feat: Added option to prevent rebuild of the image (#1970)

src/image.sh

@@ -951,3 +951,65 @@ EOF
 
   return 0
 }
+
+extractBootImage() {
+
+  local iso="$1"
+  local dir="$2"
+  local desc="$3"
+
+  local tmp="$TMP/boot-images"
+  local image="$tmp/eltorito_img1_bios.img"
+  local max_size=$((32 * 1024 * 1024))
+
+  ETFS="boot.img"
+  [ -f "$dir/$ETFS" ] && [ -s "$dir/$ETFS" ] && return 0
+
+  rm -f "$dir/$ETFS" || return 1
+  rm -rf "$tmp" || return 1
+
+  LC_ALL=C xorriso \
+      -no_rc \
+      -osirrox on \
+      -indev "$iso" \
+      -extract_boot_images "$tmp" >/dev/null 2>&1 || {
+    local rc=$?
+    rm -rf "$tmp" || true
+
+    (( rc > 128 )) && exit "$rc"
+
+    error "Failed to extract boot image from $desc ISO!"
+    return 1
+  }
+
+  if [ ! -s "$image" ]; then
+    rm -rf "$tmp" || true
+    error "Failed to locate BIOS boot image in $desc ISO!"
+    return 1
+  fi
+
+  local size
+
+  if ! size=$(stat -c%s "$image"); then
+    rm -rf "$tmp" || true
+    error "Failed to determine BIOS boot image size in $desc ISO!"
+    return 1
+  fi
+
+  if (( size > max_size )); then
+    rm -rf "$tmp" || true
+    error "The BIOS boot image in $desc ISO exceeds 32 MB!"
+    return 1
+  fi
+
+  if ! mv -f "$image" "$dir/$ETFS"; then
+    rm -rf "$tmp" || true
+    error "Failed to save boot image from $desc ISO!"
+    return 1
+  fi
+
+  rm -rf "$tmp" || return 1
+  return 0
+}
+
+return 0