The Use of "Set Data Type" Transaction in File Transfer Protocol
Clarifying how FTP's Set Data Type transaction should guide file conversion.
Bhushan, A.K., "The Use of "Set Data Type" Transaction in File Transfer Protocol", RFC 294, DOI 10.17487/RFC0294, January 1972, <https://www.rfc-editor.org/info/rfc294>.
@misc{rfc294,
series = {Request for Comments},
number = 294,
howpublished = {RFC 294},
publisher = {RFC Editor},
doi = {10.17487/RFC0294},
url = {https://www.rfc-editor.org/info/rfc294},
author = {A.K. Bhushan},
title = {{The Use of "Set Data Type" Transaction in File Transfer Protocol}},
pagetotal = 2,
year = 1972,
month = jan,
} RFC text
Contents
Network Working Group 25 January 1972 RFC 294 Abhay Bhushan, MIT NIC 8304 Categories: D.4, D.5, and D.7 Updates: RFC 265 The Use of 'Set Data Type' Transaction in File Transfer Protocol ---------------------------------------------------------------- As mentioned in RFC 265, the opcode of '00' is set aside for the clarify the use of 'set data type' in file transfer operations. In many systems such as Multics at MIT, there is no provision to identify the type of data (i.e., ASCII or numeric) stored in files. The manner in which the data is handled is context dependent. ASCII characters are stored as four 9-bit characters per 36-bit word, right justified with left most bit as zero. As efficient conversion programs exists in Multics for conversion of data from Multics' ASCII into Network ASCII, it would be useful for a user to be able to instruct the Multics server to convert data into Network ASCII in retrieve operations. It is suggested that the 'set data type' transaction be used for this purpose. The 'set data type' transaction preceding a retrieve request should be interpreted by a server to mean that the user wants to receive his data in that form. If the server is unable to convert the data into the desired form, it should return a 'set data type' of [ This RFC was put into machine readable form for entry ] [ into the online RFC archives by BBN Corp. under the ] [ direction of Alex McKenzie. 12/96 ] RFC 294 Abhay Bhushan, MIT The following examples should clarify the use of 'set data type' transactions. 1. USER SERVER ---- ------ Set data type '02' (Network ASCII) -------------------------------------> Store File X -------------------------------------> File X (in Network ASCII) -------------------------------------> End of File -------------------------------------> Acknowledge <------------------------------------- Retrieve File X -------------------------------------> File X in Network ASCII <------------------------------------- End of File <------------------------------------- 2. USER SERVER ---- ------ Set data type'03' (EBCDIC) -------------------------------------> Retrieve File Y -------------------------------------> Set data type '00' ("bit-stream") <------------------------------------- File Y as stored (no conversion) <------------------------------------- End of File <------------------------------------- Set data type '02' (Network ASCII) -------------------------------------> Retrieve File Z -------------------------------------> File Z in Network ASCII <------------------------------------- End of File <-------------------------------------
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§1Files Without a Recorded Type
RFC 294 discusses systems such as Multics, where a file does not necessarily identify whether its contents are ASCII or numeric. The way the data is handled depends on the task using it.
The RFC says Multics has conversion programs that can change its stored ASCII into Network ASCII, and proposes using the Set Data Type transaction to request that conversion for retrieval.
A file may not say what kind of data it contains. The user can ask for the form needed by the receiving system.
§2Requesting a Data Type
A Set Data Type transaction before a retrieve request tells the server the form the user wants to receive. If the server cannot convert the data into that form, it should return a Set Data Type transaction to indicate that it cannot fulfill the request.
The RFC describes Network ASCII and EBCDIC as example data types in its exchanges.
The user names a preferred data form before asking for a file. The server can convert the data or reply that it cannot.
§3Examples of Conversion
One example asks the server to store and later retrieve a file as Network ASCII. Another asks for EBCDIC but shows the server replying with data type 00, meaning bit-stream, before sending the file as stored without conversion.
A later request in the example asks for Network ASCII for a different file.
The examples show a server honoring a requested form when it can. When it cannot convert, it can send the file in its stored form instead.