403 lines
12 KiB
Go
403 lines
12 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in https://golang.org/LICENSE
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// Package csv reads and writes comma-separated values (CSV) files.
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// There are many kinds of CSV files; this package supports the format
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// described in RFC 4180.
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//
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// A csv file contains zero or more records of one or more fields per record.
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// Each record is separated by the newline character. The final record may
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// optionally be followed by a newline character.
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//
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// field1,field2,field3
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//
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// White space is considered part of a field.
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//
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// Carriage returns before newline characters are silently removed.
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//
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// Blank lines are ignored. A line with only whitespace characters (excluding
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// the ending newline character) is not considered a blank line.
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//
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// Fields which start and stop with the quote character " are called
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// quoted-fields. The beginning and ending quote are not part of the
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// field.
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//
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// The source:
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//
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// normal string,"quoted-field"
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//
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// results in the fields
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//
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// {`normal string`, `quoted-field`}
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//
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// Within a quoted-field a quote character followed by a second quote
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// character is considered a single quote.
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//
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// "the ""word"" is true","a ""quoted-field"""
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//
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// results in
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//
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// {`the "word" is true`, `a "quoted-field"`}
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//
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// Newlines and commas may be included in a quoted-field
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//
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// "Multi-line
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// field","comma is ,"
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//
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// results in
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//
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// {`Multi-line
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// field`, `comma is ,`}
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package csv
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import (
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"bufio"
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"bytes"
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"errors"
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"fmt"
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"io"
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"unicode"
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"unicode/utf8"
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)
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// A ParseError is returned for parsing errors.
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// Line numbers are 1-indexed and columns are 0-indexed.
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type ParseError struct {
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StartLine int // Line where the record starts
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Line int // Line where the error occurred
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Column int // Column (rune index) where the error occurred
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Err error // The actual error
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}
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func (e *ParseError) Error() string {
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if e.Err == ErrFieldCount {
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return fmt.Sprintf("record on line %d: %v", e.Line, e.Err)
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}
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if e.StartLine != e.Line {
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return fmt.Sprintf("record on line %d; parse error on line %d, column %d: %v", e.StartLine, e.Line, e.Column, e.Err)
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}
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return fmt.Sprintf("parse error on line %d, column %d: %v", e.Line, e.Column, e.Err)
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}
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// Unwrap returns the underlying error
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func (e *ParseError) Unwrap() error { return e.Err }
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// These are the errors that can be returned in ParseError.Err.
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var (
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ErrTrailingComma = errors.New("extra delimiter at end of line") // Deprecated: No longer used.
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ErrBareQuote = errors.New("bare \" in non-quoted-field")
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ErrQuote = errors.New("extraneous or missing \" in quoted-field")
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ErrFieldCount = errors.New("wrong number of fields")
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)
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var errInvalidDelim = errors.New("csv: invalid field or comment delimiter")
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func validDelim(r rune) bool {
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return r != 0 && r != '"' && r != '\r' && r != '\n' && utf8.ValidRune(r) && r != utf8.RuneError
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}
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// A Reader reads records from a CSV-encoded file.
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//
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// As returned by NewReader, a Reader expects input conforming to RFC 4180.
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// The exported fields can be changed to customize the details before the
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// first call to Read or ReadAll.
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//
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// The Reader converts all \r\n sequences in its input to plain \n,
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// including in multiline field values, so that the returned data does
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// not depend on which line-ending convention an input file uses.
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type Reader struct {
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// Comma is the field delimiter.
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// It is set to comma (',') by NewReader.
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// Comma must be a valid rune and must not be \r, \n,
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// or the Unicode replacement character (0xFFFD).
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Comma rune
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// Comment, if not 0, is the comment character. Lines beginning with the
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// Comment character without preceding whitespace are ignored.
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// With leading whitespace the Comment character becomes part of the
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// field, even if TrimLeadingSpace is true.
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// Comment must be a valid rune and must not be \r, \n,
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// or the Unicode replacement character (0xFFFD).
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// It must also not be equal to Comma.
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Comment rune
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// FieldsPerRecord is the number of expected fields per record.
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// If FieldsPerRecord is positive, Read requires each record to
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// have the given number of fields. If FieldsPerRecord is 0, Read sets it to
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// the number of fields in the first record, so that future records must
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// have the same field count. If FieldsPerRecord is negative, no check is
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// made and records may have a variable number of fields.
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FieldsPerRecord int
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// If LazyQuotes is true, a quote may appear in an unquoted field and a
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// non-doubled quote may appear in a quoted field.
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LazyQuotes bool
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// If TrimLeadingSpace is true, leading white space in a field is ignored.
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// This is done even if the field delimiter, Comma, is white space.
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TrimLeadingSpace bool
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// ReuseRecord controls whether calls to Read may return a slice sharing
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// the backing array of the previous call's returned slice for performance.
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// By default, each call to Read returns newly allocated memory owned by the caller.
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ReuseRecord bool
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TrailingComma bool // Deprecated: No longer used.
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r *bufio.Reader
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// numLine is the current line being read in the CSV file.
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numLine int
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// rawBuffer is a line buffer only used by the readLine method.
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rawBuffer []byte
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// recordBuffer holds the unescaped fields, one after another.
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// The fields can be accessed by using the indexes in fieldIndexes.
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// E.g., For the row `a,"b","c""d",e`, recordBuffer will contain `abc"de`
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// and fieldIndexes will contain the indexes [1, 2, 5, 6].
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recordBuffer []byte
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// fieldIndexes is an index of fields inside recordBuffer.
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// The i'th field ends at offset fieldIndexes[i] in recordBuffer.
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fieldIndexes []int
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// lastRecord is a record cache and only used when ReuseRecord == true.
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lastRecord []string
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}
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// NewReader returns a new Reader that reads from r.
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func NewReader(r io.Reader) *Reader {
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return &Reader{
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Comma: ',',
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r: bufio.NewReader(r),
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}
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}
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// Read reads one record (a slice of fields) from r.
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// If the record has an unexpected number of fields,
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// Read returns the record along with the error ErrFieldCount.
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// Except for that case, Read always returns either a non-nil
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// record or a non-nil error, but not both.
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// If there is no data left to be read, Read returns nil, io.EOF.
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// If ReuseRecord is true, the returned slice may be shared
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// between multiple calls to Read.
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func (r *Reader) Read() (record []string, err error) {
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if r.ReuseRecord {
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record, err = r.readRecord(r.lastRecord)
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r.lastRecord = record
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} else {
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record, err = r.readRecord(nil)
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}
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return record, err
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}
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// ReadAll reads all the remaining records from r.
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// Each record is a slice of fields.
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// A successful call returns err == nil, not err == io.EOF. Because ReadAll is
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// defined to read until EOF, it does not treat end of file as an error to be
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// reported.
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func (r *Reader) ReadAll() (records [][]string, err error) {
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for {
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record, err := r.readRecord(nil)
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if err == io.EOF {
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return records, nil
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}
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if err != nil {
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return nil, err
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}
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records = append(records, record)
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}
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}
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// readLine reads the next line (with the trailing endline).
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// If EOF is hit without a trailing endline, it will be omitted.
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// If some bytes were read, then the error is never io.EOF.
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// The result is only valid until the next call to readLine.
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func (r *Reader) readLine() ([]byte, error) {
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line, err := r.r.ReadSlice('\n')
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if err == bufio.ErrBufferFull {
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r.rawBuffer = append(r.rawBuffer[:0], line...)
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for err == bufio.ErrBufferFull {
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line, err = r.r.ReadSlice('\n')
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r.rawBuffer = append(r.rawBuffer, line...)
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}
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line = r.rawBuffer
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}
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if len(line) > 0 && err == io.EOF {
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err = nil
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// For backwards compatibility, drop trailing \r before EOF.
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if line[len(line)-1] == '\r' {
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line = line[:len(line)-1]
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}
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}
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r.numLine++
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// Normalize \r\n to \n on all input lines.
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if n := len(line); n >= 2 && line[n-2] == '\r' && line[n-1] == '\n' {
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line[n-2] = '\n'
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line = line[:n-1]
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}
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return line, err
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}
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// lengthNL reports the number of bytes for the trailing \n.
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func lengthNL(b []byte) int {
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if len(b) > 0 && b[len(b)-1] == '\n' {
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return 1
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}
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return 0
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}
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// nextRune returns the next rune in b or utf8.RuneError.
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func nextRune(b []byte) rune {
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r, _ := utf8.DecodeRune(b)
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return r
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}
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func (r *Reader) readRecord(dst []string) ([]string, error) {
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if r.Comma == r.Comment || !validDelim(r.Comma) || (r.Comment != 0 && !validDelim(r.Comment)) {
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return nil, errInvalidDelim
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}
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// Read line (automatically skipping past empty lines and any comments).
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var line, fullLine []byte
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var errRead error
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for errRead == nil {
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line, errRead = r.readLine()
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if r.Comment != 0 && nextRune(line) == r.Comment {
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line = nil
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continue // Skip comment lines
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}
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if errRead == nil && len(line) == lengthNL(line) {
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line = nil
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continue // Skip empty lines
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}
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fullLine = line
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break
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}
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if errRead == io.EOF {
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return nil, errRead
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}
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// Parse each field in the record.
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var err error
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const quoteLen = len(`"`)
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commaLen := utf8.RuneLen(r.Comma)
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recLine := r.numLine // Starting line for record
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r.recordBuffer = r.recordBuffer[:0]
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r.fieldIndexes = r.fieldIndexes[:0]
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parseField:
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for {
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if r.TrimLeadingSpace {
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line = bytes.TrimLeftFunc(line, unicode.IsSpace)
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}
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if len(line) == 0 || line[0] != '"' {
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// Non-quoted string field
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i := bytes.IndexRune(line, r.Comma)
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field := line
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if i >= 0 {
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field = field[:i]
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} else {
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field = field[:len(field)-lengthNL(field)]
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}
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// Check to make sure a quote does not appear in field.
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if !r.LazyQuotes {
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if j := bytes.IndexByte(field, '"'); j >= 0 {
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col := utf8.RuneCount(fullLine[:len(fullLine)-len(line[j:])])
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err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrBareQuote}
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break parseField
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}
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}
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r.recordBuffer = append(r.recordBuffer, field...)
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r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
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if i >= 0 {
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line = line[i+commaLen:]
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continue parseField
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}
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break parseField
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} else {
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// Quoted string field
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line = line[quoteLen:]
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for {
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i := bytes.IndexByte(line, '"')
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if i >= 0 {
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// Hit next quote.
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r.recordBuffer = append(r.recordBuffer, line[:i]...)
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line = line[i+quoteLen:]
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switch rn := nextRune(line); {
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case rn == '"':
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// `""` sequence (append quote).
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r.recordBuffer = append(r.recordBuffer, '"')
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line = line[quoteLen:]
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case rn == r.Comma:
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// `",` sequence (end of field).
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line = line[commaLen:]
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r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
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continue parseField
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case lengthNL(line) == len(line):
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// `"\n` sequence (end of line).
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r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
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break parseField
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case r.LazyQuotes:
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// `"` sequence (bare quote).
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r.recordBuffer = append(r.recordBuffer, '"')
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default:
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// `"*` sequence (invalid non-escaped quote).
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col := utf8.RuneCount(fullLine[:len(fullLine)-len(line)-quoteLen])
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err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrQuote}
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break parseField
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}
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} else if len(line) > 0 {
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// Hit end of line (copy all data so far).
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r.recordBuffer = append(r.recordBuffer, line...)
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if errRead != nil {
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break parseField
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}
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line, errRead = r.readLine()
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if errRead == io.EOF {
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errRead = nil
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}
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fullLine = line
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} else {
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// Abrupt end of file (EOF or error).
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if !r.LazyQuotes && errRead == nil {
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col := utf8.RuneCount(fullLine)
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err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrQuote}
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break parseField
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}
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r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
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break parseField
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}
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}
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}
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}
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if err == nil {
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err = errRead
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}
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// Create a single string and create slices out of it.
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// This pins the memory of the fields together, but allocates once.
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str := string(r.recordBuffer) // Convert to string once to batch allocations
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dst = dst[:0]
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if cap(dst) < len(r.fieldIndexes) {
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dst = make([]string, len(r.fieldIndexes))
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}
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dst = dst[:len(r.fieldIndexes)]
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var preIdx int
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for i, idx := range r.fieldIndexes {
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dst[i] = str[preIdx:idx]
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preIdx = idx
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}
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// Check or update the expected fields per record.
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if r.FieldsPerRecord > 0 {
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if len(dst) != r.FieldsPerRecord && err == nil {
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err = &ParseError{StartLine: recLine, Line: recLine, Err: ErrFieldCount}
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}
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} else if r.FieldsPerRecord == 0 {
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r.FieldsPerRecord = len(dst)
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}
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return dst, err
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}
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