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writer.go
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writer.go
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//
// (C) Copyright 2020-2021 Intel Corporation.
//
// SPDX-License-Identifier: BSD-2-Clause-Patent
//
package txtfmt
import (
"fmt"
"io"
)
// ErrWriter eliminates repetitive error handling by
// capturing an error and ignoring subsequent writes.
// The original error is available to be used by the caller.
//
// https://dave.cheney.net/2019/01/27/eliminate-error-handling-by-eliminating-errors
type ErrWriter struct {
writer io.Writer
Err error
}
// NewErrWriter returns an initialized ErrWriter.
func NewErrWriter(w io.Writer) *ErrWriter {
return &ErrWriter{writer: w}
}
func (w *ErrWriter) Write(data []byte) (int, error) {
if w.Err != nil {
return 0, w.Err
}
var n int
n, w.Err = w.writer.Write(data)
return n, w.Err
}
const (
defaultPadCount = 2
)
type (
// IndentWriter indents every line written to it.
IndentWriter struct {
writer io.Writer
padCount uint
inNewLine bool
}
// IndentWriterOption configures the IndentWriter.
IndentWriterOption func(*IndentWriter)
)
// WithPadCount sets the indent width.
func WithPadCount(count uint) IndentWriterOption {
return func(w *IndentWriter) {
w.padCount = count
}
}
// NewIndentWriter returns an initialized IndentWriter.
func NewIndentWriter(w io.Writer, opts ...IndentWriterOption) *IndentWriter {
iw := &IndentWriter{
writer: w,
padCount: defaultPadCount,
inNewLine: true,
}
for _, opt := range opts {
opt(iw)
}
return iw
}
func (w *IndentWriter) Write(data []byte) (int, error) {
if w.inNewLine {
if len(data) > 0 && data[0] != '\n' {
w.inNewLine = false
padding := fmt.Sprintf("%*c", w.padCount, ' ')
if _, err := w.writer.Write([]byte(padding)); err != nil {
return 0, err
}
}
}
for i, c := range data {
if c == '\n' {
count, err := w.writer.Write(data[:i+1])
if err != nil {
return count, err
}
w.inNewLine = true
wrote, err := w.Write(data[i+1:])
return count + wrote, err
}
}
return w.writer.Write(data)
}