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File: cvsclient.info, Node: Top, Next: Introduction, Up: (dir)

CVS Client/Server
*****************

This document describes the client/server protocol used by CVS. It does
not describe how to use or administer client/server CVS; for that, *note
the regular CVS manual: (cvs)Top. This specification applies to CVS
version 1.12.13-MirOS-0AB8.4 and up.

* Menu:

* Introduction:: What is CVS and what is the client/server protocol for?
* Goals:: Basic design decisions, requirements, scope, etc.
* Connection and Authentication:: Various ways to connect to the server
* Password scrambling:: Scrambling used by pserver
* Protocol:: Complete description of the protocol
* Protocol Notes:: Possible enhancements, limitations, etc. of the protocol

File: cvsclient.info, Node: Introduction, Next: Goals, Prev: Top, Up: Top

1 Introduction
**************

CVS is a version control system (with some additional configuration
management functionality). It maintains a central "repository" which
stores files (often source code), including past versions, information
about who modified them and when, and so on. People who wish to look at
or modify those files, known as "developers", use CVS to "check out" a
"working directory" from the repository, to "check in" new versions of
files to the repository, and other operations such as viewing the
modification history of a file. If developers are connected to the
repository by a network, particularly a slow or flaky one, the most
efficient way to use the network is with the CVS-specific protocol
described in this document.

Developers, using the machine on which they store their working
directory, run the CVS "client" program. To perform operations which
cannot be done locally, it connects to the CVS "server" program, which
maintains the repository. For more information on how to connect see
*note Connection and Authentication::.

This document describes the CVS protocol. Unfortunately, it does not
yet completely document one aspect of the protocol--the detailed
operation of each CVS command and option--and one must look at the CVS
user documentation, 'cvs.texinfo', for that information. The protocol
is non-proprietary (anyone who wants to is encouraged to implement it)
and an implementation, known as CVS, is available under the GNU General
Public License. The CVS distribution, containing this implementation,
'cvs.texinfo', and a copy (possibly more or less up to date than what
you are reading now) of this document, 'cvsclient.texi', can be found at
the usual GNU FTP sites, with a filename such as 'cvs-VERSION.tar.gz'.

This is version 1.12.13 of the protocol specification. This version
number is intended only to aid in distinguishing different versions of
this specification. Although the specification is currently maintained
in conjunction with the CVS implementation, and carries the same version
number, it also intends to document what is involved with interoperating
with other implementations (such as other versions of CVS); see *note
Requirements::. This version number should not be used by clients or
servers to determine what variant of the protocol to speak; they should
instead use the 'valid-requests' and 'Valid-responses' mechanism (*note
Protocol::), which is more flexible.

File: cvsclient.info, Node: Goals, Next: Connection and Authentication, Prev: Introduction, Up: Top

2 Goals
*******

* Do not assume any access to the repository other than via this
protocol. It does not depend on NFS, rdist, etc.

* Providing a reliable transport is outside this protocol. The
protocol expects a reliable transport that is transparent (that is,
there is no translation of characters, including characters such as
linefeeds or carriage returns), and can transmit all 256 octets
(for example for proper handling of binary files, compression, and
encryption). The encoding of characters specified by the protocol
(the names of requests and so on) is the invariant ISO 646
character set (a subset of most popular character sets including
ASCII and others). For more details on running the protocol over
the TCP reliable transport, see *note Connection and
Authentication::.

* Security and authentication are handled outside this protocol (but
see below about 'cvs kserver' and 'cvs pserver').

* The protocol makes it possible for updates to be atomic with
respect to checkins; that is if someone commits changes to several
files in one cvs command, then an update by someone else would
either get all the changes, or none of them. The current CVS
server can't do this, but that isn't the protocol's fault.

* The protocol is, with a few exceptions, transaction-based. That
is, the client sends all its requests (without waiting for server
responses), and then waits for the server to send back all
responses (without waiting for further client requests). This has
the advantage of minimizing network turnarounds and the
disadvantage of sometimes transferring more data than would be
necessary if there were a richer interaction. Another, more
subtle, advantage is that there is no need for the protocol to
provide locking for features such as making checkins atomic with
respect to updates. Any such locking can be handled entirely by
the server. A good server implementation (such as the current CVS
server) will make sure that it does not have any such locks in
place whenever it is waiting for communication with the client;
this prevents one client on a slow or flaky network from
interfering with the work of others.

* It is a general design goal to provide only one way to do a given
operation (where possible). For example, implementations have no
choice about whether to terminate lines with linefeeds or some
other character(s), and request and response names are
case-sensitive. This is to enhance interoperability. If a
protocol allows more than one way to do something, it is all too
easy for some implementations to support only some of them (perhaps
accidentally).

File: cvsclient.info, Node: Connection and Authentication, Next: Password scrambling, Prev: Goals, Up: Top

3 How to Connect to and Authenticate Oneself to the CVS server
**************************************************************

Connection and authentication occurs before the CVS protocol itself is
started. There are several ways to connect.

server
If the client has a way to execute commands on the server, and
provide input to the commands and output from them, then it can
connect that way. This could be the usual rsh (port 514) protocol,
Kerberos rsh, SSH, or any similar mechanism. The client may allow
the user to specify the name of the server program; the default is
'cvs'. It is invoked with one argument, 'server'. Once it invokes
the server, the client proceeds to start the cvs protocol.

kserver
The kerberised server listens on a port (in the current
implementation, by having inetd call "cvs kserver") which defaults
to 1999. The client connects, sends the usual kerberos
authentication information, and then starts the cvs protocol.
Note: port 1999 is officially registered for another use, and in
any event one cannot register more than one port for CVS, so
GSS-API (see below) is recommended instead of kserver as a way to
support kerberos.

pserver
The name "pserver" is somewhat confusing. It refers to both a
generic framework which allows the CVS protocol to support several
authentication mechanisms, and a name for a specific mechanism
which transfers a username and a cleartext password. Servers need
not support all mechanisms, and in fact servers will typically want
to support only those mechanisms which meet the relevant security
needs.

The pserver server listens on a port (in the current
implementation, by having inetd call "cvs pserver") which defaults
to 2401 (this port is officially registered). The client connects,
and sends the following:

* the string 'BEGIN AUTH REQUEST', a linefeed,
* the cvs root, a linefeed,
* the username, a linefeed,
* the password trivially encoded (see *note Password
scrambling::), a linefeed,
* the string 'END AUTH REQUEST', and a linefeed.

The client must send the identical string for cvs root both here
and later in the 'Root' request of the cvs protocol itself.
Servers are encouraged to enforce this restriction. The possible
server responses (each of which is followed by a linefeed) are the
following. Note that although there is a small similarity between
this authentication protocol and the cvs protocol, they are
separate.

'I LOVE YOU'
The authentication is successful. The client proceeds with
the cvs protocol itself.

'I HATE YOU'
The authentication fails. After sending this response, the
server may close the connection. It is up to the server to
decide whether to give this response, which is generic, or a
more specific response using 'E' and/or 'error'.

'E TEXT'
Provide a message for the user. After this reponse, the
authentication protocol continues with another response.
Typically the server will provide a series of 'E' responses
followed by 'error'. Compatibility note: CVS 1.9.10 and older
clients will print 'unrecognized auth response' and TEXT, and
then exit, upon receiving this response.

'error CODE TEXT'
The authentication fails. After sending this response, the
server may close the connection. The CODE is a code
describing why it failed, intended for computer consumption.
The only code currently defined is '0' which is nonspecific,
but clients must silently treat any unrecognised codes as
nonspecific. The TEXT should be supplied to the user.
Compatibility note: CVS 1.9.10 and older clients will print
'unrecognized auth response' and TEXT, and then exit, upon
receiving this response. Note that TEXT for this response, or
the TEXT in an 'E' response, is not designed for machine
parsing. More vigorous use of CODE, or future extensions,
will be needed to prove a cleaner machine-parseable indication
of what the error was.

If the client wishes to merely authenticate without starting the
cvs protocol, the procedure is the same, except BEGIN AUTH REQUEST
is replaced with BEGIN VERIFICATION REQUEST, END AUTH REQUEST is
replaced with END VERIFICATION REQUEST, and upon receipt of I LOVE
YOU the connection is closed rather than continuing.

Another mechanism is GSSAPI authentication. GSSAPI is a generic
interface to security services such as kerberos. GSSAPI is
specified in RFC2078 (GSSAPI version 2) and RFC1508 (GSSAPI version
1); we are not aware of differences between the two which affect
the protocol in incompatible ways, so we make no attempt to specify
one version or the other. The procedure here is to start with
'BEGIN GSSAPI REQUEST'. GSSAPI authentication information is then
exchanged between the client and the server. Each packet of
information consists of a two byte big endian length, followed by
that many bytes of data. After the GSSAPI authentication is
complete, the server continues with the responses described above
('I LOVE YOU', etc.).

future possibilities
There are a nearly unlimited number of ways to connect and
authenticate. One might want to allow access based on IP address
(similar to the usual rsh protocol but with different/no
restrictions on ports < 1024), to adopt mechanisms such as
Pluggable Authentication Modules (PAM), to allow users to run their
own servers under their own usernames without root access, or any
number of other possibilities. The way to add future mechanisms,
for the most part, should be to continue to use port 2401, but to
use different strings in place of 'BEGIN AUTH REQUEST'.

File: cvsclient.info, Node: Password scrambling, Next: Protocol, Prev: Connection and Authentication, Up: Top

4 Password scrambling algorithm
*******************************

The pserver authentication protocol, as described in *note Connection
and Authentication::, trivially encodes the passwords. This is only to
prevent inadvertent compromise; it provides no protection against even a
relatively unsophisticated attacker. For comparison, HTTP Basic
Authentication (as described in RFC2068) uses BASE64 for a similar
purpose. CVS uses its own algorithm, described here.

The scrambled password starts with 'A', which serves to identify the
scrambling algorithm in use. After that follows a single octet for each
character in the password, according to a fixed encoding. The values
are shown here, with the encoded values in decimal. Control characters,
space, and characters outside the invariant ISO 646 character set are
not shown; such characters are not recommended for use in passwords.
There is a long discussion of character set issues in *note Protocol
Notes::.

0 111 P 125 p 58
! 120 1 52 A 57 Q 55 a 121 q 113
" 53 2 75 B 83 R 54 b 117 r 32
3 119 C 43 S 66 c 104 s 90
4 49 D 46 T 124 d 101 t 44
% 109 5 34 E 102 U 126 e 100 u 98
& 72 6 82 F 40 V 59 f 69 v 60
' 108 7 81 G 89 W 47 g 73 w 51
( 70 8 95 H 38 X 92 h 99 x 33
) 64 9 65 I 103 Y 71 i 63 y 97
* 76 : 112 J 45 Z 115 j 94 z 62
+ 67 ; 86 K 50 k 93
, 116 < 118 L 42 l 39
- 74 = 110 M 123 m 37
. 68 > 122 N 91 n 61
/ 87 ? 105 O 35 _ 56 o 48

File: cvsclient.info, Node: Protocol, Next: Protocol Notes, Prev: Password scrambling, Up: Top

5 The CVS client/server protocol
********************************

In the following, '\n' refers to a linefeed and '\t' refers to a
horizontal tab; "requests" are what the client sends and "responses" are
what the server sends. In general, the connection is governed by the
client--the server does not send responses without first receiving
requests to do so; see *note Response intro:: for more details of this
convention.

It is typical, early in the connection, for the client to transmit a
'Valid-responses' request, containing all the responses it supports,
followed by a 'valid-requests' request, which elicits from the server a
'Valid-requests' response containing all the requests it understands.
In this way, the client and server each find out what the other supports
before exchanging large amounts of data (such as file contents).

* Menu:

General protocol conventions:

* Entries Lines:: Transmitting RCS data
* File Modes:: Read, write, execute, and possibly more...
* Filenames:: Conventions regarding filenames
* File transmissions:: How file contents are transmitted
* Strings:: Strings in various requests and responses
* Dates:: Times and dates

The protocol itself:

* Request intro:: General conventions relating to requests
* Requests:: List of requests
* Response intro:: General conventions relating to responses
* Response pathnames:: The "pathname" in responses
* Responses:: List of responses
* Text tags:: More details about the MT response

An example session, and some further observations:

* Example:: A conversation between client and server
* Requirements:: Things not to omit from an implementation
* Obsolete:: Former protocol features

File: cvsclient.info, Node: Entries Lines, Next: File Modes, Up: Protocol

5.1 Entries Lines
=================

Entries lines are transmitted as:

/ NAME / VERSION / CONFLICT / OPTIONS / TAG_OR_DATE

TAG_OR_DATE is either 'T' TAG or 'D' DATE or empty. If it is
followed by a slash, anything after the slash shall be silently ignored.

VERSION can be empty, or start with '0' or '-', for no user file, new
user file, or user file to be removed, respectively.

CONFLICT, if it starts with '+', indicates that the file had
conflicts in it. The rest of CONFLICT is '=' if the timestamp matches
the file, or anything else if it doesn't. If CONFLICT does not start
with a '+', it is silently ignored.

OPTIONS signifies the keyword expansion options (for example '-ko').
In an 'Entry' request, this indicates the options that were specified
with the file from the previous file updating response (*note Response
intro::, for a list of file updating responses); if the client is
specifying the '-k' or '-A' option to 'update', then it is the server
which figures out what overrides what.

File: cvsclient.info, Node: File Modes, Next: Filenames, Prev: Entries Lines, Up: Protocol

5.2 File Modes
==============

A mode is any number of repetitions of

MODE-TYPE = DATA

separated by ','.

MODE-TYPE is an identifier composed of alphanumeric characters.
Currently specified: 'u' for user, 'g' for group, 'o' for other (see
below for discussion of whether these have their POSIX meaning or are
more loose). Unrecognised values of MODE-TYPE are silently ignored.

DATA consists of any data not containing ',', '\0' or '\n'. For 'u',
'g', and 'o' mode types, data consists of alphanumeric characters, where
'r' means read, 'w' means write, 'x' means execute, and unrecognised
letters are silently ignored.

The two most obvious ways in which the mode matters are: (1) is it
writeable? This is used by the developer communication features, and is
implemented even on OS/2 (and could be implemented on DOS), whose notion
of mode is limited to a readonly bit. (2) is it executable? Unix CVS
users need CVS to store this setting (for shell scripts and the like).
The current CVS implementation on unix does a little bit more than just
maintain these two settings, but it doesn't really have a nice general
facility to store or version control the mode, even on unix, much less
across operating systems with diverse protection features. So all the
ins and outs of what the mode means across operating systems haven't
really been worked out (e.g. should the VMS port use ACLs to get POSIX
semantics for groups?).

File: cvsclient.info, Node: Filenames, Next: File transmissions, Prev: File Modes, Up: Protocol

5.3 Conventions regarding transmission of file names
====================================================

In most contexts, '/' is used to separate directory and file names in
filenames, and any use of other conventions (for example, that the user
might type on the command line) is converted to that form. The only
exceptions might be a few cases in which the server provides a magic
cookie which the client then repeats verbatim, but as the server has not
yet been ported beyond unix, the two rules provide the same answer (and
what to do if future server ports are operating on a repository like
e:/foo or CVS_ROOT:[FOO.BAR] has not been carefully thought out).

Characters outside the invariant ISO 646 character set should be
avoided in filenames. This restriction may need to be relaxed to allow
for characters such as '[' and ']' (see above about non-unix servers);
this has not been carefully considered (and currently implementations
probably use whatever character sets that the operating systems they are
running on allow, and/or that users specify). Of course the most
portable practice is to restrict oneself further, to the POSIX portable
filename character set as specified in POSIX.1.

File: cvsclient.info, Node: File transmissions, Next: Strings, Prev: Filenames, Up: Protocol

5.4 File transmissions
======================

File contents (noted below as FILE TRANSMISSION) can be sent in one of
two forms. The simpler form is a number of bytes, followed by a
linefeed, followed by the specified number of bytes of file contents.
These are the entire contents of the specified file. Second, if both
client and server support 'gzip-file-contents', a 'z' may precede the
length, and the 'file contents' sent are actually compressed with 'gzip'
(RFC1952/1951) compression. The length specified is that of the
compressed version of the file.

In neither case are the file content followed by any additional data.
The transmission of a file will end with a linefeed iff that file (or
its compressed form) ends with a linefeed.

The encoding of file contents depends on the value for the '-k'
option. If the file is binary (as specified by the '-kb' option in the
appropriate place), then it is just a certain number of octets, and the
protocol contributes nothing towards determining the encoding (using the
file name is one widespread, if not universally popular, mechanism). If
the file is text (not binary), then the file is sent as a series of
lines, separated by linefeeds. If the keyword expansion is set to
something other than '-ko', then it is expected that the file conform to
the RCS expectations regarding keyword expansion--in particular, that it
is in a character set such as ASCII in which 0x24 is a dollar sign
('$').

File: cvsclient.info, Node: Strings, Next: Dates, Prev: File transmissions, Up: Protocol

5.5 Strings
===========

In various contexts, for example the 'Argument' request and the 'M'
response, one transmits what is essentially an arbitrary string. Often
this will have been supplied by the user (for example, the '-m' option
to the 'ci' request will show up in the 'LOGM' response). The protocol
has no mechanism to specify the character set of such strings; it would
have been, initially, fairly safe to stick to the invariant ISO 646
character set but the existing practice is probably to just transmit
whatever the user specifies, and hope that everyone involved agrees
which character set is in use, or sticks to a common subset. In modern
times, UTF-8 should be used.

File: cvsclient.info, Node: Dates, Next: Request intro, Prev: Strings, Up: Protocol

5.6 Dates
=========

The protocol contains times and dates in various places.

For the '-D' option to the 'annotate', 'co', 'diff', 'export',
'history', 'rannotate', 'rdiff', 'rtag', 'tag', and 'update' requests,
the server should support two formats:

26 May 1997 13:01:40 -0000 ; RFC 822 as modified by RFC 1123
5/26/1997 13:01:40 GMT ; traditional

The former format is preferred; the latter however is sent by the CVS
command line client (versions 1.5 through at least 1.9).

For the '-d' option to the 'log' and 'rlog' requests, servers should
at least support RFC 822/1123 format. Clients are encouraged to use
this format too (the command line CVS client, version 1.10 and older,
just passed along the date format specified by the user, however).

The 'Mod-time' response and 'Checkin-time' request use RFC 822/1123
format (see the descriptions of that response and request for details).

For 'Notify', see the description of that request.

File: cvsclient.info, Node: Request intro, Next: Requests, Prev: Dates, Up: Protocol

5.7 Request intro
=================

By convention, requests which begin with a capital letter do not elicit
a response from the server, while all others do - save one. The
exception is 'gzip-file-contents'. Unrecognised requests will always
elicit a response from the server, even if that request begins with a
capital letter.

The term "command" means a request which expects a response (except
'valid-requests'). The general model is that the client transmits a
great number of requests, but nothing happens until the very end when
the client transmits a command. Although the intention is that
transmitting several commands in one connection should be legal,
existing servers probably have some bugs with some combinations of more
than one command, and so clients may find it necessary to make several
connections in some cases. This should be thought of as a workaround
rather than a desired attribute of the protocol.

File: cvsclient.info, Node: Requests, Next: Response intro, Prev: Request intro, Up: Protocol

5.8 Requests
============

Here are the requests:

'Root PATHNAME \n'
Response expected: no. Tell the server which 'CVSROOT' to use.
Note that PATHNAME is a local directory and _not_ a fully qualified
'CVSROOT' variable. PATHNAME must already exist; if creating a new
root, use the 'init' request, not 'Root'. PATHNAME does not
include the hostname of the server, how to access the server, etc.;
by the time the CVS protocol is in use, connection, authentication,
etc., are already taken care of.

The 'Root' request must be sent only once, and it must be sent
before any requests other than 'Valid-responses', 'valid-requests',
'UseUnchanged', 'Set', 'Global_option', 'init', 'noop', or
'version'.

'Valid-responses REQUEST-LIST \n'
Response expected: no. Tell the server what responses the client
will accept. request-list is a space separated list of tokens.
The 'Root' request need not have been previously sent.

'valid-requests \n'
Response expected: yes. Ask the server to send back a
'Valid-requests' response. The 'Root' request need not have been
previously sent.

'Command-prep COMMAND \n'
Response expected: yes. Notify the server of the command that we
are leading up to. Intended to allow the server to send a redirect
for write operations. Requires either an 'ok' or 'Redirect'
respnose.

'Referrer CVSROOT \n'
Response expected: no. Notify a primary server of a server which
referred us. Intended to allow a primary (write) server to update
the read-only mirror a client is using for reads to minimise races
on any subsequent updates from the client.

'Directory LOCAL-DIRECTORY \n'
'Relative-directory LOCAL-DIRECTORY \n'
Additional data: REPOSITORY \n. Response expected: no. Tell the
server what directory to use.

The REPOSITORY should be a directory name from a previous server
response and may be specified either relative to the PATHNAME
provided with the 'Root' request or absolute. Relative or
absolute, it must specify a path within PATHNAME.

Prior to CVS version *FIXME - release number 1.12.10?*, REPOSITORY
had to be absolute and 'Relative-directory' was not a valid
request. The 'Relative-directory' request is synonymous with
'Directory' and is provided to alert modern clients that a relative
REPOSITORY is acceptable.

Note that this both gives a default for 'Entry' and 'Modified' and
also for 'ci' and the other commands; normal usage is to send
'Directory' for each directory in which there will be an 'Entry' or
'Modified', and then a final 'Directory' for the original
directory, then the command. The LOCAL-DIRECTORY is relative to
the top level at which the command is occurring (i.e. the last
'Directory' which is sent before the command); to indicate that top
level, '.' should be sent for LOCAL-DIRECTORY.

Here is an example of where a client gets REPOSITORY and
LOCAL-DIRECTORY. Suppose that there is a module defined by

moddir 1dir

That is, one can check out 'moddir' and it will take '1dir' in the
repository and check it out to 'moddir' in the working directory.
Then an initial check out could proceed like this:

C: Root /home/kingdon/zwork/cvsroot
. . .
C: Argument moddir
C: Directory .
C: .
C: co
S: Clear-sticky moddir/
S: 1dir/
. . .
S: ok

In this example the response shown is 'Clear-sticky', but it could
be another response instead. Note that it returns two pathnames.
The first one, 'moddir/', indicates the working directory to check
out into. The second one, ending in '1dir/', indicates the
directory to pass back to the server in a subsequent 'Directory'
request. For example, a subsequent 'update' request might look
like:

C: Directory moddir
C: 1dir
. . .
C: update

For a given LOCAL-DIRECTORY, the repository will be the same for
each of the responses, so one can use the repository from whichever
response is most convenient. Typically a client will store the
repository along with the sources for each LOCAL-DIRECTORY, use
that same setting whenever operating on that LOCAL-DIRECTORY, and
not update the setting as long as the LOCAL-DIRECTORY exists.

A client is free to rename a LOCAL-DIRECTORY at any time (for
example, in response to an explicit user request). While it is
true that the server supplies a LOCAL-DIRECTORY to the client, as
noted above, this is only the default place to put the directory.
Of course, the various 'Directory' requests for a single command
(for example, 'update' or 'ci' request) should name a particular
directory with the same LOCAL-DIRECTORY.

Each 'Directory' request specifies a brand-new LOCAL-DIRECTORY and
REPOSITORY; that is, LOCAL-DIRECTORY and REPOSITORY are never
relative to paths specified in any previous 'Directory' request.

Here's a more complex example, in which we request an update of a
working directory which has been checked out from multiple places
in the repository.

C: Argument dir1
C: Directory dir1
C: mod1
. . .
C: Argument dir2
C: Directory dir2
C: mod2
. . .
C: Argument dir3
C: Directory dir3/subdir3
C: mod3
. . .
C: update

While directories 'dir1' and 'dir2' will be handled in similar
fashion to the other examples given above, 'dir3' is slightly
different from the server's standpoint. Notice that module 'mod3'
is actually checked out into 'dir3/subdir3', meaning that directory
'dir3' is either empty or does not contain data checked out from
this repository.

The above example will work correctly in CVS 1.10.1 and later. The
server will descend the tree starting from all directories
mentioned in 'Argument' requests and update those directories
specifically mentioned in 'Directory' requests.

Previous versions of CVS (1.10 and earlier) do not behave the same
way. While the descent of the tree begins at all directories
mentioned in 'Argument' requests, descent into subdirectories only
occurs if a directory has been mentioned in a 'Directory' request.
Therefore, the above example would succeed in updating 'dir1' and
'dir2', but would skip 'dir3' because that directory was not
specifically mentioned in a 'Directory' request. A functional
version of the above that would run on a 1.10 or earlier server is
as follows:

C: Argument dir1
C: Directory dir1
C: mod1
. . .
C: Argument dir2
C: Directory dir2
C: mod2
. . .
C: Argument dir3
C: Directory dir3
C: .
. . .
C: Directory dir3/subdir3
C: mod3
. . .
C: update

Note the extra 'Directory dir3' request. It might be better to use
'Emptydir' as the repository for the 'dir3' directory, but the
above will certainly work.

One more peculiarity of the 1.10 and earlier protocol is the
ordering of 'Directory' arguments. In order for a subdirectory to
be registered correctly for descent by the recursion processor, its
parent must be sent first. For example, the following would not
work to update 'dir3/subdir3':

. . .
C: Argument dir3
C: Directory dir3/subdir3
C: mod3
. . .
C: Directory dir3
C: .
. . .
C: update

The implementation of the server in 1.10 and earlier writes the
administration files for a given directory at the time of the
'Directory' request. It also tries to register the directory with
its parent to mark it for recursion. In the above example, at the
time 'dir3/subdir3' is created, the physical directory for 'dir3'
will be created on disk, but the administration files will not have
been created. Therefore, when the server tries to register
'dir3/subdir3' for recursion, the operation will silently fail
because the administration files do not yet exist for 'dir3'.

'Max-dotdot LEVEL \n'
Response expected: no. Tell the server that LEVEL levels of
directories above the directory which 'Directory' requests are
relative to will be needed. For example, if the client is planning
to use a 'Directory' request for '../../foo', it must send a
'Max-dotdot' request with a LEVEL of at least 2. 'Max-dotdot' must
be sent before the first 'Directory' request.

'Static-directory \n'
Response expected: no. Tell the server that the directory most
recently specified with 'Directory' should not have additional
files checked out unless explicitly requested. The client sends
this if the 'Entries.Static' flag is set, which is controlled by
the 'Set-static-directory' and 'Clear-static-directory' responses.

'Sticky TAGSPEC \n'
Response expected: no. Tell the server that the directory most
recently specified with 'Directory' has a sticky tag or date
TAGSPEC. The first character of TAGSPEC is 'T' for a tag, 'D' for
a date, or some other character supplied by a Set-sticky response
from a previous request to the server. The remainder of TAGSPEC
contains the actual tag or date, again as supplied by Set-sticky.

The server should remember 'Static-directory' and 'Sticky' requests
for a particular directory; the client need not resend them each
time it sends a 'Directory' request for a given directory.
However, the server is not obliged to remember them beyond the
context of a single command.

'Checkin-prog PROGRAM \n'
Response expected: no. Tell the server that the directory most
recently specified with 'Directory' has a checkin program PROGRAM.
Such a program would have been previously set with the
'Set-checkin-prog' response.

'Update-prog PROGRAM \n'
Response expected: no. Tell the server that the directory most
recently specified with 'Directory' has an update program PROGRAM.
Such a program would have been previously set with the
'Set-update-prog' response.

'Entry ENTRY-LINE \n'
Response expected: no. Tell the server what version of a file is
on the local machine. The name in ENTRY-LINE is a name relative to
the directory most recently specified with 'Directory'. If the
user is operating on only some files in a directory, 'Entry'
requests for only those files need be included. If an 'Entry'
request is sent without 'Modified', 'Is-modified', or 'Unchanged',
it means the file is lost (does not exist in the working
directory). If both 'Entry' and one of 'Modified', 'Is-modified',
or 'Unchanged' are sent for the same file, 'Entry' must be sent
first. For a given file, one can send 'Modified', 'Is-modified',
or 'Unchanged', but not more than one of these three.

'Kopt OPTION \n'
This indicates to the server which keyword expansion options to use
for the file specified by the next 'Modified' or 'Is-modified'
request (for example '-kb' for a binary file). This is similar to
'Entry', but is used for a file for which there is no entries line.
Typically this will be a file being added via an 'add' or 'import'
request. The client may not send both 'Kopt' and 'Entry' for the
same file.

'Checkin-time TIME \n'
For the file specified by the next 'Modified' request, use TIME as
the time of the checkin. The TIME is in the format specified by
RFC822 as modified by RFC1123. The client may specify any timezone
it chooses; servers will want to convert that to their own timezone
as appropriate. An example of this format is:

26 May 1997 13:01:40 -0400

There is no requirement that the client and server clocks be
synchronised. The client just sends its recommendation for a
timestamp (based on file timestamps or whatever), and the server
should just believe it (this means that the time might be in the
future, for example).

Note that this is not a general-purpose way to tell the server
about the timestamp of a file; that would be a separate request (if
there are servers which can maintain timestamp and time of checkin
separately).

This request should affect the 'import' request, and may optionally
affect the 'ci' request or other relevant requests if any.

'Modified FILENAME \n'
Response expected: no. Additional data: mode, \n, file
transmission. Send the server a copy of one locally modified file.
FILENAME is a file within the most recent directory sent with
'Directory'; it must not contain '/'. If the user is operating on
only some files in a directory, only those files need to be
included. This can also be sent without 'Entry', if there is no
entry for the file.

'Is-modified FILENAME \n'
Response expected: no. Additional data: none. Like 'Modified',
but used if the server only needs to know whether the file is
modified, not the contents.

The commands which can take 'Is-modified' instead of 'Modified'
with no known change in behavior are: 'admin', 'diff' (if and only
if two '-r' or '-D' options are specified), 'watch-on',
'watch-off', 'watch-add', 'watch-remove', 'watchers', 'editors',
'log', and 'annotate'.

For the 'status' command, one can send 'Is-modified' but if the
client is using imperfect mechanisms such as timestamps to
determine whether to consider a file modified, then the behavior
will be different. That is, if one sends 'Modified', then the
server will actually compare the contents of the file sent and the
one it derives from to determine whether the file is genuinely
modified. But if one sends 'Is-modified', then the server takes
the client's word for it. A similar situation exists for 'tag', if
the '-c' option is specified.

Commands for which 'Modified' is necessary are 'co', 'ci',
'update', and 'import'.

Commands which do not need to inform the server about a working
directory, and thus should not be sending either 'Modified' or
'Is-modified': 'rdiff', 'rtag', 'history', 'init', and 'release'.

Commands for which further investigation is warranted are:
'remove', 'add', and 'export'. Pending such investigation, the
more conservative course of action is to stick to 'Modified'.

'Unchanged FILENAME \n'
Response expected: no. Tell the server that FILENAME has not been
modified in the checked out directory. The FILENAME is a file
within the most recent directory sent with 'Directory'; it must not
contain '/'.

'UseUnchanged \n'
Response expected: no. To specify the version of the protocol
described in this document, servers must support this request
(although it need not do anything) and clients must issue it. The
'Root' request need not have been previously sent.

'Notify FILENAME \n'
Response expected: no. Tell the server that an 'edit' or 'unedit'
command has taken place. The server needs to send a 'Notified'
response, but such response is deferred until the next time that
the server is sending responses. The FILENAME is a file within the
most recent directory sent with 'Directory'; it must not contain
'/'. Additional data:
NOTIFICATION-TYPE \t TIME \t CLIENTHOST \t
WORKING-DIR \t WATCHES \n
where NOTIFICATION-TYPE is 'E' for edit, 'U' for unedit, undefined
behavior if 'C', and all other letters should be silently ignored
for future expansion. TIME is the time at which the edit or unedit
took place, in a user-readable format of the client's choice (the
server should treat the time as an opaque string rather than
interpreting it). CLIENTHOST is the name of the host on which the
edit or unedit took place, and WORKING-DIR is the pathname of the
working directory where the edit or unedit took place. WATCHES are
the temporary watches, zero or more of the following characters in
the following order: 'E' for edit, 'U' for unedit, 'C' for commit,
and all other letters should be silently ignored for future
expansion. If NOTIFICATION-TYPE is 'E' the temporary watches are
set; if it is 'U' they are cleared. If WATCHES is followed by \t
then the \t and the rest of the line should be ignored, for future
expansion.

The TIME, CLIENTHOST, and WORKING-DIR fields may not contain the
characters '+', ',', '>', ';', or '='.

Note that a client may be capable of performing an 'edit' or
'unedit' operation without connecting to the server at that time,
and instead connecting to the server when it is convenient (for
example, when a laptop is on the net again) to send the 'Notify'
requests. Even if a client is capable of deferring notifications,
it should attempt to send them immediately (one can send 'Notify'
requests together with a 'noop' request, for example), unless
perhaps if it can know that a connection would be impossible.

'Questionable FILENAME \n'
Response expected: no. Additional data: no. Tell the server to
check whether FILENAME should be ignored, and if not, next time the
server sends responses, send (in a 'M' response) '?' followed by
the directory and filename. FILENAME must not contain '/'; it
needs to be a file in the directory named by the most recent
'Directory' request.

'Case \n'
Response expected: no. Tell the server that filenames should be
matched in a case-insensitive fashion. Note that this is not the
primary mechanism for achieving case-insensitivity; for the most
part the client keeps track of the case which the server wants to
use and takes care to always use that case regardless of what the
user specifies. For example the filenames given in 'Entry' and
'Modified' requests for the same file must match in case regardless
of whether the 'Case' request is sent. The latter mechanism is
more general (it could also be used for 8.3 filenames, VMS
filenames with more than one '.', and any other situation in which
there is a predictable mapping between filenames in the working
directory and filenames in the protocol), but there are some
situations it cannot handle (ignore patterns, or situations where
the user specifies a filename and the client does not know about
that file).

Though this request will be supported into the forseeable future,
it has been the source of numerous bug reports in the past due to
the complexity of testing this functionality via the test suite and
client developers are encouraged not to use it. Instead, please
consider munging conflicting names and maintaining a map for
communicating with the server. For example, suppose the server
sends files 'case', 'CASE', and 'CaSe'. The client could write all
three files to names such as, 'case', 'case_prefix_case', and
'case_prefix_2_case' and maintain a mapping between the file names
in, for instance a new 'CVS/Map' file.

'Argument TEXT \n'
Response expected: no. Save argument for use in a subsequent
command. Arguments accumulate until an argument-using command is
given, at which point they are forgotten.

'Argumentx TEXT \n'
Response expected: no. Append \n followed by text to the current
argument being saved.

'Global_option OPTION \n'
Response expected: no. Transmit one of the global options '-q',
'-Q', '-l', '-t', '-r', or '-n'. OPTION must be one of those
strings, no variations (such as combining of options) are allowed.
For graceful handling of 'valid-requests', it is probably better to
make new global options separate requests, rather than trying to
add them to this request. The 'Root' request need not have been
previously sent.

'Gzip-stream LEVEL \n'
Response expected: no. Use zlib (RFC 1950/1951) compression to
compress all further communication between the client and the
server. As of CVS 1.12.13, this request needs to be sent as the
first non-rootless request if the server is configured with
compression level restrictions and LEVEL is outside the restricted
range. After this request is sent, all further communication must
be compressed. All further data received from the server will also
be compressed. The LEVEL argument suggests to the server the level
of compression that it should apply; it should be an integer
between 0 and 9, inclusive, where '0' means no compression and
higher numbers indicate more compression.

'Kerberos-encrypt \n'
Response expected: no. Use Kerberos encryption to encrypt all
further communication between the client and the server. This will
only work if the connection was made over Kerberos in the first
place. If both the 'Gzip-stream' and the 'Kerberos-encrypt'
requests are used, the 'Kerberos-encrypt' request should be used
first. This will make the client and server encrypt the compressed
data, as opposed to compressing the encrypted data. Encrypted data
is generally incompressible.

Note that this request does not fully prevent an attacker from
hijacking the connection, in the sense that it does not prevent
hijacking the connection between the initial authentication and the
'Kerberos-encrypt' request.

'Gssapi-encrypt \n'
Response expected: no. Use GSSAPI encryption to encrypt all
further communication between the client and the server. This will
only work if the connection was made over GSSAPI in the first
place. See 'Kerberos-encrypt', above, for the relation between
'Gssapi-encrypt' and 'Gzip-stream'.

'Gssapi-authenticate \n'
Response expected: no. Use GSSAPI authentication to authenticate
all further communication between the client and the server. This
will only work if the connection was made over GSSAPI in the first
place. Encrypted data is automatically authenticated, so using
both 'Gssapi-authenticate' and 'Gssapi-encrypt' has no effect
beyond that of 'Gssapi-encrypt'. Unlike encrypted data, it is
reasonable to compress authenticated data.

'Set VARIABLE=VALUE \n'
Response expected: no. Set a user variable VARIABLE to VALUE. The
'Root' request need not have been previously sent.

'Hostname HOSTNAME \n'
Response expected: no. Set the client hostname for an upcoming
'edit' request.

'LocalDir HOSTNAME \n'
Response expected: no. Set the local client directory name for an
upcoming 'edit' request.

'expand-modules \n'
Response expected: yes. Expand the modules which are specified in
the arguments. Returns the data in 'Module-expansion' responses.
Note that the server can assume that this is checkout or export,
not rtag or rdiff; the latter do not access the working directory
and thus have no need to expand modules on the client side.

Expand may not be the best word for what this request does. It
does not necessarily tell you all the files contained in a module,
for example. Basically it is a way of telling you which working
directories the server needs to know about in order to handle a
checkout of the specified modules.

For example, suppose that the server has a module defined by

aliasmodule -a 1dir

That is, one can check out 'aliasmodule' and it will take '1dir' in
the repository and check it out to '1dir' in the working directory.
Now suppose the client already has this module checked out and is
planning on using the 'co' request to update it. Without using
'expand-modules', the client would have two bad choices: it could
either send information about _all_ working directories under the
current directory, which could be unnecessarily slow, or it could
be ignorant of the fact that 'aliasmodule' stands for '1dir', and
neglect to send information for '1dir', which would lead to
incorrect operation.

With 'expand-modules', the client would first ask for the module to
be expanded:

C: Root /home/kingdon/zwork/cvsroot
. . .
C: Argument aliasmodule
C: Directory .
C: .
C: expand-modules
S: Module-expansion 1dir
S: ok

and then it knows to check the '1dir' directory and send requests
such as 'Entry' and 'Modified' for the files in that directory.

'ci \n'
'diff \n'
'list \n'
'tag \n'
'status \n'
'admin \n'
'history \n'
'watchers \n'
'editors \n'
'annotate \n'
Response expected: yes. Actually do a cvs command. This uses any
previous 'Argument', 'Directory', 'Entry', or 'Modified' requests,
if they have been sent. The last 'Directory' sent specifies the
working directory at the time of the operation. No provision is
made for any input from the user. This means that 'ci' must use a
'-m' argument if it wants to specify a log message.

'log \n'
Response expected: yes. Show information for past revisions. This
uses any previous 'Directory', 'Entry', or 'Modified' requests, if
they have been sent. The last 'Directory' sent specifies the
working directory at the time of the operation. Also uses previous
'Argument''s of which the canonical forms are the following (CVS
1.10 and older clients sent what the user specified, but clients
are encouraged to use the canonical forms and other forms are
deprecated):

'-b, -h, -l, -N, -R, -t'
These options go by themselves, one option per 'Argument'
request.

'-d DATE1<DATE2'
Select revisions between DATE1 and DATE2. Either date may be
omitted in which case there is no date limit at that end of
the range (clients may specify dates such as 1 Jan 1970 or 1
Jan 2038 for similar purposes but this is problematic as it
makes assumptions about what dates the server supports).
Dates are in RFC822/1123 format. The '-d' is one 'Argument'
request and the date range is a second one.

'-d DATE1<=DATE2'
Likewise but compare dates for equality.

'-d SINGLEDATE'
Select the single, latest revision dated SINGLEDATE or
earlier.

To include several date ranges and/or singledates, repeat the
'-d' option as many times as necessary.

'-rREV1:REV2'
'-rBRANCH'
'-rBRANCH.'
'-r'
Specify revisions (note that REV1 or REV2 can be omitted, or
can refer to branches). Send both the '-r' and the revision
information in a single 'Argument' request. To include
several revision selections, repeat the '-r' option.

'-s STATE'
'-w'
'-wLOGIN'
Select on states or users. To include more than one state or
user, repeat the option. Send the '-s' option as a separate
argument from the state being selected. Send the '-w' option
as part of the same argument as the user being selected.

'co \n'
Response expected: yes. Get files from the repository. This uses
any previous 'Argument', 'Directory', 'Entry', or 'Modified'
requests, if they have been sent. Arguments to this command are
module names; the client cannot know what directories they
correspond to except by (1) just sending the 'co' request, and then
seeing what directory names the server sends back in its responses,
and (2) the 'expand-modules' request.

'export \n'
Response expected: yes. Get files from the repository. This uses
any previous 'Argument', 'Directory', 'Entry', or 'Modified'
requests, if they have been sent. Arguments to this command are
module names, as described for the 'co' request. The intention
behind this command is that a client can get sources from a server
without storing CVS information about those sources. That is, a
client probably should not count on being able to take the entries
line returned in the 'Created' response from an 'export' request
and send it in a future 'Entry' request. Note that the entries
line in the 'Created' response must indicate whether the file is
binary or text, so the client can create it correctly.

'ls \n'
'rannotate \n'
'rdiff \n'
'rlist \n'
'rlog \n'
'rtag \n'
Response expected: yes. Actually do a cvs command. This uses any
previous 'Argument' requests, if they have been sent. The client
should not send 'Directory', 'Entry', or 'Modified' requests for
these commands; they are not used. Arguments to these commands are
module names, as described for 'co'. 'ls' is a synonym for
'rlist', for compatibility with CVSNT.

'init ROOT-NAME \n'
Response expected: yes. If it doesn't already exist, create a CVS
repository ROOT-NAME. Note that ROOT-NAME is a local directory and
_not_ a fully qualified 'CVSROOT' variable. The 'Root' request
need not have been previously sent.

'suck \n'
Response expected: yes. Actually do a 'cvs suck' command. This
uses a previous 'Argument' request (only one, because the 'cvs
suck' CLI command takes only one). This is an extension specific
to MirBSD, MirPorts and Debian.

'update \n'
Response expected: yes. Actually do a 'cvs update' command. This
uses any previous 'Argument', 'Directory', 'Entry', or 'Modified'
requests, if they have been sent. The last 'Directory' sent
specifies the working directory at the time of the operation. The
'-I' option is not used-files which the client can decide whether
to ignore are not mentioned and the client sends the 'Questionable'
request for others.

'import \n'
Response expected: yes. Actually do a 'cvs import' command. This
uses any previous 'Argument', 'Directory', 'Entry', or 'Modified'
requests, if they have been sent. The last 'Directory' sent
specifies the working directory at the time of the operation -
unlike most commands, the repository field of each 'Directory'
request is ignored (it merely must point somewhere within the
root). The files to be imported are sent in 'Modified' requests
(files which the client knows should be ignored are not sent; the
server must still process the CVSROOT/cvsignore file unless -I !
is sent). A log message must have been specified with a '-m'
argument.

'add \n'
Response expected: yes. Add a file or directory. This uses any
previous 'Argument', 'Directory', 'Entry', or 'Modified' requests,
if they have been sent. The last 'Directory' sent specifies the
working directory at the time of the operation.

To add a directory, send the directory to be added using
'Directory' and 'Argument' requests. For example:

C: Root /u/cvsroot
. . .
C: Argument nsdir
C: Directory nsdir
C: 1dir/nsdir
C: Directory .
C: 1dir
C: add
S: M Directory /u/cvsroot/1dir/nsdir put under version control
S: ok

You will notice that the server does not signal to the client in
any particular way that the directory has been successfully added.
The client is supposed to just assume that the directory has been
added and update its records accordingly. Note also that adding a
directory is immediate; it does not wait until a 'ci' request as
files do.

To add a file, send the file to be added using a 'Modified'
request. For example:

C: Argument nfile
C: Directory .
C: 1dir
C: Modified nfile
C: u=rw,g=r,o=r
C: 6
C: hello
C: add
S: E cvs server: scheduling file `nfile' for addition
S: Mode u=rw,g=r,o=r
S: Checked-in ./
S: /u/cvsroot/1dir/nfile
S: /nfile/0///
S: E cvs server: use 'cvs commit' to add this file permanently
S: ok

Note that the file has not been added to the repository; the only
effect of a successful 'add' request, for a file, is to supply the
client with a new entries line containing '0' to indicate an added
file. In fact, the client probably could perform this operation
without contacting the server, although using 'add' does cause the
server to perform a few more checks.

The client sends a subsequent 'ci' to actually add the file to the
repository.

Another quirk of the 'add' request is that with CVS 1.9 and older,
a pathname specified in an 'Argument' request cannot contain '/'.
There is no good reason for this restriction, and in fact more
recent CVS servers don't have it. But the way to interoperate with
the older servers is to ensure that all 'Directory' requests for
'add' (except those used to add directories, as described above),
use '.' for LOCAL-DIRECTORY. Specifying another string for
LOCAL-DIRECTORY may not get an error, but it will get you strange
'Checked-in' responses from the buggy servers.

'remove \n'
Response expected: yes. Remove a file. This uses any previous
'Argument', 'Directory', 'Entry', or 'Modified' requests, if they
have been sent. The last 'Directory' sent specifies the working
directory at the time of the operation.

Note that this request does not actually do anything to the
repository; the only effect of a successful 'remove' request is to
supply the client with a new entries line containing '-' to
indicate a removed file. In fact, the client probably could
perform this operation without contacting the server, although
using 'remove' may cause the server to perform a few more checks.

The client sends a subsequent 'ci' request to actually record the
removal in the repository.

'edit \n'
Response expected: yes. Actually do the 'cvs edit' command. This
uses any previous 'Argument', 'Directory', 'Entry', 'LocalDir', or
'Hostname' requests, if they have been sent. Unless the user has
requested that edits not be granted unless no one else is editing a
file, a local edit followed by an attempt to send 'Notify' requests
to the server is preferred.

'watch-on \n'
'watch-off \n'
'watch-add \n'
'watch-remove \n'
Response expected: yes. Actually do the 'cvs watch on', 'cvs watch
off', 'cvs watch add', and 'cvs watch remove' commands,
respectively. This uses any previous 'Argument', 'Directory',
'Entry', or 'Modified' requests, if they have been sent. The last
'Directory' sent specifies the working directory at the time of the
operation.

'release \n'
Response expected: yes. Note that a 'cvs release' command has
taken place and update the history file accordingly.

'global-list-quiet \n'
Response expected: yes. This request is a synonym for noop, but
its existance notifies the client that a '-q' option to 'list' and
'rlist' will be rejected. This, in a reverse-logic sort of way, is
here so that when it _isn't_ received, as for instance from CVSNT,
the client will know that the quiet option has to be sent as a
command option rather than a global option.

'noop \n'
Response expected: yes. This request is a null command in the
sense that it doesn't do anything, but merely (as with any other
requests expecting a response) sends back any responses pertaining
to pending errors, pending 'Notified' responses, etc. The 'Root'
request need not have been previously sent.

'update-patches \n'
Response expected: yes. This request does not actually do
anything. It is used as a signal that the server is able to
generate patches when given an 'update' request. The client must
issue the '-u' argument to 'update' in order to receive patches.

'gzip-file-contents LEVEL \n'
Response expected: no. Note that this request does not follow the
response convention stated above. 'Gzip-stream' is suggested
instead of 'gzip-file-contents' as it gives better compression; the
only reason to implement the latter is to provide compression with
CVS 1.8 and earlier. The 'gzip-file-contents' request asks the
server to compress files it sends to the client using 'gzip'
(RFC1952/1951) compression, using the specified level of
compression. If this request is not made, the server must not
compress files.

This is only a hint to the server. It may still decide (for
example, in the case of very small files, or files that already
appear to be compressed) not to do the compression. Compression is
indicated by a 'z' preceding the file length.

Availability of this request in the server indicates to the client
that it may compress files sent to the server, regardless of
whether the client actually uses this request.

'wrapper-sendme-rcsOptions \n'
Response expected: yes. Request that the server transmit mappings
from filenames to keyword expansion modes in 'Wrapper-rcsOption'
responses.

'version \n'
Response expected: yes. Request that the server transmit its
version message. The 'Root' request need not have been previously
sent.

'OTHER-REQUEST TEXT \n'
Response expected: yes. Any unrecognised request expects a
response, and does not contain any additional data. The response
will normally be something like 'error unrecognized request', but
it could be a different error if a previous request which doesn't
expect a response produced an error.

When the client is done, it drops the connection.

File: cvsclient.info, Node: Response intro, Next: Response pathnames, Prev: Requests, Up: Protocol

5.9 Introduction to Responses
=============================

After a command which expects a response, the server sends however many
of the following responses are appropriate. The server should not send
data at other times (the current implementation may violate this
principle in a few minor places, where the server is printing an error
message and exiting--this should be investigated further).

Any set of responses always ends with 'error' or 'ok'. This
indicates that the response is over.

The responses 'Checked-in', 'New-entry', 'Updated', 'Created',
'Update-existing', 'Merged', and 'Patched' are refered to as "file
updating" responses, because they change the status of a file in the
working directory in some way. The responses 'Mode', 'Mod-time', and
'Checksum' are referred to as "file update modifying" responses because
they modify the next file updating response. In no case shall a file
update modifying response apply to a file updating response other than
the next one. Nor can the same file update modifying response occur
twice for a given file updating response (if servers diagnose this
problem, it may aid in detecting the case where clients send an update
modifying response without following it by a file updating response).

File: cvsclient.info, Node: Response pathnames, Next: Responses, Prev: Response intro, Up: Protocol

5.10 The "pathname" in responses
================================

Many of the responses contain something called PATHNAME. The name is
somewhat misleading; it actually indicates a pair of pathnames. First,
a local directory name relative to the directory in which the command
was given (i.e. the last 'Directory' before the command). Then a
linefeed and a repository name. Then a slash and the filename (without
a ',v' ending).

The repository name may be absolute or relative to the PATHNAME sent
with the 'Root' request. If absolute, the repository name must begin
with the PATHNAME sent with the 'Root' request. Relative or absolute,
the repository name must specify a path underneath the 'Root' PATHNAME.

For example, for a file 'i386.mh' which is in the local directory
'gas.clean/config' and for which the repository name is
'devo/gas/config':

gas.clean/config/
devo/gas/config/i386.mh

If the server wants to tell the client to create a directory, then it
merely uses the directory in any response, as described above, and the
client should create the directory if it does not exist. Note that this
should only be done one directory at a time, in order to permit the
client to correctly store the repository for each directory. Servers
can use requests such as 'Clear-sticky', 'Clear-static-directory', or
any other requests, to create directories.

Some server implementations may poorly distinguish between a
directory which should not exist and a directory which contains no
files; in order to refrain from creating empty directories a client
should both send the '-P' option to 'update' or 'co', and should also
detect the case in which the server asks to create a directory but not
any files within it (in that case the client should remove the directory
or refrain from creating it in the first place). Note that servers
could clean this up greatly by only telling the client to create
directories if the directory in question should exist, but until servers
do this, clients will need to offer the '-P' behavior described above.

File: cvsclient.info, Node: Responses, Next: Text tags, Prev: Response pathnames, Up: Protocol

5.11 Responses
==============

Here are the responses:

'Valid-requests REQUEST-LIST \n'
Indicate what requests the server will accept. REQUEST-LIST is a
space separated list of tokens. If the server supports sending
patches, it will include 'update-patches' in this list. The
'update-patches' request does not actually do anything.

'Force-gzip \n'
Response expected: no. Indicates that the server requires
compression. The client must send a 'Gzip-stream' request, though
the requested LEVEL may be '0'.

'Referrer CVSROOT'
Request that the client store CVSROOT as the name of this server
and that this name be passed via a 'Referrer' _request_ to any
subsequent servers contacted as a result of a 'Redirect' response.
This can be useful to allow the secondary administrator to
configure the 'CVSROOT' the primary should use to update the
secondary in case the client uses a non-standard name or even a
name that is unique to the client for some reason.

'Redirect CVSROOT'
Request that the client redirect its connection to CVSROOT and
begin again. This response is only valid in response to a
'Command-prep' request. If a client receives this response, it is
expected to notify the write server it subsequently contacts of the
CVSROOT of the server which redirected it using the 'Referrer'
request. This information makes it possible for primary servers to
update the client's mirror first, hopefully minimizing race
conditions on subsequent updates from the same client.

'Checked-in PATHNAME \n'
Additional data: New Entries line, \n. This means a file PATHNAME
has been successfully operated on (checked in, added, etc.). name
in the Entries line is the same as the last component of PATHNAME.

'New-entry PATHNAME \n'
Additional data: New Entries line, \n. Like 'Checked-in', but the
file is not up to date.

'Updated PATHNAME \n'
Additional data: New Entries line, \n, mode, \n, file transmission.
A new copy of the file is enclosed. This is used for a new
revision of an existing file, or for a new file, or for any other
case in which the local (client-side) copy of the file needs to be
updated, and after being updated it will be up to date. If any
directory in pathname does not exist, create it. This response is
not used if 'Created' and 'Update-existing' are supported.

'Created PATHNAME \n'
This is just like 'Updated' and takes the same additional data, but
is used only if no 'Entry', 'Modified', or 'Unchanged' request has
been sent for the file in question. The distinction between
'Created' and 'Update-existing' is so that the client can give an
error message in several cases: (1) there is a file in the working
directory, but not one for which 'Entry', 'Modified', or
'Unchanged' was sent (for example, a file which was ignored, or a
file for which 'Questionable' was sent), (2) there is a file in the
working directory whose name differs from the one mentioned in
'Created' in ways that the client is unable to use to distinguish
files. For example, the client is case-insensitive and the names
differ only in case.

'Update-existing PATHNAME \n'
This is just like 'Updated' and takes the same additional data, but
is used only if a 'Entry', 'Modified', or 'Unchanged' request has
been sent for the file in question.

This response, or 'Merged', indicates that the server has
determined that it is OK to overwrite the previous contents of the
file specified by PATHNAME. Provided that the client has correctly
sent 'Modified' or 'Is-modified' requests for a modified file, and
the file was not modified while CVS was running, the server can
ensure that a user's modifications are not lost.

'Merged PATHNAME \n'
This is just like 'Updated' and takes the same additional data,
with the one difference that after the new copy of the file is
enclosed, it will still not be up to date. Used for the results of
a merge, with or without conflicts.

It is useful to preserve an copy of what the file looked like
before the merge. This is basically handled by the server; before
sending 'Merged' it will send a 'Copy-file' response. For example,
if the file is 'aa' and it derives from revision 1.3, the
'Copy-file' response will tell the client to copy 'aa' to
'.#aa.1.3'. It is up to the client to decide how long to keep this
file around; traditionally clients have left it around forever,
thus letting the user clean it up as desired. But another answer,
such as until the next commit, might be preferable.

'Rcs-diff PATHNAME \n'
This is just like 'Updated' and takes the same additional data,
with the one difference that instead of sending a new copy of the
file, the server sends an RCS change text. This change text is
produced by 'diff -n' (the GNU diff '-a' option may also be used).
The client must apply this change text to the existing file. This
will only be used when the client has an exact copy of an earlier
revision of a file. This response is only used if the 'update'
command is given the '-u' argument.

'Patched PATHNAME \n'
This is just like 'Rcs-diff' and takes the same additional data,
except that it sends a standard patch rather than an RCS change
text. The patch is produced by 'diff -c' for CVS 1.6 and later
(see POSIX.2 for a description of this format), or 'diff -u' for
previous versions of CVS; clients are encouraged to accept either
format. Like 'Rcs-diff', this response is only used if the
'update' command is given the '-u' argument.

The 'Patched' response is deprecated in favor of the 'Rcs-diff'
response. However, older clients (CVS 1.9 and earlier) only
support 'Patched'.

'Edit-file PATHNAME \n'
Do the client-side portion of editing a file.

'Mode MODE \n'
This MODE applies to the next file mentioned in 'Checked-in'.
'Mode' is a file update modifying response as described in *note
Response intro::.

'Mod-time TIME \n'
Set the modification time of the next file sent to TIME.
'Mod-time' is a file update modifying response as described in
*note Response intro::. The TIME is in the format specified by
RFC822 as modified by RFC1123. The server may specify any timezone
it chooses; clients will want to convert that to their own timezone
as appropriate. An example of this format is:

26 May 1997 13:01:40 -0400

There is no requirement that the client and server clocks be
synchronised. The server just sends its recommendation for a
timestamp (based on its own clock, presumably), and the client
should just believe it (this means that the time might be in the
future, for example).

If the server does not send 'Mod-time' for a given file, the client
should pick a modification time in the usual way (usually, just let
the operating system set the modification time to the time that the
CVS command is running).

'Checksum CHECKSUM\n'
The CHECKSUM applies to the next file sent (that is, 'Checksum' is
a file update modifying response as described in *note Response
intro::). In the case of 'Patched', the checksum applies to the
file after being patched, not to the patch itself. The client
should compute the checksum itself, after receiving the file or
patch, and signal an error if the checksums do not match. The
checksum is the 128 bit MD5 checksum represented as 32 hex digits
(MD5 is described in RFC1321). This response is optional, and is
only used if the client supports it (as judged by the
'Valid-responses' request).

'Copy-file PATHNAME \n'
Additional data: NEWNAME \n. Copy file PATHNAME to NEWNAME in the
same directory where it already is. This does not affect
'CVS/Entries'.

This can optionally be implemented as a rename instead of a copy.
The only use for it which currently has been identified is prior to
a 'Merged' response as described under 'Merged'. Clients can
probably assume that is how it is being used, if they want to worry
about things like how long to keep the NEWNAME file around.

'Removed PATHNAME \n'
The file has been removed from the repository (this is the case
where cvs prints 'file foobar.c is no longer pertinent').

'Remove-entry PATHNAME \n'
The file needs its entry removed from 'CVS/Entries', but the file
itself is already gone (this happens in response to a 'ci' request
which involves committing the removal of a file).

'Set-static-directory PATHNAME \n'
This instructs the client to set the 'Entries.Static' flag, which
it should then send back to the server in a 'Static-directory'
request whenever the directory is operated on. PATHNAME ends in a
slash; its purpose is to specify a directory, not a file within a
directory.

'Clear-static-directory PATHNAME \n'
Like 'Set-static-directory', but clear, not set, the flag.

'Set-sticky PATHNAME \n'
Additional data: TAGSPEC \n. Tell the client to set a sticky tag
or date, which should be supplied with the 'Sticky' request for
future operations. PATHNAME ends in a slash; its purpose is to
specify a directory, not a file within a directory. The client
should store TAGSPEC and pass it back to the server as-is, to allow
for future expansion. The first character of TAGSPEC is 'T' for a
tag, 'D' for a date, or something else for future expansion. The
remainder of TAGSPEC contains the actual tag or date.

'Clear-sticky PATHNAME \n'
Clear any sticky tag or date set by 'Set-sticky'.

'Template PATHNAME \n'
Additional data: file transmission (note: compressed file
transmissions are not supported). PATHNAME ends in a slash; its
purpose is to specify a directory, not a file within a directory.
Tell the client to store the file transmission as the template log
message, and then use that template in the future when prompting
the user for a log message.

'Set-checkin-prog DIR \n'
Additional data: PROG \n. Tell the client to set a checkin
program, which should be supplied with the 'Checkin-prog' request
for future operations.

'Set-update-prog DIR \n'
Additional data: PROG \n. Tell the client to set an update
program, which should be supplied with the 'Update-prog' request
for future operations.

'Notified PATHNAME \n'
Indicate to the client that the notification for PATHNAME has been
done. There should be one such response for every 'Notify'
request; if there are several 'Notify' requests for a single file,
the requests should be processed in order; the first 'Notified'
response pertains to the first 'Notify' request, etc.

'Module-expansion PATHNAME \n'
Return a file or directory which is included in a particular
module. PATHNAME is relative to cvsroot, unlike most pathnames in
responses. PATHNAME should be used to look and see whether some or
all of the module exists on the client side; it is not necessarily
suitable for passing as an argument to a 'co' request (for example,
if the modules file contains the '-d' option, it will be the
directory specified with '-d', not the name of the module).

'Wrapper-rcsOption PATTERN -k 'OPTION' \n'
Transmit to the client a filename pattern which implies a certain
keyword expansion mode. The PATTERN is a wildcard pattern (for
example, '*.exe'. The OPTION is 'b' for binary, and so on. Note
that although the syntax happens to resemble the syntax in certain
CVS configuration files, it is more constrained; there must be
exactly one space between PATTERN and '-k' and exactly one space
between '-k' and ''', and no string is permitted in place of '-k'
(extensions should be done with new responses, not by extending
this one, for graceful handling of 'Valid-responses').

'M TEXT \n'
A one-line message for the user. Note that the format of TEXT is
not designed for machine parsing. Although sometimes scripts and
clients will have little choice, the exact text which is output is
subject to vary at the discretion of the server and the example
output given in this document is just that, example output.
Servers are encouraged to use the 'MT' response, and future
versions of this document will hopefully standardise more of the
'MT' tags; see *note Text tags::.

'LOGM TEXT \n'
Exactly the same as 'M' but only sent if the client indicates
supporting it via 'Valid-responses', used exclusively for log
message payload (that is, in 'cvs log' and 'cvs rlog', the text
body the user originally has entered with the '-m' option to the
'ci' request).

'Mbinary \n'
Additional data: file transmission (note: compressed file
transmissions are not supported). This is like 'M', except the
contents of the file transmission are binary and should be copied
to standard output without translation to local text file
conventions. To transmit a text file to standard output, servers
should use a series of 'M' requests.

'E TEXT \n'
Same as 'M' but send to stderr not stdout.

'F \n'
Flush stderr. That is, make it possible for the user to see what
has been written to stderr (it is up to the implementation to
decide exactly how far it should go to ensure this).

'MT TAGNAME DATA \n'

This response provides for tagged text. It is similar to
SGML/HTML/XML in that the data is structured and a naive
application can also make some sense of it without understanding
the structure. The syntax is not SGML-like, however, in order to
fit into the CVS protocol better and (more importantly) to make it
easier to parse, especially in a language like perl or awk.

The TAGNAME can have several forms. If it starts with 'a' to 'z'
or 'A' to 'Z', then it represents tagged text. If the
implementation recognises TAGNAME, then it may interpret DATA in
some particular fashion. If the implementation does not recognise
TAGNAME, then it should simply treat DATA as text to be sent to the
user (similar to an 'M' response). There are two tags which are
general purpose. The 'text' tag is similar to an unrecognised tag
in that it provides text which will ordinarily be sent to the user.
The 'newline' tag is used without DATA and indicates that a newline
will ordinarily be sent to the user (there is no provision for
embedding newlines in the DATA of other tagged text responses).

If TAGNAME starts with '+' it indicates a start tag and if it
starts with '-' it indicates an end tag. The remainder of TAGNAME
should be the same for matching start and end tags, and tags should
be nested (for example one could have tags in the following order
'+bold' '+italic' 'text' '-italic' '-bold' but not '+bold'
'+italic' 'text' '-bold' '-italic'). A particular start and end
tag may be documented to constrain the tagged text responses which
are valid between them.

Note that if DATA is present there will always be exactly one space
between TAGNAME and DATA; if there is more than one space, then the
spaces beyond the first are part of DATA.

Here is an example of some tagged text responses. Note that there
is a trailing space after 'Checking in' and 'initial revision:' and
there are two trailing spaces after '<--'. Such trailing spaces
are, of course, part of DATA.

MT +checking-in
MT text Checking in
MT fname gz.tst
MT text ;
MT newline
MT rcsfile /home/kingdon/zwork/cvsroot/foo/gz.tst,v
MT text <--
MT fname gz.tst
MT newline
MT text initial revision:
MT init-rev 1.1
MT newline
MT text done
MT newline
MT -checking-in

If the client does not support the 'MT' response, the same
responses might be sent as:

M Checking in gz.tst;
M /home/kingdon/zwork/cvsroot/foo/gz.tst,v <-- gz.tst
M initial revision: 1.1
M done

For a list of specific tags, see *note Text tags::.

'error ERRNO-CODE ' ' TEXT \n'
The command completed with an error. ERRNO-CODE is a symbolic
error code (e.g. 'ENOENT'); if the server doesn't support this
feature, or if it's not appropriate for this particular message, it
just omits the errno-code (in that case there are two spaces after
'error'). Text is an error message such as that provided by
strerror(), or any other message the server wants to use. The TEXT
is like the 'M' response, in the sense that it is not particularly
intended to be machine-parsed; servers may wish to print an error
message with 'MT' responses, and then issue a 'error' response
without TEXT (although it should be noted that 'MT' currently has
no way of flagging the output as intended for standard error, the
way that the 'E' response does).

'ok \n'
The command completed successfully.

File: cvsclient.info, Node: Text tags, Next: Example, Prev: Responses, Up: Protocol

5.12 Tags for the MT tagged text response
=========================================

The 'MT' response, as described in *note Responses::, offers a way for
the server to send tagged text to the client. This section describes
specific tags. The intention is to update this section as servers add
new tags.

In the following descriptions, 'text' and 'newline' tags are omitted.
Such tags contain information which is intended for users (or to be
discarded), and are subject to change at the whim of the server. To
avoid being vulnerable to such whim, clients should look for the tags
listed here, not 'text', 'newline', or other tags.

The following tag means to indicate to the user that a file has been
updated. It is more or less redundant with the 'Created' and
'Update-existing' responses, but we don't try to specify here whether it
occurs in exactly the same circumstances as 'Created' and
'Update-existing'. The NAME is the pathname of the file being updated
relative to the directory in which the command is occurring (that is,
the last 'Directory' request which is sent before the command).

MT +updated
MT fname NAME
MT -updated

The 'importmergecmd' tag is used when doing an import which has
conflicts, or when doing an import with the '-X' flag. The client can
use it to report how to merge in the newly imported changes. The COUNT
is the number of conflicts, or the string 'No' if no conflicts occurred.
(The latter will only be sent for imports run with the '-X' flag.) The
newly imported changes can be merged by running the following command:
cvs checkout -j TAG1 -j TAG2 REPOSITORY

MT +importmergecmd
MT conflicts COUNT
MT mergetag1 TAG1
MT mergetag2 TAG2
MT repository REPOSITORY
MT -importmergecmd

File: cvsclient.info, Node: Example, Next: Requirements, Prev: Text tags, Up: Protocol

5.13 Example
============

Here is an example; lines are prefixed by 'C: ' to indicate the client
sends them or 'S: ' to indicate the server sends them.

The client starts by connecting, sending the root, and completing the
protocol negotiation. In actual practice the lists of valid responses
and requests would be longer.

C: Root /u/cvsroot
C: Valid-responses ok error Checked-in M E
C: valid-requests
S: Valid-requests Root Directory Entry Modified Argument Argumentx ci co
S: ok
C: UseUnchanged

The client wants to check out the 'supermunger' module into a fresh
working directory. Therefore it first expands the 'supermunger' module;
this step would be omitted if the client was operating on a directory
rather than a module.

C: Argument supermunger
C: Directory .
C: .
C: expand-modules

The server replies that the 'supermunger' module expands to the
directory 'supermunger' (the simplest case):

S: Module-expansion supermunger
S: ok

The client then proceeds to check out the directory. The fact that
it sends only a single 'Directory' request which specifies '.' for the
working directory means that there is not already a 'supermunger'
directory on the client.

C: Argument -N
C: Argument supermunger
C: Directory .
C: .
C: co

The server replies with the requested files. In this example, there
is only one file, 'mungeall.c'. The 'Clear-sticky' and
'Clear-static-directory' requests are sent by the current implementation
but they have no effect because the default is for those settings to be
clear when a directory is newly created.

S: Clear-sticky supermunger/
S: /u/cvsroot/supermunger/
S: Clear-static-directory supermunger/
S: /u/cvsroot/supermunger/
S: E cvs server: Updating supermunger
S: M U supermunger/mungeall.c
S: Created supermunger/
S: /u/cvsroot/supermunger/mungeall.c
S: /mungeall.c/1.1///
S: u=rw,g=r,o=r
S: 26
S: int mein () { abort (); }
S: ok

The current client implementation would break the connection here and
make a new connection for the next command. However, the protocol
allows it to keep the connection open and continue, which is what we
show here.

After the user modifies the file and instructs the client to check it
back in. The client sends arguments to specify the log message and file
to check in:

C: Argument -m
C: Argument Well, you see, it took me hours and hours to find
C: Argumentx this typo and I searched and searched and eventually
C: Argumentx had to ask John for help.
C: Argument mungeall.c

It also sends information about the contents of the working
directory, including the new contents of the modified file. Note that
the user has changed into the 'supermunger' directory before executing
this command; the top level directory is a user-visible concept because
the server should print filenames in 'M' and 'E' responses relative to
that directory.

C: Directory .
C: supermunger
C: Entry /mungeall.c/1.1///
C: Modified mungeall.c
C: u=rw,g=r,o=r
C: 26
C: int main () { abort (); }

And finally, the client issues the checkin command (which makes use
of the data just sent):

C: ci

And the server tells the client that the checkin succeeded:

S: M Checking in mungeall.c;
S: E /u/cvsroot/supermunger/mungeall.c,v <-- mungeall.c
S: E new revision: 1.2; previous revision: 1.1
S: E done
S: Mode u=rw,g=r,o=r
S: Checked-in ./
S: /u/cvsroot/supermunger/mungeall.c
S: /mungeall.c/1.2///
S: ok

File: cvsclient.info, Node: Requirements, Next: Obsolete, Prev: Example, Up: Protocol

5.14 Required versus optional parts of the protocol
===================================================

The following are part of every known implementation of the CVS protocol
(except obsolete, pre-1.5, versions of CVS) and it is considered
reasonable behavior to completely fail to work if you are connected with
an implementation which attempts to not support them. Requests: 'Root',
'Valid-responses', 'valid-requests', 'Directory', 'Entry', 'Modified',
'Unchanged', 'Argument', 'Argumentx', 'ci', 'co', 'update'. Responses:
'ok', 'error', 'Valid-requests', 'Checked-in', 'Updated', 'Merged',
'Removed', 'M', 'E'.

A server need not implement 'Repository', but in order to
interoperate with CVS 1.5 through 1.9 it must claim to implement it (in
'Valid-requests'). The client will not actually send the request.

File: cvsclient.info, Node: Obsolete, Prev: Requirements, Up: Protocol

5.15 Obsolete protocol elements
===============================

This section briefly describes protocol elements which are obsolete.
There is no attempt to document them in full detail.

There was a 'Repository' request which was like 'Directory' except it
only provided REPOSITORY, and the local directory was assumed to be
similarly named.

If the 'UseUnchanged' request was not sent, there was a 'Lost'
request which was sent to indicate that a file did not exist in the
working directory, and the meaning of sending 'Entries' without 'Lost'
or 'Modified' was different. All current clients (CVS 1.5 and later)
will send 'UseUnchanged' if it is supported.

File: cvsclient.info, Node: Protocol Notes, Prev: Protocol, Up: Top

6 Notes on the Protocol
***********************

A number of enhancements are possible. Also see the file TODO in the
CVS source distribution, which has further ideas concerning various
aspects of CVS, some of which impact the protocol. Similarly, the
<http://www.nongnu.org/cvs/> site, in particular the 'Development'
pages.

* The 'Modified' request could be speeded up by sending diffs rather
than entire files. The client would need some way to keep the
version of the file which was originally checked out; probably
requiring the use of "cvs edit" in this case is the most sensible
course (the "cvs edit" could be handled by a package like VC for
emacs). This would also allow local operation of 'cvs diff'
without arguments.

* The fact that 'pserver' requires an extra network turnaround in
order to perform authentication would be nice to avoid. This
relates to the issue of reporting errors; probably the clean
solution is to defer the error until the client has issued a
request which expects a response. To some extent this might relate
to the next item (in terms of how easy it is to skip a whole bunch
of requests until we get to one that expects a response). I know
that the kerberos code doesn't wait in this fashion, but that
probably can cause network deadlocks and perhaps future problems
running over a transport which is more transaction oriented than
TCP. On the other hand I'm not sure it is wise to make the client
conduct a lengthy upload only to find there is an authentication
failure.

* The protocol uses an extra network turnaround for protocol
negotiation ('valid-requests'). It might be nice to avoid this by
having the client be able to send requests and tell the server to
ignore them if they are unrecognised (different requests could
produce a fatal error if unrecognised). To do this there should be
a standard syntax for requests. For example, perhaps all future
requests should be a single line, with mechanisms analogous to
'Argumentx', or several requests working together, to provide
greater amounts of information. Or there might be a standard
mechanism for counted data (analogous to that used by 'Modified')
or continuation lines (like a generalised 'Argumentx'). It would
be useful to compare what HTTP is planning in this area; last I
looked they were contemplating something called Protocol Extension
Protocol but I haven't looked at the relevant IETF documents in any
detail. Obviously, we want something as simple as possible (but no
simpler).

* The scrambling algorithm in the CVS client and server actually
support more characters than those documented in *note Password
scrambling::. Someday we are going to either have to document them
all (but this is not as easy as it may look, see below), or
(gradually and with adequate process) phase out the support for
other characters in the CVS implementation. This business of
having the feature partly undocumented isn't a desirable state
long-term.

The problem with documenting other characters is that unless we
know what character set is in use, there is no way to make a
password portable from one system to another. For example, a with
a circle on top might have different encodings in different
character sets.

It _almost_ works to say that the client picks an arbitrary,
unknown character set (indeed, having the CVS client know what
character set the user has in mind is a hard problem otherwise),
and scrambles according to a certain octet<->octet mapping. There
are two problems with this. One is that the protocol has no way to
transmit character 10 decimal (linefeed), and the current server
and clients have no way to handle 0 decimal (NUL). This may cause
problems with certain multibyte character sets, in which octets 10
and 0 will appear in the middle of other characters. The other
problem, which is more minor and possibly not worth worrying about,
is that someone can type a password on one system and then go to
another system which uses a different encoding for the same
characters, and have their password not work.

The restriction to the ISO646 invariant subset is the best approach
for strings which are not particularly significant to users.
Passwords are visible enough that this is somewhat doubtful as
applied here. ISO646 does, however, have the virtue (!?) of
offending everyone. It is easy to say "But the $ is right on
people's keyboards! Surely we can't forbid that". From a human
factors point of view, that makes quite a bit of sense. The
contrary argument, of course, is that a with a circle on top, or
some of the characters poorly handled by Unicode, are on
_someone_'s keyboard.

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