# Table of contents:

# Introduction

CVR is a command introduced with MSNP2.

It is a Notification Server, and as of MSNP8 a Dispatch Server command, without either a request or response payload.

Sends the current client information and retrieves the latest available version of the client.
For the version of this command that is sent in CVR0, read CVQ.

# Client/Request

CVR TrID locale system-type system-ver system-arch requesting-library client-version {client-identification} {user-handle}

Where locale is a 16-bit hexadecimally encoded LCID. 0x0409 is the LCID for English, United States.

Where system-type is a string that defines the operating system you are using, such as winnt.

Where system-ver is the major and minor version of the operating system, such as 5.1.

Where system-arch is the architecture of the processor that is used to run the client, usually i386.

Where requesting-library is the name of the library that requested this CVR, usually MSMSGS or MSNMSGR.

Where client-version is the current client's major, minor and patch version, should be in the format of "{M}M.m.pppp".

Where client-identification is the internal name of the codebase used to create requesting-library, usually MSMSGS or an empty parameter. Added since MSNP4.

Where user-handle is the user's handle. Added since MSNP8.

# Server/Response

CVR TrID recommended-version recommended-version-2 minimum-allowed-version download-url {fallback-url}

Where recommended-version is the current version of the client for this system.

Where recommended-version-2 is (usually) the same as recommended-version, Could possibly be a maximum allowed version? (forced downgrade)

Where minimum-allowed-version is the lowest version the server considers "safe" to connect with.
If the client's client-version is lower than the server's minimum-allowed-version, the client should automatically disconnect from the server, and request an forced upgrade using the binary provided in download-url.

Where download-url is the file to download and open to update this client to recommended-version.

Where fallback-url is the URL the client opens if it failed to download download-url for any reason. Added since MSNP2.

# Examples

NOTE: This has been line-broken. Lines beginning with .. followed by a space are continuations of the previous line.

# Post-login

Only used in MSNP2 to MSNP7. 

C: CVR 1 0x0409 win 4.10 i386 MSMSGS 1.0.0863 MSMSGS
S: CVR 1 5.0.0537 5.0.0537 1.0.0863
.. http://download.microsoft.com/download/msnmessenger/install/5.0/w98nt42kmexp/en-us/setupdl.exe
.. http://messenger.microsoft.com

Client asks if user would like to update, and stays connected.

# Pre-login

Since MSNP8. 

C: CVR 2 0x0409 winnt 5.1 i386 MSNMSGR 6.0.0602 MSMSGS example@hotmail.com
S: CVR 2 7.0.0813 7.0.0813 6.2.0205
.. http://msgr.dlservice.microsoft.com/download/5/d/9/5d9bb5b2-49c7-4890-94ab-d1d5e44a0e6d/Install_MSN_Messenger.exe
.. http://messenger.msn.com

Client disconnects from server, since it sees that minimum-allowed is above it's client-version.

# Invalid client identification or version

This response may or may not disconnect you. 

C: CVR 3 0x0409 winnt 5.0 i386 MSNMSGR 99.9.9999 MSMSGS
S: 420 3
C: CVR 4 0x0409 winnt 5.0 i386 YCOMM 0.1.0023 MSMSGS
S: 420 4

# Invalid language ID 

C: CVR 5 0x1111 winnt 5.1 MSNMSGR 6.0.0602 MSMSGS example@hotmail.com
S: 710 5

# Invalid parameters 

C: CVR 6 spaghetti
S: 731 6

Server disconnects client.

# Known changes