详解Golang中创建error的方式总结与应用场景

// The error built-in interface type is the conventional interface for
// representing an error condition, with the nil value representing no error.
type error interface {
	Error() string
}

err := errors.New("this is error")

func New(text string) error {
	return &errorString{text}
}
// errorString is a trivial implementation of error.
type errorString struct {
	s string
}
func (e *errorString) Error() string {
	return e.s
}

func parsePostForm(r *Request) (vs url.Values, err error) {
	if r.Body == nil {
		err = errors.New("missing form body")
		return
	}
	ct := r.Header.Get("Content-Type")
	// 省略了后续的代码...
	return
}

func (t *Transport) roundTrip(req *Request) (*Response, error) {
	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
	ctx := req.Context()
	trace := httptrace.ContextClientTrace(ctx)
	if req.URL == nil {
		req.closeBody()
		return nil, errors.New("http: nil Request.URL")
	}
	if req.Header == nil {
		req.closeBody()
		return nil, errors.New("http: nil Request.Header")
	}
	//省略后面的代码...
}

var EOF = errors.New("EOF")

func GrepFile(patten string, filename string) (lines []string, err error) {
	//省略前面的代码...
	fd, err := os.Open(filename)
	if err != nil {
		return
	}
	reader := bufio.NewReader(fd)
	for {
		byteLine, isPrefix, er := reader.ReadLine()
		if er != nil && er != io.EOF {
			return nil, er
		}
		if er == io.EOF {
			break
		}
		//省略后面的代码...
	}

func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Field, many2many string) {
	//...
	if len(relation.foreignKeys) > 0 {
		ownForeignFields = []*Field{}
		for _, foreignKey := range relation.foreignKeys {
			if field := schema.LookUpField(foreignKey); field != nil {
				ownForeignFields = append(ownForeignFields, field)
			} else {
				schema.err = fmt.Errorf("invalid foreign key: %s", foreignKey)
				return
			}
		}
	}
	//...
}

filename := "abc.webp"
fmt.Errorf("%w:%s", errors.New("unsupported extension"), filename)

func Errorf(format string, a ...interface{}) error {
	p := newPrinter()
	p.wrapErrs = true
	p.doPrintf(format, a)
	s := string(p.buf)
	var err error
	if p.wrappedErr == nil {
		err = errors.New(s)
	} else {
		err = &wrapError{s, p.wrappedErr}
	}
	p.free()
	return err
}

type wrapError struct {
	msg string
	err error
}

const query = "..."
func (s Store) GetContract(name string) (Contract, error) {
	id := getID(name)
	rows, err := s.db.Query(query, id)
	if err != nil {
		if err == sql.ErrNoRows {
			return Contract{},
			fmt.Errorf("no contract found for %s: %w", name, err) 
		}
		// ...
	}
	// ...
}

contract, err := store.GetContract("Raul Endymion")
if err != nil {
	if errors.Is(err, sql.ErrNoRows) { 
		// Do something specific
	}
}

// PathError records an error and the operation and file path that caused it.
type PathError struct {
	Op   string
	Path string
	Err  error
}
func (e *PathError) Error() string { return e.Op + " " + e.Path + ": " + e.Err.Error() }
func (e *PathError) Unwrap() error { return e.Err }

func (d *openDir) Read([]byte) (int, error) {
	return 0, &fs.PathError{Op: "read", Path: d.f.name, Err: errors.New("is a directory")}
}

func (f *openFile) Read(b []byte) (int, error) {
	if f.offset >= int64(len(f.f.data)) {
		return 0, io.EOF
	}
	if f.offset < 0 {
		return 0, &fs.PathError{Op: "read", Path: f.f.name, Err: fs.ErrInvalid}
	}
	n := copy(b, f.f.data[f.offset:])
	f.offset += int64(n)
	return n, nil
}

ErrInvalid    = errors.New("invalid argument")

var ErrRecordNotFound = errors.New("record not found")

errors.Is(err, ErrRecordNotFound)

// setupLogRotation initializes log rotation for a single file path target.
func setupLogRotation(logOutputs []string, logRotateConfigJSON string) error {
	//...
	if err := json.Unmarshal([]byte(logRotateConfigJSON), &logRotationConfig); err != nil {
		var unmarshalTypeError *json.UnmarshalTypeError
		var syntaxError *json.SyntaxError
		switch {
		case errors.As(err, &syntaxError):
			return fmt.Errorf("improperly formatted log rotation config: %w", err)
		case errors.As(err, &unmarshalTypeError):
			return fmt.Errorf("invalid log rotation config: %w", err)
		}
	}
	zap.RegisterSink("rotate", func(u *url.URL) (zap.Sink, error) {
		logRotationConfig.Filename = u.Path[1:]
		return &logRotationConfig, nil
	})
	return nil
}