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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package csv
import (
"bufio"
"io"
"strings"
"unicode"
"unicode/utf8"
)
// A Writer writes records using CSV encoding.
//
// As returned by [NewWriter], a Writer writes records terminated by a
// newline and uses ',' as the field delimiter. The exported fields can be
// changed to customize the details before
// the first call to [Writer.Write] or [Writer.WriteAll].
//
// [Writer.Comma] is the field delimiter.
//
// If [Writer.UseCRLF] is true,
// the Writer ends each output line with \r\n instead of \n.
//
// The writes of individual records are buffered.
// After all data has been written, the client should call the
// [Writer.Flush] method to guarantee all data has been forwarded to
// the underlying [io.Writer]. Any errors that occurred should
// be checked by calling the [Writer.Error] method.
type Writer struct {
Comma rune // Field delimiter (set to ',' by NewWriter)
UseCRLF bool // True to use \r\n as the line terminator
w *bufio.Writer
}
// NewWriter returns a new Writer that writes to w.
func NewWriter(w io.Writer) *Writer {
return &Writer{
Comma: ',',
w: bufio.NewWriter(w),
}
}
// Write writes a single CSV record to w along with any necessary quoting.
// A record is a slice of strings with each string being one field.
// Writes are buffered, so [Writer.Flush] must eventually be called to ensure
// that the record is written to the underlying [io.Writer].
func (w *Writer) Write(record []string) error {
if !validDelim(w.Comma) {
return errInvalidDelim
}
for n, field := range record {
if n > 0 {
if _, err := w.w.WriteRune(w.Comma); err != nil {
return err
}
}
// If we don't have to have a quoted field then just
// write out the field and continue to the next field.
if !w.fieldNeedsQuotes(field) {
if _, err := w.w.WriteString(field); err != nil {
return err
}
continue
}
if err := w.w.WriteByte('"'); err != nil {
return err
}
for len(field) > 0 {
// Search for special characters.
i := strings.IndexAny(field, "\"\r\n")
if i < 0 {
i = len(field)
}
// Copy verbatim everything before the special character.
if _, err := w.w.WriteString(field[:i]); err != nil {
return err
}
field = field[i:]
// Encode the special character.
if len(field) > 0 {
var err error
switch field[0] {
case '"':
_, err = w.w.WriteString(`""`)
case '\r':
if !w.UseCRLF {
err = w.w.WriteByte('\r')
}
case '\n':
if w.UseCRLF {
_, err = w.w.WriteString("\r\n")
} else {
err = w.w.WriteByte('\n')
}
}
field = field[1:]
if err != nil {
return err
}
}
}
if err := w.w.WriteByte('"'); err != nil {
return err
}
}
var err error
if w.UseCRLF {
_, err = w.w.WriteString("\r\n")
} else {
err = w.w.WriteByte('\n')
}
return err
}
// Flush writes any buffered data to the underlying [io.Writer].
// To check if an error occurred during Flush, call [Writer.Error].
func (w *Writer) Flush() {
w.w.Flush()
}
// Error reports any error that has occurred during
// a previous [Writer.Write] or [Writer.Flush].
func (w *Writer) Error() error {
_, err := w.w.Write(nil)
return err
}
// WriteAll writes multiple CSV records to w using [Writer.Write] and
// then calls [Writer.Flush], returning any error from the Flush.
func (w *Writer) WriteAll(records [][]string) error {
for _, record := range records {
err := w.Write(record)
if err != nil {
return err
}
}
return w.w.Flush()
}
// fieldNeedsQuotes reports whether our field must be enclosed in quotes.
// Fields with a Comma, fields with a quote or newline, and
// fields which start with a space must be enclosed in quotes.
// We used to quote empty strings, but we do not anymore (as of Go 1.4).
// The two representations should be equivalent, but Postgres distinguishes
// quoted vs non-quoted empty string during database imports, and it has
// an option to force the quoted behavior for non-quoted CSV but it has
// no option to force the non-quoted behavior for quoted CSV, making
// CSV with quoted empty strings strictly less useful.
// Not quoting the empty string also makes this package match the behavior
// of Microsoft Excel and Google Drive.
// For Postgres, quote the data terminating string `\.`.
func (w *Writer) fieldNeedsQuotes(field string) bool {
if field == "" {
return false
}
if field == `\.` {
return true
}
if w.Comma < utf8.RuneSelf {
for i := 0; i < len(field); i++ {
c := field[i]
if c == '\n' || c == '\r' || c == '"' || c == byte(w.Comma) {
return true
}
}
} else {
if strings.ContainsRune(field, w.Comma) || strings.ContainsAny(field, "\"\r\n") {
return true
}
}
r1, _ := utf8.DecodeRuneInString(field)
return unicode.IsSpace(r1)
}
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