Dealing with Solo Carriage Returns in csv.Reader

cr_to_crlf_replacer.go

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"

	"encoding/csv"
)

// ReplaceSoloCarriageReturns wraps an io.Reader, on every call of Read it
// for instances of lonely \r replacing them with \r\n before returning to the end customer
// lots of files in the wild will come without "proper" line breaks, which irritates go's
// standard csv package. This'll fix by wrapping the reader passed to csv.NewReader:
//    rdr, err := csv.NewReader(ReplaceSoloCarriageReturns(r))
//
func ReplaceSoloCarriageReturns(data io.Reader) io.Reader {
	return crlfReplaceReader{
		rdr: bufio.NewReader(data),
	}
}

// crlfReplaceReader wraps a reader
type crlfReplaceReader struct {
	rdr *bufio.Reader
}

// Read implements io.Reader for crlfReplaceReader
func (c crlfReplaceReader) Read(p []byte) (n int, err error) {
	if len(p) == 0 {
		return
	}

	for {
		if n == len(p) {
			return
		}

		p[n], err = c.rdr.ReadByte()
		if err != nil {
			return
		}

		// any time we encounter \r & still have space, check to see if \n follows
		// if next char is not \n, add it in manually
		if p[n] == '\r' && n < len(p) {
			if pk, err := c.rdr.Peek(1); (err == nil && pk[0] != '\n') || (err != nil && err.Error() == io.EOF.Error()) {
				n++
				p[n] = '\n'
			}
		}

		n++
	}
	return
}

var csvData = []byte("col_0,col_1,col_2\ra,b,c\rd,e,f\rg,h,i\r")

// also online in the go playground: https://play.golang.org/p/Yy0xJtcMrG4
func main() {
	file := bytes.NewReader(csvData)
	rdr := csv.NewReader(ReplaceSoloCarriageReturns(file))

	for {
		rec, err := rdr.Read()
		if err != nil {
			// real programs handle errors
			return
		}
		fmt.Println(rec)
	}
}