Keep the 1904 date system when reading and writing

src/reader/xlsx/workbook.rs

@@ -41,6 +41,11 @@ pub(crate) fn read<R: io::Read + io::Seek>(
                     obj.set_attributes(&mut reader, e);
                     wb.set_workbook_view(obj);
                 }
+                b"workbookPr" => {
+                    if let Some(v) = get_attribute(e, b"date1904") {
+                        wb.set_date1904(v == "1" || v == "true");
+                    }
+                }
                 b"workbookProtection" => {
                     let mut obj = WorkbookProtection::default();
                     obj.set_attributes(&mut reader, e);

src/structs/workbook.rs

@@ -48,6 +48,7 @@ pub struct Workbook {
     pivot_caches:          Vec<(Box<str>, Box<str>, Box<str>)>,
     workbook_protection:   Option<Box<WorkbookProtection>>,
     defined_names:         Vec<DefinedName>,
+    date1904:              bool,
 }
 
 impl Workbook {
@@ -1008,6 +1009,28 @@ impl Workbook {
         self
     }
 
+    /// Whether the workbook uses the 1904 date system (`workbookPr/@date1904`).
+    ///
+    /// In the 1904 system, serial 0 is 1904-01-01 and serial 1 is 1904-01-02;
+    /// in the default 1900 system, serial 1 is 1900-01-01. From 1900-03-01 on
+    /// (past Excel's fictitious 1900-02-29), the same serial is a date 1,462
+    /// days later in the 1904 system than in the 1900 system.
+    #[inline]
+    #[must_use]
+    pub fn date1904(&self) -> bool {
+        self.date1904
+    }
+
+    /// Set whether the workbook uses the 1904 date system.
+    ///
+    /// This only changes how serial numbers are interpreted as dates; the
+    /// stored cell values are not converted.
+    #[inline]
+    pub fn set_date1904(&mut self, value: bool) -> &mut Self {
+        self.date1904 = value;
+        self
+    }
+
     /// Get Defined Name (Vec).
     #[inline]
     #[must_use]

src/writer/xlsx/workbook.rs

@@ -83,6 +83,9 @@ pub(crate) fn write<W: io::Seek + io::Write>(
 
     // workbookPr
     let mut attributes: crate::structs::AttrCollection = Vec::new();
+    if wb.date1904() {
+        attributes.push(("date1904", "1").into());
+    }
     attributes.push(("filterPrivacy", "1").into());
     // attributes.push(("defaultThemeVersion", "124226").into());
     if wb.has_macros() {

tests/date1904_roundtrip.rs

@@ -0,0 +1,79 @@
+use std::io::{
+    Cursor,
+    Read,
+};
+
+use umya_spreadsheet::{
+    reader,
+    writer,
+};
+use zip::ZipArchive;
+
+fn workbook_xml(bytes: &[u8]) -> String {
+    let mut archive = ZipArchive::new(Cursor::new(bytes)).unwrap();
+    let mut xml = String::new();
+    archive
+        .by_name("xl/workbook.xml")
+        .unwrap()
+        .read_to_string(&mut xml)
+        .unwrap();
+    xml
+}
+
+fn write(book: &umya_spreadsheet::Workbook) -> Vec<u8> {
+    let mut out = Vec::new();
+    writer::xlsx::write_writer(book, &mut out).unwrap();
+    out
+}
+
+#[test]
+fn date1904_defaults_to_false_and_is_not_written() {
+    let book = umya_spreadsheet::new_file();
+    assert!(!book.date1904());
+    assert!(!workbook_xml(&write(&book)).contains("date1904"));
+}
+
+#[test]
+fn date1904_survives_write_and_read() {
+    let mut book = umya_spreadsheet::new_file();
+    book.set_date1904(true);
+    let bytes = write(&book);
+    assert!(workbook_xml(&bytes).contains(r#"date1904="1""#));
+
+    let reread = reader::xlsx::read_reader(Cursor::new(bytes), true).unwrap();
+    assert!(reread.date1904());
+
+    // and a second save keeps it: a 1904 workbook must not silently become a
+    // 1900 one, which would move every date back by 1,462 days
+    assert!(workbook_xml(&write(&reread)).contains(r#"date1904="1""#));
+}
+
+#[test]
+fn date1904_true_spelling_is_read() {
+    let mut book = umya_spreadsheet::new_file();
+    book.set_date1904(true);
+    let bytes = write(&book);
+
+    // rewrite the attribute as xsd:boolean "true", which is also valid
+    let mut archive = ZipArchive::new(Cursor::new(bytes)).unwrap();
+    let mut out = zip::ZipWriter::new(Cursor::new(Vec::new()));
+    for i in 0..archive.len() {
+        let mut entry = archive.by_index(i).unwrap();
+        let name = entry.name().to_string();
+        let mut data = Vec::new();
+        entry.read_to_end(&mut data).unwrap();
+        if name == "xl/workbook.xml" {
+            data = String::from_utf8(data)
+                .unwrap()
+                .replace(r#"date1904="1""#, r#"date1904="true""#)
+                .into_bytes();
+        }
+        out.start_file(name, zip::write::SimpleFileOptions::default())
+            .unwrap();
+        std::io::Write::write_all(&mut out, &data).unwrap();
+    }
+    let bytes = out.finish().unwrap().into_inner();
+
+    let reread = reader::xlsx::read_reader(Cursor::new(bytes), true).unwrap();
+    assert!(reread.date1904());
+}