multify: Respect SOURCE_DATE_EPOCH variable when used from command-line

That said, we should probably encourage the use of -T0 (which doesn't write out timestamps to begin with).

panda/src/downloadertools/multify.cxx

@@ -57,6 +57,7 @@ string dont_compress_str = "jpg,png,mp3,ogg";
 // Default text extensions.  May be overridden with -X.
 string text_ext_str = "txt";
 
+time_t source_date_epoch = (time_t)-1;
 bool got_record_timestamp_flag = false;
 bool record_timestamp_flag = true;
 
@@ -430,6 +431,12 @@ add_files(const vector_string &params) {
     needs_repack = true;
   }
 
+  if (multifile->get_record_timestamp() && source_date_epoch != (time_t)-1) {
+    if (multifile->get_timestamp() > source_date_epoch) {
+      multifile->set_timestamp(source_date_epoch);
+    }
+  }
+
   if (needs_repack) {
     if (!multifile->repack()) {
       cerr << "Failed to write " << multifile_name << ".\n";
@@ -533,6 +540,12 @@ kill_files(const vector_string &params) {
     }
   }
 
+  if (multifile->get_record_timestamp() && source_date_epoch != (time_t)-1) {
+    if (multifile->get_timestamp() > source_date_epoch) {
+      multifile->set_timestamp(source_date_epoch);
+    }
+  }
+
   bool okflag = true;
 
   if (multifile->needs_repack()) {
@@ -779,6 +792,11 @@ main(int argc, char **argv) {
     }
   }
 
+  const char *source_date_epoch_str = getenv("SOURCE_DATE_EPOCH");
+  if (source_date_epoch_str != nullptr && source_date_epoch_str[0] != 0) {
+    source_date_epoch = (time_t)strtoll(source_date_epoch_str, nullptr, 10);
+  }
+
   extern char *optarg;
   extern int optind;
   static const char *optflags = "crutxkvz123456789Z:T:X:S:f:OC:ep:P:F:h";

panda/src/express/multifile.I

@@ -67,6 +67,17 @@ get_timestamp() const {
   return _timestamp;
 }
 
+/**
+ * Changes the overall mudification timestamp of the multifile.  Note that this
+ * will be reset to the current time every time you modify a subfile.
+ * Only set this if you know what you are doing!
+ */
+INLINE void Multifile::
+set_timestamp(time_t timestamp) {
+  _timestamp = timestamp;
+  _timestamp_dirty = true;
+}
+
 /**
  * Sets the flag indicating whether timestamps should be recorded within the
  * Multifile or not.  The default is true, indicating the Multifile will

panda/src/express/multifile.h

@@ -59,6 +59,7 @@ PUBLISHED:
   INLINE bool needs_repack() const;
 
   INLINE time_t get_timestamp() const;
+  INLINE void set_timestamp(time_t timestamp);
 
   INLINE void set_record_timestamp(bool record_timestamp);
   INLINE bool get_record_timestamp() const;