Author: Vagrant Cascadian <vagrant@reproducible-builds.org>
        tony mancill <tmancill@debian.org>
Description: Use SOURCE_DATE_EPOCH environment variable when set instead of
 current system time to enable reproducible generation of PDF documents.
 If you desire the previous behavior, either unset SOURCE_DATE_EPOCH or
 overwrite it to a non-integer value.
 Also see: https://reproducible-builds.org/docs/source-date-epoch/
Forwarded: not-needed
Last-Update: 2024-02-18
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=978499

--- a/fop-core/src/main/java/org/apache/fop/pdf/PDFInfo.java
+++ b/fop-core/src/main/java/org/apache/fop/pdf/PDFInfo.java
@@ -21,6 +21,8 @@
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
 import java.util.Date;
 import java.util.LinkedHashMap;
 import java.util.Map;
@@ -305,9 +307,40 @@
      * @return the requested String representation
      */
     protected static String formatDateTime(final Date time) {
+        final Date sourceDateEpoch = getSourceDateEpoch();
+        if (sourceDateEpoch != null) {
+            return formatDateTime(sourceDateEpoch, TimeZone.getTimeZone("Etc/UTC"));
+        }
         return formatDateTime(time, TimeZone.getDefault());
     }
 
+    /** @return a Date initialized from SOURCE_DATE_EPOCH or null if not set */
+    public static Date getSourceDateEpoch() {
+        // https://reproducible-builds.org/docs/source-date-epoch/
+        // https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=978499
+        final String sourceDateEpochString = getEnvVar("SOURCE_DATE_EPOCH", null);
+        if (sourceDateEpochString != null) {
+            try {
+                final Long sourcedate = (1000 * Long.parseLong(sourceDateEpochString));
+                return new Date(sourcedate);
+            } catch (NumberFormatException ignored) {
+                // ignored
+            }
+        }
+        return null;
+    }
+
+    private static String getEnvVar(String envVar, String defaultVal) {
+        try {
+            return AccessController.doPrivileged((PrivilegedAction<String>)
+                () -> System.getenv(envVar)
+            );
+        } catch(SecurityException ignored) {
+            // do nothing
+        }
+        return defaultVal;
+    }
+
     /**
      * Adds a custom property to this Info dictionary.
      */
--- a/fop-core/src/main/java/org/apache/fop/pdf/PDFMetadata.java
+++ b/fop-core/src/main/java/org/apache/fop/pdf/PDFMetadata.java
@@ -135,8 +135,12 @@
 
         //Set creation date if not available, yet
         if (info.getCreationDate() == null) {
-            Date d = new Date();
-            info.setCreationDate(d);
+            final Date sourceDateEpoch = PDFInfo.getSourceDateEpoch();
+            if (sourceDateEpoch != null) {
+                info.setCreationDate(sourceDateEpoch);
+            } else {
+                info.setCreationDate(new Date());
+            }
         }
 
         //Important: Acrobat 7's preflight check for PDF/A-1b wants the creation date in the Info
--- a/fop-core/src/main/java/org/apache/fop/render/pdf/PDFRenderingUtil.java
+++ b/fop-core/src/main/java/org/apache/fop/render/pdf/PDFRenderingUtil.java
@@ -261,8 +261,14 @@
         }
         fopXMP.mergeInto(docXMP, exclude);
         XMPBasicAdapter xmpBasic = XMPBasicSchema.getAdapter(docXMP);
-        //Metadata was changed so update metadata date
-        xmpBasic.setMetadataDate(new java.util.Date());
+        //Metadata was changed so potentially update metadata date
+        final Date sourceDateEpoch = PDFInfo.getSourceDateEpoch();
+        if (sourceDateEpoch != null) {
+            xmpBasic.setMetadataDate(sourceDateEpoch);
+        } else {
+            xmpBasic.setMetadataDate(new Date());
+        }
+
         PDFMetadata.updateInfoFromMetadata(docXMP, pdfDoc.getInfo());
 
         PDFMetadata pdfMetadata = pdfDoc.getFactory().makeMetadata(
@@ -481,7 +487,13 @@
                 augmentDictionary((PDFDictionary)currentPage.get("DPart"), extension);
             }
         } else if (type == PDFDictionaryType.PagePiece) {
-            String date = DateFormatUtil.formatPDFDate(new Date(), TimeZone.getDefault());
+            final Date sourceDateEpoch = PDFInfo.getSourceDateEpoch();
+            final String date;
+            if (sourceDateEpoch != null) {
+                date = DateFormatUtil.formatPDFDate(sourceDateEpoch, TimeZone.getTimeZone("Etc/UTC"));
+            } else {
+                date = DateFormatUtil.formatPDFDate(new Date(), TimeZone.getDefault());
+            }
             if (currentPage.get("PieceInfo") == null) {
                 currentPage.put("PieceInfo", new PDFDictionary());
                 currentPage.put("LastModified", date);
--- a/fop-core/src/main/java/org/apache/fop/pdf/FileIDGenerator.java
+++ b/fop-core/src/main/java/org/apache/fop/pdf/FileIDGenerator.java
@@ -24,8 +24,11 @@
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
 import java.util.Date;
+import java.util.TimeZone;
 import java.util.Random;
 
+import org.apache.xmlgraphics.util.DateFormatUtil;
+
 /**
  * A class to generate the File Identifier of a PDF document (the ID entry of the file
  * trailer dictionary).
@@ -85,8 +88,14 @@
         }
 
         private void generateFileID() {
-            DateFormat df = new SimpleDateFormat("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'SSS");
-            digest.update(PDFDocument.encode(df.format(new Date())));
+            final Date sourceDateEpoch = PDFInfo.getSourceDateEpoch();
+            if (sourceDateEpoch != null) {
+                digest.update(PDFDocument.encode(
+                    DateFormatUtil.formatPDFDate(sourceDateEpoch, TimeZone.getTimeZone("Etc/UTC"))));
+            } else {
+                DateFormat df = new SimpleDateFormat("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'SSS");
+                digest.update(PDFDocument.encode(df.format(new Date())));
+            }
             // Ignoring the filename here for simplicity even though it's recommended
             // by the PDF spec
             digest.update(PDFDocument.encode(String.valueOf(document.getCurrentFileSize())));