test: decouple run lifecycle tests from extproc internals (envoyproxy#1137)

**Description**

This improves the `aigw run` lifecycle test to not rely on
implementation details of how extproc is executed.
The previous test relied on how extproc uses and binds the UDS, which
couples the test to the extproc internals, making it error-prone and
less maintainable.

This PR refactors the code so that the run tests can verify the
lifecycle without relying on extproc internal details.

**Related Issues/PRs (if applicable)**

Related PR: envoyproxy#1134

**Special notes for reviewers (if applicable)**

N/A

Signed-off-by: Ignasi Barrera <[email protected]>

Author: nacx

cmd/aigw/main.go

@@ -15,6 +15,7 @@ import (
 	"github.com/alecthomas/kong"
 	ctrl "sigs.k8s.io/controller-runtime"
 
+	"github.com/envoyproxy/ai-gateway/cmd/extproc/mainlib"
 	"github.com/envoyproxy/ai-gateway/internal/version"
 )
 
@@ -84,7 +85,7 @@ func doMain(ctx context.Context, stdout, stderr io.Writer, args []string, exitFn
 			log.Fatalf("Error translating: %v", err)
 		}
 	case "run", "run <path>":
-		err = rf(ctx, c.Run, runOpts{}, stdout, stderr)
+		err = rf(ctx, c.Run, runOpts{extProcLauncher: mainlib.Main}, stdout, stderr)
 		if err != nil {
 			log.Fatalf("Error running: %v", err)
 		}

cmd/aigw/run.go

@@ -29,7 +29,6 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/client"
 	"sigs.k8s.io/yaml"
 
-	"github.com/envoyproxy/ai-gateway/cmd/extproc/mainlib"
 	"github.com/envoyproxy/ai-gateway/filterapi"
 	"github.com/envoyproxy/ai-gateway/internal/controller"
 	"github.com/envoyproxy/ai-gateway/internal/extensionserver"
@@ -69,15 +68,17 @@ type runCmdContext struct {
 	tmpdir string
 	// udsPath is the path to the UDS socket used by the AI Gateway extproc.
 	udsPath string
+	// extProcLauncher is the function used to launch the external processor.
+	extProcLauncher func(ctx context.Context, args []string, w io.Writer) error
 	// fakeClientSet is the fake client set for the k8s resources. The objects are written to this client set and updated
 	// during the translation.
 	fakeClientSet *fake.Clientset
 }
 
 // runOpts are the options for the run command.
 type runOpts struct {
-	// udsPath is the path to the UDS socket used by the AI Gateway extproc.
-	udsPath string
+	// extProcLauncher is the function used to launch the external processor.
+	extProcLauncher func(ctx context.Context, args []string, w io.Writer) error
 }
 
 // run starts the AI Gateway locally for a given configuration.
@@ -134,15 +135,19 @@ func run(ctx context.Context, c cmdRun, o runOpts, stdout, stderr io.Writer) err
 	// Write the Envoy Gateway resources into a file under resourcesTmpdir.
 	resourceYamlPath := filepath.Join(resourcesTmpdir, "config.yaml")
 	stderrLogger.Info("Creating Envoy Gateway resource file", "path", resourceYamlPath)
-	udsPath := o.udsPath
-	if udsPath == "" {
-		udsPath = filepath.Join(tmpdir, "uds.sock")
-		_ = os.Remove(udsPath)
-	}
+	udsPath := filepath.Join(tmpdir, "uds.sock")
+	_ = os.Remove(udsPath)
 
 	// Do the translation of the given AI Gateway resources Yaml into Envoy Gateway resources and write them to the file.
 	resourcesBuf := &bytes.Buffer{}
-	runCtx := &runCmdContext{envoyGatewayResourcesOut: resourcesBuf, stderrLogger: stderrLogger, udsPath: udsPath, tmpdir: tmpdir, isDebug: c.Debug}
+	runCtx := &runCmdContext{
+		envoyGatewayResourcesOut: resourcesBuf,
+		stderrLogger:             stderrLogger,
+		udsPath:                  udsPath,
+		extProcLauncher:          o.extProcLauncher,
+		tmpdir:                   tmpdir,
+		isDebug:                  c.Debug,
+	}
 	aiGatewayResourcesYaml, err := readConfig(c.Path)
 	if err != nil {
 		return err
@@ -326,7 +331,7 @@ func (runCtx *runCmdContext) mustStartExtProc(
 
 	done := make(chan error)
 	go func() {
-		if err := mainlib.Main(ctx, args, os.Stderr); err != nil {
+		if err := runCtx.extProcLauncher(ctx, args, os.Stderr); err != nil {
 			runCtx.stderrLogger.Error("Failed to run external processor", "error", err)
 			done <- fmt.Errorf("%w: %w", errExtProcRun, err)
 		}

cmd/aigw/run_test.go

@@ -8,6 +8,7 @@ package main
 import (
 	"bytes"
 	"context"
+	"errors"
 	"io"
 	"log/slog"
 	"net/http"
@@ -21,6 +22,7 @@ import (
 	"github.com/openai/openai-go/option"
 	"github.com/stretchr/testify/require"
 
+	"github.com/envoyproxy/ai-gateway/cmd/extproc/mainlib"
 	"github.com/envoyproxy/ai-gateway/filterapi"
 	internaltesting "github.com/envoyproxy/ai-gateway/internal/testing"
 )
@@ -47,7 +49,8 @@ func TestRun(t *testing.T) {
 	defer cancel()
 	done := make(chan struct{})
 	go func() {
-		require.NoError(t, run(ctx, cmdRun{Debug: true, Path: resourcePath}, runOpts{}, os.Stdout, os.Stderr))
+		opts := runOpts{extProcLauncher: mainlib.Main}
+		require.NoError(t, run(ctx, cmdRun{Debug: true, Path: resourcePath}, opts, os.Stdout, os.Stderr))
 		close(done)
 	}()
 	defer func() {
@@ -161,11 +164,14 @@ func TestRunExtprocStartFailure(t *testing.T) {
 	var (
 		resourcePath, _ = setupDefaultAIGatewayResourcesWithAvailableCredentials(t)
 		errChan         = make(chan error)
+		errExtProcMock  = errors.New("mock extproc error")
 	)
 
 	go func() {
 		errChan <- run(t.Context(), cmdRun{Debug: true, Path: resourcePath}, runOpts{
-			udsPath: "/dev/null", // This will cause the external processor to fail to start.
+			extProcLauncher: func(context.Context, []string, io.Writer) error {
+				return errExtProcMock
+			},
 		}, os.Stdout, os.Stderr)
 	}()
 
@@ -174,6 +180,7 @@ func TestRunExtprocStartFailure(t *testing.T) {
 		t.Fatalf("expected extproc start process to fail and return")
 	case err := <-errChan:
 		require.ErrorIs(t, err, errExtProcRun)
+		require.ErrorIs(t, err, errExtProcMock)
 	}
 }
 
@@ -183,6 +190,7 @@ func TestRunCmdContext_writeEnvoyResourcesAndRunExtProc(t *testing.T) {
 		stderrLogger:             slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{})),
 		envoyGatewayResourcesOut: &bytes.Buffer{},
 		tmpdir:                   t.TempDir(),
+		extProcLauncher:          mainlib.Main,
 		// UNIX doesn't like a long UDS path, so we use a short one.
 		// https://unix.stackexchange.com/questions/367008/why-is-socket-path-length-limited-to-a-hundred-chars
 		udsPath: filepath.Join("/tmp", "run.sock"),
@@ -202,7 +210,8 @@ func Test_mustStartExtProc(t *testing.T) {
 	ctx, cancel := context.WithCancel(t.Context())
 	t.Cleanup(cancel)
 	runCtx := &runCmdContext{
-		tmpdir: t.TempDir(),
+		tmpdir:          t.TempDir(),
+		extProcLauncher: mainlib.Main,
 		// UNIX doesn't like a long UDS path, so we use a short one.
 		// https://unix.stackexchange.com/questions/367008/why-is-socket-path-length-limited-to-a-hundred-chars
 		udsPath:      filepath.Join("/tmp", "run.sock"),