Refactor and separate sqlcmd errors from server erros (#160)

This commit addresses #144 which was raised to compare sqlcmd
errors based on type and not the content of error message.
A dummy function IsSqlcmdErr() has been added in SqlcmdErr interface
to distinguish Sqlcmd errors from server errors.
The only purpose of it is to distinguish SqlcmdErr interface from the
generic Error interface. From now on all sqlcmd errors should implement
SqlcmdErr interface to distinguish itself from other errors.
None of the existing errors wrap any other errors which is why unwrap()
is not implemented however, for new errors if they contain another error,
unwrap() should be implemented.

Author: apoorvdeshmukh

pkg/sqlcmd/batch_test.go

@@ -90,7 +90,7 @@ func TestBatchNextErrOnInvalidVariable(t *testing.T) {
 		cmd, _, err := b.Next()
 		assert.Nil(t, cmd, "cmd for "+test)
 		assert.Equal(t, uint(1), b.linecount, "linecount should increment on a variable syntax error")
-		assert.EqualErrorf(t, err, "Sqlcmd: Error: Syntax error at line 1.", "expected err for %s", test)
+		assert.EqualErrorf(t, err, "Sqlcmd: Error: Syntax error at line 1", "expected err for %s", test)
 	}
 }
 
@@ -165,7 +165,7 @@ func TestReadStringMalformedVariable(t *testing.T) {
 		r := []rune(test)
 		_, ok, err := b.readString(r, 1, len(test), '\'', 10)
 		assert.Falsef(t, ok, "ok for %s", test)
-		assert.EqualErrorf(t, err, "Sqlcmd: Error: Syntax error at line 10.", "expected err for %s", test)
+		assert.EqualErrorf(t, err, "Sqlcmd: Error: Syntax error at line 10", "expected err for %s", test)
 	}
 }
 

pkg/sqlcmd/errors.go

@@ -15,6 +15,26 @@ const ErrorPrefix = "Sqlcmd: Error: "
 // WarningPrefix is the prefix for all sqlcmd-generated warnings
 const WarningPrefix = "Sqlcmd: Warning: "
 
+// Common Sqlcmd error messages
+const ErrCmdDisabled = "ED and !!<command> commands, startup script, and environment variables are disabled"
+
+type SqlcmdError interface {
+	error
+	IsSqlcmdErr() bool
+}
+
+type CommonSqlcmdErr struct {
+	message string
+}
+
+func (e *CommonSqlcmdErr) Error() string {
+	return e.message
+}
+
+func (e *CommonSqlcmdErr) IsSqlcmdErr() bool {
+	return true
+}
+
 // ArgumentError is related to command line switch validation not handled by kong
 type ArgumentError struct {
 	Parameter string
@@ -25,6 +45,10 @@ func (e *ArgumentError) Error() string {
 	return ErrorPrefix + e.Rule
 }
 
+func (e *ArgumentError) IsSqlcmdErr() bool {
+	return true
+}
+
 // InvalidServerName indicates the SQLCMDSERVER variable has an incorrect format
 var InvalidServerName = ArgumentError{
 	Parameter: "server",
@@ -41,6 +65,10 @@ func (e *VariableError) Error() string {
 	return ErrorPrefix + fmt.Sprintf(e.MessageFormat, e.Variable)
 }
 
+func (e *VariableError) IsSqlcmdErr() bool {
+	return true
+}
+
 // ReadOnlyVariable indicates the user tried to set a value to a read-only variable
 func ReadOnlyVariable(variable string) *VariableError {
 	return &VariableError{
@@ -75,6 +103,10 @@ func (e *CommandError) Error() string {
 	return ErrorPrefix + fmt.Sprintf("Syntax error at line %d near command '%s'.", e.LineNumber, e.Command)
 }
 
+func (e *CommandError) IsSqlcmdErr() bool {
+	return true
+}
+
 // InvalidCommandError creates a SQLCmdCommandError
 func InvalidCommandError(command string, lineNumber uint) *CommandError {
 	return &CommandError{
@@ -83,12 +115,42 @@ func InvalidCommandError(command string, lineNumber uint) *CommandError {
 	}
 }
 
+type FileError struct {
+	err  error
+	path string
+}
+
+func (e *FileError) Error() string {
+	return e.err.Error()
+}
+
+func (e *FileError) IsSqlcmdErr() bool {
+	return true
+}
+
 // InvalidFileError indicates a file could not be opened
-func InvalidFileError(err error, path string) error {
-	return errors.New(ErrorPrefix + " Error occurred while opening or operating on file " + path + " (Reason: " + err.Error() + ").")
+func InvalidFileError(err error, filepath string) error {
+	return &FileError{
+		err:  errors.New(ErrorPrefix + " Error occurred while opening or operating on file " + filepath + " (Reason: " + err.Error() + ")."),
+		path: filepath,
+	}
+}
+
+type SyntaxError struct {
+	err error
+}
+
+func (e *SyntaxError) Error() string {
+	return e.err.Error()
+}
+
+func (e *SyntaxError) IsSqlcmdErr() bool {
+	return true
 }
 
 // SyntaxError indicates a malformed sqlcmd statement
-func syntaxError(lineNumber uint) error {
-	return fmt.Errorf("%sSyntax error at line %d.", ErrorPrefix, lineNumber)
+func syntaxError(lineNumber uint) SqlcmdError {
+	return &SyntaxError{
+		err: fmt.Errorf("%sSyntax error at line %d", ErrorPrefix, lineNumber),
+	}
 }

pkg/sqlcmd/sqlcmd.go

@@ -33,7 +33,9 @@ var (
 	// ErrCtrlC indicates execution was ended by ctrl-c or ctrl-break
 	ErrCtrlC = errors.New(WarningPrefix + "The last operation was terminated because the user pressed CTRL+C")
 	// ErrCommandsDisabled indicates system commands and startup script are disabled
-	ErrCommandsDisabled = errors.New(ErrorPrefix + "ED and !!<command> commands, startup script, and environment variables are disabled.")
+	ErrCommandsDisabled = &CommonSqlcmdErr{
+		message: ErrCmdDisabled,
+	}
 )
 
 const maxLineBuffer = 2 * 1024 * 1024 // 2Mb
@@ -215,11 +217,11 @@ func (s *Sqlcmd) SetError(e io.WriteCloser) {
 
 // WriteError writes the error on specified stream
 func (s *Sqlcmd) WriteError(stream io.Writer, err error) {
-	if strings.HasPrefix(err.Error(), ErrorPrefix) {
+	if serr, ok := err.(SqlcmdError); ok {
 		if s.GetError() != os.Stdout {
-			_, _ = s.GetError().Write([]byte(err.Error() + SqlcmdEol))
+			_, _ = s.GetError().Write([]byte(serr.Error() + SqlcmdEol))
 		} else {
-			_, _ = os.Stderr.Write([]byte(err.Error() + SqlcmdEol))
+			_, _ = os.Stderr.Write([]byte(serr.Error() + SqlcmdEol))
 		}
 	} else {
 		_, _ = stream.Write([]byte(err.Error() + SqlcmdEol))

pkg/sqlcmd/sqlcmd_test.go

@@ -104,7 +104,7 @@ func TestSqlCmdQueryAndExit(t *testing.T) {
 		s.SetOutput(nil)
 		bytes, err := os.ReadFile(file.Name())
 		if assert.NoError(t, err, "os.ReadFile") {
-			assert.Equal(t, "Sqlcmd: Error: Syntax error at line 1."+SqlcmdEol, string(bytes), "Incorrect output from Run")
+			assert.Equal(t, "Sqlcmd: Error: Syntax error at line 1"+SqlcmdEol, string(bytes), "Incorrect output from Run")
 		}
 	}
 }
@@ -471,7 +471,7 @@ func TestSqlCmdOutputAndError(t *testing.T) {
 	if assert.NoError(t, err, "s.Run(once = true)") {
 		bytes, err := os.ReadFile(errfile.Name())
 		if assert.NoError(t, err, "os.ReadFile") {
-			assert.Equal(t, "Sqlcmd: Error: Syntax error at line 1."+SqlcmdEol, string(bytes), "Expected syntax error not received for query execution")
+			assert.Equal(t, "Sqlcmd: Error: Syntax error at line 1"+SqlcmdEol, string(bytes), "Expected syntax error not received for query execution")
 		}
 	}
 	s.Query = "select '1'"
@@ -495,7 +495,7 @@ func TestSqlCmdOutputAndError(t *testing.T) {
 		}
 		bytes, err = os.ReadFile(errfile.Name())
 		if assert.NoError(t, err, "os.ReadFile errfile") {
-			assert.Equal(t, "Sqlcmd: Error: Syntax error at line 3."+SqlcmdEol, string(bytes), "Expected syntax error not found in errfile")
+			assert.Equal(t, "Sqlcmd: Error: Syntax error at line 3"+SqlcmdEol, string(bytes), "Expected syntax error not found in errfile")
 		}
 	}
 }