     [file CVSvn.texi not included]

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; see the regular CVS manual for that.  This is version CVSVN of the protocol specification---see Introduction, for more on what this version number means.

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 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 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 CVSVN 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 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 (see Protocol), which is more flexible.

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.  It is expected that it runs over TCP, UUCP, etc.

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

  * This might be a first step towards adding transactions to CVS (i.e. a set of operations is either executed atomically or none of them is executed), improving the locking, or other features.  The current server implementation is a long way from being able to do any of these things.  The protocol, however, is not known to contain any defects which would preclude them.

  * The server never has to have any CVS locks in place while it is waiting for communication with the client.  This makes things robust in the face of flaky networks.

  * Data is transferred in large chunks, which is necessary for good performance.  In fact, currently the client uploads all the data (without waiting for server responses), and then waits for one server response (which consists of a massive download of all the data).  There may be cases in which it is better to have a richer interraction, but the need for the server to release all locks whenever it waits for the client makes it complicated.

Notes on the Current Implementation
***********************************

The client is built in to the normal cvs program, triggered by a specially-formatted CVSROOT variable, for example :server:cygnus.com:/rel/cvsfiles.

The client stores what is stored in checked-out directories (including CVS).  The way these are stored is totally compatible with standard CVS.  The server requires no storage other than the repository, which also is totally compatible with standard CVS.

The current server implementation can use up huge amounts of memory when transmitting a lot of data over a slow link (i.e. the network is slower than the server can generate the data).  There is some experimental code (see SERVER_FLOWCONTROL in options.h) which should help significantly.

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

A number of enhancements are possible:

  * 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.

  * Have the client keep a copy of some part of the repository.  This allows all of cvs diff and large parts of cvs update and cvs ci to be local.  The local copy could be made consistent with the master copy at night (but if the master copy has been updated since the latest nightly re-sync, then it would read what it needs to from the master).

  * The current procedure for cvs update is highly sub-optimal if there are many modified files.  One possible alternative would be to have the client send a first request without the contents of every modified file, then have the server tell it what files it needs.  Note the server needs to do the what-needs-to-be-updated check twice (or more, if changes in the repository mean it has to ask the client for more files), because it can't keep locks open while waiting for the network.  Perhaps this whole thing is irrelevant if client-side repositories are implemented, and the rcsmerge is done by the client.

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 kerberized 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 the kerberized client and server should be changed to use port 2401 (see below), and send a different string in place of BEGIN AUTH REQUEST to identify the authentication method in use.  However, noone has yet gotten around to implementing this.

pserver
     The password authenticated 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, sends the string BEGIN AUTH REQUEST, a linefeed, the cvs root, a linefeed, the username, a linefeed, the password trivially encoded (see scramble.c in the cvs sources), a linefeed, the string END AUTH REQUEST, and a linefeed.  The server responds with I LOVE YOU and a linefeed if the authentication is successful or I HATE YOU and a linefeed if the authentication fails.  After receiving I LOVE YOU, the client proceeds with the cvs protocol. 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.

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

In the following, \n refers to a linefeed and \t refers to a horizontal tab.

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.

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).  Unrecognized 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 unrecognized 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?).

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).

Requests
========

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.  Unrecognized requests will always elicit a response from the server, even if that request begins with a capital letter.

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 newline, 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.  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 newline iff that file (or its compressed form) ends with a newline.

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.

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.

valid-requests \n
     Response expected: yes. Ask the server to send back a Valid-requests response.

Repository REPOSITORY \n
     Response expected: no.  Tell the server what repository to use.  This should be a directory name from a previous server response.  Note that this both gives a default for Entry  and Modified  and also for ci and the other commands; normal usage is to send a Repository  for each directory in which there will be an Entry  or Modified , and then a final Repository for the original directory, then the command.

Directory LOCAL-DIRECTORY \n
     Additional data: REPOSITORY \n.  Response expected: no. This is like Repository, but the local name of the directory may differ from the repository name. If the client uses this request, it affects the way the server returns pathnames; see Responses.  LOCAL-DIRECTORY is relative to the top level at which the command is occurring (i.e. the last Directory or Repository which is sent before the command); to indicate that top level, . should be send for LOCAL-DIRECTORY.

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 Repository or 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 Repository has a sticky tag or date TAGSPEC. The first character of TAGSPEC is T for a tag, or D for a date.  The remainder of TAGSPEC contains the actual tag or date.

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 Repository.  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, Unchanged, or Lost for that file the meaning depends on whether UseUnchanged has been sent; if it has been it means the file is lost, if not it means the file is unchanged.

Modified FILENAME \n
     Response expected: no.  Additional data: mode, \n, file transmission. Send the server a copy of one locally modified file.  FILENAME is relative to the most recent repository sent with Repository.  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.

Lost FILENAME \n
     Response expected: no.  Tell the server that FILENAME no longer exists.  The name is relative to the most recent repository sent with Repository.  This is used for any case in which Entry is being sent but the file no longer exists.  If the client has issued the UseUnchanged request, then this request is not used.

Unchanged FILENAME \n
     Response expected: no.  Tell the server that FILENAME has not been modified in the checked out directory.  The name is relative to the most recent repository sent with Repository.  This request can only be issued if UseUnchanged has been sent.

UseUnchanged \n
     Response expected: no.  Tell the server that the client will be indicating unmodified files with Unchanged, and that files for which no information is sent are nonexistent on the client side, not unchanged.  This is necessary for correct behavior since only the server knows what possible files may exist, and thus what files are nonexistent.

Notify FILENAME \n
     Response expected: no. Tell the server that a 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.  Response expected: no.  Additional data:

          NOTIFICATION-TYPE \t TIME \t CLIENTHOST \t
          WORKING-DIR \t WATCHES \n

     where NOTIFICATION-TYPE is E for edit or U for unedit, TIME is the time at which the edit or unedit took place, 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 to set; if it is followed by \t then the tab and the rest of the line are ignored.

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 against ignore patterns in a case-insensitive fashion.  Note that this does not apply to other comparisons---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.

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.

Gzip-stream LEVEL \n
     Response expected: no. Use RFC 1950/1951 compression to compress all further communication between the client and the server.  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 1 and 9, inclusive, where a higher number indicates 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.

Set VARIABLE=VALUE \n
     Response expected: no. Set a user variable VARIABLE to VALUE.

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.

co \n
ci \n
diff \n
tag \n
status \n
log \n
add \n
remove \n
rdiff \n
rtag \n
admin \n
export \n
history \n
watchers \n
editors \n
annotate \n
     Response expected: yes.  Actually do a cvs command.  This uses any previous Argument, Repository, Entry, Modified, or Lost requests, if they have been sent.  The last Repository 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.

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.

update \n
     Response expected: yes.  Actually do a cvs update command.  This uses any previous Argument, Repository, Entry, Modified, or Lost requests, if they have been sent.  The last Repository 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, Repository, Entry, Modified, or Lost requests, if they have been sent.  The last Repository sent specifies the working directory at the time of the operation.  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.

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, Repository, Entry, Modified, or Lost requests, if they have been sent.  The last Repository 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.

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.

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. This request asks the server to filter files it sends to the client through the gzip program, using the specified level of compression.  If this request is not made, the server must not do any compression.

     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.

OTHER-REQUEST TEXT \n
     Response expected: yes. Any unrecognized 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 command which doesn't expect a response produced an error.

When the client is done, it drops the connection.

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).

Pathnames are of the actual files operated on (i.e. they do not contain ,v endings), and are suitable for use in a subsequent Repository request.  However, if the client has used the Directory request, then it is instead a local directory name relative to the directory in which the command was given (i.e. the last Directory before the command).  Then a newline and a repository name (the pathname which is sent if Directory is not used).  Then the slash and the filename.  For example, for a file i386.mh which is in the local directory gas.clean/config and for which the repository is /rel/cvsfiles/devo/gas/config:

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

Any response always ends with error or ok.  This indicates that the response is over.

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.

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.

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.

Patched 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 a patch.  This 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.  The client must apply this patch 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.

Mode MODE \n
     This MODE applies to the next file mentioned in Checked-in.  It does not apply to any request which follows a Checked-in, New-entry, Updated, Merged, or Patched response.

Checksum CHECKSUM\n
     The CHECKSUM applies to the next file sent over via Updated, Merged, or Patched.  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.  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.

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 first character of TAGSPEC is T for a tag, or D for a date.  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).

M TEXT \n
     A one-line message for the user.

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).

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.

ok \n
     The command completed successfully.

Example
=======

Lines beginning with c> are sent by the client; lines beginning with s> are sent by the server; lines beginning with # are not part of the actual exchange.

     c> Root /rel/cvsfiles
     # In actual practice the lists of valid responses and requests would
     # be longer
     c> Valid-responses Updated Checked-in M ok error
     c> valid-requests
     s> Valid-requests Root co Modified Entry Repository ci Argument Argumentx
     s> ok
     # cvs co devo/foo
     c> Argument devo/foo
     c> co
     s> Updated /rel/cvsfiles/devo/foo/foo.c
     s> /foo.c/1.4/Mon Apr 19 15:36:47 1993 Mon Apr 19 15:36:47 1993//
     s> 26
     s> int mein () { abort (); }
     s> Updated /rel/cvsfiles/devo/foo/Makefile
     s> /Makefile/1.2/Mon Apr 19 15:36:47 1993 Mon Apr 19 15:36:47 1993//
     s> 28
     s> foo: foo.c
     s>         $(CC) -o foo $<
     s> ok
     # The current 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.
     c> Repository /rel/cvsfiles/devo/foo
     # foo.c relative to devo/foo just set as Repository.
     c> Entry /foo.c/1.4/Mon Apr 19 15:36:47 1993 Mon Apr 19 15:36:47 1993//
     c> Entry /Makefile/1.2/Mon Apr 19 15:36:47 1993 Mon Apr 19 15:36:47 1993//
     c> Modified foo.c
     c> 26
     c> int main () { abort (); }
     # cvs ci -m <log message> foo.c
     c> Argument -m
     c> Argument Well, you see, it took me hours and hours to find this typo and I
     c> Argumentx searched and searched and eventually had to ask John for help.
     c> Argument foo.c
     c> ci
     s> Checked-in /rel/cvsfiles/devo/foo/foo.c
     s> /foo.c/1.5/ Mon Apr 19 15:54:22 CDT 1993//
     s> M Checking in foo.c;
     s> M /cygint/rel/cvsfiles/devo/foo/foo.c,v  <--  foo.c
     s> M new revision: 1.5; previous revision: 1.4
     s> M done
     s> ok

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

The following are part of every known implementation of the CVS protocol 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, Repository, Entry, Modified, Argument, Argumentx, ci, co, update. Responses: ok, error, Valid-requests, Checked-in, Updated, Merged, Removed, M, E.

Failure to support the Directory, UseUnchanged, and Unchanged requests is deprecated.  CVS 1.5 and later have supported these requests and in the future it will be considered reasonable behavior to completely fail to work with an implementation which attempts to not support them.  Support for the Repository and Lost requests is deprecated; CVS clients 1.5 and later will not use them if communicating with a server which supports Directory and UseUnchanged.