plugin serverless: first draft, peer discovery on LAN:

Implement peer discovery on LAN using mDNS (via `zeroconf`).
A Peer ID is generated (via `libP2P`) per instance, and announced on backend startup.
Meanwhile, other peers are discovered on LAN. A signal is send on peer found and another
on peer lost.

There a bridge methods to find already discovered peers, and to get infos on serverless
(our own ID, adverised service name, and number of peers found).

`Zeroconf` runs in background in its own thread.

rel 479

libervia/backend/plugins/plugin_misc_serverless/models.py

@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+
+# Libervia plugin for Serverless XMPP
+# Copyright (C) 2009-2026 Jérôme Poisson (goffi@goffi.org)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from collections.abc import Iterator
+from typing import TypedDict
+
+from pydantic import BaseModel, Field, RootModel
+
+
+class DiscoverExtra(BaseModel):
+    # XXX: only a placeholder for now
+    pass
+
+
+class DiscoveredPeerInfo(TypedDict):
+    """Info stored for a discovered peer.
+
+    @ivar addrs: list of libp2p multiaddr strings, e.g. "/ip4/192.168.1.10/tcp/5299".
+        See https://github.com/multiformats/multiaddr
+    """
+
+    name: str
+    device_id: str
+    addrs: list[str]
+    metadata: dict[str, str]
+
+
+class ServerlessInfo(BaseModel):
+    """Serverless device information."""
+
+    device_id: str = Field(description="ID of the device")
+    service_name: str = Field(description="mDNS service name")
+    peer_count: int = Field(description="Number of discovered peers")
+
+
+class Node(BaseModel):
+    """Discovered peer node.
+
+    @param device_id: Identifier for the discovered device.
+    @param name: Human-readable name of the peer.
+    @param addrs: List of addresses to reach the peer.
+    @param metadata: metadata extracted from the discovery protocol.
+    """
+
+    device_id: str = Field(description="Identifier for the discovered device")
+    name: str = Field(description="Human-readable name of the peer")
+    addrs: list[str] = Field(
+        description="List of addresses (multiaddr format), see https://github.com/multiformats/multiaddr"
+    )
+    metadata: dict[str, str] = Field(
+        default_factory=dict, description="Key-value metadata from the discovery protocol"
+    )
+
+
+class DiscoverNodes(RootModel):
+    """List of discovered nodes."""
+
+    root: list[Node]
+
+    def __iter__(self) -> Iterator[Node]:  # type: ignore
+        return iter(self.root)
+
+    def __len__(self) -> int:
+        return len(self.root)
+
+    def __getitem__(self, index: int) -> Node:
+        return self.root[index]