test/bbr: add isolated integration test harness

Introduces the `BBRHarness` struct to manage isolated BBR server
instances, laying the groundwork for parallel integration testing.

Features:
- **Isolation:** Spawns a dedicated server per test on a random loopback
  port.
- **Helpers:** Provides BBR-specific assertion helpers (e.g.,
  `ExpectBBRHeader`) to reduce protobuf boilerplate.
- **Safety:** Ensures proper server shutdown and resource cleanup via
  `t.Cleanup`.

Author: LukeAVanDrie

test/integration/bbr/harness_test.go

@@ -0,0 +1,103 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package bbr
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"testing"
+
+	extProcPb "github.com/envoyproxy/go-control-plane/envoy/service/ext_proc/v3"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+
+	runserver "sigs.k8s.io/gateway-api-inference-extension/pkg/bbr/server"
+	logutil "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/util/logging"
+	"sigs.k8s.io/gateway-api-inference-extension/test/integration"
+)
+
+var logger = logutil.NewTestLogger().V(logutil.VERBOSE)
+
+// BBRHarness encapsulates the environment for a single isolated BBR test run.
+type BBRHarness struct {
+	t      *testing.T
+	ctx    context.Context
+	Client extProcPb.ExternalProcessor_ProcessClient
+
+	// Internal handles for cleanup
+	server   *runserver.ExtProcServerRunner
+	grpcConn *grpc.ClientConn
+}
+
+// NewBBRHarness boots up an isolated BBR server on a random port.
+// streaming: determines if the BBR server runs in streaming mode or unary/buffered mode.
+func NewBBRHarness(t *testing.T, ctx context.Context, streaming bool) *BBRHarness {
+	t.Helper()
+
+	// 1. Allocate Free Port
+	tcpAddr, err := integration.GetFreePort()
+	require.NoError(t, err, "failed to acquire free port for BBR server")
+	port := tcpAddr.Port
+
+	// 2. Configure BBR Server
+	// BBR is simpler than EPP; it doesn't need a K8s Manager.
+	runner := runserver.NewDefaultExtProcServerRunner(port, false)
+	runner.SecureServing = false
+	runner.Streaming = streaming
+
+	// 3. Start Server in Background
+	serverCtx, serverCancel := context.WithCancel(ctx)
+	go func() {
+		logger.Info("Starting BBR server", "port", port, "streaming", streaming)
+		if err := runner.AsRunnable(logger.WithName("bbr-server")).Start(serverCtx); err != nil {
+			// Context cancellation is expected during teardown.
+			if !strings.Contains(err.Error(), "context canceled") {
+				logger.Error(err, "BBR server stopped unexpectedly")
+			}
+		}
+	}()
+
+	// 4. Connect Client
+	// Blocking dial ensures the server is reachable before the test logic begins.
+	addr := fmt.Sprintf("127.0.0.1:%d", port)
+	conn, err := grpc.NewClient(addr, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	require.NoError(t, err, "failed to create grpc connection to BBR server")
+
+	extProcClient, err := extProcPb.NewExternalProcessorClient(conn).Process(ctx)
+	require.NoError(t, err, "failed to initialize ext_proc stream client")
+
+	h := &BBRHarness{
+		t:        t,
+		ctx:      ctx,
+		Client:   extProcClient,
+		server:   runner,
+		grpcConn: conn,
+	}
+
+	// 5. Register Cleanup
+	t.Cleanup(func() {
+		logger.Info("Tearing down BBR server", "port", port)
+		serverCancel()
+		if err := h.grpcConn.Close(); err != nil {
+			t.Logf("Warning: failed to close grpc connection: %v", err)
+		}
+	})
+
+	return h
+}

test/integration/bbr/util_test.go

@@ -0,0 +1,121 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package bbr
+
+import (
+	"encoding/json"
+
+	envoyCorev3 "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
+	extProcPb "github.com/envoyproxy/go-control-plane/envoy/service/ext_proc/v3"
+)
+
+// --- Response Expectations (Streaming) ---
+
+// ExpectBBRHeader asserts that BBR set the specific model header and cleared the route cache.
+func ExpectBBRHeader(modelName string) *extProcPb.ProcessingResponse {
+	return &extProcPb.ProcessingResponse{
+		Response: &extProcPb.ProcessingResponse_RequestHeaders{
+			RequestHeaders: &extProcPb.HeadersResponse{
+				Response: &extProcPb.CommonResponse{
+					ClearRouteCache: true,
+					HeaderMutation: &extProcPb.HeaderMutation{
+						SetHeaders: []*envoyCorev3.HeaderValueOption{
+							{
+								Header: &envoyCorev3.HeaderValue{
+									Key:      "X-Gateway-Model-Name",
+									RawValue: []byte(modelName),
+								},
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+}
+
+// ExpectBBRBodyPassThrough asserts that BBR reconstructs and passes the body through.
+// BBR buffers the body to inspect it, then sends it downstream as a single chunk (usually).
+func ExpectBBRBodyPassThrough(prompt, model string) *extProcPb.ProcessingResponse {
+	j := map[string]any{
+		"max_tokens": 100, "prompt": prompt, "temperature": 0,
+	}
+	if model != "" {
+		j["model"] = model
+	}
+	b, _ := json.Marshal(j)
+
+	return &extProcPb.ProcessingResponse{
+		Response: &extProcPb.ProcessingResponse_RequestBody{
+			RequestBody: &extProcPb.BodyResponse{
+				Response: &extProcPb.CommonResponse{
+					BodyMutation: &extProcPb.BodyMutation{
+						Mutation: &extProcPb.BodyMutation_StreamedResponse{
+							StreamedResponse: &extProcPb.StreamedBodyResponse{
+								Body:        b,
+								EndOfStream: true,
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+}
+
+// ExpectBBRNoOpHeader asserts that BBR did nothing to the headers (e.g., when no model is found).
+func ExpectBBRNoOpHeader() *extProcPb.ProcessingResponse {
+	return &extProcPb.ProcessingResponse{
+		Response: &extProcPb.ProcessingResponse_RequestHeaders{
+			RequestHeaders: &extProcPb.HeadersResponse{},
+		},
+	}
+}
+
+// --- Response Expectations (Unary) ---
+
+// ExpectBBRUnaryResponse creates expected response for unary tests where the body is mutated directly.
+func ExpectBBRUnaryResponse(modelName string) *extProcPb.ProcessingResponse {
+	resp := &extProcPb.ProcessingResponse{}
+
+	// If modelName is present, we expect header mutations.
+	if modelName != "" {
+		resp.Response = &extProcPb.ProcessingResponse_RequestBody{
+			RequestBody: &extProcPb.BodyResponse{
+				Response: &extProcPb.CommonResponse{
+					ClearRouteCache: true,
+					HeaderMutation: &extProcPb.HeaderMutation{
+						SetHeaders: []*envoyCorev3.HeaderValueOption{
+							{
+								Header: &envoyCorev3.HeaderValue{
+									Key:      "X-Gateway-Model-Name",
+									RawValue: []byte(modelName),
+								},
+							},
+						},
+					},
+				},
+			},
+		}
+	} else {
+		// Otherwise, expect a No-Op on the body.
+		resp.Response = &extProcPb.ProcessingResponse_RequestBody{
+			RequestBody: &extProcPb.BodyResponse{},
+		}
+	}
+	return resp
+}