Fail Web Page export on sheets taller than its row limit instead of dropping cells (#514)

crates/engine/src/io.rs

@@ -167,7 +167,7 @@ pub fn save_bytes(wb: &Workbook, path: &str) -> Result<Vec<u8>> {
         FileKind::Csv => Ok(wb.sheet(sheet).map(|sh| csv(wb, sh, wb.csv_delimiter.unwrap_or(b','))).unwrap_or_default()),
         FileKind::Tsv => Ok(wb.sheet(sheet).map(|sh| csv(wb, sh, b'\t')).unwrap_or_default()),
         FileKind::Json => serde_json::to_vec_pretty(wb).map_err(|e| EngineError::Other(e.to_string())),
-        FileKind::Html => Ok(to_html(wb, sheet).into_bytes()),
+        FileKind::Html => to_html(wb, sheet).map(String::into_bytes),
     }
 }
 
@@ -285,9 +285,12 @@ impl std::fmt::Write for ClipboardHtml {
     }
 }
 
+/// Most rows Save as Web Page writes. A sheet whose used range is taller fails instead of losing cells.
+const HTML_EXPORT_MAX_ROWS: u32 = 100_001;
+
 /// A sheet as a standalone HTML table (Save as Web Page).
-pub fn to_html(wb: &Workbook, sheet: usize) -> String {
-    let Some(sh) = wb.sheet(sheet) else { return String::new() };
+pub fn to_html(wb: &Workbook, sheet: usize) -> Result<String> {
+    let Some(sh) = wb.sheet(sheet) else { return Ok(String::new()) };
     let mut out = String::new();
     let _ = write!(
         out,
@@ -295,7 +298,13 @@ pub fn to_html(wb: &Workbook, sheet: usize) -> String {
         esc(&sh.name)
     );
     if let Some(r) = sh.used_range() {
-        for row in r.start.row..=r.end.row.min(r.start.row + 100_000) {
+        if r.height() > HTML_EXPORT_MAX_ROWS {
+            return Err(EngineError::Other(format!(
+                "the sheet is too tall for a web page ({} rows, at most {HTML_EXPORT_MAX_ROWS}). Save as .xlsx or CSV instead.",
+                r.height()
+            )));
+        }
+        for row in r.start.row..=r.end.row {
             if sh.is_row_hidden(row) {
                 continue;
             }
@@ -318,7 +327,7 @@ pub fn to_html(wb: &Workbook, sheet: usize) -> String {
         }
     }
     out.push_str("</table></body></html>");
-    out
+    Ok(out)
 }
 
 #[cfg(not(target_arch = "wasm32"))]
@@ -418,6 +427,20 @@ pub fn image_size(data: &[u8]) -> Option<(u32, u32)> {
 mod tests {
     use super::*;
 
+    #[test]
+    fn html_export_fails_instead_of_dropping_cells_past_the_row_limit() {
+        let mut wb = Workbook::new();
+        let sh = wb.sheet_mut(0).unwrap();
+        sh.set_value(CellRef::new(0, 0), gridcraft_core::Value::text("near"));
+        sh.set_value(CellRef::new(149_999, 0), gridcraft_core::Value::text("far"));
+        assert!(save_bytes(&wb, "book.html").is_err());
+        let sh = wb.sheet_mut(0).unwrap();
+        sh.remove_cell(CellRef::new(149_999, 0));
+        sh.set_value(CellRef::new(100_000, 0), gridcraft_core::Value::text("far"));
+        let html = String::from_utf8(save_bytes(&wb, "book.html").unwrap()).unwrap();
+        assert!(html.contains(">near</td>") && html.contains(">far</td>"));
+    }
+
     #[test]
     fn macros_are_saved_only_into_xlsm() {
         let mut wb = Workbook::new();

docs/file-format-parity.md

@@ -40,7 +40,7 @@ support comes from `crates/engine/src/io.rs` (`FileKind`), `crates/xlsx/src` and
 | `.txt` tab-delimited, Unicode text | R/W | yes (`.txt`, `.tsv`, `.tab`) | yes (displayed values) | Text Import Wizard options partly via Text to Columns |
 | `.prn` formatted text (space-delimited) | R/W | no | no | |
 | `.dif`, `.slk` (SYLK) | R/W | no | no | Small, legacy |
-| `.htm` / `.html` web page | R/W (Windows) | yes, via Get Data ▸ From HTML | yes (one sheet as a table) | Formatting not exported |
+| `.htm` / `.html` web page | R/W (Windows) | yes, via Get Data ▸ From HTML | yes (one sheet as a table; a used range taller than 100,001 rows fails with an error instead of being cut short) | Formatting not exported |
 | `.mht` / `.mhtml` single-file web page | R/W (Windows) | no | no | |
 | `.json` | via Power Query | GridCraft's own workbook JSON (debug) and JSON import | GridCraft JSON | Not Power Query's JSON shaping; notes and hyperlinks break export (#126) |
 | `.xml` with XML maps | Developer ▸ Import/Export | no | no | |