Update iso-prototype.py

src/iso-prototype.py

@@ -577,23 +577,55 @@ def sync_tree(iso, tree: Path, logical_root: PurePosixPath) -> None:
             add_file_all_namespaces(iso, root_path / name, logical)
 
 
-def rebuild_windows_eltorito(iso, tree: Path) -> None:
+def eltorito_platforms(path: Path) -> tuple[bool, bool]:
+    """Return the BIOS and UEFI platforms present in the source catalog."""
+    _descriptors, catalog_lba = parse_volume_descriptors(path)
+    catalog = parse_boot_catalog(path, catalog_lba)
+
+    if catalog is None:
+        return False, False
+
+    platforms = {
+        entry["platform_id"]
+        for entry in catalog["entries"]
+        if entry["kind"] == "boot_entry"
+    }
+
+    return 0x00 in platforms, 0xEF in platforms
+
+
+def rebuild_windows_eltorito(
+    iso,
+    tree: Path,
+    *,
+    include_bios: bool,
+    include_uefi: bool,
+) -> None:
     """Replace imported hidden boot entries with complete extracted images.
 
     Microsoft installation media commonly stores the El Torito boot images as
-    hidden extents.  When PyCdlib opens such an ISO, the catalog's 512-byte load
+    hidden extents. When PyCdlib opens such an ISO, the catalog's 512-byte load
     count is not enough to recover the real size of the hidden UEFI FAT image.
     Writing the imported entry back can therefore truncate it to one sector.
 
-    Rebuild the catalog from the files extracted by the normal Windows image
-    preparation flow instead.  Short root-level ISO9660 names are intentional:
-    the boot images only need stable Directory Records for PyCdlib and do not
-    need to be exposed through the UDF namespace used by Windows Setup.
+    Rebuild only the platforms that existed in the original ISO. This preserves
+    BIOS-only media such as Windows 7 x86 while retaining both BIOS and UEFI on
+    modern hybrid installation media.
     """
+    if not include_bios and not include_uefi:
+        return
+
     bios_source = tree / "boot/etfsboot.com"
     uefi_source = tree / "efi/microsoft/boot/efisys_noprompt.bin"
 
-    missing = [str(path) for path in (bios_source, uefi_source) if not path.is_file()]
+    missing: list[str] = []
+
+    if include_bios and not bios_source.is_file():
+        missing.append(str(bios_source))
+
+    if include_uefi and not uefi_source.is_file():
+        missing.append(str(uefi_source))
+
     if missing:
         raise PrototypeError(
             "Cannot rebuild Windows El Torito catalog; missing boot image(s): "
@@ -604,45 +636,60 @@ def rebuild_windows_eltorito(iso, tree: Path) -> None:
     uefi_iso_path = "/PYUEFI.BIN;1"
 
     print("Rebuilding El Torito catalog from extracted boot images:")
-    print(f"  BIOS: {bios_source} ({bios_source.stat().st_size} bytes)")
-    print(f"  UEFI: {uefi_source} ({uefi_source.stat().st_size} bytes)")
+
+    if include_bios:
+        print(f"  BIOS: {bios_source} ({bios_source.stat().st_size} bytes)")
+
+    if include_uefi:
+        print(f"  UEFI: {uefi_source} ({uefi_source.stat().st_size} bytes)")
 
     # These private root-level records avoid depending on the source ISO's very
-    # small ISO9660 tree.  The original Microsoft files remain available via UDF.
-    for iso_path in (bios_iso_path, uefi_iso_path):
+    # small ISO9660 tree. The original Microsoft files remain available via UDF.
+    required_records: list[tuple[Path, str]] = []
+
+    if include_bios:
+        required_records.append((bios_source, bios_iso_path))
+
+    if include_uefi:
+        required_records.append((uefi_source, uefi_iso_path))
+
+    for source, iso_path in required_records:
         try:
             iso.get_record(iso_path=iso_path)
         except Exception:
-            continue
-        iso.rm_file(iso_path=iso_path)
+            pass
+        else:
+            iso.rm_file(iso_path=iso_path)
 
-    iso.add_file(str(bios_source), iso_path=bios_iso_path)
-    iso.add_file(str(uefi_source), iso_path=uefi_iso_path)
+        iso.add_file(str(source), iso_path=iso_path)
 
-    # Match the production genisoimage settings: no-emulation BIOS boot, eight
-    # 512-byte sectors loaded, and a boot info table patched into etfsboot.com.
-    iso.add_eltorito(
-        bios_iso_path,
-        boot_load_size=8,
-        platform_id=0x00,
-        boot_info_table=True,
-        media_name="noemul",
-        bootable=True,
-        boot_load_seg=0,
-    )
-
-    # A second add_eltorito() call creates an alternate catalog section.  Leaving
-    # boot_load_size unset makes PyCdlib use the complete EFI FAT image rather
-    # than the misleading one-sector count imported from Microsoft media.
-    iso.add_eltorito(
-        uefi_iso_path,
-        platform_id=0xEF,
-        efi=True,
-        media_name="noemul",
-        bootable=True,
-        boot_load_seg=0,
-    )
+    if include_bios:
+        # Match the production genisoimage settings: no-emulation BIOS boot,
+        # eight 512-byte sectors loaded, and a boot info table patched into
+        # etfsboot.com.
+        iso.add_eltorito(
+            bios_iso_path,
+            boot_load_size=8,
+            platform_id=0x00,
+            boot_info_table=True,
+            media_name="noemul",
+            bootable=True,
+            boot_load_seg=0,
+        )
 
+    if include_uefi:
+        # A second add_eltorito() call creates an alternate catalog section.
+        # Leaving boot_load_size unset makes PyCdlib use the complete EFI FAT
+        # image rather than the misleading one-sector count imported from
+        # Microsoft media.
+        iso.add_eltorito(
+            uefi_iso_path,
+            platform_id=0xEF,
+            efi=True,
+            media_name="noemul",
+            bootable=True,
+            boot_load_seg=0,
+        )
 
 def build_pycdlib(args: argparse.Namespace) -> None:
     try:
@@ -663,6 +710,13 @@ def build_pycdlib(args: argparse.Namespace) -> None:
         print(f"Opening source ISO: {source}")
         iso.open(str(source))
 
+        include_bios, include_uefi = eltorito_platforms(source)
+        print(
+            "Imported El Torito platforms:"
+            f" BIOS={'yes' if include_bios else 'no'},"
+            f" UEFI={'yes' if include_uefi else 'no'}"
+        )
+
         # Microsoft media may import hidden El Torito records with an invalid
         # index_in_parent. The Dockerfile applies a temporary PyCdlib fix that
         # recovers the real child index, allowing this removal to succeed.
@@ -679,7 +733,12 @@ def build_pycdlib(args: argparse.Namespace) -> None:
             print(f"Synchronizing tree: {logical}")
             sync_tree(iso, tree, logical)
 
-        rebuild_windows_eltorito(iso, tree)
+        rebuild_windows_eltorito(
+            iso,
+            tree,
+            include_bios=include_bios,
+            include_uefi=include_uefi,
+        )
 
         print("Checking PyCdlib consistency...")
         iso.force_consistency()