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RFC1468 - Japanese Character Encoding for Internet Messages

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

Network Working Group J. Murai

Request for Comments: 1468 Keio University

M. Crispin

Panda Programming

E. van der Poel

June 1993

Japanese Character Encoding for Internet Messages

Status of this Memo

This memo provides information for the Internet community. It does

not specify an Internet standard. Distribution of this memo is

unlimited.

IntrodUCtion

This document describes the encoding used in electronic mail [RFC822]

and network news [RFC1036] messages in several Japanese networks. It

was first specified by and used in JUNET [JUNET]. The encoding is now

also widely used in Japanese IP communities.

The name given to this encoding is "ISO-2022-JP", which is intended

to be used in the "charset" parameter field of MIME headers (see

[MIME1] and [MIME2]).

Description

The text starts in ASCII [ASCII], and switches to Japanese characters

through an escape sequence. For example, the escape sequence ESC $ B

(three bytes, hexadecimal values: 1B 24 42) indicates that the bytes

following this escape sequence are Japanese characters, which are

encoded in two bytes each. To switch back to ASCII, the escape

sequence ESC ( B is used.

The following table gives the escape sequences and the character sets

used in ISO-2022-JP messages. The ISOREG number is the registration

number in ISO's registry [ISOREG].

Esc Seq Character Set ISOREG

ESC ( B ASCII 6

ESC ( J JIS X 0201-1976 ("Roman" set) 14

ESC $ @ JIS X 0208-1978 42

ESC $ B JIS X 0208-1983 87

Note that JIS X 0208 was called JIS C 6226 until the name was changed

on March 1st, 1987. Likewise, JIS C 6220 was renamed JIS X 0201.

The "Roman" character set of JIS X 0201 [JISX0201] is identical to

ASCII except for backslash () and tilde (~). The backslash is

replaced by the Yen sign, and the tilde is replaced by overline. This

set is Japan's national variant of ISO 646 [ISO646].

The JIS X 0208 [JISX0208] character sets consist of Kanji, Hiragana,

Katakana and some other symbols and characters. Each character takes

up two bytes.

For further details about the JIS Japanese national character set

standards, refer to [JISX0201] and [JISX0208]. For further

information about the escape sequences, see [ISO2022] and [ISOREG].

If there are JIS X 0208 characters on a line, there must be a switch

to ASCII or to the "Roman" set of JIS X 0201 before the end of the

line (i.e., before the CRLF). This means that the next line starts in

the character set that was switched to before the end of the previous

line.

Also, the text must end in ASCII.

Other restrictions are given in the Formal Syntax below.

Formal Syntax

The notational conventions used here are identical to those used in

RFC822 [RFC822].

The * (asterisk) convention is as follows:

l*m something

meaning at least l and at most m somethings, with l and m taking

default values of 0 and infinity, respectively.

message = headers 1*( CRLF *single-byte-char *segment

single-byte-seq *single-byte-char )

; see also [MIME1] "body-part"

; note: must end in ASCII

headers = <see [RFC822] "fields" and [MIME1] "body-part">

segment = single-byte-segment / double-byte-segment

single-byte-segment = single-byte-seq 1*single-byte-char

double-byte-segment = double-byte-seq 1*( one-of-94 one-of-94 )

single-byte-seq = ESC "(" ( "B" / "J" )

double-byte-seq = ESC "$" ( "@" / "B" )

CRLF = CR LF

; ( Octal, Decimal.)

ESC = <ISO 2022 ESC, escape> ; ( 33, 27.)

SI = <ISO 2022 SI, shift-in> ; ( 17, 15.)

SO = <ISO 2022 SO, shift-out> ; ( 16, 14.)

CR = <ASCII CR, carriage return>; ( 15, 13.)

LF = <ASCII LF, linefeed> ; ( 12, 10.)

one-of-94 = <any one of 94 values> ; (41-176, 33.-126.)

7BIT = <any 7-bit value> ; ( 0-177, 0.-127.)

single-byte-char = <any 7BIT, including bare CR & bare LF, but NOT

including CRLF, and not including ESC, SI, SO>

MIME Considerations

The name given to the JUNET character encoding is "ISO-2022-JP". This

name is intended to be used in MIME messages as follows:

Content-Type: text/plain; charset=iso-2022-jp

The ISO-2022-JP encoding is already in 7-bit form, so it is not

necessary to use a Content-Transfer-Encoding header. It should be

noted that applying the Base64 or Quoted-Printable encoding will

render the message unreadable in current JUNET software.

ISO-2022-JP may also be used in MIME Part 2 headers. The "B"

encoding should be used with ISO-2022-JP text.

Background Information

The JUNET encoding was described in the JUNET User's Guide [JUNET]

(JUNET Riyou No Tebiki Dai Ippan).

The encoding is based on the particular usage of ISO 2022 announced

by 4/1 (see [ISO2022] for details). However, the escape sequence

normally used for this announcement is not included in ISO-2022-JP

messages.

The Kana set of JIS X 0201 is not used in ISO-2022-JP messages.

In the past, some systems erroneously used the escape sequence ESC (

H in JUNET messages. This escape sequence is officially registered

for a Swedish character set [ISOREG], and should not be used in ISO-

2022-JP messages.

Some systems do not distinguish between ESC ( B and ESC ( J or

between ESC $ @ and ESC $ B for display. However, when relaying a

message to another system, the escape sequences must not be altered

in any way.

The human user (not implementor) should try to keep lines within 80

display columns, or, preferably, within 75 (or so) columns, to allow

insertion of ">" at the beginning of each line in excerpts. Each JIS

X 0208 character takes up two columns, and the escape sequences do

not take up any columns. The implementor is reminded that JIS X 0208

characters take up two bytes and should not be split in the middle to

break lines for displaying, etc.

The JIS X 0208 standard was revised in 1990, to add two characters at

the end of the table. Although ISO 2022 specifies special additional

escape sequences to indicate the use of revised character sets, it is

suggested here not to make use of this special escape sequence in

ISO-2022-JP text, even if the two characters added to JIS X 0208 in

1990 are used.

For further information about Japanese character encodings such as PC

codes, FTP locations of implementations, etc, see "Electronic

Handling of Japanese Text" [JPN.INF].

References

[ASCII] American National Standards Institute, "Coded character set

-- 7-bit American national standard code for information

interchange", ANSI X3.4-1986.

[ISO646] International Organization for Standardization (ISO),

"Information technology -- ISO 7-bit coded character set for

information interchange", International Standard, Ref. No. ISO/IEC

646:1991.

[ISO2022] International Organization for Standardization (ISO),

"Information processing -- ISO 7-bit and 8-bit coded character sets

-- Code extension techniques", International Standard, Ref. No. ISO

2022-1986 (E).

[ISOREG] International Organization for Standardization (ISO),

"International Register of Coded Character Sets To Be Used With

Escape Sequences".

[JISX0201] Japanese Standards Association, "Code for Information

Interchange", JIS X 0201-1976.

[JISX0208] Japanese Standards Association, "Code of the Japanese

graphic character set for information interchange", JIS X 0208-1978,

-1983 and -1990.

[JPN.INF] Ken R. Lunde <lunde@adobe.com>, "Electronic Handling of

Japanese Text", March 1992,

msi.umn.edu(128.101.24.1):pub/lunde/japan[123].inf

[JUNET] JUNET Riyou No Tebiki Sakusei Iin Kai (JUNET User's Guide

Drafting Committee), "JUNET Riyou No Tebiki (Dai Ippan)" ("JUNET

User's Guide (First Edition)"), February 1988.

[MIME1] Borenstein N., and N. Freed, "MIME (Multipurpose

Internet Mail Extensions): Mechanisms for Specifying and

Describing the Format of Internet Message Bodies", RFC1341,

Bellcore, Innosoft, June 1992.

[MIME2] Moore, K., "Representation of Non-ASCII Text in Internet

Message Headers", RFC1342, University of Tennessee, June 1992.

[RFC822] Crocker, D., "Standard for the Format of ARPA Internet

Text Messages", STD 11, RFC822, UDEL, August 1982.

[RFC1036] Horton M., and R. Adams, "Standard for Interchange of USENET

Messages", RFC1036, AT&T Bell Laboratories, Center for Seismic

Studies, December 1987.

Acknowledgements

Many people assisted in drafting this document. The authors wish to

thank in particular Akira Kato, Masahiro Sekiguchi and Ken'ichi

Handa.

Security Considerations

Security issues are not discussed in this memo.

Authors' Addresses

Jun Murai

Keio University

5322 Endo, Fujisawa

Kanagawa 252 Japan

Fax: +81 466 49 1101

EMail: jun@wide.ad.jp

Mark Crispin

Panda Programming

6158 Lariat Loop NE

Bainbridge Island, WA 98110-2098

USA

Phone: +1 206 842 2385

EMail: MRC@PANDA.COM

Erik M. van der Poel

A-105 Park Avenue

4-4-10 Ohta, Kisarazu

Chiba 292 Japan

Phone: +81 438 22 5836

Fax: +81 438 22 5837

EMail: erik@poel.juice.or.jp

 
 
 
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