src/encoding/csv/reader.go - go - Git at Google (original) (raw)
// 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, except that [Writer] uses LF
// instead of CRLF as newline character by default.
//
// 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
}