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- ZEO Network Protocol (sans authentication)
- ==========================================
-
- This document describes the ZEO network protocol. It assumes that the
- optional authentication protocol isn't used. At the lowest
- level, the protocol consists of sized messages. All communication
- between the client and server consists of sized messages. A sized
- message consists of a 4-byte unsigned big-endian content length,
- followed by the content. There are two subprotocols, for protocol
- negotiation, and for normal operation. The normal operation protocol
- is a basic RPC protocol.
-
- In the protocol negotiation phase, the server sends a protocol
- identifier to the client. The client chooses a protocol to use to the
- server. The client or the server can fail if it doesn't like the
- protocol string sent by the other party. After sending their protocol
- strings, the client and server switch to RPC mode.
-
- The RPC protocol uses messages that are pickled tuples consisting of:
-
- message_id
- The message id is used to match replies with requests, allowing
- multiple outstanding synchronous requests.
-
- async_flag
- An integer 0 for a regular (2-way) request and 1 for a one-way
- request. Two-way requests have a reply. One way requests don't.
- ZRS tries to use as many one-way requests as possible to avoid
- network round trips.
-
- name
- The name of a method to call. If this is the special string
- ".reply", then the message is interpreted as a return from a
- synchronous call.
-
- args
- A tuple of positional arguments or returned values.
-
- After making a connection and negotiating the protocol, the following
- interactions occur:
-
- - The client requests the authentication protocol by calling
- getAuthProtocol. For this discussion, we'll assume the server
- returns None. Note that if the server doesn't require
- authentication, this step is optional.
-
- - The client calls register passing a storage identifier and a
- read-only flag. The server doesn't return a value, but it may raise
- an exception either if the storage doesn't exist, or if the
- storage is readonly and the read-only flag passed by the client is
- false.
-
- At this point, the client and server send each other messages as
- needed. The client may make regular or one-way calls to the
- server. The server sends replies and one-way calls to the client.
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