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ProcsLink - IPC over Netlink Socket

Introduction

This module is used for interprocess communication (IPC) for processes in difference namespaces. I designed and wrote this module because existing IPC libraries are not suitable for inter-namespaces communication.

Currently, I have implemented a JSON-RPC interface.

Install from PyPI

sudo pip install procslink

API Usage Demo

Run JSON-RPC server

import os
from procslink import RPCPeer

class MyAPI(object):
    def hello(self, name):
        s = "Hello, %s!" % name
        print(s)
        return s

rpc_server = RPCPeer()
print("Server's nl_pid is %s." % rpc_server.nl_pid)
rpc_server.register_functions_in_object(MyAPI())
rpc_server.run_server_forever()

Run JSON-RPC client

from procslink import RPCPeer

# server_nl_pid is server's nl_pid
rpc_client = RPCPeer()
rpc_client.talk_to(server_nl_pid).hello("Rayson Zhu")

Parse bytes to message objects

# suppose data is a raw Netlink message bytes
netlink_message = NetlinkMessage.from_bytes(data)
procslink_message = ProcslinkMessage.from_bytes(netlink_message.payload)
jsonrpc_request = JSONRPCRequest.from_bytes(procslink_message.payload)

Convert message objects to raw bytes

jsonrpc_response = JSONRPCResponse(id=123, result=True)
procslink_header = ProcslinkMessageHeader(
    payload_type=ProcslinkMessageHeader.PAYLOAD_TYPE_JSONRPC2_RESPONSE)
procslink_message = ProcslinkMessage(procslink_header,
    jsonrpc_response.to_bytes()))
netlink_header = NetlinkMessageHeader(nlmsg_pid=sender_nl_pid)
netlink_message = NetlinkMessage(netlink_header,
    procslink_message.to_bytes())
data = netlink_message.to_bytes()

Design

Messages are delivered over Netlink(7). Before reading this document, you should read the above link first.

ProcsLink uses the following message format:

+-----------------------+
| nlmsghdr              |
+-----------------------+
| procslinkhdr          |
+-----------------------+
| JSON-RPC message      |
+-----------------------+

Where

  • nlmsghdr is the raw Netlink header.
  • procslinkhdr is our own defined header for extension (because we may run different protocolsother than JSON-RPC in the future),
  • JSON-RPC message is the JSON-RPC request/response body encoded in UTF-8. JSON-RPC 2.0 is used.

Following is the defination of struct procslinkhdr:

/* connectorhdr (8 bytes) */
struct procslinkhdr {
    uint16_t version; /* version number, default: 1 */
    uint16_t flag; /* reserved */
    uint32_t length; /* message length including this header */
    uint16_t payload_type; /* payload_type message type ID */
    uint16_t reserved; /* reserved */
    uint32_t seq; /* sequence number */
    uint64_t timestamp; /* when this message is sent */
};

Dependencies

Directory Structure

+ procslink
  - __init__.py
  - common.py
  - jsonrpc.py
  - netlink.py
  - procslink.py

Where

  • __init__.py defines the JSON-RPC server/client: RPCPeer.
  • common.py defines the base class for message headers and messages.
  • netlink.py defines NetlinkMessageHeader and NetlinkMessage, which are abstraction for Netlink header and whole netlink meesages.
  • procslink.py defines message data structures for the Procslink message layer.
  • jsonrpc.py defines models for JSON-RPC 2.0 request object, response object, and error object, etc.