path: root/gnu/usr.bin/cvs/doc/cvsclient.texi

\input texinfo @c -*- texinfo -*-

@setfilename cvsclient.info
@include CVSvn.texi

@node Top
@top 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 @value{CVSVN} of the protocol
specification---@xref{Introduction} for more on what this version number
means.

@menu
* Introduction::      What is CVS and what is the client/server protocol for?
* Goals::             Basic design decisions, requirements, scope, etc.
* Notes::             Notes on the current implementation
* Protocol Notes::    Possible enhancements, limitations, etc. of the protocol
* Connection and Authentication::  Various ways to connect to the server
* Protocol::          Complete description of the protocol
@end menu

@node Introduction
@chapter Introduction

CVS is a version control system (with some additional configuration
management functionality).  It maintains a central @dfn{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 @dfn{developers}, use
CVS to @dfn{check out} a @dfn{working directory} from the repository, to
@dfn{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 @dfn{client} program.  To perform operations
which cannot be done locally, it connects to the CVS @dfn{server}
program, which maintains the repository.  For more information on how
to connect see @ref{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, @file{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, @file{cvs.texinfo}, and a copy (possibly more or less up
to date than what you are reading now) of this document,
@file{cvsclient.texi}, can be found at the usual GNU FTP sites, with a
filename such as @file{cvs-@var{version}.tar.gz}.

This is version @value{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 @xref{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 @code{valid-requests} and
@code{Valid-responses} mechanism (@pxref{Protocol}), which is more
flexible.

@node Goals
@chapter Goals

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

@item
Providing a reliable transport is outside this protocol.  It is expected
that it runs over TCP, UUCP, etc.

@item
Security and authentication are handled outside this protocol (but see
below about @samp{cvs kserver} and @samp{cvs pserver}).

@item
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.

@item
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.

@item
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.
@end itemize

@node Notes
@chapter Notes on the Current Implementation

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

The client stores what is stored in checked-out directories (including
@file{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 @code{SERVER_FLOWCONTROL} in options.h) which
should help significantly.

@node Protocol Notes
@chapter Notes on the Protocol

A number of enhancements are possible:

@itemize @bullet
@item
The @code{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 @code{cvs diff} without arguments.

@item
Have the client keep a copy of some part of the repository.  This allows
all of @code{cvs diff} and large parts of @code{cvs update} and
@code{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).

@item
The current procedure for @code{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.
@end itemize

@node Connection and Authentication
@chapter 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.

@table @asis
@item 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 @code{cvs}.  It is
invoked with one argument, @code{server}.  Once it invokes the server,
the client proceeds to start the cvs protocol.

@item 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 @samp{BEGIN
AUTH REQUEST} to identify the authentication method in use.  However,
noone has yet gotten around to implementing this.

@item 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 @samp{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
@samp{END AUTH REQUEST}, and a linefeed.  The server responds with
@samp{I LOVE YOU} and a linefeed if the authentication is successful or
@samp{I HATE YOU} and a linefeed if the authentication fails.  After
receiving @samp{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 @samp{BEGIN AUTH REQUEST} is
replaced with @samp{BEGIN VERIFICATION REQUEST}, @samp{END AUTH REQUEST}
is replaced with @samp{END VERIFICATION REQUEST}, and upon receipt of
@samp{I LOVE YOU} the connection is closed rather than continuing.
@end table

@node Protocol
@chapter The CVS client/server protocol

In the following, @samp{\n} refers to a linefeed and @samp{\t} refers
to a horizontal tab.

@menu
* Entries Lines::               
* Modes::                       
* Filenames::                       Conventions regarding filenames
* Requests::                    
* Responses::                   
* Example::                     
* Requirements::
@end menu

@node Entries Lines
@section Entries Lines

Entries lines are transmitted as:

@example
/ @var{name} / @var{version} / @var{conflict} / @var{options} / @var{tag_or_date}
@end example

@var{tag_or_date} is either @samp{T} @var{tag} or @samp{D} @var{date}
or empty.  If it is followed by a slash, anything after the slash
shall be silently ignored.

@var{version} can be empty, or start with @samp{0} or @samp{-}, for no
user file, new user file, or user file to be removed, respectively.

@c FIXME: should distinguish sender and receiver behavior here; the
@c "anything else" and "does not start with" are intended for future
@c expansion, and we should specify a sender behavior.
@var{conflict}, if it starts with @samp{+}, indicates that the file had
conflicts in it.  The rest of @var{conflict} is @samp{=} if the
timestamp matches the file, or anything else if it doesn't.  If
@var{conflict} does not start with a @samp{+}, it is silently ignored.

@node Modes
@section Modes

A mode is any number of repetitions of

@example
@var{mode-type} = @var{data}
@end example

separated by @samp{,}.

@var{mode-type} is an identifier composed of alphanumeric characters.
Currently specified: @samp{u} for user, @samp{g} for group, @samp{o}
for other (see below for discussion of whether these have their POSIX
meaning or are more loose).  Unrecognized values of @var{mode-type}
are silently ignored.

@var{data} consists of any data not containing @samp{,}, @samp{\0} or
@samp{\n}.  For @samp{u}, @samp{g}, and @samp{o} mode types, data
consists of alphanumeric characters, where @samp{r} means read, @samp{w}
means write, @samp{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?).

@node Filenames
@section Conventions regarding transmission of file names

In most contexts, @samp{/} 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).

@node Requests
@section 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 @samp{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 @var{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 @samp{gzip-file-contents}, a @samp{z} may
precede the length, and the `file contents' sent are actually compressed
with @samp{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 newline iff that file (or its
compressed form) ends with a newline.

@table @code
@item Root @var{pathname} \n
Response expected: no.  Tell the server which @code{CVSROOT} to use.
Note that @var{pathname} is a local directory and @emph{not} a fully
qualified @code{CVSROOT} variable.  @var{pathname} must
already exist; if creating a new root, use the @code{init} request, not
@code{Root}.  @var{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.

@item Valid-responses @var{request-list} \n
Response expected: no.
Tell the server what responses the client will accept.
request-list is a space separated list of tokens.

@item valid-requests \n
Response expected: yes.
Ask the server to send back a @code{Valid-requests} response.

@item Repository @var{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 @code{Entry } and @code{Modified } and
also for @code{ci} and the other commands; normal usage is to send a
@code{Repository } for each directory in which there will be an
@code{Entry } or @code{Modified }, and then a final @code{Repository }
for the original directory, then the command.

@item Directory @var{local-directory} \n
Additional data: @var{repository} \n.  Response expected: no.
This is like @code{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 @ref{Responses}.  @var{local-directory} is relative to
the top level at which the command is occurring (i.e. the last
@code{Directory} or @code{Repository} which is sent before the command);
to indicate that top level, @samp{.} should be send for
@var{local-directory}.

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

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

@item Sticky @var{tagspec} \n
Response expected: no.  Tell the server that the directory most recently
specified with @code{Repository} has a sticky tag or date @var{tagspec}.
The first character of @var{tagspec} is @samp{T} for a tag, or @samp{D}
for a date.  The remainder of @var{tagspec} contains the actual tag or
date.

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

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

@item Entry @var{entry-line} \n
Response expected: no.  Tell the server what version of a file is on the
local machine.  The name in @var{entry-line} is a name relative to the
directory most recently specified with @code{Repository}.  If the user
is operating on only some files in a directory, @code{Entry} requests
for only those files need be included.  If an @code{Entry} request is
sent without @code{Modified}, @code{Unchanged}, or @code{Lost} for that
file the meaning depends on whether @code{UseUnchanged} has been sent;
if it has been it means the file is lost, if not it means the file is
unchanged.

@item Modified @var{filename} \n
Response expected: no.  Additional data: mode, \n, file transmission.
Send the server a copy of one locally modified file.  @var{filename} is
relative to the most recent repository sent with @code{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 @code{Entry},
if there is no entry for the file.

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

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

@item UseUnchanged \n
Response expected: no.  Tell the server that the client will be
indicating unmodified files with @code{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.

@item Notify @var{filename} \n
Response expected: no.
Tell the server that a @code{edit} or @code{unedit} command has taken
place.  The server needs to send a @code{Notified} response, but such
response is deferred until the next time that the server is sending
responses.  Response expected: no.  Additional data:
@example
@var{notification-type} \t @var{time} \t @var{clienthost} \t
@var{working-dir} \t @var{watches} \n
@end example
where @var{notification-type} is @samp{E} for edit or @samp{U} for
unedit, @var{time} is the time at which the edit or unedit took place,
@var{clienthost} is the name of the host on which the edit or unedit
took place, and @var{working-dir} is the pathname of the working
directory where the edit or unedit took place.  @var{watches} are the
temporary watches to set; if it is followed by \t then the tab and the
rest of the line are ignored.

@item Questionable @var{filename} \n
Response expected: no.  Additional data: no.  Tell the server to check
whether @var{filename} should be ignored, and if not, next time the
server sends responses, send (in a @code{M} response) @samp{?} followed
by the directory and filename.  @var{filename} must not contain
@samp{/}; it needs to be a file in the directory named by the most
recent @code{Directory} request.
@c FIXME: the bit about not containing / is true of most of the
@c requests, but isn't documented and should be.

@item 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 @code{Entry} and
@code{Modified} requests for the same file must match in case regardless
of whether the @code{Case} request is sent.

@item Argument @var{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.

@item Argumentx @var{text} \n
Response expected: no.  Append \n followed by text to the current
argument being saved.

@item Global_option @var{option} \n
Response expected: no.
Transmit one of the global options @samp{-q}, @samp{-Q}, @samp{-l},
@samp{-t}, @samp{-r}, or @samp{-n}.  @var{option} must be one of those
strings, no variations (such as combining of options) are allowed.  For
graceful handling of @code{valid-requests}, it is probably better to
make new global options separate requests, rather than trying to add
them to this request.

@item Gzip-stream @var{level} \n
Response expected: no.
Use zlib (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 @var{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.

@item 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 @code{Gzip-stream} and
the @code{Kerberos-encrypt} requests are used, the
@code{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.

@item Set @var{variable}=@var{value} \n
Response expected: no.
Set a user variable @var{variable} to @var{value}.

@item expand-modules \n
Response expected: yes.  Expand the modules which are specified in the
arguments.  Returns the data in @code{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.

@item co \n
@itemx ci \n
@itemx diff \n
@itemx tag \n
@itemx status \n
@itemx log \n
@itemx add \n
@itemx remove \n
@itemx rdiff \n
@itemx rtag \n
@itemx admin \n
@itemx export \n
@itemx history \n
@itemx watchers \n
@itemx editors \n
@itemx annotate \n
Response expected: yes.  Actually do a cvs command.  This uses any
previous @code{Argument}, @code{Repository}, @code{Entry},
@code{Modified}, or @code{Lost} requests, if they have been sent.  The
last @code{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 @code{ci} must use a @code{-m} argument if it wants to
specify a log message.

@itemx init @var{root-name} \n
Response expected: yes.  If it doesn't already exist, create a @sc{cvs}
repository @var{root-name}.  Note that @var{root-name} is a local
directory and @emph{not} a fully qualified @code{CVSROOT} variable.  The
@code{Root} request need not have been previously sent.

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

@item import \n
Response expected: yes.  Actually do a @code{cvs import} command.  This
uses any previous @code{Argument}, @code{Repository}, @code{Entry},
@code{Modified}, or @code{Lost} requests, if they have been sent.  The
last @code{Repository} sent specifies the working directory at the time
of the operation.  The files to be imported are sent in @code{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 @code{-m}
argument.

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

@item release \n
Response expected: yes.  Note that a @code{cvs release} command has
taken place and update the history file accordingly.

@item 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 @code{Notified} responses, etc.

@item 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 @code{update}
request.  The client must issue the @code{-u} argument to @code{update}
in order to receive patches.

@item gzip-file-contents @var{level} \n
Response expected: no.  Note that this request does not follow the
response convention stated above.  @code{Gzip-stream} is suggested
instead of @code{gzip-file-contents} as it gives better compression; the
only reason to implement the latter is to provide compression with
@sc{cvs} 1.8 and earlier.  The @code{gzip-file-contents} request asks
the server to compress files it sends to the client using @code{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
@samp{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.

@item @var{other-request} @var{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
@samp{error  unrecognized request}, but it could be a different error if
a previous command which doesn't expect a response produced an error.
@end table

When the client is done, it drops the connection.

@node Responses
@section 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).

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

@example
gas.clean/config/
/rel/cvsfiles/devo/gas/config/i386.mh
@end example

Any response always ends with @samp{error} or @samp{ok}.  This indicates
that the response is over.

@table @code
@item Valid-requests @var{request-list} \n
Indicate what requests the server will accept.  @var{request-list}
is a space separated list of tokens.  If the server supports sending
patches, it will include @samp{update-patches} in this list.  The
@samp{update-patches} request does not actually do anything.

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

@item New-entry @var{pathname} \n
Additional data: New Entries line, \n.  Like @code{Checked-in}, but the
file is not up to date.

@item Updated @var{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 @code{Created} and
@code{Update-existing} are supported.

@item Created @var{pathname} \n
This is just like @code{Updated} and takes the same additional data, but
is used only if no @code{Entry}, @code{Modified}, or
@code{Unchanged} request has been sent for the file in question.  The
distinction between @code{Created} and @code{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 @code{Entry},
@code{Modified}, or @code{Unchanged} was sent (for example, a file which
was ignored, or a file for which @code{Questionable} was sent), (2)
there is a file in the working directory whose name differs from the one
mentioned in @code{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.

@item Update-existing @var{pathname} \n
This is just like @code{Updated} and takes the same additional data, but
is used only if a @code{Entry}, @code{Modified}, or @code{Unchanged}
request has been sent for the file in question.

@item Merged @var{pathname} \n
This is just like @code{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.

@item Patched @var{pathname} \n
This is just like @code{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 @samp{diff -c} for
@sc{cvs} 1.6 and later (see POSIX.2 for a description of this format),
or @samp{diff -u} for previous versions of @sc{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 @code{update} command is given the @samp{-u} argument.

@item Mode @var{mode} \n
This @var{mode} applies to the next file mentioned in
@code{Checked-in}.  It does not apply to any request which follows a
@code{Checked-in}, @code{New-entry}, @code{Updated}, @code{Merged}, or
@code{Patched} response.

@item Checksum @var{checksum}\n
The @var{checksum} applies to the next file sent over via
@code{Updated}, @code{Merged}, or @code{Patched}.  In the case of
@code{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 @code{Valid-responses} request).

@item Copy-file @var{pathname} \n
Additional data: @var{newname} \n.  Copy file @var{pathname} to
@var{newname} in the same directory where it already is.  This does not
affect @code{CVS/Entries}.

@item Removed @var{pathname} \n
The file has been removed from the repository (this is the case where
cvs prints @samp{file foobar.c is no longer pertinent}).

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

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

@item Clear-static-directory @var{pathname} \n
Like @code{Set-static-directory}, but clear, not set, the flag.

@item Set-sticky @var{pathname} \n
Additional data: @var{tagspec} \n.  Tell the client to set a sticky tag
or date, which should be supplied with the @code{Sticky} request for
future operations.  @var{pathname} ends in a slash; its purpose is to
specify a directory, not a file within a directory.  The first character
of @var{tagspec} is @samp{T} for a tag, or @samp{D} for a date.  The
remainder of @var{tagspec} contains the actual tag or date.

@item Clear-sticky @var{pathname} \n
Clear any sticky tag or date set by @code{Set-sticky}.

@item Template @var{pathname} \n
Additional data: file transmission (note: compressed file transmissions
are not supported).  @var{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.

@item Set-checkin-prog @var{dir} \n
Additional data: @var{prog} \n.  Tell the client to set a checkin
program, which should be supplied with the @code{Checkin-prog} request
for future operations.

@item Set-update-prog @var{dir} \n
Additional data: @var{prog} \n.  Tell the client to set an update
program, which should be supplied with the @code{Update-prog} request
for future operations.

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

@item Module-expansion @var{pathname} \n Return a file or directory
which is included in a particular module.  @var{pathname} is relative
to cvsroot, unlike most pathnames in responses.  @var{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 @code{co} request (for example, if the modules file
contains the @samp{-d} option, it will be the directory specified with
@samp{-d}, not the name of the module).

@item M @var{text} \n
A one-line message for the user.

@item E @var{text} \n
Same as @code{M} but send to stderr not stdout.

@item F \n
@c FIXME: The second sentence, defining "flush", is somewhat off the top
@c of my head.  Is there some text we can steal from ANSI C or someplace
@c which is more carefully thought out?
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).

@item error @var{errno-code} @samp{ } @var{text} \n
The command completed with an error.  @var{errno-code} is a symbolic
error code (e.g. @code{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
@samp{error}).  Text is an error message such as that provided by
strerror(), or any other message the server wants to use.

@item ok \n
The command completed successfully.
@end table

@node Example
@section Example

@c FIXME: Use Directory, not Repository!
@c FIXME-less-important: Use Created and Update-existing, not Updated.
@c FIXME: the presence of timestamps in the entries lines is not right.

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

@example
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
@end example

@node Requirements
@section 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.

@bye