File Transfer Protocol
RFC 354
Document | Type |
RFC
- Unknown
(July 1972)
Obsoleted by RFC 542
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Authors | |||
Last updated | 2013-03-02 | ||
RFC stream | Legacy stream | ||
Formats | |||
IESG | Responsible AD | (None) | |
Send notices to | (None) |
RFC 354
| | Marker | Marker | Marker | Marker | | | 8 bits | 8 bits | 8 bits | 8 bits | | | Marker | Marker | SP | SP | | | 8 bits | 8 bits | 8 bits | 8 bits | 4 Hasp The file is transmitted as a sequence of 8-bit bytes in the standard Hasp-compressed data format (document to be issued by Bob Braden, UCLA). This mode achieves considerable compression of data for print files. Record structures are allowed in the Hasp mode. III.D Error Recovery and Restart There is no provision for detecting bits lost or scrambled in data transfer. This issue is perhaps handled best at the NCP level where it benefits most users. However, a restart procedure is provided to protect user from system failures (such as failure of either HOST, FTP-process, or the IMP subnet). The restart procedure is defined only for the block mode of data transfer. It requires the sender of data to insert a special marker code in teh data stream with some marker information. The marker information has meaning only to the sender, but must consist of printable ASCII characters. The printable ASCII characters are defined to be codes 33. through 126. (i.e., not including codes 0. through 31. and the characters SP and DEL). The marker could represent a bit-count,a record-count, or any other information by wich a system may identify a data checkpoint. The receiver of data, if it implements the restart procedure, would then mark the corresponding position of this marker in the receiving system, and return this information to the user. In the event of a system failure, the user can restart the data transfer by identifying the marker point with the FTP restart procedure. The following examples Illustrate the use of the restart procedure. 1. When server is the sender of data, the server-FTP process inserts an appropriate marker block in the data stream at a convenient data point. The user-FTP process receiving the data, marks the coressponding data point in its file system and conveys the last known sender and receiver marker information to the user. In the event of system failure, the user or user-FTP process restarts the server at the [Page 12] The File Transfer Protocol July 8, 1972 last server marker by sending a restart command with the server's marker code at its argument. The restart command is transmitted over the TELNET connection and is immediately followed by the command (such as store or retrieve) which was being executed when the system failure occured. 2. When user is the sender of data, the user-FTP process inserts the appropriate marker block in the data stream. The server-FTP process receiving the data, marks the corresponding data point in its file system. The server does not store this marker but conveys the last known sender and receiver marker information to the user over the TELNET connections by appropriate reply codes. The user or the user-FTP process then restarts transfer in a manner identical to that described in the first example. IV. FILE TRANSFER FUNCTIONS The TELNET connections on which FTP commands and replies are transmitted, are initiated by the user-FTP process via an ICP to a standard server socket. FTP commands are then transmitted from user to server, and replies are transmitted from server to user. The user file transfer functions invoive sending the FTP commands, interpreting the replies received and transferring data over the data connection in the specified manner. The server file transfer functions involve accepting and interpreting FTP commands, sending replies, setting up the data connection, and transferring data. IV.A FTP Commands FTP commands are ASCII terminated by the ASCII character sequence CRLF (Carriage Return follow by Line Feed). The command codes themselves are ASCII alpabetic characters terminated by the ASCII character 'space' (code = 32.). For convenience, the command codes are defined to be four (or less) ASCII alphanumeric characters (including both upper and lower case alphabetic characters). The command codes and the semantics of commands are described in this section, but the detailed syntax of commands is specified in Section V.b, the reply sequence are discussed in Section V.C, and scenarios illustrating the use of commands are provided in Section V.D. FTP commands may be partitioned as those specifying access-control identifiers, data transfer parameters, or FTP service requests. [Page 13] The File Transfer Protocol July 8, 1972 IV.A.1 Access Control Commands The following commands specify access control identifiers (command codes are shown in parentheses). User name (USER) - The argument field is an ASCII string identifying the user. The user identification is that wich is required by the server for access to its file system. This command will normally be the first command transmitted by the user after the TELNET connections are made (some servers may require this). Additional identification information in the form of pasword command may also be required by some servers. Password (PASS) - The argument field is an ASCII string identifying the user's password. This command must be immediately preceded by the user name command, and together it completes the user's identifecation for access control. IV.A.2 Data Transfer Commands All data transfer parameters have default values, and the commands specifying data transfer parameters are required only if the default parameter values are to be changed. The default value is teh last specified value, or if no value has been specified, the standard default value specified here. This implies that the server must "remember" the applicable default values. The commands may be in any order except that they must precede the FTP service request. The following commands specify data transfer parameters. Byte size (BYTE) - The argument is an ASCII-represented decimal integer (1 through 255), specifying the byte size for the data connection for local byte and image representation types. The default byte size is 8 bits. The byte size is always 8 bits in the ASCII and Print file representation types. A server may reject specific byte size/type combinations by sending an appropriate reply. Data socket (SOCK) - The argument is a HOST-socket specification for the data socket to be used in data connection. There may be two data sockets, one from server to user and the other for user to server data transfer. An odd socket number defines a send socket and an even socket number defines a receive socket. The default HOST is the user HOST to which TELNET connections are made. The default data sockets are (U+4) and (U+5) where U is the socket number used in the TELNET ICP and the TELNET connections are on sockets (U+2) and (U+3). [Page 14] The File Transfer Protocol July 8, 1972 Representation Type (TYPE) - The argument is a single ASCII character code specifying the representation types described in section III.B. The following codes are assigned for type: A - ASCII I - Image L - Local Byte P - Print file in ASCII E - EBCDIC print file The default representation type is ASCII File Structure (STRU) - The argument is a single ASCII character code specifying file structure described in section III.C. The following codes are assigned for structure: F - File (no record structure) R - Record structure The default structure is File (i.e., no records). Transfer Mode (MODE) - The argument is a single ASCII character code specifying the data transfer modes described in Section III.C. The following codes are assigned for transfer modes: S - Stream (bytes, close is EOF) B - Block (Header with descriptor and count) T - Text (TELNET control mode for EOR, EOF) H - Hasp (specially formatted compressed data) The default transfer mode is Stream. IV.A.3 FTP Service Commands. The FTP service commands define the file transfer or the file system function requested by the user. The argument of an FTP service command will normally be a pathname. the syntax of pathnames must conform to server site conventions (with standard defaults applicable), except that ASCII characters must be used (in conformance with the TELNET Protool). The suggested default handling is to use the last specified device directory or file name, or the standard default defined for local users. The commands may be in any order except that a "rename from" command, must be followed by a "rename to" command, and some servers may require an "allocate" command before a "store" command. The data when transferred in response to FTP service commands shall always be over the data connection. The following commands specify FTP service requests: [Page 15] The File Transfer Protocol July 8, 1972 Retrieve (RETR) - This command achieves the transfer of a copy of file specified in pathname, from server to user site. The status and contents of a file at server site shall be unaffected. Store (STOR) - This command achieves the transfer of a copy of file from user to server site. If file specified in pathname exists at the server site, then its contents shall be replaced by the contents of the file being transferred. A new file is created at the server site if the file specified in pathname does not already exist. Append (with create) (APPE) - This command achieves the transfer of data from using to serving site. If file specified in pathname exists at the server site, then the data transferred shall be appended to that file, otherwise the file specified in pathname shall be created at the server site. Rename from (RNFR) - This command specifies the file which is to be renamed. This command must be immediately followed by a "rename to" command specifying the new file pathname. Delete (DELE) - This command causes teh file specified in pathname to be deleted at the server site. If an extra level of protection is desired (such as the query, "Do you really wish to delete?"), it should be provided by the user-FTP process. List (LIST) - This command causes a list to be sent from server to user site. If pathname specifies a directory, the server should transfer a list of files in the specified directory. If pathname specifies a file then server should send current information on the file. This command may be used to obtain the contents of a file directory (the response should be sent in ASCII type) or test the existence of a file and its current status. Allocate (ALLO) - This command my be required by some servers to reserve sufficient storage to accomodate the new file to be transferred. The command field shall be a decimal integer representing the number of bytes (of size specified by the byte size command) of storage to be reserved for the file. This command shall be followed by a store or append command. The ALLO command should be treated as a NO-OP (no operation) by thuse servers which do not require that the maximum size of the file be declared beforehand. Restart (REST) - The argument field represents the server marker at which file transfer is to be restarted. This command does not cause file transfer but "spaces" over the file to the specified [Page 16] The File Transfer Protocol July 8, 1972 data checkpoint. This command shall be immediately followed by the appropriate FTP service command which shall cause file transfer to resume. Status (STAT) - This command shall cause a status response to be sent over the TELNET connection in form of a reply. The command may have an argument field such as a pathname. if the argument is a pathname, the command is analogous to the "list" command except that data shall be transferred in ASCII on the TELNET connection. If no argument is specified, the server should return general status information about the server FTP process. This may include service availability, the current settings for the relevant FTP parameters (including default settings), and the status of command execution and connections. Abort (ABOR) - This command indicates to the server to abort the previous FTP service command and any associated transfer of data. The abort command should be preceded by the TELNET SYNCH condition (indicated by the combination of the DATA MARK and the INS). No action is to be taken if the previous command has been completed (including data transfer). The TELNET connections is not to be closed by the server, but the data connection may be closed. An appropriate reply should be sent by the server. Logout (BYE) - This command terminates a USER and if file transfer is not in progress, closes the TELNET connection. If file transfer is in progress, the connection will remain open for result response and will then close. During the interim a new USER command (and no other command) is acceptable. An unexpected close on TELNET connection will cause the server to take the effective action of an abort (ABOR) and a logout (BYE). IV.B FTP Replies The server sends FTP replies to user over the TELNET connections in response to FTP commands. The FTP replies constitute the acknowledgement or completion code (including errors). The FTP-server replies are formatted for human or program interpretation. The replies consist of a leading three digit numeric code followed by a space followed by a text explanation of the code. The numeric codes are assigned by groups and for ease of interpretation by programs in a manner consistent with other protocols such as the RJE protocol. The three digits of the code are to be interpredet as follows: [Page 17] The File Transfer Protocol July 8, 1972 a) The first digit specifies type of response as indicated below: 000 These replies are purely informative and constitute neither a positive nor a negative acknowledgement. 1xx informative replies to status inrequiries. These constitute a positive acknowledgment to the status command. 2xx Positive acknowledgment of previous command or other successful action. 3xx Incomplete information. Activity cannot proceed without further specification and input. 4xx Unsuccessful reply. The request is correctly specified but the server is unsuccessful in corretly fulfilling it. 5xx Incorrect or illegal command. The command or its parameters were invalid or incomplete from a syntactic viewpoint, or the command its inconsistent with a previous command. The command in question has been completely ignored. 6xx - 9xx Reserved for future expansion. b) The second digit specifies the general category to which the response refers: x00-x29 General purpose replies, not assignable to other categories. x30 Primary access. Informative replies to the "log-on" attempt. x40 Secondary access. The primary server is commenting on its ability to access a secondary service. x5x FTP results. x6x RJE resutls. x7x-x9x Reserved for future expansion. [Page 18] The File Transfer Protocol July 8, 1972 c) the final digit specifies a particular message type. Since the code is designed for an automaton process to interpret, it is not necessary for every variation of a reply to have a unique number. Only the basic meaning of replies need have unique numbers. The text of a reply can explain the specific reason for that reply to a human user. Each TELNET line (ended by CRLF) from the server is intended to be a complete reply message. if it is necessary to continue the text of a reply onto following lines, then those continuation replies contain the special reply code of three spaces. It should be noted that text of replies are intended for a human user. Only the reply codes and in some instances the first line of text are intended for programs. The assigned reply codes relating to FTP are: 000 General information message (site, time of day, etc.) 030 Server availibility information. 050 FTP commentary or user information. 100 System status reply. 150 File status reply. 151 Directory listing reply. 200 Last command received correctly. 201 An ABORT has terminated activity, as requested. 202 Abort request ignored, no activity in progress. 230 User is "logged in". may proceed. 231 User is "logged out". Service terminated. 232 Logout command noted, will complete when transfer done. 250 FTP file transfer started correctly. 251 FTP Restart-marker reply Text is: MARK yyyy = mmmm where yyyy is user's data stream marker (yours) and mmmm is server's equivalent marker (mine) (Note the spaces between the markers and '='). 252 FTP transfer completed correctly. 253 Rename completed. 254 Delete completed. 255 FTP server data socket reply Text is: SOCK nnnn where nnnn is decimal integer representing the server socket for data connection. 300 Connection greeting message, awaiting input. 301 Current command incomplete (no CRLF for long time). 330 Enter password (may be sent with hide-your-input). 400 This service not implemented. 401 This service not accepting users now, goodbye. 430 Log-on time or tries exceeded, goodbye. 431 Log-on unsuccessful. User and/or password invalid. 432 User not valid for this service. [Page 19] The File Transfer Protocol July 8, 1972 434 Log-out forced by operator action. Phone site. 435 Log-out forced by system problem. 436 Service shutting down, goodbye. 450 FTP: File not found. 451 FTP: File access denied to you. 452 FTP: File transfer incomplete, data connection closed. 453 FTP: File transfer incomplete, insufficient storage space. 500 Last command line completely unrecognized. 501 Syntax of last command in incorrect. 502 Last command incomplete, parameters missing. 503 Last command invalid (ignored), illegal parameter combination. 504 Last command invalid, action not possible at this time. 505 Last command conflicts illegally with previous command(s). 506 Requested action not implemented by the server. V. DECLARATIVE SPECIFICATIONS V.A. Connections The server-FTP process at the server site shall "listen" on Socket 3, via its server-TELNET. The user or user-FTP process at the user site shall initiate the full-duplex TELNET connections via its user-TELNET performing the ARPANET standard initial connection protocol (ICP) to server socket 3. The TELNET connections shall be closed by the user site upon completion of use. The user site shall "listen" on the specified data socket or sockets (a send and/or a receive socket). The server site shall initiate the data connection using the specified data socket and byte size. The direction of data connection and the data socket used shall be determined by the FTP service command. The server shall send a reply to the user indicating the server data socket so that the user may ensure the security of data transfer. This can be done at any time prior to the first transfer of data over a data connection. The data connection shall be closed by the server site under the conditions described is Section III.A. The server should in general send a reply before closing the data connection to avoid problems at the user end. V.B. Commands The commands are ASCII character strings transmitted over the TELNET connections as described in section IV.A. The command functions and semantics are described in sections IV.A.1, IV.A.2, IV.A,3, and IV.A.4. The command syntax is specified here. [Page 20] The File Transfer Protocol July 8, 1972 The commands begin with a command code followed by an argument field. The command codes are four of less ASCII alphabetic characters. Upper and lower case alphabetic characters are to be treated identically. Thus any of the following may represent the retrieve command: RETR Retr retr ReTr rETr The command codes and the argument fields are separated by one or more spaces. The argument field consists of a variable length ASCII character string ending with the character sequence CRLF (Carriage Return immediately followed by Line Feed). In the following section on syntax it should be stressed that all characters in the argument field are ASCII characters. Thus a decimal integer shall mean an ASCII represented decimal integer. The following are all the currently defined FTP commands: USER <user name> CRLF PASS <password> CRLF BYTE <byte size> CRLF SOCK <HOST-socket> CRLF TYPE <type code> CRLF STRU <structure code> CRLF MODE <mode code> CRLF RETR <pathname> CRLF STOR <pathname> CRLF APPE <pathname> CRLF RNFR <pathname> CRLF RNTO <pathname> CRLF DELE <pathname> CRLF LIST <pathname> CRLF ALLO <decimal integer> CRLF REST <marker> CRLF STAT <pathname> CRLF ABOR <empty> CRLF Bye <empty> CRLF The syntax of the above argument fields (using BNF notation where aplicable) is: <username> ::= <string> <password> ::= <string> <string> ::= <empty> | <char> | <char><string> <char> ::= any of the 128 ASCII characters except CR and LF. <marker> ::= <pr string> [Page 21] The File Transfer Protocol July 8, 1972 <pr string> ::= <empty> | <pr char> | <pr char><pr string> <pr char> ::= any ASCII code 33 through 126. <byte size> ::= any decimal integer 1 through 255. <HOST-socket> ::= <socket> | <HOST number>,<socket> <HOST number> ::= a decimal integer specifying an ARPANET HOST. <socket> ::= decimal integer between o and (2**32)-1 <type code> ::= A|I|L|P|E <structure code> ::= F|R <mode code> ::= S|B|T|H <pathname> ::= <string> <decimal integer> ::= <digit> | <digit><decimal integer> <digit> ::= 0|1|2|3|4|5|6|7|8|9| <empty> ::= the null string (specifies use of default). V.C Sequencing of Commands and Replies The communication between the user and server is intended to be an alternating dialogue. As such, the user issues an FTP command and the server responds with a prompt primary reply. The user should wait for this initial primary success of failure response before sending further commands. A second type of reply is sent asynchronously with respect to user commands. These replies may for example report on the progress or completion of file transfer and as such are secondary replies to file transfer commands. The third class of replies are informational and spontaneous replies which may arrive at any time. These replies are listed below as spontaneous. COMMAND-REPLY CORRESPONDENCE TABLE COMMAND SUCCESS FAIL USER 230,330 430-432,500-505 PASS 230 430-432,500-505 BYE 231,232 430-432,500-505 BYTE 200 500-506 SOCK 200 500-506 TYPE 200 500-506 MODE 200 500-506 RETR 250 450,451,500-506 Secondary Reply 252 452 STOR 250 451,451,500-506 Secondary Reply 252 452,453 APPE 250 451,451,500-506 Secondary Reply 252 452,453 [Page 22] The File Transfer Protocol July 8, 1972 RNFR 200 450,451,500-506 RNTO 253 450,451,500-505 DELE 254 450,451,500-506 LIST 250 450,453,500-506 Secondary Reply 252 452 ALLO 200 500-506 STAT 100,150,151 450,451,500-506 REST 200 500-506 ABOR 201,202 500-505 Spontaneous 0xx,300,301 400,401,434-436 Replies 251,255 V.D. Tyical FTP Scenarious 1. TIP User wanting o transfer file from FOST X to local printer: a) TIP user opens TELNET connections by ICP to HOST X, socket 3. b) The following commands and replies are exchanged: TIP HOST X USER username CRLF --------> <------- 330 Enter Password CRLF PASS password CRLF --------> <------- 230 User logged in CRLF SOCK 65538 CRLF --------> <------- 200 Command received OK CRLF RETR this.file CRLF --------> <------- 255 SOCK 5533 CRLF (HOST X initiates data connection to TIP socket 65538, i.e., PORT 1 receive) <------- 250 File transfer started BYE CRLF ------_-> <------- 252 File transfer completed c) HOST X closes the TELNET and data connections. Note: The TIP user should be in line mode and can thus use local TIP editing such as character delete. [Page 23] The File Transfer Protocol July 8, 1972 2. User at Host U wanting to transfer files to/from HOST S: In general the user would communicate to the server via a mediating user-FTP process. The following may be a typical scenario. The user-FTP prompts are shown in parenthesis, '---->' represents commands from HOST U to HOST S, and '<----' represents replies from HOST S to HOST U. Local Commands by User Action Involved ftp (host) multics CR ICP to HOST S, socket 3, establishing TELNET connections. username Doe CR USER DoeCRLF ----> <---- 330 passwordCRLF password mumble CR PASS mumbleCRLF ----> <---- 230 Doe logged in.CRLF retrieve (local type ASCIICR (local pathname) test 1 CR USER-FTP open local file in ASCII. (for. pathname) test.pl1CR RETR test.pl1 CRLF ----> <---- 255 SOCK 1233CRLF Server makes data connection to (U+4). <---- 250 File transfer startsCRLF <---- 252 File transfer completeCRLF type imageCR TYPE |CRLF ----> <---- 200 Command OKCRLF byte 36CR BYTE 36CRLF ----> <---- 200 Command OKCRLF store (local type) ImageCR (local pathname) file dumpCR User-FTP opens local file in Image. (for. pathname) >udd>cn>fdCR STOR >udd>cn>fdCRLF ----> <---- 451 Access deniedCRLF terminate BYECRLF <---- 231 Doe logged outCRLF Server closes all connections. [Page 24] The File Transfer Protocol July 8, 1972 ACKNOWLEDGEMENTS The work on file transfer protocol has involved many people. This document reports the work of a group rather than the author alone. The author gratefully acknowledges the conributions of the following: Bob Braden UCLA-CCCN Arvola Chan MIT-MAC Bill Crowther BBN-TIP Eric Harslem RAND John Heafner RAND Chuck Holland UCSD Alex McKenzie BBN (NET) Bob Metcalfe XPARC Jon Postel UCLA Neal Ryan MIT-MAC Bob Sundberg HARVARD Ray Tomlinson BBN (TENEX) Dick Watson SRI-ARC Jim White SRI-ARC Richard Winter CCA [ This RFC was put into machine readable form for entry ] [ into the online RFC archives by Gottfried Janik 9/97 ] [Page 25]