fix(gun): scope named connection processes to the local node

grpc/CHANGELOG.md

@@ -5,6 +5,11 @@
 ### Behavior Changes
 
   * The Mint adapter now enforces the requested `:timeout`/`:deadline` on unary receives. A unary call that never receives a response fails with `DEADLINE_EXCEEDED` after the documented 10s default instead of blocking indefinitely, and an explicit `:deadline` now takes precedence over `:timeout`.
+
+### Bug Fixes
+
+  * The Gun adapter no longer shares a named channel's connection process across Erlang nodes. It was registered in `:global`, so a node connecting with a `:name` already used on another node adopted the remote connection process; `connect/2` returned `{:ok, channel}`, but every RPC on it then raised `ArgumentError` because `GRPC.Stub.call/5` calls `Process.alive?/1` on the connection pid and that raises for remote pids. Connection processes are now registered in the node-local `GRPC.Client.Registry`, so reuse is per node.
+
 ## v1.0.4 (2026-0-15)
 
 ### Bug Fixes

grpc/lib/grpc/client/adapters/gun/connection_process.ex

@@ -13,6 +13,9 @@ defmodule GRPC.Client.Adapters.Gun.ConnectionProcess do
   Request-specific Gun messages are routed to per-stream response processes, so
   this process only needs to manage connection-level lifecycle and stream
   bookkeeping.
+
+  Named channels are registered in the node-local `GRPC.Client.Registry` under
+  `{ref, host, port}`, so a connection is reused by every caller on the node.
   """
 
   use GenServer
@@ -177,7 +180,7 @@ defmodule GRPC.Client.Adapters.Gun.ConnectionProcess do
   end
 
   defp via(channel) do
-    {:global, {__MODULE__, owner_key(channel)}}
+    {:via, Registry, {GRPC.Client.Registry, {__MODULE__, owner_key(channel)}}}
   end
 
   defp start_response_process do

grpc/test/grpc/adapters/gun_test.exs

@@ -2,6 +2,7 @@ defmodule GRPC.Client.Adapters.GunTest do
   use GRPC.Client.DataCase, async: true
 
   alias GRPC.Client.Adapters.Gun
+  alias GRPC.Client.Adapters.Gun.ConnectionProcess
 
   defmodule Endpoint do
     use GRPC.Endpoint
@@ -97,6 +98,46 @@ defmodule GRPC.Client.Adapters.GunTest do
                  ]
                )
     end
+
+    test "reuses the connection process for a named channel", %{
+      port: port,
+      credential: credential
+    } do
+      channel =
+        build(:channel, port: port, host: "localhost", cred: credential, ref: make_ref())
+
+      assert {:ok, %{adapter_payload: %{conn_pid: conn_pid}} = connected} =
+               Gun.connect(channel, [])
+
+      on_exit(fn -> Gun.disconnect(connected) end)
+
+      assert {:ok, %{adapter_payload: %{conn_pid: ^conn_pid}}} = Gun.connect(channel, [])
+
+      assert [{^conn_pid, _}] =
+               Registry.lookup(
+                 GRPC.Client.Registry,
+                 {ConnectionProcess, {channel.ref, channel.host, channel.port}}
+               )
+    end
+
+    test "does not reuse the connection process for an unnamed channel", %{
+      port: port,
+      credential: credential
+    } do
+      channel = build(:channel, port: port, host: "localhost", cred: credential)
+
+      assert {:ok, %{adapter_payload: %{conn_pid: first_pid}} = first} = Gun.connect(channel, [])
+
+      assert {:ok, %{adapter_payload: %{conn_pid: second_pid}} = second} =
+               Gun.connect(channel, [])
+
+      on_exit(fn ->
+        Gun.disconnect(first)
+        Gun.disconnect(second)
+      end)
+
+      refute first_pid == second_pid
+    end
   end
 
   describe "disconnect/1" do

grpc/test/grpc/client/connection_test.exs

@@ -378,11 +378,28 @@ defmodule GRPC.Client.ConnectionTest do
       target = "ipv4:127.0.0.1:#{port}"
       ref = :shared_channel
 
-      assert {:ok, %Channel{ref: ^ref}} =
+      assert {:ok, %Channel{ref: ^ref} = channel1} =
                @peer.call(peer1, Connection, :connect, [target, [name: ref]])
 
-      assert {:ok, %Channel{ref: ^ref}} =
+      assert {:ok, %Channel{ref: ^ref} = channel2} =
                @peer.call(peer2, Connection, :connect, [target, [name: ref]])
+
+      # Each node must own its own adapter connection. Adopting another node's
+      # connection process leaves the channel unusable: `GRPC.Stub.call/5`
+      # checks `Process.alive?(conn_pid)` on every RPC, and `Process.alive?/1`
+      # raises ArgumentError on a remote pid.
+      %{adapter_payload: %{conn_pid: conn_pid1}} = channel1
+      %{adapter_payload: %{conn_pid: conn_pid2}} = channel2
+
+      assert node(conn_pid1) == node1
+      assert node(conn_pid2) == node2
+
+      point = %Routeguide.Point{latitude: 409_146_138, longitude: -746_188_906}
+
+      for {peer, channel} <- [{peer1, channel1}, {peer2, channel2}] do
+        assert {:ok, %Routeguide.Feature{}} =
+                 @peer.call(peer, Routeguide.RouteGuide.Stub, :get_feature, [channel, point])
+      end
     end
   end