headers: fail Build on missing native exports and assert MI/COM layouts (#2739)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/headers/lazyproc/lazyproc_test.go

@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: Apache-2.0
+//
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+
+package lazyproc_test
+
+import (
+	"errors"
+	"strings"
+	"testing"
+
+	"github.com/prometheus-community/windows_exporter/internal/headers/lazyproc"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/windows"
+)
+
+func TestFind(t *testing.T) {
+	t.Parallel()
+
+	kernel32 := windows.NewLazySystemDLL("kernel32.dll")
+	missingDLL := windows.NewLazySystemDLL("windows_exporter_missing.dll")
+
+	t.Run("all present", func(t *testing.T) {
+		t.Parallel()
+
+		require.NoError(t, lazyproc.Find(kernel32, kernel32.NewProc("GetTickCount64"), kernel32.NewProc("GetSystemInfo")))
+		require.NoError(t, lazyproc.Find(kernel32))
+	})
+
+	t.Run("missing export", func(t *testing.T) {
+		t.Parallel()
+
+		err := lazyproc.Find(kernel32, kernel32.NewProc("GetTickCount64"), kernel32.NewProc("WindowsExporterMissingExport"))
+		require.ErrorIs(t, err, errors.ErrUnsupported)
+		require.ErrorContains(t, err, "WindowsExporterMissingExport")
+	})
+
+	t.Run("missing DLL is reported once", func(t *testing.T) {
+		t.Parallel()
+
+		err := lazyproc.Find(missingDLL, missingDLL.NewProc("A"), missingDLL.NewProc("B"))
+		require.ErrorIs(t, err, errors.ErrUnsupported)
+		require.Equal(t, 1, strings.Count(err.Error(), "windows_exporter_missing.dll"), err.Error())
+
+		// The loader error stays text only, so the error has a single cause.
+		require.NotErrorIs(t, err, windows.ERROR_MOD_NOT_FOUND)
+
+		var lazyErr *lazyproc.Error
+
+		require.ErrorAs(t, err, &lazyErr)
+		require.Equal(t, "windows_exporter_missing.dll", lazyErr.DLL)
+		require.Len(t, lazyErr.Missing, 1)
+	})
+
+	t.Run("Once", func(t *testing.T) {
+		t.Parallel()
+
+		load := lazyproc.Once(kernel32, kernel32.NewProc("WindowsExporterMissingExport"))
+
+		first := load()
+		require.ErrorIs(t, first, errors.ErrUnsupported)
+		// The cached error is returned again.
+		require.Same(t, first, load())
+	})
+}