diff options
Diffstat (limited to 'src/encoding/csv/writer.go')
-rw-r--r-- | src/encoding/csv/writer.go | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/src/encoding/csv/writer.go b/src/encoding/csv/writer.go new file mode 100644 index 000000000..17e7bb7f5 --- /dev/null +++ b/src/encoding/csv/writer.go @@ -0,0 +1,139 @@ +// 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 to a CSV encoded file. +// +// 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 Write or WriteAll. +// +// Comma is the field delimiter. +// +// If UseCRLF is true, the Writer ends each record with \r\n instead of \n. +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), + } +} + +// Writer 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. +func (w *Writer) Write(record []string) (err error) { + for n, field := range record { + if n > 0 { + if _, err = w.w.WriteRune(w.Comma); err != nil { + return + } + } + + // 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 + } + continue + } + if err = w.w.WriteByte('"'); err != nil { + return + } + + for _, r1 := range field { + switch r1 { + 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') + } + default: + _, err = w.w.WriteRune(r1) + } + if err != nil { + return + } + } + + if err = w.w.WriteByte('"'); err != nil { + return + } + } + if w.UseCRLF { + _, err = w.w.WriteString("\r\n") + } else { + err = w.w.WriteByte('\n') + } + return +} + +// Flush writes any buffered data to the underlying io.Writer. +// To check if an error occurred during the Flush, call Error. +func (w *Writer) Flush() { + w.w.Flush() +} + +// Error reports any error that has occurred during a previous Write or Flush. +func (w *Writer) Error() error { + _, err := w.w.Write(nil) + return err +} + +// WriteAll writes multiple CSV records to w using Write and then calls Flush. +func (w *Writer) WriteAll(records [][]string) (err error) { + for _, record := range records { + err = w.Write(record) + if err != nil { + return err + } + } + return w.w.Flush() +} + +// fieldNeedsQuotes returns true if 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 termating string `\.`. +func (w *Writer) fieldNeedsQuotes(field string) bool { + if field == "" { + return false + } + if field == `\.` || strings.IndexRune(field, w.Comma) >= 0 || strings.IndexAny(field, "\"\r\n") >= 0 { + return true + } + + r1, _ := utf8.DecodeRuneInString(field) + return unicode.IsSpace(r1) +} |