Making and parsing messages¶
The core of Jeepney is code to build, serialise and deserialise D-Bus messages.
Making messages¶
D-Bus has four message types. Three, method call, method return and error, are used in a request-reply pattern. The fourth, signal, is a broadcast message with no reply.
Method call messages are most conveniently made with a message generator class, which can be autogenerated. One layer down from this is
new_method_call()
, which takes aDBusAddress
object.Method return and error messages are made with
new_method_return()
andnew_error()
, passing the method call message which they are replying to.signal messages are made with
new_signal()
, which takes aDBusAddress
representing the sender.
All of these return a Message
object. Message.serialise()
converts it to bytes, but none of these core methods ever send a message.
See the integration layer for that.
Signatures¶
DBus is strongly typed, and every message has a signature describing the body
data. These are strings using characters such as i
for a signed 32-bit
integer. See the DBus specification
for the full list.
Jeepney does not try to guess or discover the signature when you build a message: your code must explicitly specify a signature for every message. However, Jeepney can help you write this code: see Generating D-Bus wrappers.
In most cases, DBus types have an obvious corresponding type in Python. However, a few types require further explanation:
DBus ARRAY are Python lists, except for arrays of DICT_ENTRY, which are dicts.
DBus STRUCT are Python tuples.
DBus VARIANT are 2-tuples
(signature, data)
. E.g. to put a string into a variant field, you would pass the data("s", "my string")
.Jeepney does not (yet) support sending or receiving file descriptors.