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rather than being a single large module. Refer to the individual module
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docstrings for details.
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The smart protocol provides a way to send a requests and corresponding
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responses to communicate with a remote bzr process.
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At the bottom level there is either a socket, pipes, or an HTTP
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request/response. We call this layer the *medium*. It is responsible for
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carrying bytes between a client and server. For sockets, we have the
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idea that you have multiple requests and get a read error because the other side
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did shutdown. For pipes we have read pipe which will have a zero read which
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marks end-of-file. For HTTP server environment there is no end-of-stream
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because each request coming into the server is independent.
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So we need a wrapper around pipes and sockets to seperate out requests from
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substrate and this will give us a single model which is consistent for HTTP,
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On top of the medium is the *protocol*. This is the layer that deserialises
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bytes into the structured data that requests and responses consist of.
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Version one of the protocol (for requests and responses) is described by::
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RESPONSE := MESSAGE_V1
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MESSAGE_V1 := ARGS BODY
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ARGS := ARG [MORE_ARGS] NEWLINE
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MORE_ARGS := SEP ARG [MORE_ARGS]
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BODY := LENGTH NEWLINE BODY_BYTES TRAILER
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LENGTH := decimal integer
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TRAILER := "done" NEWLINE
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That is, a tuple of arguments separated by Ctrl-A and terminated with a newline,
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followed by length prefixed body with a constant trailer. Note that although
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arguments are not 8-bit safe (they cannot include 0x01 or 0x0a bytes without
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breaking the protocol encoding), the body is.
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Version two of the request protocol is::
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REQUEST_V2 := "bzr request 2" NEWLINE MESSAGE_V1
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Version two of the response protocol is::
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RESPONSE_V2 := "bzr request 2" NEWLINE MESSAGE_V1
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Future versions should follow this structure, like version two does::
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FUTURE_MESSAGE := VERSION_STRING NEWLINE REST_OF_MESSAGE
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This is that clients and servers can read bytes up to the first newline byte to
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determine what version a message is.
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For compatibility will all versions (past and future) of bzr clients, servers
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that receive a request in an unknown protocol version should respond with a
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single-line error terminated with 0x0a (NEWLINE), rather than structured
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response prefixed with a version string.
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Request/Response processing
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---------------------------
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On top of the protocol is the logic for processing requests (on the server) or
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responses (on the client).
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MEDIUM (factory for protocol, reads bytes & pushes to protocol,
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uses protocol to detect end-of-request, sends written
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bytes to client) e.g. socket, pipe, HTTP request handler.
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PROTOCOL(serialization, deserialization) accepts bytes for one
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request, decodes according to internal state, pushes
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structured data to handler. accepts structured data from
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handler and encodes and writes to the medium. factory for
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HANDLER (domain logic) accepts structured data, operates state
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machine until the request can be satisfied,
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sends structured data to the protocol.
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Request handlers are registered in `bzrlib.smart.request`.
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CLIENT domain logic, accepts domain requests, generated structured
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data, reads structured data from responses and turns into
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domain data. Sends structured data to the protocol.
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Operates state machines until the request can be delivered
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(e.g. reading from a bundle generated in bzrlib to deliver a
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Possibly this should just be RemoteBzrDir, RemoteTransport,
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PROTOCOL (serialization, deserialization) accepts structured data for one
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request, encodes and writes to the medium. Reads bytes from the
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medium, decodes and allows the client to read structured data.
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MEDIUM (accepts bytes from the protocol & delivers to the remote server.
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Allows the potocol to read bytes e.g. socket, pipe, HTTP request.
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The domain logic is in `bzrlib.remote`: `RemoteBzrDir`, `RemoteBranch`, and so
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Server-side request handlers are registered in the `bzrlib.smart.request`
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The domain logic is in `bzrlib.remote`: `RemoteBzrDir`, `RemoteBranch`,
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There is also an plain file-level transport that calls remote methods to
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manipulate files on the server in `bzrlib.transport.remote`.
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Paths are passed across the network. The client needs to see a namespace that
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includes any repository that might need to be referenced, and the client needs
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to know about a root directory beyond which it cannot ascend.
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Servers run over ssh will typically want to be able to access any path the user
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can access. Public servers on the other hand (which might be over http, ssh
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or tcp) will typically want to restrict access to only a particular directory
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and its children, so will want to do a software virtual root at that level.
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In other words they'll want to rewrite incoming paths to be under that level
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(and prevent escaping using ../ tricks.)
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URLs that include ~ should probably be passed across to the server verbatim
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and the server can expand them. This will proably not be meaningful when
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limited to a directory?
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The protocol is described in doc/developers/network-protocol.txt.
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# TODO: _translate_error should be on the client, not the transport because
added
removed
bzrlib/smart/__init__.py
