rpcd package里面包含了多个模块，session，ubus插件等，是opewnrt的基础组件，只是很少关注到。

1、session会话机制

rpcd工具包里面提供了标准的session生成、更新、老化机制，可以供其他模式使用，在openwrt上面就是uhttpd会使用到。

1.1 查看命令支持：

root@openwrt:/# ubus -v list session
'session' @a0264f96
        "create":{"timeout":"Integer"}
        "list":{"ubus_rpc_session":"String"}
        "grant":{"ubus_rpc_session":"String","scope":"String","objects":"Array"}
        "revoke":{"ubus_rpc_session":"String","scope":"String","objects":"Array"}
        "access":{"ubus_rpc_session":"String","scope":"String","object":"String","function":"String"}
        "set":{"ubus_rpc_session":"String","values":"Table"}
        "get":{"ubus_rpc_session":"String","keys":"Array"}
        "unset":{"ubus_rpc_session":"String","keys":"Array"}
        "destroy":{"ubus_rpc_session":"String"}
        "login":{"username":"String","password":"String","timeout":"Integer"}

1.2 创建session

ubus call session create '{"timeout": 3600}'
{
        "ubus_rpc_session": "8c1af812b4b148fcbb92434c74cf61c1",
        "timeout": 3600,
        "expires": 3600,
        "acls": {

        },
        "data": {

        }
}

另外一种创建session的方法，通过账号密码登录生成，这种就是我们web经常用的，用户输入账号密码，验证成功则生成session。

root@zihome:~# ubus call session login '{"username": "root","password":"admin"}'
{
        "ubus_rpc_session": "f6267d1a1614debca586cb96f0eb3586",
        "timeout": 300,
        "expires": 300,
        "acls": {
                "access-group": {
                        "unauthenticated": [
                                "read"
                        ]
                },
                "ubus": {
                        "session": [
                                "access",
                                "login"
                        ]
                }
        },
        "data": {
                "username": "root"
        }
}

1.3 列出所有session信息

可以看到剩余时间expires会倒计时减少，还有这个session的acl、data信息。

root@openwrt:~# ubus call session list
{
        "ubus_rpc_session": "693837073d22c086964053a64d38595e",
        "timeout": 300,
        "expires": 119,
        "acls": {
                "access-group": {
                        "unauthenticated": [
                                "read"
                        ]
                },
                "ubus": {
                        "session": [
                                "access",
                                "login"
                        ]
                }
        },
        "data": {
                "username": "root"
        }
}

1.4 获取指定session是否存在

在uhttpd应用中，需要判断这个session是否还在有效期内。

• 如果不再有效期内，web页面就要回返到登录页面；
• 如果在有效期内，那就更新expires时间到timeout时间，重新开始计时。

使用get接口获取，如果session不在有效期就返回失败；在有效期就返回data，同时更新时间戳。

root@openwrt:~# ubus call session get '{"ubus_rpc_session": "10b583862c4ef8df9242eea92dbed255"}'
Command failed: Not found
root@openwrt:~# ubus call session get '{"ubus_rpc_session": "b57ced1afb3d0bc01848fc7b0c8ffcf1"}'
{
        "values": {
                "username": "root"
        }
}

当然使用list也可以，也会刷新时间戳。

root@openwrt:~# ubus call session list '{"ubus_rpc_session": "b57ced1afb3d0bc01848fc7b0c8ffcf1"}'
{
        "ubus_rpc_session": "b57ced1afb3d0bc01848fc7b0c8ffcf1",
        "timeout": 300,
        "expires": 300,
        "acls": {
                "access-group": {
                        "unauthenticated": [
                                "read"
                        ]
                },
                "ubus": {
                        "session": [
                                "access",
                                "login"
                        ]
                }
        },
        "data": {
                "username": "root"
        }
}

1.5 session清除

主动清除这个session，类似web页面的登出。

root@openwrt:~# ubus call session destroy '{"ubus_rpc_session": "e35cd677ad7c9cb584d2915861fcac88"}'

https://openwrt.org/docs/guide-developer/ubus/session

2、ubus可执行文件功能

这个是openwrt官网对rpcd的介绍

https://oldwiki.archive.openwrt.org/doc/techref/rpcd

3、ubus_over_http功能

how to use ubus over http in openwrt 12.09
：https://www.cnblogs.com/nicephil/p/6768381.html#e4bdbfe794a8e696b9e6b395_2

openwrt-rpcd服务ACL配置错误风险分析：https://www.cnblogs.com/hac425/p/9416854.html

cat /etc/config/rpcd 
config login
        option username 'root'
        option password '$p$root'
        list read '*'
        list write '*'

http://10.1.2.203/ubus

{
    "jsonrpc":"2.0",
    "id":1,
    "method":"call",
    "params":[
        "00000000000000000000000000000000",
        "session",
        "login",
        {
            "username":"root",
            "password":"admin"
        }
    ]
}

{
    "jsonrpc":"2.0",
    "id":1,
    "method":"call",
    "params":[
        "bfe0946e9fdaed2c7900e71ebb570f83",
        "file",
        "read",
        {
            "path":"/etc/passwd"
        }
    ]
}

https://openwrt.org/docs/techref/ubus#access_to_ubus_over_http

{ "jsonrpc": "2.0",
  "id": <unique-id-to-identify-request>, 
  "method": "call",
  "params": [
             <ubus_rpc_session>, <ubus_object>, <ubus_method>, 
             { <ubus_arguments> }
            ]
}

{ "jsonrpc": "2.0", "id": 1, "method": "call", "params": [ "c1ed6c7b025d0caca723a816fa61b668", "file", "read", { "path": "/etc/board.json" } ] }