Encoding:
Encoding Header Field for Internet Messages
This RFC proposes an elective experimental Encoding header field to permit the mailing of multi-part, multi-structured messages.
この
The use of Encoding updates RFC 1049 (Content-Type), and is a suggested update to RFCs 1113, 1114, and 1115 (Privacy Enhancement) [4,7,8].
Distribution of this memo is unlimited.
このメモの配布は無制限とします。
RFC 822 [2] defines an electronic mail message to consist of two parts, the message header and the message body, separated by an apparently blank line.
The Encoding header field permits the message body itself to be further broken up into parts, each part also separated from the next by an apparently blank line.
Thus, conceptually, a message has a header part, followed by one or more body parts, all separated by blank lines.
従って、
Each body part has an encoding type. The default (no Encoding field in the header) is a message body of one part of type "text".
各
The Encoding field consists of one or more subfields, separated by commas. Each subfield corresponds to a part of the message, in the order of that part's appearance. A subfield consists of a line count, a keyword defining the encoding, and optional information relevant only to the specific encoding. The line count is optional in the last subfield.
The format of the Encoding field is:
[<count> <keyword> [<options>], ]* [<count>] <keyword> [<options>]
where:
ここで、
<count> := a decimal integer
<keyword> := a single alphanumeric token starting with an alpha
<options> := keyword-dependent optionsThe line count is a decimal number specifying the number of text lines in the part. Parts are separated by a blank line, which is not included in the count of either the proceeding or following part. Because a count always begins with a digit and a keywords always begins with an letter, it is always possible to determine if the count is present. (The count is first because it is the only information of interest when skipping over the part.)
行数はその部分に含まれる文章の行の数を十進数で指定します。 部分と部分は空行で分離しますが、この空行は前後どちらの部分の行数にも含めません。 行数は常に数字で始まり、鍵語は常に英字で始まるので、 行数が指定されているかどうかを常に判定可能です。 (部分を1つ読み飛ばすために必要なのは行数だけですから、 行数を最初に置いています。)
The count is not required on the last or only part.
行数は最後の部分や部分が1つだけの時には必須ではありません。
The keyword defines the encoding type. The keyword is a common single word name for the encoding type. The keywords are not case-sensitive.
鍵語は符号化型を指定します。鍵語は符号化型を表す共通の 1語の名前です。鍵語は大文字・小文字を区別しません。
The list of standard keywords is intended to be the same as the list used for the Content-Type: header described in [6]. This RFC proposes additions to the list. Implementations can then treat "Content-Type" as an alias of "Encoding", which will always have only one body part.
標準の鍵語は
The optional information is used to specify additional keyword-specific information needed for interpreting the contents of the encoded part. It is any sequence of tokens not containing a comma.
省略可能な情報で、鍵語に依存して符号化部分の内容を解釈するのに必要な情報を指定するために使います。
In general, version numbers for encodings, when not actually available within the contents of the encoded information, will be handled as options.
通常符号化の版番号は、 符号化された情報の内容に実際に利用できない時に選択肢として扱います。
Comments enclosed in parentheses may, of course, be inserted anywhere in the Encoding field. Mail reading systems may pass the comments to their clients. Comments must not be used by mail reading systems for content interpretation; that is the function of options.
括弧で括られた
This section describes some of the defined encodings used.
この章では使用する符号化のいくつかを説明します。
As with the other keyword-defined parts of the header format standard, extensions in the form of new keywords are expected and welcomed. Several basic principles should be followed in adding encodings:
頭の書式の規格の他の鍵語で定義する部分同様に新しい鍵語の拡張が予期・ 歓迎されます。符号化を追加するときは幾つかの基本的な原則に従うべきです。
- The keyword should be the most common single word name for the encoding, including acronyms if appropriate. The intent is that different implementors will be likely to choose the same name for the same encoding.
鍵語は符号化の1単語の最も共通な名前を、適当なら略称を含めて使うべきです。 そうすれば異なる実装が同じ符号化に同じ名前を選ぶでしょう。
- Keywords not be too general: "binary" would have been a bad choice for the "hex" encoding.
鍵語は一般的過ぎないように。 binary を hex
符号化に使うのはよくないでしょう。
- The encoding should be as free from unnecessary idiosyncracies as possible, except when conforming to an existing standard, in which case there is nothing that can be done.
符号化はできる限り特異的でないものとするべきです。 ただし既存の規格に適合する場合はどうしようもありません。
- The encoding should, if possible, use only the 7 bit ASCII printing characters if it is a complete transformation of a source document (e.g., "hex" or "uuencode"). If it is essentially a text format, the full range may be used. If there is an external standard, the character set may already be defined.
符号化は原始文書の完全な変形なら可能な限り7ビット
や
)。
本質的に文章書式なら自由な範囲を使って構いません。
外部規格なら
Keywords beginning with "X-" are permanently reserved to implementation-specific use. No standard registered encoding keyword will ever begin with "X-".
This indicates that the message is in no particular encoded format, but is to be presented to the user as is.
これはメッセージが特定の符号化書式を使っておらず、 利用者にそのまま提示されることを示します。
The full range of the ASCII character set is used. The message is expected to consist of lines of reasonable length (less than 1000 characters).
On some transport services, only the 7 bit subset of ASCII can be used. Where full 8 bit transparency is available, the text is assumed to be ISO 8859-1 [3] (ASCII-8).
転送サービスによっては
This encoding indicates that the body part is itself in the format of an Internet message, with its own header part and body part(s). A "message" body part's message header may be a full internet message header or it may consist only of an Encoding field.
この符号化は本体部分自体が頭部分と本体部分(群)を持ったインターネット・メッセージの書式であることを示します。
Using the message encoding on returned mail makes it practical for a mail reading system to implement a reliable resending function, if the mailer generates it when returning contents. It is also useful in a "copy append" MUA operation.
返却メイルにメッセージ符号化を使えば、
メイル読取りシステムが内容を返却するときにメイル器がこれを生成すれば確実に再送信する機能を実装できます。
複製して追記
する
Message encoding is also used when mapping to X.400 to handle recursively included X.400 P2 messages.
メッセージ符号化は
The encoding indicates that the body part contains binary data, encoded as 2 hexadecimal digits per byte, highest significant nibble first.
この符号化は本体部分がバイナリ・データを
1バイト辺り十六進数字2桁
(最上位
Lines consist of an even number of hexadecimal digits. Blank lines are not permitted. The decode process must accept lines with between 2 and 1000 characters, inclusive.
十六進数字偶数個の行から成ります。空行は認められません。 符号化処理は文字数2文字以上1000文字以下 (両端を含みます。) の行を受付けなければなりません。
EVFU (Electronic Vertical Format Unit) specifies that each line begins with a one-character "channel selector". The original purpose was to select a channel on a paper tape loop controlling the printer.
This encoding is sometimes called "FORTRAN" format. It is the default output format of FORTRAN programs on a number of computer systems.
The legal characters are '0' to '9', '+', '-', and space. These correspond to the 12 rows (and absence of a punch) on a printer control tape (used when the control unit was electromechanical).
The channels that have generally agreed definitions are:
1 advances to the first print line on the next page
0 skip a line, i.e., double-space
+ over-print the preceeding line
- skip 2 lines, i.e., triple-space
(space) print on the next line, single-spaceThe EDI (Electronic Document Interchange) keyword indicates that the message or part is a business document, formatted according to ANSI X12 or related standards.
The first word after the EDI keyword indicates the particular interchange standard.
A message containing a note and 2 X12 purchase orders might have an encoding of:
Encoding: 17 TEXT, 146 EDI X12, 69 EDI X12
The Encoding header field provides a mechanism for mapping multi-part messages between CCITT X.400 [1] and RFC 822.
The X.400 keyword specifies a section that is converted from an X.400 body part type not known to the gateway, or not corresponding to a useful internet encoding.
If the message transits another gate, or if the receiving user has the appropriate software, it can be decoded and used.
The X.400 keyword is followed by a second token indicating the method used. The simplest form is "X.400 HEX", with the complete X.409 encoding of the body part in hexadecimal. More compact is "X.400 3/4", using the 3-byte to 4-character encoding as specified in RFC 1113, section 4.3.2.4.
The uuencode keyword specifies a section consisting of the output of the uuencode program supplied as part of uucp.
The encrypted keyword indicates that the section is encrypted with the methods in RFC 1115 [8]. This replaces the possible use of RFC 934 [5] encapsulation.
[1] International Telegraph and Telephone Consultative Committee,
"Data Communication Networks: Message Handling Systems", In CCITT
Recommendations X.400 to X.430, VIIIth Plenary Assembly, Malaga-
Torremolinos, 1984, Fascicle VIII.7 ("Red Book"). [2] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", RFC 822, University of Delaware, August 1982. [3] International Organization for Standardization, "Information
processing - 8-bit single-byte coded graphic character sets -
Part 1: Latin alphabet No. 1", ISO 8859-1, ISO, 1987. [4] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
I -- Message Encipherment and Authentication Procedures", RFC
1113, IAB Privacy Task Force, August 1989. [5] Rose, M., and E. Stefferud, "Proposed Standard for Message
Encapsulation", RFC 943, University of Delaware and NMA, January
1985. [6] Sirbu, M., "Content-type Header Field for Internet Messages", RFC
1049, CMU, March 1988. [7] Kent, S., and J. Linn, "Privacy Enhancement for Internet
Electronic Mail: Part II -- Certificate-Based Key Management",
RFC 1114, IAB Privacy Task Force, August 1989. [8] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
III -- Algorithms, Modes, and Identifiers", RFC 1115, IAB Privacy
Task Force, August 1989.Security issues are not addressed in this memo.
David Robinson 10-30 Prime Computer, Inc. 500 Old Connecticut Path Framingham, MA 01701
Phone: +1 508 879 2960 x1774
Email: DRB@Relay.Prime.COM
Robert Ullmann 10-30 Prime Computer, Inc. 500 Old Connecticut Path Framingham, MA 01701
Phone: +1 508 879 2960 x1736
Email: Ariel@Relay.Prime.COM
The use of Encoding updates RFC 1049 (Content-Type), and is a suggested update to RFCs 1113, 1114, and 1115 (Privacy Enhancement) [4,7,8].
などと訳の分からないことをいっているが、
この当時の
The list of standard keywords is intended to be the same as the list used for the Content-Type: header described in [6]. This RFC proposes additions to the list. Implementations can then treat "Content-Type" as an alias of "Encoding", which will always have only one body part. (3.3 <keyword>)
そもそも定義がこんないい加減なんで気が引けるのだが、
[<count> <keyword> [<options>], ]* [<count>] <keyword> [<options>]
where:
<count> := a decimal integer <keyword> := a single alphanumeric token starting with an alpha <options> := keyword-dependent options
<options> に沿うとする部分は
; 区切りの複数のオプションだったはずだ。
, 区切りのリストだ!
となると判断は微妙に面倒になる。
欄本体 := *(CFWS 部分欄 CFWS ",") CFWS 最後の部分欄 CFWS 部分欄 := 行数 CFWS 鍵語 *(CFWS 鍵語 )最後の部分欄 := [行数 CFWS ] 鍵語 *(CFWS 鍵語 )行数 := 1*DIGIT ;; 十進数 鍵語 := ALPHA *(ALPHA / DIGIT / "-" / ".") ;; 大文字 ・小文字 を区別しませんHYPHEN-MINUS FULL STOP "X-" で始まる名前は実装規定の複数指定した場合 (
入れ子の鍵語の順序には意味があり、
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Encoding 欄について
(
MIME より人可読性を優先してるような。そういう面では MIME の方が 遥かに先進的。 MIME も色々アレだけど、 Encoding: 領域よりは MIME で良かったかも。
Encoding: 107 Text
Encoding: 458 uuencode LZW tar (Unix binary object)これは、もとのデータが