Create parition info parsing library

to be used both here (when trying to find the partition UUID using a
label) and on the kairos side when updating the file after calling
kcrypt to encrypt a partition (which causes the UUID to change).

Signed-off-by: Dimitris Karakasilis <dimitris@karakasilis.me>

pkg/partition_info/partition_info.go

@@ -0,0 +1,59 @@
+package partition_info
+
+import (
+	"io/ioutil"
+	"strings"
+
+	"github.com/pkg/errors"
+	"gopkg.in/yaml.v3"
+)
+
+// PartitionInfo maps a partition label to a partition UUID.
+// It's used in order to be able to ask the kcrypt-challenger for the passphrase
+// using the partition label, even when the label is not accessible (e.g. before
+// decrypting the partition). The UUID can be used to lookup the partition label
+// and make the request.
+type PartitionInfo map[string]string
+
+// UpdatePartitionLabelMapping takes partition information as a string argument
+// the the form: `label:name:uuid` (that's what the `kcrypt encrypt` command returns
+// on success. This function stores it in the PartitionInfoFile yaml file for
+// later use.
+func UpdatePartitionLabelMapping(partitionData, file string) error {
+	partitionInfo, err := ParsePartitionInfoFile(file)
+	if err != nil {
+		return err
+	}
+
+	parts := strings.Split(partitionData, ":")
+	partitionInfo[parts[0]] = parts[2]
+
+	return UpdatePartitionInfoFile(partitionInfo, file)
+}
+
+func ParsePartitionInfoFile(file string) (PartitionInfo, error) {
+	var result PartitionInfo
+
+	yamlFile, err := ioutil.ReadFile(file)
+	if err != nil {
+		return result, errors.Wrap(err, "reading the partition info file")
+	}
+	err = yaml.Unmarshal(yamlFile, &result)
+	if err != nil {
+		return result, errors.Wrap(err, "unmarshalling partition info file")
+	}
+
+	return result, nil
+}
+
+func UpdatePartitionInfoFile(partitionInfo PartitionInfo, file string) error {
+	data, err := yaml.Marshal(&partitionInfo)
+	if err != nil {
+		return errors.Wrap(err, "marshalling the new partition info to yaml")
+	}
+	err = ioutil.WriteFile(file, data, 0)
+	if err != nil {
+		return errors.Wrap(err, "writing back the partition info file")
+	}
+	return nil
+}