Network Working Group
Request for Comments: 4180
Category: Informational
 Y. Shafranovich
SolidMatrix Technologies, Inc.
October 2005
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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 © 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. Definition of the CSV Format
3. MIME Type Registration of text/csv
4. IANA Considerations
5. Security Considerations
6. Acknowledgments
7. References
7.1. Normative References
7.2. Informative References

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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

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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]

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   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).

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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.

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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.

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Author's Address

Yakov Shafranovich
SolidMatrix Technologies, Inc.

EMail: ietf@shaftek.org 

   URI:   http://www.shaftek.org

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