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Copyright (C) The Internet Society (2005).

Abstract

This document defines MIME types "text/csv" and "text/comma-separated-values" which used for Comma-Separated Values (CSV) files.

Table of Contents

1.  Introduction
2.  MIME Type Registration of text/csv and text/comma-separated-values
3.  IANA Considerations
4.  Security Considerations
5.  References
    5.1  Normative References
    5.2  Informative References
§  Author's Address
A.  Appendix A - Discussion of the CSV format
§  Intellectual Property and Copyright Statements

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 file is very common it has never been formally documented. Additionally, while the IANA MIME registration tree includes a registraton 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, many of which vary from system to system. This document seeks to formally register two MIME types for CSV in accordance with RFC 2048Freed, N., Klensin, J. and J. Postel, Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures, November 1996.[4].

2. MIME Type Registration of text/csv and text/comma-separated-values

This section provides the media-type registration application (as per RFC 2048Freed, N., Klensin, J. and J. Postel, Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures, November 1996.[4], which will be submitted to IANA after IESG approval of this document.

To: ietf-types@iana.org

Subject: Registration of MIME media types text/csv and text/comma-separated-values

MIME media type name: text

MIME subtype name: csv, comma-separated-values

Required parameters: none

Optional parameters: charset

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

Encoding considerations:

While section 4.1.1. of RFC 2046Freed, N. and N. Borenstein, Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types, November 1996.[1] stipulates that "text" subtypes MUST use a CRLF sequence as a line break, in practice that is not always true for CSV. Therefore, implementors should be aware that either CR or CRLF maybe used as a line break for this format.

Security considerations:

CSV files contain passive text data which should not pose any risks. However, it is possible in theory that malicious binary data maybe included in order to exploit potential buffer overruns in the program processing CSV data. Additionally, private data maybe 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 different implementations as described in appendix A. The most common difference among various format is whether double quotes (") are used to enclose strings. Implementors should "be conservative in what you do, be liberal in what you accept from others" (RFC 793Postel, J., Transmission Control Protocol, September 1981.[2]) when processing CSV files.

Published specification:

While numerous private specifications exist for various programs and systems, there is no single "master" specification for this format. A sampling of formats and discussion of differences is included in appendix A.

Applications which 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

3. IANA Considerations

After IESG approval, IANA is expected to register these two types "text/csv" and "text/comma-separated-values" using the application provided in this document.

4. Security Considerations

See discussion above

5. References

5.1 Normative References

5.2 Informative References

Author's Address

Appendix A. Appendix A - Discussion of the CSV format

While there are various specifications and implementations for the CSV format (for ex. [5]Repici, J., HOW-TO: The Comma Separated Value (CSV) File Format, 2004., [6]Edoceo, Inc., CSV Standard File Format, 2004., [7]Rodger, R. and O. Shanaghy, Documentation for Ricebridge CSV Manager, February 2005. and [8]Raymond, E., The Art of Unix Programming, Chapter 5, September 2003.), no formal specification exists. This causes a wide variety of interpretations for CSV files. While this document does not seek to document the CSV format, nevertheless we want to document the format that seems to be followed by most implementations:

1. Each record is located on a separate line delimited by a line break (either CR or CR/LF). For example:
   
   aaa,bbb,ccc CRLF
   zzz,yyy,xxx CRLF
2. The last record in the file may or may not have an ending linebreak. 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 will usually contain the same number of fields as the records in the rest of the file. 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, delimited by commas. The last field in the record may or may 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. For example:
   
   "aaa","bbb","ccc" CRLF
   zzz,yyy,xxx
6. Field containing line breaks (CR or CR/LF) 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 enclosed fields, then double-quotes inside fields must be surounded by double quotes. For example:
   
   "aaa","b"""bb","ccc"
8. Whitespace immediately before and after commas maybe removed unless it appears inside double-quotes. For example:
   
   zzz, yyy , xxx
   
   would be processed as if it was:
   
   zzz,yyy,xxx

The ABNF grammarCrocker, D., Ed. and P. Overell, Augmented BNF for Syntax Specifications: ABNF, November 1997.[3] appears as follows:

COMMA = %x2C

file = [header] *record

end-of-field = COMMA / (CR / CRLF)

header = *(*WSP field *WSP end-of-field)

record = *(*WSP field *WSP end-of-field)

field = escaped / non-escaped

escaped = DQUOTE *(VCHAR / CR / CRLF / 3*DQUOTE) DQUOTE

non-escaped = *VCHAR

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