Enable GVariant supprt?

[qingxiang-jia]

I am using the generated code for a method that expects a variant. It turns out, the exact signature is:

(sa{sv}ssssssssavav)

where the receiving side (IBus) expects at least one element in the last av, and it expects a specific format for that element:

(sa{sv}ssssssssusssssss)

Here is a more detailed description of the format in case my words are not descriptive. My implementation is here.

The problem is, the other side doesn't recognize it. But not all calls to IBus fails. This time I did read the book. I feel it's because IBus uses GVariant and zvariant by default doesn't use it. I went through code for zvariant and it seems I can enable this feature by

zbus = { version = "3.13.1", default-features = false, features = ["tokio", "gvariant"] }
zvariant = { version = "3.14.0", features = ["gvariant"] }

But given that IBus still doesn't recognize the payload, I think either I didn't enable GVariant correctly or my theory isn't correct.

[zeenix]

GVariant has nothing to do with Variant type. The types zbus::zvariant::{Value, OwnedValue} are what you're looking for.

GVariant is an incompatible format to dbus and none of the existing bus implementations support it so you can only use that in p2p connections.

[qingxiang-jia]

Maybe we are talking about two different things? I am asking this because the receiving side (IBus) that throws the error uses exactly GVariant to deserialize the message I send using zbus. Here is where that happens.

[zeenix]

Our book says:

Outside of D-Bus context, a modified form of this format, GVariant is very commonly used for efficient storage of arbitrary data and is also supported by this crate.

[qingxiang-jia]

Thanks for pointing this out. This is the part I read too. I checked the IBus code again. It is indeed using GLib and GVariant. I guess that's probably the reason it rejected my payload (since it's not using GVariant)? I am no where near the expertise on DBus than you do. But the working Go code uses godbus, and here is one thing the author mentions. My understanding is, godbus supports GVariant and uses it by default. This could be the reason that my Go code is working. Again, I am not an expert so it's just my guess.

[zeenix]

It is indeed using GLib and GVariant.

glib uses GVariant format but for dbus it does the conversion from/to dbus format for you. There is GVariant the format/protocol and then there is a Variant the type and glib combines it all through GVariant type.

Trust me, you DO NOT need GVariant (the format).

My understanding is, godbus supports GVariant and uses it by default.

That's impossible since the bus does not support the format.

---

We even provide macros for you to be easily able to convert your types to/from Value (which corresponds to the Variant D-Bus type, with signature v). I'd suggest reading the dbus spec instead of learning about D-Bus through code bases you're not familiar with.

[zeenix]

There is also glib reference manual:

GVariant is largely compatible with D-Bus. Almost all types of GVariant instances can be sent over D-Bus. See GVariantType for exceptions. (However, GVariant's serialisation format is not the same as the serialisation format of a D-Bus message body: use GDBusMessage, in the gio library, for those.)

[qingxiang-jia]

I see. Thanks for the answers. I will probably try dbus-monitor and see what's the difference between the payload send by zbus and the Go code.

Trust me, you DO NOT need GVariant (the format).

Yes. I do. I didn't know that glib does the conversion. Knowledge about these things seem to be pretty lacking.

I'd suggest reading the dbus spec instead of learning about D-Bus through code bases you're not familiar with.

Good point. Will do.