1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package csv 6 7 import ( 8 "bufio" 9 "io" 10 "strings" 11 "unicode" 12 "unicode/utf8" 13 ) 14 15 // A Writer writes records to a CSV encoded file. 16 // 17 // As returned by NewWriter, a Writer writes records terminated by a 18 // newline and uses ',' as the field delimiter. The exported fields can be 19 // changed to customize the details before the first call to Write or WriteAll. 20 // 21 // Comma is the field delimiter. 22 // 23 // If UseCRLF is true, the Writer ends each record with \r\n instead of \n. 24 type Writer struct { 25 Comma rune // Field delimiter (set to ',' by NewWriter) 26 UseCRLF bool // True to use \r\n as the line terminator 27 w *bufio.Writer 28 } 29 30 // NewWriter returns a new Writer that writes to w. 31 func NewWriter(w io.Writer) *Writer { 32 return &Writer{ 33 Comma: ',', 34 w: bufio.NewWriter(w), 35 } 36 } 37 38 // Writer writes a single CSV record to w along with any necessary quoting. 39 // A record is a slice of strings with each string being one field. 40 func (w *Writer) Write(record []string) error { 41 for n, field := range record { 42 if n > 0 { 43 if _, err := w.w.WriteRune(w.Comma); err != nil { 44 return err 45 } 46 } 47 48 // If we don't have to have a quoted field then just 49 // write out the field and continue to the next field. 50 if !w.fieldNeedsQuotes(field) { 51 if _, err := w.w.WriteString(field); err != nil { 52 return err 53 } 54 continue 55 } 56 if err := w.w.WriteByte('"'); err != nil { 57 return err 58 } 59 60 for _, r1 := range field { 61 var err error 62 switch r1 { 63 case '"': 64 _, err = w.w.WriteString(`""`) 65 case '\r': 66 if !w.UseCRLF { 67 err = w.w.WriteByte('\r') 68 } 69 case '\n': 70 if w.UseCRLF { 71 _, err = w.w.WriteString("\r\n") 72 } else { 73 err = w.w.WriteByte('\n') 74 } 75 default: 76 _, err = w.w.WriteRune(r1) 77 } 78 if err != nil { 79 return err 80 } 81 } 82 83 if err := w.w.WriteByte('"'); err != nil { 84 return err 85 } 86 } 87 var err error 88 if w.UseCRLF { 89 _, err = w.w.WriteString("\r\n") 90 } else { 91 err = w.w.WriteByte('\n') 92 } 93 return err 94 } 95 96 // Flush writes any buffered data to the underlying io.Writer. 97 // To check if an error occurred during the Flush, call Error. 98 func (w *Writer) Flush() { 99 w.w.Flush() 100 } 101 102 // Error reports any error that has occurred during a previous Write or Flush. 103 func (w *Writer) Error() error { 104 _, err := w.w.Write(nil) 105 return err 106 } 107 108 // WriteAll writes multiple CSV records to w using Write and then calls Flush. 109 func (w *Writer) WriteAll(records [][]string) error { 110 for _, record := range records { 111 err := w.Write(record) 112 if err != nil { 113 return err 114 } 115 } 116 return w.w.Flush() 117 } 118 119 // fieldNeedsQuotes reports whether our field must be enclosed in quotes. 120 // Fields with a Comma, fields with a quote or newline, and 121 // fields which start with a space must be enclosed in quotes. 122 // We used to quote empty strings, but we do not anymore (as of Go 1.4). 123 // The two representations should be equivalent, but Postgres distinguishes 124 // quoted vs non-quoted empty string during database imports, and it has 125 // an option to force the quoted behavior for non-quoted CSV but it has 126 // no option to force the non-quoted behavior for quoted CSV, making 127 // CSV with quoted empty strings strictly less useful. 128 // Not quoting the empty string also makes this package match the behavior 129 // of Microsoft Excel and Google Drive. 130 // For Postgres, quote the data terminating string `\.`. 131 func (w *Writer) fieldNeedsQuotes(field string) bool { 132 if field == "" { 133 return false 134 } 135 if field == `\.` || strings.ContainsRune(field, w.Comma) || strings.ContainsAny(field, "\"\r\n") { 136 return true 137 } 138 139 r1, _ := utf8.DecodeRuneInString(field) 140 return unicode.IsSpace(r1) 141 } 142
