed _psl_compile_time derived from $SOURCE_DATE_EPOCH if set
+
+Making packages build byte-for-byte reproducibly from a given
+toolchain+source makes it much easier to corroborate builds by testing
+against other build infrastructure.
+
+By default, libpsl currently embeds the current unix timestamp in
+_psl_compile_time, which makes it bytewise incompatible if it is
+rebuild even on the same machine one second later.
+
+Dropping _psl_compile_time and psl_builtin_compile_time() would fix
+this, but would cause an API/ABI change for the library.  The next
+time libpsl goes through an API/ABI change anyway, this might be worth
+consideration, but maybe such a simple change doesn't warrant an
+SONAME bump, so this changeset proposes to embed the environment
+variable $SOURCE_DATE_EPOCH if it is set during build, falling back to
+the current behavior if $SOURCE_DATE_EPOCH is unset.
+
+See https://wiki.debian.org/ReproducibleBuilds/TimestampsProposal for
+more information about $SOURCE_DATE_EPOCH.
+---
+ src/psl2c.c | 6 +++++-
+ 1 file changed, 5 insertions(+), 1 deletion(-)
+
+diff --git a/src/psl2c.c b/src/psl2c.c
+index e634a97..1fc5877 100644
+--- a/src/psl2c.c
++++ b/src/psl2c.c
+@@ -157,6 +157,7 @@ int main(int argc, const char **argv)
+ 		struct stat st;
+ 		size_t cmdsize = 16 + strlen(argv[1]);
+ 		char *cmd = alloca(cmdsize), checksum[64] = "";
++		char *source_date_epoch = NULL;
+ 
+ #if 0
+ 		/* include library code did not generate punycode, so let's do it for the builtin data */
+@@ -177,7 +178,10 @@ int main(int argc, const char **argv)
+ 		if (stat(argv[1], &st) != 0)
+ 			st.st_mtime = 0;
+ 		fprintf(fpout, "static time_t _psl_file_time = %lu;\n", st.st_mtime);
+-		fprintf(fpout, "static time_t _psl_compile_time = %lu;\n", time(NULL));
++		if (source_date_epoch = getenv("SOURCE_DATE_EPOCH"))
++			fprintf(fpout, "static time_t _psl_compile_time = %lu;\n", atol(source_date_epoch));
++		else
++			fprintf(fpout, "static time_t _psl_compile_time = %lu;\n", time(NULL));
+ 		fprintf(fpout, "static const char _psl_sha1_checksum[] = \"%s\";\n", checksum);
+ 		fprintf(fpout, "static const char _psl_filename[] = \"%s\";\n", argv[1]);
+ 

debian/patches/series

@@ -1 +1,2 @@
 0001-enable-build-of-docs.patch
+0002-Embed-_psl_compile_time-derived-from-SOURCE_DATE_EPO.patch