fix: detect JPEG XL images

lua/image/utils/magic.lua

@@ -15,6 +15,11 @@ local image_signatures = {
   pdf = "%PDF",
 }
 
+local jxl_signatures = {
+  "\xFF\x0A",
+  "\x00\x00\x00\x0CJXL \x0D\x0A\x87\x0A",
+}
+
 local function read_file_header(file, num_bytes)
   if not file then return nil end
   local current_pos = file:seek()
@@ -68,6 +73,13 @@ M.detect_format = function(path)
     return nil
   end
 
+  for _, signature in ipairs(jxl_signatures) do
+    if check_signature_match(header, "jxl", signature) then
+      file:close()
+      return "jxl"
+    end
+  end
+
   for format, signature in pairs(image_signatures) do
     if check_signature_match(header, format, signature) then
       if format == "jpeg" then

tests/utils/magic_spec.lua

@@ -52,6 +52,23 @@ describe("magic", function()
     end)
   end
 
+  it("detects JPEG XL codestream and container signatures", function()
+    local signatures = {
+      "\xFF\x0A",
+      "\x00\x00\x00\x0CJXL \x0D\x0A\x87\x0A",
+    }
+
+    for _, signature in ipairs(signatures) do
+      local path = vim.fn.tempname()
+      local file = assert(io.open(path, "wb"))
+      file:write(signature)
+      file:close()
+      assert.are.same("jxl", detect_format(path))
+      assert.is_true(require("image/utils/magic").is_image(path))
+      vim.fn.delete(path)
+    end
+  end)
+
   it("returns nil for non-existent files", function()
     assert.is_nil(detect_format("tests/test_data/nonexistent.png"))
   end)