github.com/Bytom/bytom@v1.1.2-0.20210127130405-ae40204c0b09/errors/writer.go (about)

     1  package errors
     2  
     3  import "io"
     4  
     5  // NewWriter returns a new Writer that writes to w
     6  // until an error is returned.
     7  func NewWriter(w io.Writer) *Writer {
     8  	return &Writer{w: w}
     9  }
    10  
    11  // Writer is in an implementation of the
    12  // "sticky error writer" pattern as described
    13  // in https://blog.golang.org/errors-are-values.
    14  //
    15  // A Writer makes one call
    16  // on the underlying writer for each call to Write,
    17  // until an error is returned. From that point on,
    18  // it makes no calls on the underlying writer,
    19  // and returns the same error value every time.
    20  type Writer struct {
    21  	w   io.Writer
    22  	n   int64
    23  	err error
    24  }
    25  
    26  // Write makes one call on the underlying writer
    27  // if no error has previously occurred.
    28  func (w *Writer) Write(buf []byte) (n int, err error) {
    29  	if w.err != nil {
    30  		return 0, w.err
    31  	}
    32  	n, w.err = w.w.Write(buf)
    33  	w.n += int64(n)
    34  	return n, w.err
    35  }
    36  
    37  // Err returns the first error encountered by Write, if any.
    38  func (w *Writer) Err() error {
    39  	return w.err
    40  }
    41  
    42  // Written returns the number of bytes written
    43  // to the underlying writer.
    44  func (w *Writer) Written() int64 {
    45  	return w.n
    46  }