fix(mint): return errors for non-200 responses

grpc/CHANGELOG.md

@@ -9,6 +9,7 @@
 
 ### Bug Fixes
 
+  * The Mint adapter now returns `{:error, %GRPC.RPCError{}}` instead of raising when a response's HTTP status is not 200, like the Gun adapter.
   * 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)

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

@@ -249,8 +249,18 @@ if Code.ensure_loaded?(Mint.HTTP) do
       state
     end
 
+    defp process_response({:status, request_ref, 200}, state) do
+      State.update_response_status(state, request_ref, 200)
+    end
+
     defp process_response({:status, request_ref, status}, state) do
-      State.update_response_status(state, request_ref, status)
+      state
+      |> State.update_response_status(request_ref, status)
+      |> consume_or_cancel_stream(
+        request_ref,
+        :error,
+        GRPC.RPCError.exception(GRPC.Status.internal(), "status got is #{status} instead of 200")
+      )
     end
 
     defp process_response({:headers, request_ref, headers}, state) do

grpc/test/grpc/adapters/mint/connection_process_test.exs

@@ -625,6 +625,34 @@ defmodule GRPC.Client.Adapters.Mint.ConnectionProcessTest do
     end
   end
 
+  describe "handle_info - non-200 responses" do
+    setup :quiet_connection
+    setup :valid_stream_request
+    setup :valid_stream_response
+
+    test "reports the HTTP status to the stream response process",
+         %{stream_response_pid: response_pid, state: state} do
+      # A proxy answering with a plain HTTP error: a HEADERS frame whose only
+      # header is `:status` (static table index 8) with the value "502".
+      stream_id = state.conn.next_stream_id - 2
+      headers_frame = <<5::24, 0x01, 0x04, stream_id::32, 0x08, 0x03, "502">>
+      message = {:tcp, state.conn.socket, headers_frame}
+
+      assert {:noreply, new_state} = ConnectionProcess.handle_info(message, state)
+
+      # the connection is untouched, only this request failed
+      assert Mint.HTTP.open?(new_state.conn)
+
+      # the caller-facing stream response process got the status as an error
+      response_state = :sys.get_state(response_pid)
+
+      assert [
+               {:error, %GRPC.RPCError{status: 13, message: "status got is 502 instead of 200"}}
+               | _headers
+             ] = :queue.to_list(response_state.responses)
+    end
+  end
+
   describe "retry_timeout/1" do
     test "returns exponentially increasing timeouts" do
       t1 = ConnectionProcess.retry_timeout(1)