path: root/gnu/usr.bin/cvs/doc/cvsclient.info-1

This is Info file cvsclient.info, produced by Makeinfo version 1.67
from the input file ../../work/ccvs/doc/cvsclient.texi.


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; see the
regular CVS manual for that.  This is version 1.9.26 of the protocol
specification--*Note 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.
* 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

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 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 1.9.26 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

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 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

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
     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 unrecognized 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.

     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

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

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

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

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

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).  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?).


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

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

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: Request intro,  Prev: File transmissions,  Up: Protocol

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).  The protocol has no mechanism to specify the
character set of such strings; it would be 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.


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

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


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

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', or `init'.

`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.

`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.  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 send 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: /home/kingdon/zwork/cvsroot
          C: co
          S: Clear-sticky moddir/
          S: /home/kingdon/zwork/cvsroot/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: /home/kingdon/zwork/cvsroot/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.

`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, or `D'
     for a date.  The remainder of TAGSPEC contains the actual tag or
     date.

     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.

`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 `Directory'.  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 name is relative to
     the most recent repository sent with `Directory'.

`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.

`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, `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 to set.  If WATCHES is
     followed by \t then the \t and the rest of the line should be
     ignored, for future expansion.

     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).

`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 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 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.

     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'.

     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
     `Gssapi-encrypt' request.

`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.

     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
     `Gssapi-authenticate' request.

`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.

     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: /home/kingdon/zwork/cvsroot
          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'
`tag \n'
`status \n'
`log \n'
`remove \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.

`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.

`rdiff \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
     this command; they are not used.  Arguments to these commands are
     module names, as described for `co'.

`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', `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.  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: /u/cvsroot/1dir/nsdir
          C: Directory .
          C: /u/cvsroot/1dir
          C: add
          S: M Directory /u/cvsroot/1dir/nsdir added to the repository
          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: /u/cvsroot/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.

`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.

`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.  `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.

`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.