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89 lines
3.1 KiB
Plaintext
89 lines
3.1 KiB
Plaintext
This is kind of informal and may be wrong, but it helped me. It's
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basically a summary of clientserver.c and authenticate.c.
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-- Martin Pool <mbp@samba.org>
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This is the protocol used for rsync --daemon; i.e. connections to port
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873 rather than invocations over a remote shell.
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When the server accepts a connection, it prints a greeting
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@RSYNCD: <version>.<subprotocol>
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where <version> is the numeric version (see PROTOCOL_VERSION in rsync.h)
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'.' is a literal period, and <subprotocol> is the numeric subprotocol
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version (see SUBPROTOCOL_VERSION -- it will be 0 for final releases).
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Protocols prior to 30 only output <version> alone. The daemon expects
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to see a similar greeting back from the client. For protocols prior to
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30, an absent ".<subprotocol>" value is assumed to be 0. For protocol
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30, an absent value is a fatal error. The daemon then follows this line
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with a free-format text message-of-the-day (if any is defined).
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The server is now in the connected state. The client can either send
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the command
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#list
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to get a listing of modules, or the name of a module. After this, the
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connection is now bound to a particular module. Access per host for
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this module is now checked, as is per-module connection limits.
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If authentication is required to use this module, the server will say
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@RSYNCD: AUTHREQD <challenge>
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where <challenge> is a random string of base64 characters. The client
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must respond with
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<user> <response>
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where <user> is the username they claim to be, and <response> is the
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base64 form of the MD4 hash of challenge+password.
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At this point the server applies all remaining constraints before
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handing control to the client, including switching uid/gid, setting up
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include and exclude lists, moving to the root of the module, and doing
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chroot.
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If the login is acceptable, then the server will respond with
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@RSYNCD: OK
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The client now writes some rsync options, as if it were remotely
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executing the command. The server parses these arguments as if it had
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just been invoked with them, but they're added to the existing state.
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So if the client specifies a list of files to be included or excluded,
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they'll defer to existing limits specified in the server
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configuration.
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At this point the client and server both switch to using a
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multiplexing layer across the socket. The main point of this is to
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allow the server to asynchronously pass errors back, while still
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allowing streamed and pipelined data.
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Unfortunately, the multiplex protocol is not used at every stage. We
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start up in plain socket mode and then change over by calling
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io_start_buffering. Of course both the client and the server have to
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do this at the same point.
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The server then talks to the client as normal across the socket,
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passing checksums, file lists and so on. For documentation of that,
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stay tuned (or write it yourself!).
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------------
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Protocol version changes
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30 (2007-10-04, 3.0.0pre1)
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The use of a ".<subprotocol>" number was added to
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@RSYNCD: <version>.<subprotocol>
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25 (2001-08-20, 2.4.7pre2)
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Send an explicit "@RSYNC EXIT" command at the end of the
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module listing. We never intentionally end the transmission
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by just closing the socket anymore.
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