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Source file src/encoding/csv/reader.go

Documentation: encoding/csv

     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 reads and writes comma-separated values (CSV) files.
     6  // There are many kinds of CSV files; this package supports the format
     7  // described in RFC 4180.
     8  //
     9  // A csv file contains zero or more records of one or more fields per record.
    10  // Each record is separated by the newline character. The final record may
    11  // optionally be followed by a newline character.
    12  //
    13  //	field1,field2,field3
    14  //
    15  // White space is considered part of a field.
    16  //
    17  // Carriage returns before newline characters are silently removed.
    18  //
    19  // Blank lines are ignored. A line with only whitespace characters (excluding
    20  // the ending newline character) is not considered a blank line.
    21  //
    22  // Fields which start and stop with the quote character " are called
    23  // quoted-fields. The beginning and ending quote are not part of the
    24  // field.
    25  //
    26  // The source:
    27  //
    28  //	normal string,"quoted-field"
    29  //
    30  // results in the fields
    31  //
    32  //	{`normal string`, `quoted-field`}
    33  //
    34  // Within a quoted-field a quote character followed by a second quote
    35  // character is considered a single quote.
    36  //
    37  //	"the ""word"" is true","a ""quoted-field"""
    38  //
    39  // results in
    40  //
    41  //	{`the "word" is true`, `a "quoted-field"`}
    42  //
    43  // Newlines and commas may be included in a quoted-field
    44  //
    45  //	"Multi-line
    46  //	field","comma is ,"
    47  //
    48  // results in
    49  //
    50  //	{`Multi-line
    51  //	field`, `comma is ,`}
    52  package csv
    53  
    54  import (
    55  	"bufio"
    56  	"bytes"
    57  	"errors"
    58  	"fmt"
    59  	"io"
    60  	"unicode"
    61  	"unicode/utf8"
    62  )
    63  
    64  // A ParseError is returned for parsing errors.
    65  // Line numbers are 1-indexed and columns are 0-indexed.
    66  type ParseError struct {
    67  	StartLine int   // Line where the record starts
    68  	Line      int   // Line where the error occurred
    69  	Column    int   // Column (rune index) where the error occurred
    70  	Err       error // The actual error
    71  }
    72  
    73  func (e *ParseError) Error() string {
    74  	if e.Err == ErrFieldCount {
    75  		return fmt.Sprintf("record on line %d: %v", e.Line, e.Err)
    76  	}
    77  	if e.StartLine != e.Line {
    78  		return fmt.Sprintf("record on line %d; parse error on line %d, column %d: %v", e.StartLine, e.Line, e.Column, e.Err)
    79  	}
    80  	return fmt.Sprintf("parse error on line %d, column %d: %v", e.Line, e.Column, e.Err)
    81  }
    82  
    83  // These are the errors that can be returned in ParseError.Err.
    84  var (
    85  	ErrTrailingComma = errors.New("extra delimiter at end of line") // Deprecated: No longer used.
    86  	ErrBareQuote     = errors.New("bare \" in non-quoted-field")
    87  	ErrQuote         = errors.New("extraneous or missing \" in quoted-field")
    88  	ErrFieldCount    = errors.New("wrong number of fields")
    89  )
    90  
    91  var errInvalidDelim = errors.New("csv: invalid field or comment delimiter")
    92  
    93  func validDelim(r rune) bool {
    94  	return r != 0 && r != '"' && r != '\r' && r != '\n' && utf8.ValidRune(r) && r != utf8.RuneError
    95  }
    96  
    97  // A Reader reads records from a CSV-encoded file.
    98  //
    99  // As returned by NewReader, a Reader expects input conforming to RFC 4180.
   100  // The exported fields can be changed to customize the details before the
   101  // first call to Read or ReadAll.
   102  //
   103  // The Reader converts all \r\n sequences in its input to plain \n,
   104  // including in multiline field values, so that the returned data does
   105  // not depend on which line-ending convention an input file uses.
   106  type Reader struct {
   107  	// Comma is the field delimiter.
   108  	// It is set to comma (',') by NewReader.
   109  	// Comma must be a valid rune and must not be \r, \n,
   110  	// or the Unicode replacement character (0xFFFD).
   111  	Comma rune
   112  
   113  	// Comment, if not 0, is the comment character. Lines beginning with the
   114  	// Comment character without preceding whitespace are ignored.
   115  	// With leading whitespace the Comment character becomes part of the
   116  	// field, even if TrimLeadingSpace is true.
   117  	// Comment must be a valid rune and must not be \r, \n,
   118  	// or the Unicode replacement character (0xFFFD).
   119  	// It must also not be equal to Comma.
   120  	Comment rune
   121  
   122  	// FieldsPerRecord is the number of expected fields per record.
   123  	// If FieldsPerRecord is positive, Read requires each record to
   124  	// have the given number of fields. If FieldsPerRecord is 0, Read sets it to
   125  	// the number of fields in the first record, so that future records must
   126  	// have the same field count. If FieldsPerRecord is negative, no check is
   127  	// made and records may have a variable number of fields.
   128  	FieldsPerRecord int
   129  
   130  	// If LazyQuotes is true, a quote may appear in an unquoted field and a
   131  	// non-doubled quote may appear in a quoted field.
   132  	LazyQuotes bool
   133  
   134  	// If TrimLeadingSpace is true, leading white space in a field is ignored.
   135  	// This is done even if the field delimiter, Comma, is white space.
   136  	TrimLeadingSpace bool
   137  
   138  	// ReuseRecord controls whether calls to Read may return a slice sharing
   139  	// the backing array of the previous call's returned slice for performance.
   140  	// By default, each call to Read returns newly allocated memory owned by the caller.
   141  	ReuseRecord bool
   142  
   143  	TrailingComma bool // Deprecated: No longer used.
   144  
   145  	r *bufio.Reader
   146  
   147  	// numLine is the current line being read in the CSV file.
   148  	numLine int
   149  
   150  	// rawBuffer is a line buffer only used by the readLine method.
   151  	rawBuffer []byte
   152  
   153  	// recordBuffer holds the unescaped fields, one after another.
   154  	// The fields can be accessed by using the indexes in fieldIndexes.
   155  	// E.g., For the row `a,"b","c""d",e`, recordBuffer will contain `abc"de`
   156  	// and fieldIndexes will contain the indexes [1, 2, 5, 6].
   157  	recordBuffer []byte
   158  
   159  	// fieldIndexes is an index of fields inside recordBuffer.
   160  	// The i'th field ends at offset fieldIndexes[i] in recordBuffer.
   161  	fieldIndexes []int
   162  
   163  	// lastRecord is a record cache and only used when ReuseRecord == true.
   164  	lastRecord []string
   165  }
   166  
   167  // NewReader returns a new Reader that reads from r.
   168  func NewReader(r io.Reader) *Reader {
   169  	return &Reader{
   170  		Comma: ',',
   171  		r:     bufio.NewReader(r),
   172  	}
   173  }
   174  
   175  // Read reads one record (a slice of fields) from r.
   176  // If the record has an unexpected number of fields,
   177  // Read returns the record along with the error ErrFieldCount.
   178  // Except for that case, Read always returns either a non-nil
   179  // record or a non-nil error, but not both.
   180  // If there is no data left to be read, Read returns nil, io.EOF.
   181  // If ReuseRecord is true, the returned slice may be shared
   182  // between multiple calls to Read.
   183  func (r *Reader) Read() (record []string, err error) {
   184  	if r.ReuseRecord {
   185  		record, err = r.readRecord(r.lastRecord)
   186  		r.lastRecord = record
   187  	} else {
   188  		record, err = r.readRecord(nil)
   189  	}
   190  	return record, err
   191  }
   192  
   193  // ReadAll reads all the remaining records from r.
   194  // Each record is a slice of fields.
   195  // A successful call returns err == nil, not err == io.EOF. Because ReadAll is
   196  // defined to read until EOF, it does not treat end of file as an error to be
   197  // reported.
   198  func (r *Reader) ReadAll() (records [][]string, err error) {
   199  	for {
   200  		record, err := r.readRecord(nil)
   201  		if err == io.EOF {
   202  			return records, nil
   203  		}
   204  		if err != nil {
   205  			return nil, err
   206  		}
   207  		records = append(records, record)
   208  	}
   209  }
   210  
   211  // readLine reads the next line (with the trailing endline).
   212  // If EOF is hit without a trailing endline, it will be omitted.
   213  // If some bytes were read, then the error is never io.EOF.
   214  // The result is only valid until the next call to readLine.
   215  func (r *Reader) readLine() ([]byte, error) {
   216  	line, err := r.r.ReadSlice('\n')
   217  	if err == bufio.ErrBufferFull {
   218  		r.rawBuffer = append(r.rawBuffer[:0], line...)
   219  		for err == bufio.ErrBufferFull {
   220  			line, err = r.r.ReadSlice('\n')
   221  			r.rawBuffer = append(r.rawBuffer, line...)
   222  		}
   223  		line = r.rawBuffer
   224  	}
   225  	if len(line) > 0 && err == io.EOF {
   226  		err = nil
   227  		// For backwards compatibility, drop trailing \r before EOF.
   228  		if line[len(line)-1] == '\r' {
   229  			line = line[:len(line)-1]
   230  		}
   231  	}
   232  	r.numLine++
   233  	// Normalize \r\n to \n on all input lines.
   234  	if n := len(line); n >= 2 && line[n-2] == '\r' && line[n-1] == '\n' {
   235  		line[n-2] = '\n'
   236  		line = line[:n-1]
   237  	}
   238  	return line, err
   239  }
   240  
   241  // lengthNL reports the number of bytes for the trailing \n.
   242  func lengthNL(b []byte) int {
   243  	if len(b) > 0 && b[len(b)-1] == '\n' {
   244  		return 1
   245  	}
   246  	return 0
   247  }
   248  
   249  // nextRune returns the next rune in b or utf8.RuneError.
   250  func nextRune(b []byte) rune {
   251  	r, _ := utf8.DecodeRune(b)
   252  	return r
   253  }
   254  
   255  func (r *Reader) readRecord(dst []string) ([]string, error) {
   256  	if r.Comma == r.Comment || !validDelim(r.Comma) || (r.Comment != 0 && !validDelim(r.Comment)) {
   257  		return nil, errInvalidDelim
   258  	}
   259  
   260  	// Read line (automatically skipping past empty lines and any comments).
   261  	var line, fullLine []byte
   262  	var errRead error
   263  	for errRead == nil {
   264  		line, errRead = r.readLine()
   265  		if r.Comment != 0 && nextRune(line) == r.Comment {
   266  			line = nil
   267  			continue // Skip comment lines
   268  		}
   269  		if errRead == nil && len(line) == lengthNL(line) {
   270  			line = nil
   271  			continue // Skip empty lines
   272  		}
   273  		fullLine = line
   274  		break
   275  	}
   276  	if errRead == io.EOF {
   277  		return nil, errRead
   278  	}
   279  
   280  	// Parse each field in the record.
   281  	var err error
   282  	const quoteLen = len(`"`)
   283  	commaLen := utf8.RuneLen(r.Comma)
   284  	recLine := r.numLine // Starting line for record
   285  	r.recordBuffer = r.recordBuffer[:0]
   286  	r.fieldIndexes = r.fieldIndexes[:0]
   287  parseField:
   288  	for {
   289  		if r.TrimLeadingSpace {
   290  			line = bytes.TrimLeftFunc(line, unicode.IsSpace)
   291  		}
   292  		if len(line) == 0 || line[0] != '"' {
   293  			// Non-quoted string field
   294  			i := bytes.IndexRune(line, r.Comma)
   295  			field := line
   296  			if i >= 0 {
   297  				field = field[:i]
   298  			} else {
   299  				field = field[:len(field)-lengthNL(field)]
   300  			}
   301  			// Check to make sure a quote does not appear in field.
   302  			if !r.LazyQuotes {
   303  				if j := bytes.IndexByte(field, '"'); j >= 0 {
   304  					col := utf8.RuneCount(fullLine[:len(fullLine)-len(line[j:])])
   305  					err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrBareQuote}
   306  					break parseField
   307  				}
   308  			}
   309  			r.recordBuffer = append(r.recordBuffer, field...)
   310  			r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
   311  			if i >= 0 {
   312  				line = line[i+commaLen:]
   313  				continue parseField
   314  			}
   315  			break parseField
   316  		} else {
   317  			// Quoted string field
   318  			line = line[quoteLen:]
   319  			for {
   320  				i := bytes.IndexByte(line, '"')
   321  				if i >= 0 {
   322  					// Hit next quote.
   323  					r.recordBuffer = append(r.recordBuffer, line[:i]...)
   324  					line = line[i+quoteLen:]
   325  					switch rn := nextRune(line); {
   326  					case rn == '"':
   327  						// `""` sequence (append quote).
   328  						r.recordBuffer = append(r.recordBuffer, '"')
   329  						line = line[quoteLen:]
   330  					case rn == r.Comma:
   331  						// `",` sequence (end of field).
   332  						line = line[commaLen:]
   333  						r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
   334  						continue parseField
   335  					case lengthNL(line) == len(line):
   336  						// `"\n` sequence (end of line).
   337  						r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
   338  						break parseField
   339  					case r.LazyQuotes:
   340  						// `"` sequence (bare quote).
   341  						r.recordBuffer = append(r.recordBuffer, '"')
   342  					default:
   343  						// `"*` sequence (invalid non-escaped quote).
   344  						col := utf8.RuneCount(fullLine[:len(fullLine)-len(line)-quoteLen])
   345  						err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrQuote}
   346  						break parseField
   347  					}
   348  				} else if len(line) > 0 {
   349  					// Hit end of line (copy all data so far).
   350  					r.recordBuffer = append(r.recordBuffer, line...)
   351  					if errRead != nil {
   352  						break parseField
   353  					}
   354  					line, errRead = r.readLine()
   355  					if errRead == io.EOF {
   356  						errRead = nil
   357  					}
   358  					fullLine = line
   359  				} else {
   360  					// Abrupt end of file (EOF or error).
   361  					if !r.LazyQuotes && errRead == nil {
   362  						col := utf8.RuneCount(fullLine)
   363  						err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrQuote}
   364  						break parseField
   365  					}
   366  					r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
   367  					break parseField
   368  				}
   369  			}
   370  		}
   371  	}
   372  	if err == nil {
   373  		err = errRead
   374  	}
   375  
   376  	// Create a single string and create slices out of it.
   377  	// This pins the memory of the fields together, but allocates once.
   378  	str := string(r.recordBuffer) // Convert to string once to batch allocations
   379  	dst = dst[:0]
   380  	if cap(dst) < len(r.fieldIndexes) {
   381  		dst = make([]string, len(r.fieldIndexes))
   382  	}
   383  	dst = dst[:len(r.fieldIndexes)]
   384  	var preIdx int
   385  	for i, idx := range r.fieldIndexes {
   386  		dst[i] = str[preIdx:idx]
   387  		preIdx = idx
   388  	}
   389  
   390  	// Check or update the expected fields per record.
   391  	if r.FieldsPerRecord > 0 {
   392  		if len(dst) != r.FieldsPerRecord && err == nil {
   393  			err = &ParseError{StartLine: recLine, Line: recLine, Err: ErrFieldCount}
   394  		}
   395  	} else if r.FieldsPerRecord == 0 {
   396  		r.FieldsPerRecord = len(dst)
   397  	}
   398  	return dst, err
   399  }
   400  

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