rpcd (OpenWrt ubus RPC backend server)

The code is published under ISC and can be found via git at git://nbd.name/luci2/rpcd.git or via http at http://nbd.name/gitweb.cgi?p=luci2/rpcd.git;a=summary. It's included in OpenWrt since r37877.

plugin executables

It is possible to expose shell script functionality over ubus by using rpcd plugin executables functionality. Executables stored in /usr/libexec/rpcd/ directory will be runned by rpcd. Lets look at the following example:

$ cat << EOF > /usr/libexec/rpcd/foo
#!/bin/sh

case "$1" in
	list)
		echo '{ "bar": { "arg1": true, "arg2": 32, "arg3": "str" }, "toto": { } }'
	;;
	call)
		case "$2" in
			bar)
				# read the arguments
				read input;

				# optionally log the call
				logger -t "foo" "call" "$2" "$input"

				# return json object or an array
				echo '{ "hello": "world" }'
			;;
			toto)
				# return json object or an array
				echo '[ "item1", "item2", "item3" ]'
			;;
		esac
	;;
esac
EOF
$ chmod +x /usr/libexec/rpcd/foo

This will create new ubus functions which then can be used:

$ ubus list -v
...
'foo' @686f0592
	"bar":{"arg1":"Boolean","arg2":"Integer","arg3":"String"}
	"toto":{}
...
$ ubus call -S foo bar '{"arg1": true }'
{{"hello":"world"}}
$ ubus call -S foo toto
{["item1","item2","item3"]}

On startup rpcd will call all executables in /usr/libexec/rpcd/ with argv[1] set to "list". For a plugin, which responds with a valid list of methods and signatures, ubus method with appropriate arguments will be created. When a method provided by the plugin is about to be invoked, rpcd calls the binary with argv[1] set to "call" and argv[2] set to the invoked method name. The actual data is then sent by the ubus client via stdin.

The method signature is a simple object containing key:value pairs. The argument type is inferred from the value. If the value is a string (regardless of the contents) it is registered as string, if the value is a bool true or false, its registered as bool, if the value is an integer, it is registered as either int8, int16, int32 or int64 depending on the value ("foo": 16 will be INT16, "foo": 64 will be INT64, "foo": 8 will be INT8 and everything else will be INT32).

It is enough to issue '/etc/init.d/rpcd reload' to make it pick up new plugin executables, that way one does not lose active sessions.

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doc/techref/rpcd.txt · Last modified: 2014/06/04 10:33 by luka12345