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  func (e *ParseError) Unwrap() error { return e.Err }
    84  
    85  // These are the errors that can be returned in ParseError.Err.
    86  var (
    87  	ErrTrailingComma = errors.New("extra delimiter at end of line") // Deprecated: No longer used.
    88  	ErrBareQuote     = errors.New("bare \" in non-quoted-field")
    89  	ErrQuote         = errors.New("extraneous or missing \" in quoted-field")
    90  	ErrFieldCount    = errors.New("wrong number of fields")
    91  )
    92  
    93  var errInvalidDelim = errors.New("csv: invalid field or comment delimiter")
    94  
    95  func validDelim(r rune) bool {
    96  	return r != 0 && r != '"' && r != '\r' && r != '\n' && utf8.ValidRune(r) && r != utf8.RuneError
    97  }
    98  
    99  // A Reader reads records from a CSV-encoded file.
   100  //
   101  // As returned by NewReader, a Reader expects input conforming to RFC 4180.
   102  // The exported fields can be changed to customize the details before the
   103  // first call to Read or ReadAll.
   104  //
   105  // The Reader converts all \r\n sequences in its input to plain \n,
   106  // including in multiline field values, so that the returned data does
   107  // not depend on which line-ending convention an input file uses.
   108  type Reader struct {
   109  	// Comma is the field delimiter.
   110  	// It is set to comma (',') by NewReader.
   111  	// Comma must be a valid rune and must not be \r, \n,
   112  	// or the Unicode replacement character (0xFFFD).
   113  	Comma rune
   114  
   115  	// Comment, if not 0, is the comment character. Lines beginning with the
   116  	// Comment character without preceding whitespace are ignored.
   117  	// With leading whitespace the Comment character becomes part of the
   118  	// field, even if TrimLeadingSpace is true.
   119  	// Comment must be a valid rune and must not be \r, \n,
   120  	// or the Unicode replacement character (0xFFFD).
   121  	// It must also not be equal to Comma.
   122  	Comment rune
   123  
   124  	// FieldsPerRecord is the number of expected fields per record.
   125  	// If FieldsPerRecord is positive, Read requires each record to
   126  	// have the given number of fields. If FieldsPerRecord is 0, Read sets it to
   127  	// the number of fields in the first record, so that future records must
   128  	// have the same field count. If FieldsPerRecord is negative, no check is
   129  	// made and records may have a variable number of fields.
   130  	FieldsPerRecord int
   131  
   132  	// If LazyQuotes is true, a quote may appear in an unquoted field and a
   133  	// non-doubled quote may appear in a quoted field.
   134  	LazyQuotes bool
   135  
   136  	// If TrimLeadingSpace is true, leading white space in a field is ignored.
   137  	// This is done even if the field delimiter, Comma, is white space.
   138  	TrimLeadingSpace bool
   139  
   140  	// ReuseRecord controls whether calls to Read may return a slice sharing
   141  	// the backing array of the previous call's returned slice for performance.
   142  	// By default, each call to Read returns newly allocated memory owned by the caller.
   143  	ReuseRecord bool
   144  
   145  	TrailingComma bool // Deprecated: No longer used.
   146  
   147  	r *bufio.Reader
   148  
   149  	// numLine is the current line being read in the CSV file.
   150  	numLine int
   151  
   152  	// rawBuffer is a line buffer only used by the readLine method.
   153  	rawBuffer []byte
   154  
   155  	// recordBuffer holds the unescaped fields, one after another.
   156  	// The fields can be accessed by using the indexes in fieldIndexes.
   157  	// E.g., For the row `a,"b","c""d",e`, recordBuffer will contain `abc"de`
   158  	// and fieldIndexes will contain the indexes [1, 2, 5, 6].
   159  	recordBuffer []byte
   160  
   161  	// fieldIndexes is an index of fields inside recordBuffer.
   162  	// The i'th field ends at offset fieldIndexes[i] in recordBuffer.
   163  	fieldIndexes []int
   164  
   165  	// lastRecord is a record cache and only used when ReuseRecord == true.
   166  	lastRecord []string
   167  }
   168  
   169  // NewReader returns a new Reader that reads from r.
   170  func NewReader(r io.Reader) *Reader {
   171  	return &Reader{
   172  		Comma: ',',
   173  		r:     bufio.NewReader(r),
   174  	}
   175  }
   176  
   177  // Read reads one record (a slice of fields) from r.
   178  // If the record has an unexpected number of fields,
   179  // Read returns the record along with the error ErrFieldCount.
   180  // Except for that case, Read always returns either a non-nil
   181  // record or a non-nil error, but not both.
   182  // If there is no data left to be read, Read returns nil, io.EOF.
   183  // If ReuseRecord is true, the returned slice may be shared
   184  // between multiple calls to Read.
   185  func (r *Reader) Read() (record []string, err error) {
   186  	if r.ReuseRecord {
   187  		record, err = r.readRecord(r.lastRecord)
   188  		r.lastRecord = record
   189  	} else {
   190  		record, err = r.readRecord(nil)
   191  	}
   192  	return record, err
   193  }
   194  
   195  // ReadAll reads all the remaining records from r.
   196  // Each record is a slice of fields.
   197  // A successful call returns err == nil, not err == io.EOF. Because ReadAll is
   198  // defined to read until EOF, it does not treat end of file as an error to be
   199  // reported.
   200  func (r *Reader) ReadAll() (records [][]string, err error) {
   201  	for {
   202  		record, err := r.readRecord(nil)
   203  		if err == io.EOF {
   204  			return records, nil
   205  		}
   206  		if err != nil {
   207  			return nil, err
   208  		}
   209  		records = append(records, record)
   210  	}
   211  }
   212  
   213  // readLine reads the next line (with the trailing endline).
   214  // If EOF is hit without a trailing endline, it will be omitted.
   215  // If some bytes were read, then the error is never io.EOF.
   216  // The result is only valid until the next call to readLine.
   217  func (r *Reader) readLine() ([]byte, error) {
   218  	line, err := r.r.ReadSlice('\n')
   219  	if err == bufio.ErrBufferFull {
   220  		r.rawBuffer = append(r.rawBuffer[:0], line...)
   221  		for err == bufio.ErrBufferFull {
   222  			line, err = r.r.ReadSlice('\n')
   223  			r.rawBuffer = append(r.rawBuffer, line...)
   224  		}
   225  		line = r.rawBuffer
   226  	}
   227  	if len(line) > 0 && err == io.EOF {
   228  		err = nil
   229  		// For backwards compatibility, drop trailing \r before EOF.
   230  		if line[len(line)-1] == '\r' {
   231  			line = line[:len(line)-1]
   232  		}
   233  	}
   234  	r.numLine++
   235  	// Normalize \r\n to \n on all input lines.
   236  	if n := len(line); n >= 2 && line[n-2] == '\r' && line[n-1] == '\n' {
   237  		line[n-2] = '\n'
   238  		line = line[:n-1]
   239  	}
   240  	return line, err
   241  }
   242  
   243  // lengthNL reports the number of bytes for the trailing \n.
   244  func lengthNL(b []byte) int {
   245  	if len(b) > 0 && b[len(b)-1] == '\n' {
   246  		return 1
   247  	}
   248  	return 0
   249  }
   250  
   251  // nextRune returns the next rune in b or utf8.RuneError.
   252  func nextRune(b []byte) rune {
   253  	r, _ := utf8.DecodeRune(b)
   254  	return r
   255  }
   256  
   257  func (r *Reader) readRecord(dst []string) ([]string, error) {
   258  	if r.Comma == r.Comment || !validDelim(r.Comma) || (r.Comment != 0 && !validDelim(r.Comment)) {
   259  		return nil, errInvalidDelim
   260  	}
   261  
   262  	// Read line (automatically skipping past empty lines and any comments).
   263  	var line, fullLine []byte
   264  	var errRead error
   265  	for errRead == nil {
   266  		line, errRead = r.readLine()
   267  		if r.Comment != 0 && nextRune(line) == r.Comment {
   268  			line = nil
   269  			continue // Skip comment lines
   270  		}
   271  		if errRead == nil && len(line) == lengthNL(line) {
   272  			line = nil
   273  			continue // Skip empty lines
   274  		}
   275  		fullLine = line
   276  		break
   277  	}
   278  	if errRead == io.EOF {
   279  		return nil, errRead
   280  	}
   281  
   282  	// Parse each field in the record.
   283  	var err error
   284  	const quoteLen = len(`"`)
   285  	commaLen := utf8.RuneLen(r.Comma)
   286  	recLine := r.numLine // Starting line for record
   287  	r.recordBuffer = r.recordBuffer[:0]
   288  	r.fieldIndexes = r.fieldIndexes[:0]
   289  parseField:
   290  	for {
   291  		if r.TrimLeadingSpace {
   292  			line = bytes.TrimLeftFunc(line, unicode.IsSpace)
   293  		}
   294  		if len(line) == 0 || line[0] != '"' {
   295  			// Non-quoted string field
   296  			i := bytes.IndexRune(line, r.Comma)
   297  			field := line
   298  			if i >= 0 {
   299  				field = field[:i]
   300  			} else {
   301  				field = field[:len(field)-lengthNL(field)]
   302  			}
   303  			// Check to make sure a quote does not appear in field.
   304  			if !r.LazyQuotes {
   305  				if j := bytes.IndexByte(field, '"'); j >= 0 {
   306  					col := utf8.RuneCount(fullLine[:len(fullLine)-len(line[j:])])
   307  					err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrBareQuote}
   308  					break parseField
   309  				}
   310  			}
   311  			r.recordBuffer = append(r.recordBuffer, field...)
   312  			r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
   313  			if i >= 0 {
   314  				line = line[i+commaLen:]
   315  				continue parseField
   316  			}
   317  			break parseField
   318  		} else {
   319  			// Quoted string field
   320  			line = line[quoteLen:]
   321  			for {
   322  				i := bytes.IndexByte(line, '"')
   323  				if i >= 0 {
   324  					// Hit next quote.
   325  					r.recordBuffer = append(r.recordBuffer, line[:i]...)
   326  					line = line[i+quoteLen:]
   327  					switch rn := nextRune(line); {
   328  					case rn == '"':
   329  						// `""` sequence (append quote).
   330  						r.recordBuffer = append(r.recordBuffer, '"')
   331  						line = line[quoteLen:]
   332  					case rn == r.Comma:
   333  						// `",` sequence (end of field).
   334  						line = line[commaLen:]
   335  						r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
   336  						continue parseField
   337  					case lengthNL(line) == len(line):
   338  						// `"\n` sequence (end of line).
   339  						r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
   340  						break parseField
   341  					case r.LazyQuotes:
   342  						// `"` sequence (bare quote).
   343  						r.recordBuffer = append(r.recordBuffer, '"')
   344  					default:
   345  						// `"*` sequence (invalid non-escaped quote).
   346  						col := utf8.RuneCount(fullLine[:len(fullLine)-len(line)-quoteLen])
   347  						err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrQuote}
   348  						break parseField
   349  					}
   350  				} else if len(line) > 0 {
   351  					// Hit end of line (copy all data so far).
   352  					r.recordBuffer = append(r.recordBuffer, line...)
   353  					if errRead != nil {
   354  						break parseField
   355  					}
   356  					line, errRead = r.readLine()
   357  					if errRead == io.EOF {
   358  						errRead = nil
   359  					}
   360  					fullLine = line
   361  				} else {
   362  					// Abrupt end of file (EOF or error).
   363  					if !r.LazyQuotes && errRead == nil {
   364  						col := utf8.RuneCount(fullLine)
   365  						err = &ParseError{StartLine: recLine, Line: r.numLine, Column: col, Err: ErrQuote}
   366  						break parseField
   367  					}
   368  					r.fieldIndexes = append(r.fieldIndexes, len(r.recordBuffer))
   369  					break parseField
   370  				}
   371  			}
   372  		}
   373  	}
   374  	if err == nil {
   375  		err = errRead
   376  	}
   377  
   378  	// Create a single string and create slices out of it.
   379  	// This pins the memory of the fields together, but allocates once.
   380  	str := string(r.recordBuffer) // Convert to string once to batch allocations
   381  	dst = dst[:0]
   382  	if cap(dst) < len(r.fieldIndexes) {
   383  		dst = make([]string, len(r.fieldIndexes))
   384  	}
   385  	dst = dst[:len(r.fieldIndexes)]
   386  	var preIdx int
   387  	for i, idx := range r.fieldIndexes {
   388  		dst[i] = str[preIdx:idx]
   389  		preIdx = idx
   390  	}
   391  
   392  	// Check or update the expected fields per record.
   393  	if r.FieldsPerRecord > 0 {
   394  		if len(dst) != r.FieldsPerRecord && err == nil {
   395  			err = &ParseError{StartLine: recLine, Line: recLine, Err: ErrFieldCount}
   396  		}
   397  	} else if r.FieldsPerRecord == 0 {
   398  		r.FieldsPerRecord = len(dst)
   399  	}
   400  	return dst, err
   401  }
   402  

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