hyperv: Replace SplitLines with FirstLine

In the hyperv code, there are many occurrences of
resp := os.SplitLines(stdout)
if resp[0] == ...

This does not check if `resp` is empty before trying to reference it,
which recently triggered a panic in crc (
#3764 )

This code adds a `FirstLine` helper which will return an empty string
if stdout is "".

This should fix #3764

pkg/drivers/hyperv/hyperv_windows.go

@@ -94,18 +94,18 @@ func (d *Driver) GetState() (state.State, error) {
 		return state.Error, fmt.Errorf("Failed to find the VM status: %v - %s", err, stderr)
 	}
 
-	resp := crcstrings.SplitLines(stdout)
-	if len(resp) < 1 {
+	resp := crcstrings.FirstLine(stdout)
+	if resp == "" {
 		return state.Error, fmt.Errorf("unexpected Hyper-V state %s", stdout)
 	}
 
-	switch resp[0] {
+	switch resp {
 	case "Starting", "Running", "Stopping":
 		return state.Running, nil
 	case "Off":
 		return state.Stopped, nil
 	default:
-		return state.Error, fmt.Errorf("unexpected Hyper-V state %s", resp[0])
+		return state.Error, fmt.Errorf("unexpected Hyper-V state %s", resp)
 	}
 }
 
@@ -398,12 +398,12 @@ func (d *Driver) GetIP() (string, error) {
 		return "", err
 	}
 
-	resp := crcstrings.SplitLines(stdout)
-	if len(resp) < 1 {
+	resp := crcstrings.FirstLine(stdout)
+	if resp == "" {
 		return "", fmt.Errorf("IP not found")
 	}
 
-	return resp[0], nil
+	return resp, nil
 }
 
 func (d *Driver) GetSharedDirs() ([]drivers.SharedDir, error) {

pkg/drivers/hyperv/powershell_windows.go

@@ -31,8 +31,8 @@ func hypervAvailable() error {
 		return err
 	}
 
-	resp := crcstrings.SplitLines(stdout)
-	if resp[0] != "Hyper-V" {
+	resp := crcstrings.FirstLine(stdout)
+	if resp != "Hyper-V" {
 		return ErrNotInstalled
 	}
 
@@ -62,8 +62,8 @@ func isHypervAdministrator() bool {
 		return false
 	}
 
-	resp := crcstrings.SplitLines(stdout)
-	return resp[0] == "True"
+	resp := crcstrings.FirstLine(stdout)
+	return resp == "True"
 }
 
 func isWindowsAdministrator() (bool, error) {
@@ -72,8 +72,8 @@ func isWindowsAdministrator() (bool, error) {
 		return false, err
 	}
 
-	resp := crcstrings.SplitLines(stdout)
-	return resp[0] == "True", nil
+	resp := crcstrings.FirstLine(stdout)
+	return resp == "True", nil
 }
 
 func quote(text string) string {

pkg/strings/strings.go

@@ -25,3 +25,12 @@ func SplitLines(input string) []string {
 
 	return output
 }
+
+func FirstLine(input string) string {
+	lines := SplitLines(input)
+	if len(lines) == 0 {
+		return ""
+	}
+
+	return lines[0]
+}

pkg/strings/strings_test.go

@@ -93,3 +93,46 @@ func TestSplitLines(t *testing.T) {
 		}
 	})
 }
+
+type firstLineTest struct {
+	input     string
+	firstLine string
+}
+
+var firstLineTests = map[string]firstLineTest{
+	"ThreeLines": {
+		input:     "line1\nline2\nline3\n",
+		firstLine: "line1",
+	},
+	"ThreeLinesNoFinalEOL": {
+		input:     "line1\nline2\nline3",
+		firstLine: "line1",
+	},
+	"WindowsEOL": {
+		input:     "line1\r\nline2\r\nline3\r\n",
+		firstLine: "line1",
+	},
+	"EmptyString": {
+		input:     "",
+		firstLine: "",
+	},
+	"EOLOnly": {
+		input:     "\n",
+		firstLine: "",
+	},
+	"NoEOL": {
+		input:     "line1",
+		firstLine: "line1",
+	},
+}
+
+func TestFirstLine(t *testing.T) {
+	t.Run("FirstLine", func(t *testing.T) {
+		for name, test := range firstLineTests {
+			t.Run(name, func(t *testing.T) {
+				firstLine := FirstLine(test.input)
+				assert.Equal(t, test.firstLine, firstLine)
+			})
+		}
+	})
+}