Convert all of the launcher crates to use prost.

[raskchanky]

This is the last of the crates in the habitat repo to be converted from
protobuf to prost. Note that unlike the supervisor and
butterfly, I decided against including the generated code in the repo.

It's also worth noting that unlike our approach with the protobuf crate,
we're not actually using the structs generated by prost except at the
edges. Prost rightfully uses Options to represent optional fields and
since all of our protobuf messages have all optional fields, the
ergonomics of using Prost generated structs is sub-optimal. For this
reason, we have our own set of internal structs that mirror the Prost
ones that we use in the launcher and launcher-client crates, and
launcher-protocol is the only crate that knows about the Prost generated
structs.

Closes #6073

Signed-off-by: Josh Black raskchanky@gmail.com

[thesentinels]

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[baumanj]

Looks good to me, but if you're interested I think we can make it a bit simpler and avoid the need for macros

[baumanj]

Here's an alternate approach that doesn't need macros:

We can consolidate the MessageStatic, and FromProto traits into LauncherMessage, and by adding an associated type to hold the Prost-generated struct, we get:

pub trait LauncherMessage
where
    Self: Clone + fmt::Debug,
{
    type Generated: prost::Message + Default + From<Self>;
    const MESSAGE_ID: &'static str;

    fn from_proto(value: Self::Generated) -> Result<Self>;

    fn from_bytes(bytes: &[u8]) -> Result<Self> {
        let decoded = Self::Generated::decode(bytes)?;
        Self::from_proto(decoded)
    }

    fn to_bytes(&self) -> Result<Vec<u8>> {
        let envelope = Self::Generated::from(self.clone());
        let mut buf = bytes::BytesMut::with_capacity(envelope.encoded_len());
        envelope.encode(&mut buf)?;
        Ok(buf.to_vec())
    }
}

The impl changes follow from that, but here's a full diff if you want to go that way.

[raskchanky]

This is exactly the solution I was trying to find from the beginning. Thank you so much for this.

[christophermaier]

Looks good... I had a couple suggestions, but I'm eager to extend this pattern to our other protocol crates.

[christophermaier]

It's minor, but I've found it useful to have things under crate:: to actually be defined in the current crate. We end up doing this because we've got this over in lib.rs

habitat/components/launcher-client/src/lib.rs

Lines 15 to 16 in 6784490

	use habitat_core as core;
	use habitat_launcher_protocol as protocol;

Thus, core and protocol are actually symbols "in our crate".

For something like this, I like to do:

use crate::error::{Error, Result};
use habitat_core::os::process::Pid;
use habitat_launcher_protocol::{self as protocol, Error as ProtocolError};

(and often, that self as protocol can be refactored away with a bit more typing.

[raskchanky]

Gotcha, will update

[christophermaier]

You could streamline these a bit with this:

msg.svc_user = user.map(|u| u.to_string());
msg.svc_group = group.map(|g| g.to_string());
msg.svc_user_id = user_id;
msg.svc_group_id = group_id;

msg.svc_password = password.map(|p| p.to_string());

[raskchanky]

That's awesome, will do.

[christophermaier]

@raskchanky Actually, if you wanna get really wild, try this:

let msg = protocol::Spawn {
    binary: bin.as_ref().to_path_buf().to_string_lossy().into_owned(),
    svc_user: user.map(|u| u.to_string()),
    svc_group: group.map(|g| g.to_string()),
    svc_user_id: user_id,
    svc_group_id: group_id,
    svc_password: password.map(|p| p.to_string()),
    env: env,
    id: id.to_string(),
    ..Default::default()
};

[raskchanky]

😲

[christophermaier]

This pattern could be used on all these messages, actually. Kinda nice to reduce the mutability of everything to the bare minimum.

[christophermaier]

@raskchanky Looks great! Once the release is out, let's merge this!

Appveyor timed out (sigh)... so I restarted it.