Add conversions to ISO-8601 date format

ChangeLog

@@ -1,3 +1,8 @@
+2022-05-30  Jay Berkenbilt  <ejb@ql.org>
+
+        * Add QUtil::qpdf_time_to_iso8601 and QUtil::pdf_time_to_iso8601
+        for converting PDF/qpdf timestamps to ISO-8601 date format.
+
 2022-05-18  Jay Berkenbilt  <ejb@ql.org>
 
         * Add QUtil::FileCloser to the public API. This is a simple inline

include/qpdf/QUtil.hh

@@ -284,6 +284,10 @@ namespace QUtil
     QPDF_DLL
     std::string qpdf_time_to_pdf_time(QPDFTime const&);
 
+    // Convert QPDFTime to a second-granularity ISO-8601 timestamp.
+    QPDF_DLL
+    std::string qpdf_time_to_iso8601(QPDFTime const&);
+
     // Convert a PDF timestamp string to a QPDFTime. If syntactically
     // valid, return true and fill in qtm. If not valid, return false,
     // and do not modify qtm. If qtm is null, just check the validity
@@ -291,6 +295,11 @@ namespace QUtil
     QPDF_DLL
     bool pdf_time_to_qpdf_time(std::string const&, QPDFTime* qtm = nullptr);
 
+    // Convert PDF timestamp to a second-granularity ISO-8601
+    // timestamp. If syntactically valid, return true and initialize
+    // iso8601. Otherwise, return false.
+    bool pdf_time_to_iso8601(std::string const& pdf_time, std::string& iso8601);
+
     // Return a string containing the byte representation of the UTF-8
     // encoding for the unicode value passed in.
     QPDF_DLL

libqpdf/QUtil.cc

@@ -984,6 +984,32 @@ QUtil::qpdf_time_to_pdf_time(QPDFTime const& qtm)
         QUtil::int_to_string(qtm.second, 2) + tz_offset);
 }
 
+std::string
+QUtil::qpdf_time_to_iso8601(QPDFTime const& qtm)
+{
+    std::string tz_offset;
+    int t = qtm.tz_delta;
+    if (t == 0) {
+        tz_offset = "Z";
+    } else {
+        if (t < 0) {
+            t = -t;
+            tz_offset += "+";
+        } else {
+            tz_offset += "-";
+        }
+        tz_offset += QUtil::int_to_string(t / 60, 2) + ":" +
+            QUtil::int_to_string(t % 60, 2);
+    }
+    return (
+        QUtil::int_to_string(qtm.year, 4) + "-" +
+        QUtil::int_to_string(qtm.month, 2) + "-" +
+        QUtil::int_to_string(qtm.day, 2) + "T" +
+        QUtil::int_to_string(qtm.hour, 2) + ":" +
+        QUtil::int_to_string(qtm.minute, 2) + ":" +
+        QUtil::int_to_string(qtm.second, 2) + tz_offset);
+}
+
 bool
 QUtil::pdf_time_to_qpdf_time(std::string const& str, QPDFTime* qtm)
 {
@@ -1018,6 +1044,17 @@ QUtil::pdf_time_to_qpdf_time(std::string const& str, QPDFTime* qtm)
     return true;
 }
 
+bool
+QUtil::pdf_time_to_iso8601(std::string const& pdf_time, std::string& iso8601)
+{
+    QPDFTime qtm;
+    if (pdf_time_to_qpdf_time(pdf_time, &qtm)) {
+        iso8601 = qpdf_time_to_iso8601(qtm);
+        return true;
+    }
+    return false;
+}
+
 std::string
 QUtil::toUTF8(unsigned long uval)
 {

libtests/qtest/qutil/qutil.out

@@ -127,7 +127,10 @@ rename over existing
 delete file
 ---- timestamp
 D:20210209144925-05'00'
+2021-02-09T14:49:25-05:00
 D:20210210011925+05'30'
+2021-02-10T01:19:25+05:30
 D:20210209191925Z
+2021-02-09T19:19:25Z
 ---- is_long_long
 done

libtests/qutil.cc

@@ -656,10 +656,14 @@ timestamp_test()
 {
     auto check = [](QUtil::QPDFTime const& t) {
         std::string pdf = QUtil::qpdf_time_to_pdf_time(t);
-        std::cout << pdf << std::endl;
+        std::string iso8601 = QUtil::qpdf_time_to_iso8601(t);
+        std::cout << pdf << std::endl << iso8601 << std::endl;
         QUtil::QPDFTime t2;
+        std::string iso8601_2;
         assert(QUtil::pdf_time_to_qpdf_time(pdf, &t2));
         assert(QUtil::qpdf_time_to_pdf_time(t2) == pdf);
+        assert(QUtil::pdf_time_to_iso8601(pdf, iso8601_2));
+        assert(iso8601 == iso8601_2);
     };
     check(QUtil::QPDFTime(2021, 2, 9, 14, 49, 25, 300));
     check(QUtil::QPDFTime(2021, 2, 10, 1, 19, 25, -330));