blueprints: fix filesystem customizations to allow toml Undecoded()

The current toml filesytem customizations will decode a
`FilesystemCustomization` as a map[string]interface{}. This means
that the underlying toml engine will not konw what keys inside the
map are decoded and which are not decoded. This lead to the issue
osbuild/bootc-image-builder#655 in
`bootc-image-builder` where we check if we have unencoded entries
and if so error (in this case incorrectly).

This commit fixes the issue by moving the toml decoding from the
struct/map[string]interface{} to primitive types. It's a bit
ugly as is (partly because of the limited go type system) but
with that the tests pass and len(meta.Undecoded()) is the expected
zero.

I opened BurntSushi/toml#425 to see if
there is another way via a custom unmarshaler.

pkg/blueprint/customizations.go

@@ -301,7 +301,7 @@ func (c *Customizations) GetFilesystemsMinSize() uint64 {
 	}
 	var agg uint64
 	for _, m := range c.Filesystem {
-		agg += m.MinSize
+		agg += uint64(m.MinSize)
 	}
 	// This ensures that file system customization `size` is a multiple of
 	// sector size (512)

pkg/blueprint/filesystem_customizations.go

@@ -10,31 +10,36 @@ import (
 )
 
 type FilesystemCustomization struct {
-	Mountpoint string `json:"mountpoint,omitempty" toml:"mountpoint,omitempty"`
-	MinSize    uint64 `json:"minsize,omitempty" toml:"minsize,omitempty"`
+	Mountpoint Mountpoint `json:"mountpoint,omitempty" toml:"mountpoint,omitempty"`
+	MinSize    MinSize    `json:"minsize,omitempty" toml:"minsize,omitempty"`
 }
 
-func (fsc *FilesystemCustomization) UnmarshalTOML(data interface{}) error {
-	d, _ := data.(map[string]interface{})
+type Mountpoint string
 
-	switch d["mountpoint"].(type) {
+func (mt *Mountpoint) UnmarshalTOML(d interface{}) error {
+	switch d.(type) {
 	case string:
-		fsc.Mountpoint = d["mountpoint"].(string)
+		*mt = Mountpoint(d.(string))
 	default:
-		return fmt.Errorf("TOML unmarshal: mountpoint must be string, got %v of type %T", d["mountpoint"], d["mountpoint"])
+		return fmt.Errorf("TOML unmarshal: mountpoint must be string, got %v of type %T", d, d)
 	}
+	return nil
+}
 
-	switch d["minsize"].(type) {
+type MinSize uint64
+
+func (ms *MinSize) UnmarshalTOML(d interface{}) error {
+	switch d.(type) {
 	case int64:
-		fsc.MinSize = uint64(d["minsize"].(int64))
+		*ms = MinSize(d.(int64))
 	case string:
-		minSize, err := common.DataSizeToUint64(d["minsize"].(string))
+		minSize, err := common.DataSizeToUint64(d.(string))
 		if err != nil {
 			return fmt.Errorf("TOML unmarshal: minsize is not valid filesystem size (%w)", err)
 		}
-		fsc.MinSize = minSize
+		*ms = MinSize(minSize)
 	default:
-		return fmt.Errorf("TOML unmarshal: minsize must be integer or string, got %v of type %T", d["minsize"], d["minsize"])
+		return fmt.Errorf("TOML unmarshal: minsize must be integer or string, got %v of type %T", d, d)
 	}
 
 	return nil
@@ -49,21 +54,21 @@ func (fsc *FilesystemCustomization) UnmarshalJSON(data []byte) error {
 
 	switch d["mountpoint"].(type) {
 	case string:
-		fsc.Mountpoint = d["mountpoint"].(string)
+		fsc.Mountpoint = Mountpoint(d["mountpoint"].(string))
 	default:
 		return fmt.Errorf("JSON unmarshal: mountpoint must be string, got %v of type %T", d["mountpoint"], d["mountpoint"])
 	}
 
 	// The JSON specification only mentions float64 and Go defaults to it: https://go.dev/blog/json
 	switch d["minsize"].(type) {
 	case float64:
-		fsc.MinSize = uint64(d["minsize"].(float64))
+		fsc.MinSize = MinSize(d["minsize"].(float64))
 	case string:
 		minSize, err := common.DataSizeToUint64(d["minsize"].(string))
 		if err != nil {
 			return fmt.Errorf("JSON unmarshal: minsize is not valid filesystem size (%w)", err)
 		}
-		fsc.MinSize = minSize
+		fsc.MinSize = MinSize(minSize)
 	default:
 		return fmt.Errorf("JSON unmarshal: minsize must be float64 number or string, got %v of type %T", d["minsize"], d["minsize"])
 	}
@@ -75,7 +80,7 @@ func (fsc *FilesystemCustomization) UnmarshalJSON(data []byte) error {
 func CheckMountpointsPolicy(mountpoints []FilesystemCustomization, mountpointAllowList *pathpolicy.PathPolicies) error {
 	var errs []error
 	for _, m := range mountpoints {
-		if err := mountpointAllowList.Check(m.Mountpoint); err != nil {
+		if err := mountpointAllowList.Check(string(m.Mountpoint)); err != nil {
 			errs = append(errs, err)
 		}
 	}

pkg/blueprint/filesystem_customizations_test.go

@@ -120,3 +120,19 @@ path "/boot/" must be canonical`
 	err := blueprint.CheckMountpointsPolicy(mps, policy)
 	assert.EqualError(t, err, expectedErr)
 }
+
+func TestReadConfigNoUndecoded(t *testing.T) {
+	testTOML := `
+mountpoint = "/foo"
+minsize = 1000
+`
+
+	var fsc blueprint.FilesystemCustomization
+	meta, err := toml.Decode(testTOML, &fsc)
+	assert.NoError(t, err)
+	assert.Equal(t, blueprint.FilesystemCustomization{
+		Mountpoint: "/foo",
+		MinSize:    1000,
+	}, fsc)
+	assert.Equal(t, 0, len(meta.Undecoded()))
+}