Common Format and MIME Type for Comma-Separated Values (CSV) Files

Network Working Group                                    Y. Shafranovich
Request for Comments: 4180                SolidMatrix Technologies, Inc.
Category: Informational                                     October 2005


   Common Format and MIME Type for Comma-Separated Values (CSV) Files

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This RFC documents the format used for Comma-Separated Values (CSV)
   files and registers the associated MIME type "text/csv".

Table of Contents

   1. Introduction ....................................................2
   2. Definition of the CSV Format ....................................2
   3. MIME Type Registration of text/csv ..............................4
   4. IANA Considerations .............................................5
   5. Security Considerations .........................................5
   6. Acknowledgments .................................................6
   7. References ......................................................6
      7.1. Normative References .......................................6
      7.2. Informative References .....................................6

1.  Introduction

   The comma separated values format (CSV) has been used for exchanging
   and converting data between various spreadsheet programs for quite
   some time.  Surprisingly, while this format is very common, it has
   never been formally documented.  Additionally, while the IANA MIME
   registration tree includes a registration for
   "text/tab-separated-values" type, no MIME types have ever been
   registered with IANA for CSV.  At the same time, various programs and
   operating systems have begun to use different MIME types for this
   format.  This RFC documents the format of comma separated values
   (CSV) files and formally registers the "text/csv" MIME type for CSV
   in accordance with RFC 2048 [1].

2.  Definition of the CSV Format

   While there are various specifications and implementations for the
   CSV format (for ex. [4], [5], [6] and [7]), there is no formal
   specification in existence, which allows for a wide variety of
   interpretations of CSV files.  This section documents the format that
   seems to be followed by most implementations:

   1.  Each record is located on a separate line, delimited by a line
       break (CRLF).  For example:

       aaa,bbb,ccc CRLF
       zzz,yyy,xxx CRLF

   2.  The last record in the file may or may not have an ending line
       break.  For example:

       aaa,bbb,ccc CRLF
       zzz,yyy,xxx

   3.  There maybe an optional header line appearing as the first line
       of the file with the same format as normal record lines.  This
       header will contain names corresponding to the fields in the file
       and should contain the same number of fields as the records in
       the rest of the file (the presence or absence of the header line
       should be indicated via the optional "header" parameter of this
       MIME type).  For example:

       field_name,field_name,field_name CRLF
       aaa,bbb,ccc CRLF
       zzz,yyy,xxx CRLF

   4.  Within the header and each record, there may be one or more
       fields, separated by commas.  Each line should contain the same
       number of fields throughout the file.  Spaces are considered part
       of a field and should not be ignored.  The last field in the
       record must not be followed by a comma.  For example:

       aaa,bbb,ccc

   5.  Each field may or may not be enclosed in double quotes (however
       some programs, such as Microsoft Excel, do not use double quotes
       at all).  If fields are not enclosed with double quotes, then
       double quotes may not appear inside the fields.  For example:

       "aaa","bbb","ccc" CRLF
       zzz,yyy,xxx

   6.  Fields containing line breaks (CRLF), double quotes, and commas
       should be enclosed in double-quotes.  For example:

       "aaa","b CRLF
       bb","ccc" CRLF
       zzz,yyy,xxx

   7.  If double-quotes are used to enclose fields, then a double-quote
       appearing inside a field must be escaped by preceding it with
       another double quote.  For example:

       "aaa","b""bb","ccc"

   The ABNF grammar [2] appears as follows:

   file = [header CRLF] record *(CRLF record) [CRLF]

   header = name *(COMMA name)

   record = field *(COMMA field)

   name = field

   field = (escaped / non-escaped)

   escaped = DQUOTE *(TEXTDATA / COMMA / CR / LF / 2DQUOTE) DQUOTE

   non-escaped = *TEXTDATA

   COMMA = %x2C

   CR = %x0D ;as per section 6.1 of RFC 2234 [2]
   DQUOTE =  %x22 ;as per section 6.1 of RFC 2234 [2]

   LF = %x0A ;as per section 6.1 of RFC 2234 [2]

   CRLF = CR LF ;as per section 6.1 of RFC 2234 [2]

   TEXTDATA =  %x20-21 / %x23-2B / %x2D-7E

3.  MIME Type Registration of text/csv

   This section provides the media-type registration application (as per
   RFC 2048 [1].

   To: ietf-types@iana.org

   Subject: Registration of MIME media type text/csv

   MIME media type name: text

   MIME subtype name: csv

   Required parameters: none

   Optional parameters: charset, header

      Common usage of CSV is US-ASCII, but other character sets defined
      by IANA for the "text" tree may be used in conjunction with the
      "charset" parameter.

      The "header" parameter indicates the presence or absence of the
      header line.  Valid values are "present" or "absent".
      Implementors choosing not to use this parameter must make their
      own decisions as to whether the header line is present or absent.

   Encoding considerations:

      As per section 4.1.1. of RFC 2046 [3], this media type uses CRLF
      to denote line breaks.  However, implementors should be aware that
      some implementations may use other values.

   Security considerations:

      CSV files contain passive text data that should not pose any
      risks.  However, it is possible in theory that malicious binary
      data may be included in order to exploit potential buffer overruns
      in the program processing CSV data.  Additionally, private data
      may be shared via this format (which of course applies to any text
      data).

   Interoperability considerations:

      Due to lack of a single specification, there are considerable
      differences among implementations.  Implementors should "be
      conservative in what you do, be liberal in what you accept from
      others" (RFC 793 [8]) when processing CSV files.  An attempt at a
      common definition can be found in Section 2.

      Implementations deciding not to use the optional "header"
      parameter must make their own decision as to whether the header is
      absent or present.

   Published specification:

      While numerous private specifications exist for various programs
      and systems, there is no single "master" specification for this
      format.  An attempt at a common definition can be found in Section
      2.

   Applications that use this media type:

      Spreadsheet programs and various data conversion utilities

   Additional information:

      Magic number(s): none

      File extension(s): CSV

      Macintosh File Type Code(s): TEXT

   Person & email address to contact for further information:

      Yakov Shafranovich <ietf@shaftek.org>

   Intended usage: COMMON

   Author/Change controller: IESG

4.  IANA Considerations

   The IANA has registered the MIME type "text/csv" using the
   application provided in Section 3 of this document.

5.  Security Considerations

   See discussion above in section 3.

6.  Acknowledgments

   The author would like to thank Dave Crocker, Martin Duerst, Joel M.
   Halpern, Clyde Ingram, Graham Klyne, Bruce Lilly, Chris Lilley, and
   members of the IESG for their helpful suggestions.  A special word of
   thanks goes to Dave for helping with the ABNF grammar.

   The author would also like to thank Henrik Lefkowetz, Marshall Rose,
   and the folks at xml.resource.org for providing many of the tools
   used for preparing RFCs and Internet drafts.

   A special thank you goes to L.T.S.

7.  References

7.1.  Normative References

   [1]  Freed, N., Klensin, J., and J. Postel, "Multipurpose Internet
        Mail Extensions (MIME) Part Four: Registration Procedures", BCP
        13, RFC 2048, November 1996.

   [2]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.

   [3]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part Two: Media Types", RFC 2046, November
        1996.

7.2.  Informative References

   [4]  Repici, J., "HOW-TO: The Comma Separated Value (CSV) File
        Format", 2004,
        <http://www.creativyst.com/Doc/Articles/CSV/CSV01.htm>.

   [5]  Edoceo, Inc., "CSV Standard File Format", 2004,
        <http://www.edoceo.com/utilis/csv-file-format.php>.

   [6]  Rodger, R. and O. Shanaghy, "Documentation for Ricebridge CSV
        Manager", February 2005,
        <http://www.ricebridge.com/products/csvman/reference.htm>.

   [7]  Raymond, E., "The Art of Unix Programming, Chapter 5", September
        2003,
        <http://www.catb.org/~esr/writings/taoup/html/ch05s02.html>.

   [8]  Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
        September 1981.

Author's Address

   Yakov Shafranovich
   SolidMatrix Technologies, Inc.

   EMail: ietf@shaftek.org
   URI:   http://www.shaftek.org

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