src/encoding/csv/reader.go - go - Git at Google

 // 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 reads and writes comma-separated values (CSV) files.
 // There are many kinds of CSV files; this package supports the format
 // described in RFC 4180.
 //
 // A csv file contains zero or more records of one or more fields per record.
 // Each record is separated by the newline character. The final record may
 // optionally be followed by a newline character.
 //
 //	field1,field2,field3
 //
 // White space is considered part of a field.
 //
 // Carriage returns before newline characters are silently removed.
 //
 // Blank lines are ignored. A line with only whitespace characters (excluding
 // the ending newline character) is not considered a blank line.
 //
 // Fields which start and stop with the quote character " are called
 // quoted-fields. The beginning and ending quote are not part of the
 // field.
 //
 // The source:
 //
 //	normal string,"quoted-field"
 //
 // results in the fields
 //
 //	{`normal string`, `quoted-field`}
 //
 // Within a quoted-field a quote character followed by a second quote
 // character is considered a single quote.
 //
 //	"the ""word"" is true","a ""quoted-field"""
 //
 // results in
 //
 //	{`the "word" is true`, `a "quoted-field"`}
 //
 // Newlines and commas may be included in a quoted-field
 //
 //	"Multi-line
 //	field","comma is ,"
 //
 // results in
 //
 //	{`Multi-line
 //	field`, `comma is ,`}
 package csv

 import (
 	"bufio"
 	"bytes"
 	"errors"
 	"fmt"
 	"io"
 	"unicode"
 	"unicode/utf8"
 )

 // A ParseError is returned for parsing errors.
 // Line and column numbers are 1-indexed.
 type ParseError struct {
 	StartLine int   // Line where the record starts
 	Line      int   // Line where the error occurred
 	Column    int   // Column (1-based byte index) where the error occurred
 	Err       error // The actual error
 }

 func (e *ParseError) Error() string {
 	if e.Err == ErrFieldCount {
 		return fmt.Sprintf("record on line %d: %v", e.Line, e.Err)
 	}
 	if e.StartLine != e.Line {
 		return fmt.Sprintf("record on line %d; parse error on line %d, column %d: %v", e.StartLine, e.Line, e.Column, e.Err)
 	}
 	return fmt.Sprintf("parse error on line %d, column %d: %v", e.Line, e.Column, e.Err)
 }

 func (e *ParseError) Unwrap() error { return e.Err }

 // These are the errors that can be returned in [ParseError.Err].
 var (
 	ErrBareQuote  = errors.New("bare \" in non-quoted-field")
 	ErrQuote      = errors.New("extraneous or missing \" in quoted-field")
 	ErrFieldCount = errors.New("wrong number of fields")

 	// Deprecated: ErrTrailingComma is no longer used.
 	ErrTrailingComma = errors.New("extra delimiter at end of line")
 )

 var errInvalidDelim = errors.New("csv: invalid field or comment delimiter")

 func validDelim(r rune) bool {
 	return r != 0 && r != '"' && r != '\r' && r != '\n' && utf8.ValidRune(r) && r != utf8.RuneError
 }

 // A Reader reads records from a CSV-encoded file.
 //
 // As returned by [NewReader], a Reader expects input conforming to RFC 4180.
 // The exported fields can be changed to customize the details before the
 // first call to [Reader.Read] or [Reader.ReadAll].
 //
 // The Reader converts all \r\n sequences in its input to plain \n,
 // including in multiline field values, so that the returned data does
 // not depend on which line-ending convention an input file uses.
 type Reader struct {
 	// Comma is the field delimiter.
 	// It is set to comma (',') by NewReader.
 	// Comma must be a valid rune and must not be \r, \n,
 	// or the Unicode replacement character (0xFFFD).
 	Comma rune

 	// Comment, if not 0, is the comment character. Lines beginning with the
 	// Comment character without preceding whitespace are ignored.
 	// With leading whitespace the Comment character becomes part of the
 	// field, even if TrimLeadingSpace is true.
 	// Comment must be a valid rune and must not be \r, \n,
 	// or the Unicode replacement character (0xFFFD).
 	// It must also not be equal to Comma.
 	Comment rune

 	// FieldsPerRecord is the number of expected fields per record.
 	// If FieldsPerRecord is positive, Read requires each record to
 	// have the given number of fields. If FieldsPerRecord is 0, Read sets it to
 	// the number of fields in the first record, so that future records must
 	// have the same field count. If FieldsPerRecord is negative, no check is
 	// made and records may have a variable number of fields.
 	FieldsPerRecord int

 	// If LazyQuotes is true, a quote may appear in an unquoted field and a
 	// non-doubled quote may appear in a quoted field.
 	LazyQuotes bool

 	// If TrimLeadingSpace is true, leading white space in a field is ignored.
 	// This is done even if the field delimiter, Comma, is white space.
 	TrimLeadingSpace bool

 	// ReuseRecord controls whether calls to Read may return a slice sharing
 	// the backing array of the previous call's returned slice for performance.
 	// By default, each call to Read returns newly allocated memory owned by the caller.
 	ReuseRecord bool

 	// Deprecated: TrailingComma is no longer used.
 	TrailingComma bool

 	r *bufio.Reader

 	// numLine is the current line being read in the CSV file.
 	numLine int

 	// offset is the input stream byte offset of the current reader position.
 	offset int64

 	// rawBuffer is a line buffer only used by the readLine method.
 	rawBuffer []byte

 	// recordBuffer holds the unescaped fields, one after another.
 	// The fields can be accessed by using the indexes in fieldIndexes.
 	// E.g., For the row `a,"b","c""d",e`, recordBuffer will contain `abc"de`
 	// and fieldIndexes will contain the indexes [1, 2, 5, 6].
 	recordBuffer []byte

 	// fieldIndexes is an index of fields inside recordBuffer.
 	// The i'th field ends at offset fieldIndexes[i] in recordBuffer.
 	fieldIndexes []int

 	// fieldPositions is an index of field positions for the
 	// last record returned by Read.
 	fieldPositions []position

 	// lastRecord is a record cache and only used when ReuseRecord == true.
 	lastRecord []string
 }

 // NewReader returns a new Reader that reads from r.
 func NewReader(r io.Reader) *Reader {
 	return &Reader{
 		Comma: ',',
 		r:     bufio.NewReader(r),
 	}
 }

 // Read reads one record (a slice of fields) from r.
 // If the record has an unexpected number of fields,
 // Read returns the record along with the error [ErrFieldCount].
 // If the record contains a field that cannot be parsed,
 // Read returns a partial record along with the parse error.
 // The partial record contains all fields read before the error.
 // If there is no data left to be read, Read returns nil, [io.EOF].
 // If [Reader.ReuseRecord] is true, the returned slice may be shared
 // between multiple calls to Read.
 func (r *Reader) Read() (record []string, err error) {
 	if r.ReuseRecord {
 		record, err = r.readRecord(r.lastRecord)
 		r.lastRecord = record
 	} else {
 		record, err = r.readRecord(nil)
 	}
 	return record, err
 }

 // FieldPos returns the line and column corresponding to
 // the start of the field with the given index in the slice most recently
 // returned by [Reader.Read]. Numbering of lines and columns starts at 1;
 // columns are counted in bytes, not runes.
 //
 // If this is called with an out-of-bounds index, it panics.
 func (r *Reader) FieldPos(field int) (line, column int) {
 	if field < 0 || field >= len(r.fieldPositions) {
 		panic("out of range index passed to FieldPos")
 	}
 	p := &r.fieldPositions[field]
 	return p.line, p.col
 }

 // InputOffset returns the input stream byte offset of the current reader
 // position. The offset gives the location of the end of the most recently
 // read row and the beginning of the next row.
 func (r *Reader) InputOffset() int64 {
 	return r.offset
 }

 // pos holds the position of a field in the current line.
 type position struct {
 	line, col int
 }

 // ReadAll reads all the remaining records from r.
 // Each record is a slice of fields.
 // A successful call returns err == nil, not err == [io.EOF]. Because ReadAll is
 // defined to read until EOF, it does not treat end of file as an error to be
 // reported.
 func (r *Reader) ReadAll() (records [][]string, err error) {
 	for {
 		record, err := r.readRecord(nil)
 		if err == io.EOF {
 			return records, nil
 		}
 		if err != nil {
 			return nil, err
 		}
 		records = append(records, record)
 	}
 }

 // readLine reads the next line (with the trailing endline).
 // If EOF is hit without a trailing endline, it will be omitted.
 // If some bytes were read, then the error is never [io.EOF].
 // The result is only valid until the next call to readLine.
 func (r *Reader) readLine() ([]byte, error) {
 	line, err := r.r.ReadSlice('\n')
 	if err == bufio.ErrBufferFull {
 		r.rawBuffer = append(r.rawBuffer[:0], line...)
 		for err == bufio.ErrBufferFull {
 			line, err = r.r.ReadSlice('\n')
 			r.rawBuffer = append(r.rawBuffer, line...)
 		}
 		line = r.rawBuffer
 	}
 	readSize := len(line)
 	if readSize > 0 && err == io.EOF {
 		err = nil
 		// For backwards compatibility, drop trailing \r before EOF.
 		if line[readSize-1] == '\r' {
 			line = line[:readSize-1]
 		}
 	}
 	r.numLine++
 	r.offset += int64(readSize)
 	// Normalize \r\n to \n on all input lines.
 	if n := len(line); n >= 2 && line[n-2] == '\r' && line[n-1] == '\n' {
 		line[n-2] = '\n'
 		line = line[:n-1]
 	}
 	return line, err
 }

 // lengthNL reports the number of bytes for the trailing \n.
 func lengthNL(b []byte) int {
 	if len(b) > 0 && b[len(b)-1] == '\n' {
 		return 1
 	}
 	return 0
 }

 // nextRune returns the next rune in b or utf8.RuneError.
 func nextRune(b []byte) rune {
 	r, _ := utf8.DecodeRune(b)
 	return r
 }

 func (r *Reader) readRecord(dst []string) ([]string, error) {
 	if r.Comma == r.Comment || !validDelim(r.Comma) || (r.Comment != 0 && !validDelim(r.Comment)) {
 		return nil, errInvalidDelim
 	}

 	// Read line (automatically skipping past empty lines and any comments).
 	var line []byte
 	var errRead error
 	for errRead == nil {
 		line, errRead = r.readLine()
 		if r.Comment != 0 && nextRune(line) == r.Comment {
 			line = nil
 			continue // Skip comment lines
 		}
 		if errRead == nil && len(line) == lengthNL(line) {
 			line = nil
 			continue // Skip empty lines
 		}
 		break
 	}
 	if errRead == io.EOF {
 		return nil, errRead
 	}

 	// Parse each field in the record.
 	var err error
 	const quoteLen = len(`"`)
 	commaLen := utf8.RuneLen(r.Comma)
 	recLine := r.numLine // Starting line for record
 	r.recordBuffer = r.recordBuffer[:0]
 	r.fieldIndexes = r.fieldIndexes[:0]
 	r.fieldPositions = r.fieldPositions[:0]
 	pos := position{line: r.numLine, col: 1}
 parseField:
 	for {
 		if r.TrimLeadingSpace {
 			i := bytes.IndexFunc(line, func(r rune) bool {
 				return !unicode.IsSpace(r)
 			})
 			if i < 0 {
 				i = len(line)
 				pos.col -= lengthNL(line)
 			}
 			line = line[i:]
 			pos.col += i
 		}
 		if len(line) == 0 || line[0] != '"' {
 			// Non-quoted string field
 			i := bytes.IndexRune(line, r.Comma)
 			field := line
 			if i >= 0 {
 				field = field[:i]
 			} else {
 				field = field[:len(field)-lengthNL(field)]
 			}
 			// Check to make sure a quote does not appear in field.
 			if !r.LazyQuotes {
 				if j := bytes.IndexByte(field, '"'); j >= 0 {
 					col := pos.col + j
 					err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrBareQuote}
 					break parseField
 				}
 			}
 			r.recordBuffer = append(r.recordBuffer, field...)
 			r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
 			r.fieldPositions = append(r.fieldPositions, pos)
 			if i >= 0 {
 				line = line[i+commaLen:]
 				pos.col += i + commaLen
 				continue parseField
 			}
 			break parseField
 		} else {
 			// Quoted string field
 			fieldPos := pos
 			line = line[quoteLen:]
 			pos.col += quoteLen
 			for {
 				i := bytes.IndexByte(line, '"')
 				if i >= 0 {
 					// Hit next quote.
 					r.recordBuffer = append(r.recordBuffer, line[:i]...)
 					line = line[i+quoteLen:]
 					pos.col += i + quoteLen
 					switch rn := nextRune(line); {
 					case rn == '"':
 						// `""` sequence (append quote).
 						r.recordBuffer = append(r.recordBuffer, '"')
 						line = line[quoteLen:]
 						pos.col += quoteLen
 					case rn == r.Comma:
 						// `",` sequence (end of field).
 						line = line[commaLen:]
 						pos.col += commaLen
 						r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
 						r.fieldPositions = append(r.fieldPositions, fieldPos)
 						continue parseField
 					case lengthNL(line) == len(line):
 						// `"\n` sequence (end of line).
 						r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
 						r.fieldPositions = append(r.fieldPositions, fieldPos)
 						break parseField
 					case r.LazyQuotes:
 						// `"` sequence (bare quote).
 						r.recordBuffer = append(r.recordBuffer, '"')
 					default:
 						// `"*` sequence (invalid non-escaped quote).
 						err = &ParseError{StartLine: recLine, Line: r.numLine, Column: pos.col - quoteLen, Err: ErrQuote}
 						break parseField
 					}
 				} else if len(line) > 0 {
 					// Hit end of line (copy all data so far).
 					r.recordBuffer = append(r.recordBuffer, line...)
 					if errRead != nil {
 						break parseField
 					}
 					pos.col += len(line)
 					line, errRead = r.readLine()
 					if len(line) > 0 {
 						pos.line++
 						pos.col = 1
 					}
 					if errRead == io.EOF {
 						errRead = nil
 					}
 				} else {
 					// Abrupt end of file (EOF or error).
 					if !r.LazyQuotes && errRead == nil {
 						err = &ParseError{StartLine: recLine, Line: pos.line, Column: pos.col, Err: ErrQuote}
 						break parseField
 					}
 					r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
 					r.fieldPositions = append(r.fieldPositions, fieldPos)
 					break parseField
 				}
 			}
 		}
 	}
 	if err == nil {
 		err = errRead
 	}

 	// Create a single string and create slices out of it.
 	// This pins the memory of the fields together, but allocates once.
 	str := string(r.recordBuffer) // Convert to string once to batch allocations
 	dst = dst[:0]
 	if cap(dst) < len(r.fieldIndexes) {
 		dst = make([]string, len(r.fieldIndexes))
 	}
 	dst = dst[:len(r.fieldIndexes)]
 	var preIdx int
 	for i, idx := range r.fieldIndexes {
 		dst[i] = str[preIdx:idx]
 		preIdx = idx
 	}

 	// Check or update the expected fields per record.
 	if r.FieldsPerRecord > 0 {
 		if len(dst) != r.FieldsPerRecord && err == nil {
 			err = &ParseError{
 				StartLine: recLine,
 				Line:      recLine,
 				Column:    1,
 				Err:       ErrFieldCount,
 			}
 		}
 	} else if r.FieldsPerRecord == 0 {
 		r.FieldsPerRecord = len(dst)
 	}
 	return dst, err
 }
	// 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 reads and writes comma-separated values (CSV) files.
	// There are many kinds of CSV files; this package supports the format
	// described in RFC 4180.
	//
	// A csv file contains zero or more records of one or more fields per record.
	// Each record is separated by the newline character. The final record may
	// optionally be followed by a newline character.
	//
	// field1,field2,field3
	//
	// White space is considered part of a field.
	//
	// Carriage returns before newline characters are silently removed.
	//
	// Blank lines are ignored. A line with only whitespace characters (excluding
	// the ending newline character) is not considered a blank line.
	//
	// Fields which start and stop with the quote character " are called
	// quoted-fields. The beginning and ending quote are not part of the
	// field.
	//
	// The source:
	//
	// normal string,"quoted-field"
	//
	// results in the fields
	//
	// {`normal string`, `quoted-field`}
	//
	// Within a quoted-field a quote character followed by a second quote
	// character is considered a single quote.
	//
	// "the ""word"" is true","a ""quoted-field"""
	//
	// results in
	//
	// {`the "word" is true`, `a "quoted-field"`}
	//
	// Newlines and commas may be included in a quoted-field
	//
	// "Multi-line
	// field","comma is ,"
	//
	// results in
	//
	// {`Multi-line
	// field`, `comma is ,`}
	package csv

	import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"unicode"
	"unicode/utf8"
	)

	// A ParseError is returned for parsing errors.
	// Line and column numbers are 1-indexed.
	type ParseError struct {
	StartLine int // Line where the record starts
	Line int // Line where the error occurred
	Column int // Column (1-based byte index) where the error occurred
	Err error // The actual error
	}

	func (e *ParseError) Error() string {
	if e.Err == ErrFieldCount {
	return fmt.Sprintf("record on line %d: %v", e.Line, e.Err)
	}
	if e.StartLine != e.Line {
	return fmt.Sprintf("record on line %d; parse error on line %d, column %d: %v", e.StartLine, e.Line, e.Column, e.Err)
	}
	return fmt.Sprintf("parse error on line %d, column %d: %v", e.Line, e.Column, e.Err)
	}

	func (e *ParseError) Unwrap() error { return e.Err }

	// These are the errors that can be returned in [ParseError.Err].
	var (
	ErrBareQuote = errors.New("bare \" in non-quoted-field")
	ErrQuote = errors.New("extraneous or missing \" in quoted-field")
	ErrFieldCount = errors.New("wrong number of fields")

	// Deprecated: ErrTrailingComma is no longer used.
	ErrTrailingComma = errors.New("extra delimiter at end of line")
	)

	var errInvalidDelim = errors.New("csv: invalid field or comment delimiter")

	func validDelim(r rune) bool {
	return r != 0 && r != '"' && r != '\r' && r != '\n' && utf8.ValidRune(r) && r != utf8.RuneError
	}

	// A Reader reads records from a CSV-encoded file.
	//
	// As returned by [NewReader], a Reader expects input conforming to RFC 4180.
	// The exported fields can be changed to customize the details before the
	// first call to [Reader.Read] or [Reader.ReadAll].
	//
	// The Reader converts all \r\n sequences in its input to plain \n,
	// including in multiline field values, so that the returned data does
	// not depend on which line-ending convention an input file uses.
	type Reader struct {
	// Comma is the field delimiter.
	// It is set to comma (',') by NewReader.
	// Comma must be a valid rune and must not be \r, \n,
	// or the Unicode replacement character (0xFFFD).
	Comma rune

	// Comment, if not 0, is the comment character. Lines beginning with the
	// Comment character without preceding whitespace are ignored.
	// With leading whitespace the Comment character becomes part of the
	// field, even if TrimLeadingSpace is true.
	// Comment must be a valid rune and must not be \r, \n,
	// or the Unicode replacement character (0xFFFD).
	// It must also not be equal to Comma.
	Comment rune

	// FieldsPerRecord is the number of expected fields per record.
	// If FieldsPerRecord is positive, Read requires each record to
	// have the given number of fields. If FieldsPerRecord is 0, Read sets it to
	// the number of fields in the first record, so that future records must
	// have the same field count. If FieldsPerRecord is negative, no check is
	// made and records may have a variable number of fields.
	FieldsPerRecord int

	// If LazyQuotes is true, a quote may appear in an unquoted field and a
	// non-doubled quote may appear in a quoted field.
	LazyQuotes bool

	// If TrimLeadingSpace is true, leading white space in a field is ignored.
	// This is done even if the field delimiter, Comma, is white space.
	TrimLeadingSpace bool

	// ReuseRecord controls whether calls to Read may return a slice sharing
	// the backing array of the previous call's returned slice for performance.
	// By default, each call to Read returns newly allocated memory owned by the caller.
	ReuseRecord bool

	// Deprecated: TrailingComma is no longer used.
	TrailingComma bool

	r *bufio.Reader

	// numLine is the current line being read in the CSV file.
	numLine int

	// offset is the input stream byte offset of the current reader position.
	offset int64

	// rawBuffer is a line buffer only used by the readLine method.
	rawBuffer []byte

	// recordBuffer holds the unescaped fields, one after another.
	// The fields can be accessed by using the indexes in fieldIndexes.
	// E.g., For the row `a,"b","c""d",e`, recordBuffer will contain `abc"de`
	// and fieldIndexes will contain the indexes [1, 2, 5, 6].
	recordBuffer []byte

	// fieldIndexes is an index of fields inside recordBuffer.
	// The i'th field ends at offset fieldIndexes[i] in recordBuffer.
	fieldIndexes []int

	// fieldPositions is an index of field positions for the
	// last record returned by Read.
	fieldPositions []position

	// lastRecord is a record cache and only used when ReuseRecord == true.
	lastRecord []string
	}

	// NewReader returns a new Reader that reads from r.
	func NewReader(r io.Reader) *Reader {
	return &Reader{
	Comma: ',',
	r: bufio.NewReader(r),
	}
	}

	// Read reads one record (a slice of fields) from r.
	// If the record has an unexpected number of fields,
	// Read returns the record along with the error [ErrFieldCount].
	// If the record contains a field that cannot be parsed,
	// Read returns a partial record along with the parse error.
	// The partial record contains all fields read before the error.
	// If there is no data left to be read, Read returns nil, [io.EOF].
	// If [Reader.ReuseRecord] is true, the returned slice may be shared
	// between multiple calls to Read.
	func (r *Reader) Read() (record []string, err error) {
	if r.ReuseRecord {
	record, err = r.readRecord(r.lastRecord)
	r.lastRecord = record
	} else {
	record, err = r.readRecord(nil)
	}
	return record, err
	}

	// FieldPos returns the line and column corresponding to
	// the start of the field with the given index in the slice most recently
	// returned by [Reader.Read]. Numbering of lines and columns starts at 1;
	// columns are counted in bytes, not runes.
	//
	// If this is called with an out-of-bounds index, it panics.
	func (r *Reader) FieldPos(field int) (line, column int) {
	if field < 0 \|\| field >= len(r.fieldPositions) {
	panic("out of range index passed to FieldPos")
	}
	p := &r.fieldPositions[field]
	return p.line, p.col
	}

	// InputOffset returns the input stream byte offset of the current reader
	// position. The offset gives the location of the end of the most recently
	// read row and the beginning of the next row.
	func (r *Reader) InputOffset() int64 {
	return r.offset
	}

	// pos holds the position of a field in the current line.
	type position struct {
	line, col int
	}

	// ReadAll reads all the remaining records from r.
	// Each record is a slice of fields.
	// A successful call returns err == nil, not err == [io.EOF]. Because ReadAll is
	// defined to read until EOF, it does not treat end of file as an error to be
	// reported.
	func (r *Reader) ReadAll() (records [][]string, err error) {
	for {
	record, err := r.readRecord(nil)
	if err == io.EOF {
	return records, nil
	}
	if err != nil {
	return nil, err
	}
	records = append(records, record)
	}
	}

	// readLine reads the next line (with the trailing endline).
	// If EOF is hit without a trailing endline, it will be omitted.
	// If some bytes were read, then the error is never [io.EOF].
	// The result is only valid until the next call to readLine.
	func (r *Reader) readLine() ([]byte, error) {
	line, err := r.r.ReadSlice('\n')
	if err == bufio.ErrBufferFull {
	r.rawBuffer = append(r.rawBuffer[:0], line...)
	for err == bufio.ErrBufferFull {
	line, err = r.r.ReadSlice('\n')
	r.rawBuffer = append(r.rawBuffer, line...)
	}
	line = r.rawBuffer
	}
	readSize := len(line)
	if readSize > 0 && err == io.EOF {
	err = nil
	// For backwards compatibility, drop trailing \r before EOF.
	if line[readSize-1] == '\r' {
	line = line[:readSize-1]
	}
	}
	r.numLine++
	r.offset += int64(readSize)
	// Normalize \r\n to \n on all input lines.
	if n := len(line); n >= 2 && line[n-2] == '\r' && line[n-1] == '\n' {
	line[n-2] = '\n'
	line = line[:n-1]
	}
	return line, err
	}

	// lengthNL reports the number of bytes for the trailing \n.
	func lengthNL(b []byte) int {
	if len(b) > 0 && b[len(b)-1] == '\n' {
	return 1
	}
	return 0
	}

	// nextRune returns the next rune in b or utf8.RuneError.
	func nextRune(b []byte) rune {
	r, _ := utf8.DecodeRune(b)
	return r
	}

	func (r *Reader) readRecord(dst []string) ([]string, error) {
	if r.Comma == r.Comment \|\| !validDelim(r.Comma) \|\| (r.Comment != 0 && !validDelim(r.Comment)) {
	return nil, errInvalidDelim
	}

	// Read line (automatically skipping past empty lines and any comments).
	var line []byte
	var errRead error
	for errRead == nil {
	line, errRead = r.readLine()
	if r.Comment != 0 && nextRune(line) == r.Comment {
	line = nil
	continue // Skip comment lines
	}
	if errRead == nil && len(line) == lengthNL(line) {
	line = nil
	continue // Skip empty lines
	}
	break
	}
	if errRead == io.EOF {
	return nil, errRead
	}

	// Parse each field in the record.
	var err error
	const quoteLen = len(`"`)
	commaLen := utf8.RuneLen(r.Comma)
	recLine := r.numLine // Starting line for record
	r.recordBuffer = r.recordBuffer[:0]
	r.fieldIndexes = r.fieldIndexes[:0]
	r.fieldPositions = r.fieldPositions[:0]
	pos := position{line: r.numLine, col: 1}
	parseField:
	for {
	if r.TrimLeadingSpace {
	i := bytes.IndexFunc(line, func(r rune) bool {
	return !unicode.IsSpace(r)
	})
	if i < 0 {
	i = len(line)
	pos.col -= lengthNL(line)
	}
	line = line[i:]
	pos.col += i
	}
	if len(line) == 0 \|\| line[0] != '"' {
	// Non-quoted string field
	i := bytes.IndexRune(line, r.Comma)
	field := line
	if i >= 0 {
	field = field[:i]
	} else {
	field = field[:len(field)-lengthNL(field)]
	}
	// Check to make sure a quote does not appear in field.
	if !r.LazyQuotes {
	if j := bytes.IndexByte(field, '"'); j >= 0 {
	col := pos.col + j
	err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrBareQuote}
	break parseField
	}
	}
	r.recordBuffer = append(r.recordBuffer, field...)
	r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
	r.fieldPositions = append(r.fieldPositions, pos)
	if i >= 0 {
	line = line[i+commaLen:]
	pos.col += i + commaLen
	continue parseField
	}
	break parseField
	} else {
	// Quoted string field
	fieldPos := pos
	line = line[quoteLen:]
	pos.col += quoteLen
	for {
	i := bytes.IndexByte(line, '"')
	if i >= 0 {
	// Hit next quote.
	r.recordBuffer = append(r.recordBuffer, line[:i]...)
	line = line[i+quoteLen:]
	pos.col += i + quoteLen
	switch rn := nextRune(line); {
	case rn == '"':
	// `""` sequence (append quote).
	r.recordBuffer = append(r.recordBuffer, '"')
	line = line[quoteLen:]
	pos.col += quoteLen
	case rn == r.Comma:
	// `",` sequence (end of field).
	line = line[commaLen:]
	pos.col += commaLen
	r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
	r.fieldPositions = append(r.fieldPositions, fieldPos)
	continue parseField
	case lengthNL(line) == len(line):
	// `"\n` sequence (end of line).
	r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
	r.fieldPositions = append(r.fieldPositions, fieldPos)
	break parseField
	case r.LazyQuotes:
	// `"` sequence (bare quote).
	r.recordBuffer = append(r.recordBuffer, '"')
	default:
	// `"*` sequence (invalid non-escaped quote).
	err = &ParseError{StartLine: recLine, Line: r.numLine, Column: pos.col - quoteLen, Err: ErrQuote}
	break parseField
	}
	} else if len(line) > 0 {
	// Hit end of line (copy all data so far).
	r.recordBuffer = append(r.recordBuffer, line...)
	if errRead != nil {
	break parseField
	}
	pos.col += len(line)
	line, errRead = r.readLine()
	if len(line) > 0 {
	pos.line++
	pos.col = 1
	}
	if errRead == io.EOF {
	errRead = nil
	}
	} else {
	// Abrupt end of file (EOF or error).
	if !r.LazyQuotes && errRead == nil {
	err = &ParseError{StartLine: recLine, Line: pos.line, Column: pos.col, Err: ErrQuote}
	break parseField
	}
	r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
	r.fieldPositions = append(r.fieldPositions, fieldPos)
	break parseField
	}
	}
	}
	}
	if err == nil {
	err = errRead
	}

	// Create a single string and create slices out of it.
	// This pins the memory of the fields together, but allocates once.
	str := string(r.recordBuffer) // Convert to string once to batch allocations
	dst = dst[:0]
	if cap(dst) < len(r.fieldIndexes) {
	dst = make([]string, len(r.fieldIndexes))
	}
	dst = dst[:len(r.fieldIndexes)]
	var preIdx int
	for i, idx := range r.fieldIndexes {
	dst[i] = str[preIdx:idx]
	preIdx = idx
	}

	// Check or update the expected fields per record.
	if r.FieldsPerRecord > 0 {
	if len(dst) != r.FieldsPerRecord && err == nil {
	err = &ParseError{
	StartLine: recLine,
	Line: recLine,
	Column: 1,
	Err: ErrFieldCount,
	}
	}
	} else if r.FieldsPerRecord == 0 {
	r.FieldsPerRecord = len(dst)
	}
	return dst, err
	}