Error handeling by means of errors.Is

dummy.go

@@ -0,0 +1,17 @@
+package stty
+
+type dummy struct{
+    err error
+}
+
+func (d *dummy) SetBaudRate(portPath string, baudrate int) error {
+    return d.err
+}
+
+func (d *dummy) CheckBaudRate(portPath string) (baudrate int, err error) {
+    return 0, d.err
+}
+
+func (d *dummy) TestBaudRate(portPath string, baudrate int) error {
+    return d.err
+}

error.go

@@ -0,0 +1,37 @@
+package stty
+
+import(
+    "fmt"
+)
+
+func errStack(err1 error, err2 error) error {
+    return fmt.Errorf("%w: %w", err1, err2)
+}
+
+func ERR_NOT_TTY() error {
+    return fmt.Errorf("File is not a tty")
+}
+
+func ERR_CANNOT_OPEN_FILE() error {
+    return fmt.Errorf("Can not open file")
+}
+
+func ERR_NO_WRITE_ACCESS() error {
+    return fmt.Errorf("No write access")
+}
+
+func ERR_STTY_MISSING() error {
+    return fmt.Errorf("Stty is missing")
+}
+
+func ERR_BAUDRATE_NOT_SUPPORTED() error {
+    return fmt.Errorf("Selected baudrate is not supported")
+}
+
+func ERR_SET_BAUDRATE_FAILED() error {
+    return fmt.Errorf("Failed to set baudrate using stty")
+}
+
+func ERR_CHECK_BAUDRATE_FAILED() error {
+    return fmt.Errorf("Failed to check baudrate using stty")
+}

real.go

@@ -0,0 +1,46 @@
+package stty
+
+import(
+    "os/exec"
+    "fmt"
+)
+
+type real struct {
+}
+
+func (r *real) SetBaudRate(portPath string, baudrate int) error {
+	setBaudRateCMD := exec.Command("stty", "-F", portPath, fmt.Sprint(baudrate))
+	_, err := setBaudRateCMD.Output()
+    return errStack(ERR_SET_BAUDRATE_FAILED(), err)
+}
+
+func (r *real) CheckBaudRate(portPath string) (baudrate int, err error) {
+	checkBaudRateCMD := exec.Command("stty", "-F", portPath, "speed")
+	sttyOutput, err := checkBaudRateCMD.Output()
+	if err != nil {
+		return 0, err
+	}
+
+	_, err = fmt.Sscan(string(sttyOutput), &baudrate)
+	if err != nil {
+		return 0, err
+	}
+	return baudrate, nil
+}
+
+func (r *real) TestBaudRate(portPath string, baudrate int) error {
+	err := r.SetBaudRate(portPath, baudrate)
+	if err != nil {
+		return err
+	}
+
+	newBaudRate, err := r.CheckBaudRate(portPath)
+	if err != nil {
+		return errStack(ERR_CHECK_BAUDRATE_FAILED(), err)
+	}
+
+	if newBaudRate == baudrate {
+		return nil
+	}
+	return ERR_BAUDRATE_NOT_SUPPORTED() 
+}

stty.go

@@ -1,76 +1,47 @@
 package stty
 
 import (
-	"fmt"
 	"os"
     "golang.org/x/sys/unix"
 	"golang.org/x/term"
 	"os/exec"
 )
 
-type stty struct {
+type stty interface{
+    SetBaudRate(portPath string, baudrate int) error
+    CheckBaudRate(portPath string) (baudrate int, err error)
+    TestBaudRate(portPath string, baudrate int) error
+}
+
+var cmd stty
+
+func CMD() stty {
+    return cmd
+}
+
+func init() {
+	checkSttyCMD := exec.Command("stty", "--version")
+	sttyOutput, err := checkSttyCMD.Output()
+	if err != nil || len(sttyOutput) == 0 {
+        cmd = &dummy{errStack(ERR_STTY_MISSING(),err)}
+	}
+	cmd = &real{}
 }
 
 func ValidateTtyFile(filepath string) error {
     file, err := os.Open(filepath)
 	if err != nil {
-		return err
+        return errStack(ERR_CANNOT_OPEN_FILE(), err)
 	}
 	defer file.Close()
 
 	err = unix.Access(filepath, unix.W_OK)
 	if err != nil {
-		return err
+		return errStack(ERR_NO_WRITE_ACCESS(), err)
 	}
 
 	if term.IsTerminal(int(file.Fd())) {
 		return nil
 	}
-	return fmt.Errorf("File is not a tty.")
-}
-
-func Get() (*stty, error) {
-	checkSttyCMD := exec.Command("stty", "--version")
-	sttyOutput, err := checkSttyCMD.Output()
-	if err != nil || len(sttyOutput) == 0 {
-		return nil, fmt.Errorf("Stty is missing. Because: " + err.Error())
-	}
-	return &stty{}, nil
-}
-
-func (s *stty) SetBaudRate(portPath string, baudrate int) error {
-	setBaudRateCMD := exec.Command("stty", "-F", portPath, fmt.Sprint(baudrate))
-	_, err := setBaudRateCMD.Output()
-	return err
-}
-
-func (s *stty) CheckBaudRate(portPath string) (baudrate int, err error) {
-	checkBaudRateCMD := exec.Command("stty", "-F", portPath, "speed")
-	sttyOutput, err := checkBaudRateCMD.Output()
-	if err != nil {
-		return 0, fmt.Errorf("Failed to invoke stty. Because: " + err.Error())
-	}
-
-	_, err = fmt.Sscan(string(sttyOutput), &baudrate)
-	if err != nil {
-		return 0, fmt.Errorf("Failed to read baudrate from stty output. Because:" + err.Error())
-	}
-	return baudrate, nil
-}
-
-func (s *stty) TestBaudRate(portPath string, baudrate int) (error) {
-	err := s.SetBaudRate(portPath, baudrate)
-	if err != nil {
-		return fmt.Errorf("Failed to set baudrate using stty. Because: " + err.Error())
-	}
-
-	newBaudRate, err := s.CheckBaudRate(portPath)
-	if err != nil {
-		return fmt.Errorf("Failed to check baudrate using stty. Because: " + err.Error())
-	}
-
-	if newBaudRate == baudrate {
-		return nil
-	}
-	return fmt.Errorf("Selected baudrate is not supported.") 
+	return ERR_NOT_TTY()
 }