Request for Comments: 1037 S. Keene
December 1987
NFILE - A File Access Protocol
STATUS OF THIS MEMO
This document includes a specification of the NFILE file access
protocol and its underlying levels of protocol, the Token List
Transport Layer and Byte Stream with Mark. The goal of this
specification is to promote discussion of the ideas described here,
and to encourage designers of future file protocols to take advantage
of these ideas. A secondary goal is to make the specification
available to sites that might benefit from implementing NFILE. The
distribution of this document is unlimited.
TABLE OF CONTENTS
Page
1. INTRODUCTION 3
2. NFILE PROTOCOL LAYERING 4
3. OVERVIEW OF AN NFILE SESSION 5
4. NFILE CONTROL AND DATA CONNECTIONS 6
5. NFILE FILE OPENING MODES 7
6. NFILE CHARACTER SET 9
7. CONVENTIONS USED IN THIS DOCUMENT 10
7.1 Mapping Data Types Into Token List Representation 10
7.2 Format of NFILE Commands and Responses 10
7.3 Data Channel Handles and Direct File Identifiers 13
7.4 Syntax of File and Directory Pathname Arguments 13
7.5 Format of NFILE File Property/Value Pairs 14
8. NFILE COMMANDS 16
8.1 ABORT Command 16
8.2 CHANGE-PROPERTIES Command 16
8.3 CLOSE Command 17
8.4 COMPLETE Command 19
8.5 CONTINUE Command 20
8.6 CREATE-DIRECTORY Command 21
8.7 CREATE-LINK Command 21
8.8 DATA-CONNECTION Command 22
8.9 DELETE Command 23
8.10 DIRECT-OUTPUT Command 23
8.11 DIRECTORY Command 24
8.11.1 NFILE DIRECTORY Data Format 26
8.12 DISABLE-CAPABILITIES Command 27
8.13 ENABLE-CAPABILITIES Command 28
8.14 EXPUNGE Command 28
8.15 FILEPOS Command 29
8.15.1 Implementation Hint for FILEPOS Command 30
8.16 FINISH Command 30
8.17 HOME-DIRECTORY Command 31
8.18 LOGIN Command 32
8.19 MULTIPLE-FILE-PLISTS Command 34
8.20 OPEN Command 35
8.20.1 NFILE OPEN Optional Keyword/Value Pairs 39
8.20.2 NFILE OPEN Response Return Values 45
8.21 PROPERTIES Command 47
8.22 READ Command 49
8.23 RENAME Command 50
8.24 RESYNCHRONIZE-DATA-CHANNEL Command 51
8.24.1 Implementation Hints for RESYNCHRONIZE-DATA- 51
CHANNEL Command
8.25 UNDATA-CONNECTION Command 52
9. NFILE RESYNCHRONIZATION PROCEDURE 53
9.1 NFILE Control Connection Resynchronization 54
9.2 NFILE Data Connection Resynchronization 55
10. NFILE ERRORS AND NOTIFICATIONS 58
10.1 Notifications From the NFILE Server 58
10.2 NFILE Command Response Errors 59
10.3 NFILE Asynchronous Errors 60
10.4 NFILE Three-letter Error Codes 61
11. TOKEN LIST TRANSPORT LAYER 65
11.1 Introduction to the Token List Transport Layer 65
11.2 Token List Stream 66
11.2.1 Types of Tokens and Token Lists 66
11.2.2 Token List Stream Example 68
11.2.3 Mapping of Lisp Objects to Token List Stream 70
Representation
11.2.4 Aborting and the Token List Stream 71
11.3 Token List Data Stream 72
12. BYTE STREAM WITH MARK 73
12.1 Discussion of Byte Stream with Mark 73
12.2 Byte Stream with Mark Abortable States 75
13. POSSIBLE FUTURE EXTENSIONS 77
APPENDIX A. NORMAL TRANSLATION MODE 79
APPENDIX B. RAW TRANSLATION MODE 83
APPENDIX C. SUPER-IMAGE TRANSLATION MODE 84
NOTES 86
LIST OF TABLES
TABLE 1. TRANSLATIONS FROM NFILE CHARACTERS TO UNIX CHARACTERS 80
TABLE 2. TRANSLATIONS FROM UNIX CHARACTERS TO NFILE CHARACTERS 80
TABLE 3. TRANSLATIONS FROM NFILE TO PDP-10 CHARACTERS 81
TABLE 4. TRANSLATIONS FROM PDP-10 CHARACTERS TO NFILE 82
CHARACTERS
TABLE 5. SUPER-IMAGE TRANSLATION FROM NFILE TO ASCII 84
TABLE 6. SUPER-IMAGE TRANSLATION FROM ASCII TO NFILE 85
1. INTRODUCTION
NFILE stands for "New File Protocol". NFILE was originally designed
as a replacement for an older protocol named QFILE, with the goal of
solving robustness problems of QFILE, hence the name "New File
Protocol".
NFILE was designed and implemented at Symbolics by Bernard S.
Greenberg. Mike McMahon made important contributions, especially in
the design and implementation of the Byte Stream with Mark and Token
List Transport layers. NFILE has been used successfully for file
access between Symbolics computers since 1985. NFILE servers have
been written for UNIX hosts as well. NFILE is intended for use by
any type of file system, not just the native Symbolics file system.
NFILE is a file access protocol that supports a large set of
operations on files and directories on remote systems, including:
- Reading and writing entire files
- Reading and writing selected portions of files
- Deleting and renaming files
- Creating links
- Listing, creating, and expunging directories
- Listing and changing the properties of files
- Enabling and disabling access capabilities on a remote
host
NFILE supports file transfer of binary or character files.
The NFILE server provides information about any errors that occur in
the course of a command. In addition, NFILE has a robust scheme for
handling aborts on the user side.
This specification defines NFILE user version 2 and server version 2.
We do not envision NFILE as an unchanging protocol, but rather as a
protocol that could continue to develop if additional requirements
are identified though the process of this Request for Comments. The
design of NFILE makes room for various useful extensions. Some of
the extensions that we are considering are described later on in this
document: See the section "Possible Future Extensions", section 13.
2. NFILE PROTOCOL LAYERING
NFILE is a layered file protocol. The layers are:
+-----------------------------------------------+
|client program or user interface |
+-----------------------------------------------+
|NFILE |
+-----------------------------------------------+
|Token List Transport Layer |
+-----------------------------------------------+
|Byte Stream with Mark |
+-----------------------------------------------+
|reliable host-host byte transmission protocol |
+-----------------------------------------------+
Byte Stream with Mark is a simple protocol that guarantees that an
out-of-band signal can be transmitted in the case of program
interruption. Byte Stream with Mark is to be layered upon extant
byte stream protocols. An important goal of the NFILE design was
that NFILE could be built on any byte stream. It is currently
implemented on TCP and Chaosnet. See the section "Byte Stream with
Mark", section 12.
The Token List Transport Layer is a protocol that facilitates the
transmission of simple structured data, such as lists. See the
section "Token List Transport Layer", section 11.
The NFILE commands and command responses are transmitted in "token
lists". See the section "NFILE Commands", section 8.
This specification does not include a client program or user
interface to the protocol. In the Symbolics implementation, the
normal file operations transparently invoke NFILE, when the remote
host is known to support NFILE. Another possible interface to NFILE
would be through a dedicated client program that would issue NFILE
commands in response to explicit requests by the user.
3. OVERVIEW OF AN NFILE SESSION
An NFILE session is a dialogue between two hosts. The host that
initiates the NFILE session is known as the "user side", and the
other host is the "server side". The user side sends all NFILE
commands. The server receives each command, processes it, and
responds to it, indicating the success or failure of the command.
The user side keeps track of commands sent and command responses
received by using "transaction identifiers" to identify each command.
The user side generates a transaction identifier (which must be
unique per this dialogue) for each command, and sends the transaction
identifier to the server along with the command. Each NFILE server
response includes the transaction identifier of the command with
which the response is associated. The server is not required to
respond to commands in the same order that the user gave them.
The user side sends NFILE commands over a bidirectional network
connection called the "control connection". The server sends its
command responses on the same control connection. The control
connection governing the NFILE session is established at the
beginning of the session. If the control connection is ever broken,
the NFILE session is ended.
Whereas NFILE commands and responses are transmitted on the control
connection, file data is transferred over "data channels". An "input
data channel" transfers data from server to user. An "output data
channel" transfers data from user to server. Each input data channel
is associated with an output data channel; together these two
channels comprise a "data connection".
Often more than one NFILE activity is occurring at any given time.
For example, several files can be open and transferring data
simultaneously; one or more commands can be in process at the same
time; and the server can be simultaneously transmitting directory
lists and processing further commands. This happens in an
implementation in which the user side has multiple processes, and
several processes share a single NFILE server.
4. NFILE CONTROL AND DATA CONNECTIONS
The user and server communicate through a single control connection
and a set of data connections. Data connections are established and
disestablished by NFILE commands. The user side sends NFILE commands
to the server over the control connection. The server responds to
every user command over this control connection. The actual file
data is transmitted over the data connections.
User aborts can disrupt the normal flow of data on the control
connection and data connections. An important aspect of any file
protocol is the way it handles user aborts. NFILE uses a
resynchronization procedure to bring the affected control connection
or data channel from an unknown, unsafe state into a known state.
After resynchronization, the control connection or data channel can
be reused. See the section "NFILE Resynchronization Procedure",
section 9.
THE CONTROL CONNECTION
An NFILE session is begun when the NFILE user program connects to a
remote host and establishes a network connection. This initial
connection is the control conection of the dialogue. If TCP is used
as the underlying protocol, contact NFILE's well-known port, 59. If
Chaos is used, use the contact name "NFILE".
The control connection is the vehicle used by the user to send its
commands, and the server to send its command responses. These types
of communication occur over the NFILE control connection:
- The user side sends NFILE commands.
- The server sends command responses.
- The server sends "notifications" and "asynchronous errors".
See the section "NFILE Errors and Notifications", section 10.
- During resynchronization (a special circumstance) either the
user or server sends a mark.
All commands, command responses, and other data flowing over the
NFILE control connection are transmitted in the format of "top-level
token lists". The control connection expects never to receive "loose
tokens"; that is, tokens not contained in token lists.
DATA CONNECTIONS
Data connections are established and discarded at user request, by
means of two NFILE commands: DATA-CONNECTION and UNDATA-CONNECTION.
Each data connection is associated with a specific control
connection, which is the same control connection that caused the data
connection to be established.
Each data connection is composed of two "data channels". Each data
channel is capable of sending data in one direction. The term "input
channel" refers to the data channel that transmits data from the
server to the user side; "output channel" refers to the data channel
that transmits data from the user to the server side. Throughout the
NFILE documentation, the terms "input channel" and "output channel"
are seen from the perspective of the user side. A single data
channel can be used for one data transfer after another.
The format of the data transferred on the data channels is defined as
a "token list data stream". See the section "Token List Data
Stream", section 11.3. When the end of data is reached, the keyword
token EOF is sent. Occasionally, token lists are transmitted over
the data channels, such as asynchronous error descriptions.
5. NFILE FILE OPENING MODES
The NFILE OPEN command opens a file for reading, writing, or "direct
access" at the server host. That means, in general, asking the host
file system to access the file and obtaining a file number, pointer,
or other quantity for subsequent rapid access to the file; this is
called an "opening". The term "opening" translates to a file stream
in Symbolics terminology, a JFN in TOPS-20 terminology, and a file
descriptor in UNIX terminology. An opening usually keeps track of
how many bytes have been read or written, and other bookkeeping
information.
NFILE supports two ways of transferring file data, "data stream mode"
and "direct access mode". A single mode is associated with each
opening. Note that an NFILE dialogue can have more than one opening,
and thus use both modes.
DATA STREAM MODE:
Data stream mode of file transfer is the default mode of NFILE's OPEN
command. Data stream mode is appropriate when the entire file is
transferred, either from user to server, or from server to user.
Data stream mode is used more often than direct access mode.
The OPEN command includes a "handle" argument, which identifies the
data channel to be used to transfer the data. The handle is used in
subsequent commands to reference this particular opening. When a
data stream opening is requested with the OPEN command, the file is
opened and the data begins to flow immediately.
The sending side transmits the entire contents of the specified file
over the specified data channel as rapidly as the network permits.
When the sending side reaches the end of the file, it transmits a
special control token to signal end of file. The receiving side
expects an uninterrupted stream of bytes to appear immediately on its
side of the data channel.
The user gives the CLOSE command to terminate a data stream transfer.
CLOSE results in closing the file.
DIRECT ACCESS MODE:
Direct access mode enables reading or writing data from a given
starting point in a file through a specified number of bytes. In
direct access mode, data is requested and sent in individual
transactions. To request a direct access mode opening, the OPEN
command is used with a DIRECT-FILE-ID argument. (In data stream
mode, no DIRECT-FILE-ID is supplied.) The direct file identifier is
used in subsequent commands to reference the direct access opening.
When a file is opened in direct access mode, the flow of data does
not start immediately. Rather, the user gives either a READ command
(to request data to flow from server to user) or a DIRECT-OUTPUT
command (to request data to flow from user to server). When reading,
the READ command allows the user to specify the starting point and
the number of bytes of data to transfer. When writing, the FILEPOS
command can be used to specify the starting point, before the
DIRECT-OUTPUT command is given. The user can give many READ and
DIRECT-OUTPUT commands, one after another.
The user side terminates the direct access transfer by using the
CLOSE command. The ABORT command can be given to terminate without
transmitting all of the specified bytes.
6. NFILE CHARACTER SET
The NFILE character set <1> is an extension of standard ASCII. NFILE
command and response names use only the standard ASCII characters.
However, the protocol supports the transfer of the non-ASCII
characters in the NFILE character set; these characters might be
stored in files, or might be used in pathnames.
Servers on machines that do not natively use the NFILE character set
must perform character set translations for character openings,
depending on the requested translation mode. No translation is
required for binary openings. There are three translation modes for
character openings: NORMAL, RAW, and SUPER-IMAGE. Each mode
specifies a way to translate between the server's native set and the
NFILE character set.
NORMAL mode is the default of the OPEN command. The translation for
NORMAL mode ensures that a file containing characters in the NFILE
character set can be written to a remote host and read back intact.
OPEN has optional keyword arguments to specify RAW or SUPER-IMAGE.
RAW mode means to perform no translation whatsoever. SUPER-IMAGE
mode is intended for use by PDP-10 family machines only. It is
included largely as an illustration of a system-dependent extension.
The details of each translation mode are given in Appendices:
See the section "NORMAL Translation Mode", Appendix A. See the
section "RAW Translation Mode", Appendix B. See the section
"SUPER-IMAGE Translation Mode", Appendix C.
The use of the NFILE character set brings up a difficulty involved
with determining an exact position within a character file. Some
NFILE characters expand to more than one native character on some
servers. Thus, for character files, when we speak of a given
position in a file or the length of a file, we must specify whether
we are speaking in "NFILE units" or "server units", because the
counting of characters is different. This causes major problems in
file position reckoning for character files. Specifically, it is
futile for a user side to carefully monitor file position during
output by counting characters, when character translation is in
effect. The server's operating system interface for "position to
point x in a file" necessarily operates in server units, but the user
side has counted in NFILE units. The user side cannot try to
second-guess the translation-counting process without losing host-
independence. See the section "FILEPOS NFILE Command".
7. CONVENTIONS USED IN THIS DOCUMENT
7.1 Mapping Data Types Into Token List Representation
Throughout this NFILE specification, the data types of arguments,
return values, asynchronous error descriptions, and notifications are
described as being strings, integers, dates, time intervals, and so
on. However, each conceptual data type must be mapped into the
appropriate token list representation for transmission. The mapping
of conceptual data types to token list representation is shown here:
Conceptual Type Token List Representation
----------------------------------------------------------------
Keyword A keyword token
Keyword list A token list of keyword tokens
Integer A numeric data token
String A data token containing the characters of the
string in the NFILE character set.
Boolean Truth The token known as BOOLEAN-TRUTH.
Boolean False The empty token list.
Date A numeric data token. The date is expressed in
Universal Time format, which measures a time as
the number of seconds since January 1, 1900, at
midnight GMT.
Date-or-never Can be either a date or the empty token list,
representing "never". "Never" is used for
values such as the time a directory was last
expunged, if it has never been expunged.
Time interval A numeric data token. The time interval is
expressed in seconds. A time interval
indicating "never" is represented by the empty
token list.
7.2 Format of NFILE Commands and Responses
Each command description begins by giving the command format and
response format. Here is the beginning of the DATA-CONNECTION
command description:
Command: (DATA-CONNECTION tid new-input-handle new-output-handle)
Response: (DATA-CONNECTION tid connection-identifier)
The command descriptions follow these conventions:
1. NFILE commands and responses are transmitted as top-level token
lists.
Top-level token lists are enclosed in parentheses in these
command descriptions. These parentheses are not sent literally
across the control or data connections, but are a shorthand
representation of special control tokens that delimit top-level
token lists. Specifically, TOP-LEVEL-LIST-BEGIN starts a top-
level token list; TOP-LEVEL-LIST-END ends a top-level token list.
2. NFILE command names are keywords.
The command name is required in every command and command
response. All NFILE command names are keywords. Keywords appear
in the NFILE documentation as their names in uppercase. For
example, DATA-CONNECTION and DELETE are two command names.
3. A unique transaction identifier (tid) identifies each command.
The transaction identifier is a string made up by the user side
to identify this particular transaction, which is composed of the
command and the response associated with this command. The
transaction identifier is abbreviated in the command descriptions
as tid. Transaction identifiers are limited to fifteen
characters in length. The transaction identifier is required in
every command and command response.
OPTIONAL ARGUMENTS
Many NFILE commands have "optional arguments". Optional arguments
can be supplied (with appropriate values), or left out. If optional
arguments are left out, their omission must be made explicit by means
of substituting the empty token list in their place. The only
exception to that rule is for trailing optional arguments or return
values, which can be omitted without including the empty token list.
For example, the text of the DELETE command description explains that
either a handle or a pathname must be supplied, but not both;
therefore, one of them is an optional argument. Here is the command
format of DELETE:
(DELETE tid handle pathname)
If you supply a handle and no pathname, the command format is:
(DELETE tid handle)
If you supply a pathname and no handle, the command format is:
(DELETE tid empty-token-list pathname)
The empty token list in the token list stream appears as a LIST-BEGIN
followed immediately by a LIST-END.
OPTIONAL KEYWORD/VALUE PAIRS
Four NFILE commands have "optional keyword/value pairs". These
commands are: COMPLETE, LOGIN, OPEN, and READ. Optional
keyword/value pairs can be either included in the command or omitted
entirely. There is no need to substitute the empty token list for
ommitted optional keyword tokens, unlike optional arguments. The
order of the option keyword/value pairs is not significant.
If included, optional keyword/value pairs are a sequence of
alternating keywords and values. The values associated with the
keywords can be keywords, lists, strings, Booleans, integers, dates,
date-or-never's, and time intervals. The text of each command
description states what type of value is appropriate for each
optional keyword.
Optional keyword/value pairs appear in the text as the keyword only,
in uppercase letters. For example, here is the format of the LOGIN
command:
Command Format:
(LOGIN tid user password FILE-SYSTEM USER-VERSION)
FILE-SYSTEM and USER-VERSION are two optional keywords associated
with the LOGIN command. The user side can supply USER-VERSION, and
omit FILE-SYSTEM as shown in this example:
(LOGIN x105 tjones let-me-in USER-VERSION 2)
As seen above, the optional keyword/value pair USER-VERSION, if
supplied in a command, consists of the keyword USER-VERSION followed
by the value to be used for that keyword (in this example, 2).
7.3 Data Channel Handles and Direct File Identifiers
Several NFILE commands require an argument that specifies an opening.
This kind of argument is called a handle in the command description.
It is always a string type argument. A handle can be either a data
channel handle or a direct file identifier, depending on the mode of
the opening:
Data Stream
The handle must identify a data channel that is bound to an opening.
Direct Access
In general, the handle must be a direct file identifier. A direct
file identifier specifies a direct access opening. It is the same as
the value supplied in the DIRECT-FILE-ID keyword/value pair in the
OPEN command. It is used for all operations that identify an opening
rather than a data channel.
Two NFILE commands applicable to direct access openings are
exceptions to the general rule. The handle supplied in ABORT and
CONTINUE cannot be a direct file identifier, but must be a data
channel handle instead.
7.4 Syntax of File and Directory Pathname Arguments
Some arguments and return values in the NFILE command descriptions
represent file pathnames. These are strings in the pathname syntax
native to the server host. These pathnames contain no host
identifiers of any kind. These pathnames must be fully defaulted, in
the sense that they have a directory and file name (and file type, if
the server operating system supports file types). If appropriate, a
device is referenced in the pathname. If the server file system
supports version numbers, there is always an explicit version number,
even if that number or other specification is that system's
representation of "newest" or "oldest".
Here are some examples of file pathnames, for different server hosts:
Server Host Example of File Pathname
------------------------------------------------------------
UNIX /usr/max/life.c
TOPS-20 ps:<max>life.bin.17
VMS MACD:[MAX]LIFE.FOR;3
Symbolics LMFS >max>life.lisp.newest
------------------------------------------------------------
The CREATE-DIRECTORY and HOME-DIRECTORY commands take a directory as
an argument. In NFILE commands, a directory is represented by a
string that names the directory. In most cases this string is in the
syntax native to the server host. However in some cases the native
format is modified somewhat to clarify that the string names a
directory, and not a file. For example, a directory on UNIX is
represented by "/usr/max/", not "/usr/max".
Here are some examples of directory pathnames for different server
hosts:
Server Host Example of Directory Pathname
------------------------------------------------------------
UNIX /usr/max/
TOPS-20 <max>
VMS MACD:[MAX]
Symbolics LMFS >max>hacks>
------------------------------------------------------------
7.5 Format of NFILE File Property/Value Pairs
Several NFILE commands request information regarding the properties
of files or directories. These commands include: DIRECTORY,
MULTIPLE-FILE-PLISTS, PROPERTIES, and CHANGE-PROPERTIES. This
section describes how file property information is conveyed over the
token list stream.
File property information is usually sent in property/value pairs,
where the property identifies the property, and the following value
gives the value of that property for the specified file.
Each property is denoted either by a keyword or an integer. You can
mix both ways of specifying properties (keyword or integer) within a
single description. An integer is interpreted as an index into the
Property Index Table, an array of property keywords. The server can
optionally send a Property Index Table to the user during the
execution of the LOGIN command, although it is not required. This
greatly reduces the length of transmissions.
In command arguments, file properties cannot be specified with
integers; keywords must be used to specify file properties in command
arguments. Integers can be used to denote file properties only in
command responses.
We now list the keywords associated with file properties. This list
is not intended to be restrictive. If a programmer implementing
NFILE needs a new keyword, a new keyword (not on this list) can be
invented. The type of value of any new keywords is by default
string. The keywords are sorted here by conceptual data type:
Data type Keywords denoting file properties
----------------------------------------------------------------
Integers BLOCK-SIZE, BYTE-SIZE, GENERATION-RETENTION-COUNT,
LENGTH-IN-BLOCKS, LENGTH-IN-BYTES,
DEFAULT-GENERATION-RETENTION-COUNT
Dates CREATION-DATE, MODIFICATION-DATE
Date-or-never's REFERENCE-DATE, INCREMENTAL-DUMP-DATE,
COMPLETE-DUMP-DATE, DATE-LAST-EXPUNGED,
EXPIRATION-DATE
Time intervals AUTO-EXPUNGE-INTERVAL
Keyword Lists SETTABLE-PROPERTIES, LINK-TRANSPARENCIES,
DEFAULT-LINK-TRANSPARENCIES
Boolean values DELETED, DONT-DELETE, DONT-DUMP, DONT-REAP,
SUPERSEDE-PROTECT, NOT-BACKED-UP, OFFLINE,
TEMPORARY, CHARACTERS, DIRECTORY
Strings ACCOUNT, AUTHOR, LINK-TO, PHYSICAL-VOLUME,
PROTECTION, VOLUME-NAME, PACK-NUMBER, READER,
DISK-SPACE-DESCRIPTION, and any keywords not
on this list
Note that these keyword names are intended to imply the semantics of
the properties. For a discussion of the semantics of CREATION-DATE:
See the section "NFILE OPEN Response Return Values", section 8.20.2.
The "Reference Guide to Streams, Files, and I/O" in the Symbolics
documentation set details the semantics that Symbolics associates
with these properties.
8. NFILE COMMANDS
It is important to understand the conventions used in each of the
following command descriptions. See the section "Conventions Used in
This Document", section 7.
8.1 ABORT Command
Command: (ABORT tid input-handle)
Response: (ABORT tid)
ABORT cleanly interrupts and prematurely terminates a single direct
access mode data transfer initiated with READ. The required input-
handle string argument identifies a data channel on which an input
transfer is currently taking place; this must be a direct access
transfer. input-handle must identify a data channel; it cannot be a
direct file identifier.
Upon receiving the ABORT command, the server checks to see if a
transfer is still active on that channel. If so, the server
terminates the transfer by telling the data connection logical
process to stop transferring bytes of data. The user side needs to
issue this command only when there are outstanding unread bytes.
This excludes the case of the data channel having been disestablished
or reallocated by the user side.
Whether or not a transfer is active on that channel, the user side
puts the data channel into the unsafe state. Before the data channel
can be used again, it must be resynchronized.
8.2 CHANGE-PROPERTIES Command
Command: (CHANGE-PROPERTIES tid handle pathname property-pairs)
Response: (CHANGE-PROPERTIES tid)
CHANGE-PROPERTIES changes one or more properties of a file. Either a
handle or a pathname must be given, but not both. Whichever one is
given must be supplied as a string. handle identifies a data channel
that is bound to an open file; it can be a direct file identifier.
pathname identifies a file on the server machine.
property-pairs is a required token list of keyword/value pairs, where
the name of the property to be changed is the keyword, and the
desired new property value is the value.
The properties that can be changed are host-dependent, as are any
restrictions on the values of those properties. The properties that
can be changed are the same as those returned as settable-properties,
in the command response for the PROPERTIES command.
The server tries to modify all the properties listed in property-
pairs to the desired new values. There is currently no definition
about what should be done if the server can successfully change some
properties but not others.
For further information on file property keywords and associated
values: See the section "Format of NFILE File Property/Value Pairs",
section 7.5.
8.3 CLOSE Command
Command: (CLOSE tid handle abort-p)
Response: (CLOSE tid truename binary-p other-properties)
CLOSE terminates a data transfer, and frees a data channel. The
handle must be a data channel handle for a data stream opening, or a
direct file identifier for a direct access opening. If a data
channel is given, a transfer must be active on that handle. If
abort-p is supplied as Boolean truth, the file is close-aborted, as
described below.
"Closing the file" has different implications specific to each
operating system. It generally implies invalidation of the pointer
or logical identifier obtained from the operating system when the
file was "opened", and freeing of operating system and/or job
resources associated with active file access. For output files, it
involves ensuring that every last bit sent by the user has been
successfully written to disk. The server should not send a
successful response until all these things have completed
successfully.
In either data stream or direct access mode, the user can request the
server to close-abort the file, instead of simply closing it. To
close-abort a file means to close it in such a way, if possible, that
it is as if the file had never been opened. In the specific case of
a file being created, it must appear as if the file had never been
created. This might be more difficult to implement on certain
operating systems than others, but tricks with temporary names and
close-time renamings by the server can usually be used to implement
close-abort in these cases. In the case of a file being appended to,
close-abort means to forget the appended data.
AN UNSUCCESSFUL CLOSE OPERATION
For the normal CLOSE operation (not a close-abort), after writing
every last bit sent by the user to disk, and before closing the file,
the server checks the data channel specified by handle to see if an
asynchronous error is outstanding on that channel. That is, the
server must determine whether it has sent an asynchronous error
description to the user, to which the user has not yet responded with
a CONTINUE command. If so, the server is unable to close the file,
and therefore sends a command error response indicating that an error
is pending on the channel. The appropriate three-letter error code
is EPC. See the section "NFILE Errors and Notifications", section
10.
A SUCCESSFUL CLOSE OPERATION
The return values for OPEN and CLOSE are syntactically identical, but
the values might change between the time of the file being opened and
when it is closed. For example, the truename return value is
supplied after all the close-time renaming of output files is done
and the version numbers resolved (for operating systems supporting
version numbers). Therefore, on some systems the truename of a file
has one value at the time it is opened, and a different value when it
has been closed. For a description of the CLOSE return values: See
the section "NFILE OPEN Response Return Values", section 8.20.2.
If the user gives the CLOSE command with abort-p supplied as Boolean
truth, thus requesting a close-abort of the file, the server need not
check whether an asynchronous error description is outstanding on the
channel. The server simply close-aborts the file.
8.4 COMPLETE Command
Command: (COMPLETE tid string pathname DIRECTION NEW-OK DELETED)
Response: (COMPLETE tid new-string success)
COMPLETE performs file pathname completion.
string is a partial filename typed by the user and pathname is the
default name against which it is being typed. Both string and
pathname are required arguments, and are of type string. The
remaining arguments are optional keyword/value pairs.
NEW-OK is Boolean; if followed by Boolean truth, the server should
allow either a file that already exists, or a file that does not yet
exist. The default of NEW-OK is false; that is, the server does not
consider files that do not already exist.
DELETED is a Boolean type argument; if followed by Boolean truth, the
server is instructed to look for files that have been deleted but not
yet expunged, as well as non-deleted files. The default is to ignore
soft-deleted files.
DIRECTION can be followed by READ, to indicate that the file is to be
read. If the file is to be written, DIRECTION can be followed by
WRITE. The default is READ.
The filename is completed according to the files present in the host
file system, and the expanded string new-string is returned. New-
string is always a string containing a file name: either the
original string, or a new, more specific string. The value of
success indicates the status of the completion. The keyword value OLD
or NEW means complete success, whereas the empty token list means
failure. The following values of success are possible:
Value Meaning
----------------------------------------------------------------
OLD Success: the string completed to the name of
a file that exists.
NEW Success: the string completed to the name of
a file that could be created.
Empty token list Failure due to one of these reasons:
The file is on a file system that does not
support completion. new-string is supplied as
the unchanged string.
There is no possible completion. new-string
is supplied as the unchanged string.
There is more than one possible completion.
The given string is completed up to the first
point of ambiguity, and the result is supplied
as new-string.
A directory name was completed. Completion
was not successful because additional
components to the right of this directory
remain to be specified. The string is
completed through the directory name and the
delimiter that follows it, and the result is
returned in new-string.
The semantics of COMPLETE are not documented here. See the
"Reference Guide to Streams, Files, and I/O" in the Symbolics
documentation set for the recommended semantics of COMPLETE.
8.5 CONTINUE Command
Command: (CONTINUE tid handle)
Response: (CONTINUE tid)
CONTINUE resumes a data transfer that was temporarily suspended due
to an asynchronous error. Each asynchronous error description has an
optional argument of RESTARTABLE, indicating whether it makes any
sense to try to continue after this particular error occurred.
CONTINUE tries to resume the data transfer if the error is
potentially recoverable, according to the RESTARTABLE argument in the
asynchronous error description. For a discussion of asynchronous
errors: See the section "NFILE Errors and Notifications", section
10.
handle is a required string-type argument that refers to the handle
of the data channel that received an asynchronous error. That data
channel could have been in use for a data stream or direct access
transfer. handle cannot be a direct file identifier.
If the asynchronous error description does not contain the
RESTARTABLE argument, and the user issues the CONTINUE command
anyway, the server gives a command error response.
8.6 CREATE-DIRECTORY Command
Command: (CREATE-DIRECTORY tid pathname property-pairs)
Response: (CREATE-DIRECTORY tid dir-truename)
CREATE-DIRECTORY creates a directory on the remote file system. The
required pathname argument is a string identifying the pathname of
the directory to be created. The return value dir-truename is the
pathname of the directory that was successfully created. Both of
these pathnames are directory pathnames: See the section "Syntax of
File and Directory Pathname Arguments", section 7.4.
property-pairs is a keyword/value list of properties that further
define the attributes of the directory to be created. The allowable
keywords and associated values are operating system dependent;
typically they indicate arguments to be given to the native primitive
for creating directories.
If property-pairs is supplied as the empty token list, default access
and creation attributes apply and should be assured by the server.
See the section "Format of NFILE File Property/Value Pairs", section
7.5.
8.7 CREATE-LINK Command
Command: (CREATE-LINK tid pathname target-pathname properties)
Response: (CREATE-LINK tid link-truename)
CREATE-LINK creates a link on the remote file system.
pathname is the pathname of the link to be created; target-pathname
is the place in the file system to which the link points. Both are
required arguments. The return value link-truename names the
resulting link.
If a server on a file system that does not support links receives the
CREATE-LINK command, it sends a command error response.
The arguments pathname and target-pathname, and the return value
link-truename, are all strings in the full pathname syntax of the
server host. See the section "Syntax of File and Directory Pathname
Arguments", section 7.4.
The required properties argument is a token list of keyword/value
pairs. These properties and their values specify certain attributes
to be given to the link. The allowable keywords and associated
values are operating system dependent; typically they indicate
arguments to be given to the native primitive for creating links.
If no property pairs are given in the command, the server should
apply a reasonable default set of attributes to the link. See the
section "Format of NFILE File Property/Value Pairs", section 7.5.
8.8 DATA-CONNECTION Command
Command: (DATA-CONNECTION tid new-input-handle new-output-handle)
Response: (DATA-CONNECTION tid connection-identifier)
DATA-CONNECTION enablesthe user side to initiate the establishment of
a new data connection. The user side supplies two required string
arguments, new-input-handle and new-output-handle. These arguments
are used by subsequent commands to reference the two data channels
that constitute the data connection now being created. new-input-
handle describes the server-to-user data channel, and new-output-
handle describes the user-to-server channel. new-input-handle and
new-output-handle cannot refer to any data channels already in use.
Upon receiving the DATA-CONNECTION command, the server arranges for a
logical port (called socket or contact name on some networks) to be
made available on the foreign host machine. When the server has made
that port available, it must inform the user of its identity. The
server relays that information in the command response, in the
required connection-identifier, a string. The server then listens on
the port named by connection-identifier, and waits for the user side
to connect to it.
Upon receiving the success command response, the user side supplies
the connection-identifier to the local network implementation, in
order to connect to the specified port. The data connection is not
fully established until the user side connects successfully to that
port. This command is unusual in that the successful command
response does not signify the completion of the command; it indicates
only that the server has fulfilled its responsibility in the process
of establishing a data connection.
The connection-identifier informs the user of the correct identity of
the logical port that the server has provided. NFILE expects the
connection-identifier to be a string. For TCP this string is the
port number represented in decimal. For Chaosnet, this string is the
contact name. The connection-identifier is used only once; in all
subsequent NFILE commands that need to reference either of the data
channels that constitute this data connection, the new-input-handle
and new-output-handle are used.
For background information: See the section "NFILE Control and Data
Connections", section 4.
8.9 DELETE Command
Command: (DELETE tid handle pathname)
Response: (DELETE tid)
DELETE deletes a file on the remote file system.
Either a handle or a pathname must be supplied, but not both. If
given, the handle must be a data channel handle for a data stream
opening, or a direct file identifier for a direct access opening.
pathname is a string in the full pathname syntax of the server host.
See the section "Syntax of File and Directory Pathname Arguments",
section 7.4.
With a pathname supplied, the DELETE command causes the specified
file to be deleted. DELETE has different results depending on the
operating system involved. That is, DELETE causes soft deletion on
TOPS-20 and LMFS, and hard deletion on UNIX and Multics. If an
attempt is made to delete a delete-through link on a Symbolics LMFS,
its target is deleted instead.
If the handle argument is supplied to DELETE, the server deletes the
open file bound to the data channel specified by handle at close
time. This is true in both the output and input cases.
8.10 DIRECT-OUTPUT Command
Command: (DIRECT-OUTPUT tid direct-handle output-handle)
Response: (DIRECT-OUTPUT tid)
DIRECT-OUTPUT starts and stops output data flow for a direct access
file opening. DIRECT-OUTPUT explicitly controls binding and
unbinding of an output data channel to a direct access opening.
direct-handle is a required argument, and output-handle is optional.
If supplied, output-handle is a request to bind an output data
channel (indicated by output-handle) to the direct access opening
designated by the direct-handle. The specified output data channel
must be free. The server binds the data channel and begins accepting
data from that connection and writing it to the opening.
If the output-handle is omitted, this is a request to unbind the
channel and terminate the active output transfer.
8.11 DIRECTORY Command
Command: (DIRECTORY tid input-handle pathname control-keywords
properties)
Response: (DIRECTORY tid)
DIRECTORY returns a directory listing including the identities and
attributes for logically related groups of files, directories, and
links. If the command is successful, a single token list containing
the requested information is sent over the data channel specified by
input-handle, and the data channel is then implicitly freed by both
sides <2>. For details on the format of the token list: See the
section "NFILE DIRECTORY Data Format", section 8.11.1.
pathname specifies the files that are to be described; it is a string
in the full pathname syntax of the server host. See the section
"Syntax of File and Directory Pathname Arguments", section 7.4.
The pathname generally contains wildcard characters, in operating-
system-specific format, describing potential file name matches. Most
operating systems provide a facility that accepts such a pathname and
returns information about all files matching this pathname. Some
operating systems allow wildcard (potential multiple) matches in the
directory or device portions of the pathname; other operating systems
do not. There is no clear contract at this time about what is
expected of servers on systems that do not allow wildcard matches (or
some kinds of wild card matches), when presented with a wildcard.
properties is a token list of keywords that are the names of
properties. If properties is omitted or supplied as the empty token
list, the server sends along all properties. If any properties are
supplied, the user is requesting the server to send only those
properties.
control-keywords ARGUMENT TO DIRECTORY
control-keywords is a token list of keywords. The control-keywords
affect the way the DIRECTORY command works on the server machine.
Although some of the options below request the server to limit (by
some filter) the data to be returned, it is never an error if the
server returns more information than is requested.
The following keywords are recognized:
DELETED
Includes soft-deleted files in the directory list. Without this
option, they must not be included. Such files have the DELETED
property indicated as true" among their properties. DELETED is
ignored on systems that do not support soft deletion.
DIRECTORIES-ONLY
This option changes the semantics of DIRECTORY fairly drastically.
Normally, the server returns information about all files,
directories, and links whose pathnames match the supplied pathname.
This means that for each file, directory, or link to be listed, its
directory name must match the potentially wildcarded) directory name
in the supplied pathname, its file name must match the file name in
the supplied pathname, and so on.