testing remove_headers

- remove_headers_removes_simple_page_number - passes
- remove_headers_removes_word_plus_page_number - fails

The second test hist the mechanism WITH the first-occurrence
however, that seems like a bug... why should "page #" ever
be kept?

Author: ultrasaurus

tests/test_remove_headers.rs

@@ -0,0 +1,188 @@
+//! Tests for `remove_headers` page-number
+//! detector, which uses two purely structural signals — position (top or
+//! bottom margin band) and shape (a short number, or a number that
+//! varies page to page) — with no concept of "page number" beyond that.
+
+use pdf_oxide::PdfDocument;
+
+// ---------------- test helper: build_pdf_with_page_extras -------------------
+//
+// two fn used only by build_pdf_with_page_extras write one object each,
+// recording its offset as they go:
+// - `buf`      the buffer we're writing into
+// - `off[id]`  start of object definition
+
+// -- write a plain dictionary object --
+fn obj(buf: &mut Vec<u8>, off: &mut [usize], id: usize, body: &str) {
+    off[id] = buf.len();
+    buf.extend_from_slice(format!("{id} 0 obj\n{body}\nendobj\n").as_bytes());
+}
+
+// -- write a `stream` object - used here for page content --
+fn stream(buf: &mut Vec<u8>, off: &mut [usize], id: usize, data: &[u8]) {
+    off[id] = buf.len();
+    buf.extend_from_slice(format!("{id} 0 obj\n<< /Length {} >>\nstream\n", data.len()).as_bytes());
+    buf.extend_from_slice(data);
+    buf.extend_from_slice(b"\nendstream\nendobj\n");
+}
+
+/// Minimal single-page-content PDF builder: N pages, each with a body
+/// paragraph plus arbitrary extra content-stream text supplied per page.
+fn build_pdf_with_page_extras(
+    page_count: usize,
+    extra_per_page: impl Fn(usize) -> String,
+) -> Vec<u8> {
+    // buffer for the PDF we're building
+    let mut buf: Vec<u8> = Vec::new();
+
+    // `off[N]` = byte offset where object N's bytes start, filled in as
+    // each object is written below. `xref_off` (further down) separately
+    // records where the xref table itself starts.
+    let mut off = vec![0usize; 4 + page_count * 2];
+
+    // PDF File header
+    buf.extend_from_slice(b"%PDF-1.7\n%\xE2\xE3\xCF\xD3\n");
+
+    // Catalog
+    obj(&mut buf, &mut off, 1, "<< /Type /Catalog /Pages 2 0 R >>");
+
+    // Pages tree root
+    // Build the /Kids array value ahead of time: "5 0 R 7 0 R 9 0 R ..."
+    // — one indirect reference per page object we're about to create.
+    // (Page objects are 5, 7, 9, ... because each page also needs a
+    // content-stream object right before it: 4, 6, 8, ... — see the loop
+    // below.)
+    let kids: String = (0..page_count)
+        .map(|i| format!("{} 0 R", 5 + i * 2))
+        .collect::<Vec<_>>()
+        .join(" ");
+    obj(
+        &mut buf,
+        &mut off,
+        2,
+        &format!("<< /Type /Pages /Kids [{kids}] /Count {page_count} >>"),
+    );
+
+    // Font resource
+    obj(
+        &mut buf,
+        &mut off,
+        3,
+        "<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >>",
+    );
+
+    // --- One content stream + one page object, per page ---
+    for i in 0..page_count {
+        let content_id = 4 + i * 2; // 4, 6, 8, ...
+        let page_id = 5 + i * 2; // 5, 7, 9, ...
+
+        // text object per page + whatever the test wants to insert
+        let content = format!(
+            "BT /F1 12 Tf 1 0 0 1 72 400 Tm (Body text placeholder) Tj ET\n{}",
+            extra_per_page(i)
+        );
+        stream(&mut buf, &mut off, content_id, content.as_bytes());
+
+        // Page object:
+        // physical size - `/MediaBox`, in points `[0 0 612 792]` is US Letter
+        // resources it can reference by name - `/Resources`
+        // -  just our one font as `/F1`
+        // object w/ drawing instructions `/Contents` with content-stream object
+        obj(
+            &mut buf,
+            &mut off,
+            page_id,
+            &format!(
+                "<< /Type /Page /Parent 2 0 R /MediaBox [0 0 612 792] \
+                 /Resources << /Font << /F1 3 0 R >> >> /Contents {content_id} 0 R >>"
+            ),
+        );
+    }
+
+    // Cross-reference table - `xref_off`
+    // flat table mapping object number -> byte offset
+    // records where THIS table itself starts (needed for the trailer).
+    let xref_off = buf.len();
+    let total_objs = off.len();
+    buf.extend_from_slice(format!("xref\n0 {}\n", total_objs).as_bytes());
+
+    // fixed, required first entry marking object 0 as "free"
+    buf.extend_from_slice(b"0000000000 65535 f \n");
+
+    // one `NNNNNNNNNN 00000 n` line per real object, `n` meaning "in use",
+    // giving its 10-digit zero-padded byte offset
+    for offset in &off[1..] {
+        buf.extend_from_slice(format!("{:010} 00000 n \n", offset).as_bytes());
+    }
+
+    // Trailer
+    buf.extend_from_slice(
+        format!(
+            "trailer\n<< /Size {} /Root 1 0 R >>\nstartxref\n{}\n%%EOF\n",
+            total_objs, xref_off
+        )
+        .as_bytes(),
+    );
+    buf
+}
+
+/// The simplest, most basic case: a bare page number ("1", "2", "3", ...)
+/// alone on its own line in the header band, changing every page — the
+/// textbook definition of a page number. `is_bare_page_number_text` marks
+/// this unconditionally per page (isolated + short + digits-only), with
+/// no cross-page signature lookup and no first-occurrence exemption
+/// involved, so this is core, expected behavior that should already work
+/// correctly on `main`.
+#[test]
+fn remove_headers_removes_simple_page_number() {
+    let bytes = build_pdf_with_page_extras(5, |i| {
+        format!("BT /F1 10 Tf 1 0 0 1 300 760 Tm ({}) Tj ET\n", i + 1)
+    });
+    let doc = PdfDocument::from_bytes(bytes).unwrap();
+    doc.remove_headers(0.5).unwrap();
+
+    for page in 0..5 {
+        let text = doc.extract_text(page).unwrap();
+        assert!(
+            text.contains("Body text placeholder"),
+            "page {page}: body wrongly removed: {text:?}"
+        );
+        let page_number = format!("{}", page + 1);
+        assert!(
+            !text.contains(&page_number),
+            "page {page}: page number {page_number:?} should have been removed: {text:?}"
+        );
+    }
+}
+
+/// One step up from a bare digit: "page 1", "page 2", ... — not digits-only
+/// (it has letters too), so `is_bare_page_number_text` doesn't apply at
+/// all. This has to go through the cross-page signature detector instead:
+/// `normalize_artifact_signature` turns "page 1" into "page #", sees that
+/// shape recur across pages with the digit changing, and flags it as a
+/// page number that way.
+#[test]
+fn remove_headers_removes_word_plus_page_number() {
+    let bytes = build_pdf_with_page_extras(5, |i| {
+        format!("BT /F1 10 Tf 1 0 0 1 280 760 Tm (page {}) Tj ET\n", i + 1)
+    });
+    let doc = PdfDocument::from_bytes(bytes).unwrap();
+    doc.remove_headers(0.5).unwrap();
+
+    for page in 0..5 {
+        let text = doc.extract_text(page).unwrap();
+        assert!(
+            text.contains("Body text placeholder"),
+            "page {page}: body wrongly removed: {text:?}"
+        );
+    }
+
+    for page in 0..5 {
+        let text = doc.extract_text(page).unwrap();
+        let marker = format!("page {}", page + 1);
+        assert!(
+            !text.contains(&marker),
+            "page {page}: marker {marker:?} should have been removed: {text:?}"
+        );
+    }
+}