Correctly use context in plugin and provide alternative _WithContext methods

[Marton6]

This PR ensures that the extism plugin struct does not store a context object in itself as this is not idiomatic Go and leads to unexpected behavior. Instead, a context object is passed to each plugin method call that runs a long running operation.

To not break the interface of the SDK, the existing SDK method signatures were preserved, but they were changed to use context.Background under the hood. Next to these, alternative _WithContext methods were added, which allow the caller to provide a custom context object.

[mhmd-azeez]

Thank you very much for the PR, to understand the new behavior better, i think it's good to add these two test cases:

// make sure cancelling the context given to NewPlugin doesn't affect plugin calls
func TestContextCancel(t *testing.T) {
	manifest := manifest("sleep.wasm")
	manifest.Config["duration"] = "0" // sleep for 0 seconds

	ctx, cancel := context.WithCancel(context.Background())
	config := PluginConfig{
		ModuleConfig:  wazero.NewModuleConfig().WithSysWalltime(),
		EnableWasi:    true,
		RuntimeConfig: wazero.NewRuntimeConfig().WithCloseOnContextDone(true),
	}

	plugin, err := NewPlugin(ctx, manifest, config, []HostFunction{})

	if err != nil {
		t.Errorf("Could not create plugin: %v", err)
	}

	defer plugin.Close()
	cancel() // cancel the parent context

	exit, out, err := plugin.CallWithContext(context.Background(), "run_test", []byte{})

	if assertCall(t, err, exit) {
		assert.Equal(t, "slept for 0 seconds", string(out))
	}
}

// make sure we can still turn on experimental wazero features
func TestEnableExperimentalFeature(t *testing.T) {
	var buf bytes.Buffer

	// Set context to one that has an experimental listener
	ctx := context.WithValue(context.Background(), experimental.FunctionListenerFactoryKey{}, logging.NewLoggingListenerFactory(&buf))

	manifest := manifest("sleep.wasm")
	manifest.Config["duration"] = "0" // sleep for 0 seconds

	config := PluginConfig{
		ModuleConfig:  wazero.NewModuleConfig().WithSysWalltime(),
		EnableWasi:    true,
		RuntimeConfig: wazero.NewRuntimeConfig().WithCloseOnContextDone(true),
	}

	plugin, err := NewPlugin(ctx, manifest, config, []HostFunction{})

	if err != nil {
		t.Errorf("Could not create plugin: %v", err)
	}

	defer plugin.Close()

	var buf2 bytes.Buffer
	ctx = context.WithValue(context.Background(), experimental.FunctionListenerFactoryKey{}, logging.NewLoggingListenerFactory(&buf2))
	exit, out, err := plugin.CallWithContext(ctx, "run_test", []byte{})

	if assertCall(t, err, exit) {
		assert.Equal(t, "slept for 0 seconds", string(out))

		assert.NotEmpty(t, buf.String())
		assert.Empty(t, buf2.String())
	}
}

These two both pass currently, I think the behavior is acceptable, but I am curious about your opinions @nilslice @zshipko

[Marton6]

Thank you very much for the PR, to understand the new behavior better, i think it's good to add these two test cases:

// make sure cancelling the context given to NewPlugin doesn't affect plugin calls
func TestContextCancel(t *testing.T) {
	manifest := manifest("sleep.wasm")
	manifest.Config["duration"] = "0" // sleep for 0 seconds

	ctx, cancel := context.WithCancel(context.Background())
	config := PluginConfig{
		ModuleConfig:  wazero.NewModuleConfig().WithSysWalltime(),
		EnableWasi:    true,
		RuntimeConfig: wazero.NewRuntimeConfig().WithCloseOnContextDone(true),
	}

	plugin, err := NewPlugin(ctx, manifest, config, []HostFunction{})

	if err != nil {
		t.Errorf("Could not create plugin: %v", err)
	}

	defer plugin.Close()
	cancel() // cancel the parent context

	exit, out, err := plugin.CallWithContext(context.Background(), "run_test", []byte{})

	if assertCall(t, err, exit) {
		assert.Equal(t, "slept for 0 seconds", string(out))
	}
}

// make sure we can still turn on experimental wazero features
func TestEnableExperimentalFeature(t *testing.T) {
	var buf bytes.Buffer

	// Set context to one that has an experimental listener
	ctx := context.WithValue(context.Background(), experimental.FunctionListenerFactoryKey{}, logging.NewLoggingListenerFactory(&buf))

	manifest := manifest("sleep.wasm")
	manifest.Config["duration"] = "0" // sleep for 0 seconds

	config := PluginConfig{
		ModuleConfig:  wazero.NewModuleConfig().WithSysWalltime(),
		EnableWasi:    true,
		RuntimeConfig: wazero.NewRuntimeConfig().WithCloseOnContextDone(true),
	}

	plugin, err := NewPlugin(ctx, manifest, config, []HostFunction{})

	if err != nil {
		t.Errorf("Could not create plugin: %v", err)
	}

	defer plugin.Close()

	var buf2 bytes.Buffer
	ctx = context.WithValue(context.Background(), experimental.FunctionListenerFactoryKey{}, logging.NewLoggingListenerFactory(&buf2))
	exit, out, err := plugin.CallWithContext(ctx, "run_test", []byte{})

	if assertCall(t, err, exit) {
		assert.Equal(t, "slept for 0 seconds", string(out))

		assert.NotEmpty(t, buf.String())
		assert.Empty(t, buf2.String())
	}
}

These two both pass currently, I think the behavior is acceptable, but I am curious about your opinions @nilslice @zshipko

Thanks for the tests. I've added them to the test suite!

[zshipko]

Just a few small changes, but otherwise looks good!