distro: use the new function in GetHostDistroName

The function now works even without /etc/os-release (which is rare
but possible). The function now also no longer panics if ID or
VERSION_ID aren't set. Some tests were added to cover everything.

pkg/distro/host.go

@@ -10,17 +10,22 @@ import (
 	"strings"
 )
 
+// variable so that it can be overridden in tests
+var getHostDistroNameTree = "/"
+
 // GetHostDistroName returns the name of the host distribution, such as
 // "fedora-32" or "rhel-8.2". It does so by reading the /etc/os-release file.
 func GetHostDistroName() (string, error) {
-	f, err := os.Open("/etc/os-release")
+	osrelease, err := ReadOSReleaseFromTree(getHostDistroNameTree)
 	if err != nil {
-		return "", err
+		return "", fmt.Errorf("cannot get the host distro name: %w", err)
 	}
-	defer f.Close()
-	osrelease, err := readOSRelease(f)
-	if err != nil {
-		return "", err
+
+	if _, ok := osrelease["ID"]; !ok {
+		return "", errors.New("cannot get the host distro name: missing ID field in os-release")
+	}
+	if _, ok := osrelease["VERSION_ID"]; !ok {
+		return "", errors.New("cannot get the host distro name: missing VERSION_ID field in os-release")
 	}
 
 	name := osrelease["ID"] + "-" + osrelease["VERSION_ID"]

pkg/distro/host_test.go

@@ -10,6 +10,46 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestGetHostDistroName(t *testing.T) {
+	backup := getHostDistroNameTree
+	defer func() { getHostDistroNameTree = backup }()
+	getHostDistroNameTree = t.TempDir()
+
+	require.NoError(t, os.MkdirAll(path.Join(getHostDistroNameTree, "etc"), 0755))
+	require.NoError(t,
+		os.WriteFile(path.Join(getHostDistroNameTree, "etc/os-release"), []byte("ID=toucanOS\nVERSION_ID=42\n"), 0600),
+	)
+
+	name, err := GetHostDistroName()
+	require.NoError(t, err)
+	require.Equal(t, "toucanOS-42", name)
+}
+func TestGetHostDistroNameUnhappy(t *testing.T) {
+	backup := getHostDistroNameTree
+	defer func() { getHostDistroNameTree = backup }()
+	getHostDistroNameTree = t.TempDir()
+
+	require.NoError(t, os.MkdirAll(path.Join(getHostDistroNameTree, "etc"), 0755))
+
+	// no file at all
+	_, err := GetHostDistroName()
+	require.ErrorContains(t, err, "cannot get the host distro name: failed to read os-release")
+
+	// missing ID
+	require.NoError(t,
+		os.WriteFile(path.Join(getHostDistroNameTree, "etc/os-release"), []byte("VERSION_ID=toucanOS\n"), 0600),
+	)
+	_, err = GetHostDistroName()
+	require.ErrorContains(t, err, "cannot get the host distro name: missing ID field")
+
+	// missing VERSION_ID
+	require.NoError(t,
+		os.WriteFile(path.Join(getHostDistroNameTree, "etc/os-release"), []byte("ID=42\n"), 0600),
+	)
+	_, err = GetHostDistroName()
+	require.ErrorContains(t, err, "cannot get the host distro name: missing VERSION_ID field")
+}
+
 func TestOSRelease(t *testing.T) {
 	var cases = []struct {
 		Input     string