promise: run callbacks on resolution

context.go

@@ -117,6 +117,14 @@ func (c *Context) Global() *Object {
 	return &Object{v}
 }
 
+// PerformMicrotaskCheckpoint runs the default MicrotaskQueue until empty.
+// This is used to make progress on Promises.
+func (c *Context) PerformMicrotaskCheckpoint() {
+	c.register()
+	defer c.deregister()
+	C.IsolatePerformMicrotaskCheckpoint(c.iso.ptr)
+}
+
 // Close will dispose the context and free the memory.
 // Access to any values assosiated with the context after calling Close may panic.
 func (c *Context) Close() {

promise.go

@@ -85,3 +85,41 @@ func (p *Promise) Result() *Value {
 	val := &Value{ptr, p.ctx}
 	return val
 }
+
+// Then accepts 1 or 2 callbacks.
+// The first is invoked when the promise has been fulfilled.
+// The second is invoked when the promise has been rejected.
+// The returned Promise resolves after the callback finishes execution.
+//
+// V8 only invokes the callback when processing "microtasks".
+// The default MicrotaskPolicy processes them when the call depth decreases to 0.
+// Call (*Context).PerformMicrotaskCheckpoint to trigger it manually.
+func (p *Promise) Then(cbs ...FunctionCallback) *Promise {
+	p.ctx.register()
+	defer p.ctx.deregister()
+
+	var ptr C.ValuePtr
+	switch len(cbs) {
+	case 1:
+		cbID := p.ctx.iso.registerCallback(cbs[0])
+		ptr = C.PromiseThen(p.ptr, C.int(cbID))
+	case 2:
+		cbID1 := p.ctx.iso.registerCallback(cbs[0])
+		cbID2 := p.ctx.iso.registerCallback(cbs[1])
+		ptr = C.PromiseThen2(p.ptr, C.int(cbID1), C.int(cbID2))
+
+	default:
+		panic("1 or 2 callbacks required")
+	}
+	return &Promise{&Object{&Value{ptr, p.ctx}}}
+}
+
+// Catch invokes the given function if the promise is rejected.
+// See Then for other details.
+func (p *Promise) Catch(cb FunctionCallback) *Promise {
+	p.ctx.register()
+	defer p.ctx.deregister()
+	cbID := p.ctx.iso.registerCallback(cb)
+	ptr := C.PromiseCatch(p.ptr, C.int(cbID))
+	return &Promise{&Object{&Value{ptr, p.ctx}}}
+}

promise_test.go

@@ -10,7 +10,7 @@ import (
 	"rogchap.com/v8go"
 )
 
-func TestPromise(t *testing.T) {
+func TestPromiseFulfilled(t *testing.T) {
 	t.Parallel()
 
 	iso, _ := v8go.NewIsolate()
@@ -25,6 +25,19 @@ func TestPromise(t *testing.T) {
 		t.Errorf("unexpected state for Promise, want Pending (0) got: %v", s)
 	}
 
+	var thenInfo *v8go.FunctionCallbackInfo
+	prom1thenVal := prom1.Then(func(info *v8go.FunctionCallbackInfo) *v8go.Value {
+		thenInfo = info
+		return nil
+	})
+	prom1then, _ := prom1thenVal.AsPromise()
+	if prom1then.State() != v8go.Pending {
+		t.Errorf("unexpected state for dependent Promise, want Pending got: %v", prom1then.State())
+	}
+	if thenInfo != nil {
+		t.Error("unexpected call of Then prior to resolving the promise")
+	}
+
 	val1, _ := v8go.NewValue(iso, "foo")
 	res1.Resolve(val1)
 
@@ -36,6 +49,20 @@ func TestPromise(t *testing.T) {
 		t.Errorf("expected the Promise result to match the resolve value, but got: %s", result)
 	}
 
+	if thenInfo == nil {
+		t.Errorf("expected Then to be called, was not")
+	}
+	if len(thenInfo.Args()) != 1 || thenInfo.Args()[0].String() != "foo" {
+		t.Errorf("expected promise to be called with [foo] args, was: %+v", thenInfo.Args())
+	}
+}
+
+func TestPromiseRejected(t *testing.T) {
+	t.Parallel()
+
+	iso, _ := v8go.NewIsolate()
+	ctx, _ := v8go.NewContext(iso)
+
 	res2, _ := v8go.NewPromiseResolver(ctx)
 	val2, _ := v8go.NewValue(iso, "Bad Foo")
 	res2.Reject(val2)
@@ -44,4 +71,36 @@ func TestPromise(t *testing.T) {
 	if s := prom2.State(); s != v8go.Rejected {
 		t.Fatalf("unexpected state for Promise, want Rejected (2) got: %v", s)
 	}
+
+	var thenInfo *v8go.FunctionCallbackInfo
+	var then2Fulfilled, then2Rejected bool
+	prom2.
+		Catch(func(info *v8go.FunctionCallbackInfo) *v8go.Value {
+			thenInfo = info
+			return nil
+		}).
+		Then(
+			func(_ *v8go.FunctionCallbackInfo) *v8go.Value {
+				then2Fulfilled = true
+				return nil
+			},
+			func(_ *v8go.FunctionCallbackInfo) *v8go.Value {
+				then2Rejected = true
+				return nil
+			},
+		)
+	ctx.PerformMicrotaskCheckpoint()
+	if thenInfo == nil {
+		t.Fatalf("expected Then to be called on already-resolved promise, but was not")
+	}
+	if len(thenInfo.Args()) != 1 || thenInfo.Args()[0].String() != val2.String() {
+		t.Fatalf("expected [%v], was: %+v", val2, thenInfo.Args())
+	}
+
+	if then2Fulfilled {
+		t.Fatalf("unexpectedly called onFulfilled")
+	}
+	if !then2Rejected {
+		t.Fatalf("expected call to onRejected, got none")
+	}
 }

v8go.cc

@@ -160,6 +160,11 @@ IsolatePtr NewIsolate() {
   return static_cast<IsolatePtr>(iso);
 }
 
+void IsolatePerformMicrotaskCheckpoint(IsolatePtr ptr) {
+  ISOLATE_SCOPE(ptr)
+  iso->PerformMicrotaskCheckpoint();
+}
+
 void IsolateDispose(IsolatePtr ptr) {
   if (ptr == nullptr) {
     return;
@@ -1077,6 +1082,54 @@ int PromiseState(ValuePtr ptr) {
   return promise->State();
 }
 
+ValuePtr PromiseThen(ValuePtr ptr, int callback_ref) {
+  LOCAL_VALUE(ptr)
+  Local<Promise> promise = value.As<Promise>();
+  Local<Integer> cbData = Integer::New(iso, callback_ref);
+  Local<Function> func = Function::New(local_ctx, FunctionTemplateCallback, cbData)
+    .ToLocalChecked();
+  Local<Promise> result = promise->Then(local_ctx, func).ToLocalChecked();
+  m_value* promise_val = new m_value;
+  promise_val->iso = iso;
+  promise_val->ctx = ctx;
+  promise_val->ptr =
+      Persistent<Value, CopyablePersistentTraits<Value>>(iso, promise);
+  return tracked_value(ctx, promise_val);
+}
+
+ValuePtr PromiseThen2(ValuePtr ptr, int on_fulfilled_ref, int on_rejected_ref) {
+  LOCAL_VALUE(ptr)
+  Local<Promise> promise = value.As<Promise>();
+  Local<Integer> onFulfilledData = Integer::New(iso, on_fulfilled_ref);
+  Local<Function> onFulfilledFunc = Function::New(local_ctx, FunctionTemplateCallback, onFulfilledData)
+    .ToLocalChecked();
+  Local<Integer> onRejectedData = Integer::New(iso, on_rejected_ref);
+  Local<Function> onRejectedFunc = Function::New(local_ctx, FunctionTemplateCallback, onRejectedData)
+    .ToLocalChecked();
+  Local<Promise> result = promise->Then(local_ctx, onFulfilledFunc, onRejectedFunc).ToLocalChecked();
+  m_value* promise_val = new m_value;
+  promise_val->iso = iso;
+  promise_val->ctx = ctx;
+  promise_val->ptr =
+      Persistent<Value, CopyablePersistentTraits<Value>>(iso, promise);
+  return tracked_value(ctx, promise_val);
+}
+
+ValuePtr PromiseCatch(ValuePtr ptr, int callback_ref) {
+  LOCAL_VALUE(ptr)
+  Local<Promise> promise = value.As<Promise>();
+  Local<Integer> cbData = Integer::New(iso, callback_ref);
+  Local<Function> func = Function::New(local_ctx, FunctionTemplateCallback, cbData)
+    .ToLocalChecked();
+  Local<Promise> result = promise->Catch(local_ctx, func).ToLocalChecked();
+  m_value* promise_val = new m_value;
+  promise_val->iso = iso;
+  promise_val->ctx = ctx;
+  promise_val->ptr =
+      Persistent<Value, CopyablePersistentTraits<Value>>(iso, promise);
+  return tracked_value(ctx, promise_val);
+}
+
 ValuePtr PromiseResult(ValuePtr ptr) {
   LOCAL_VALUE(ptr)
   Local<Promise> promise = value.As<Promise>();

v8go.h

@@ -50,6 +50,7 @@ typedef struct {
 
 extern void Init();
 extern IsolatePtr NewIsolate();
+extern void IsolatePerformMicrotaskCheckpoint(IsolatePtr ptr);
 extern void IsolateDispose(IsolatePtr ptr);
 extern void IsolateTerminateExecution(IsolatePtr ptr);
 extern IsolateHStatistics IsolationGetHeapStatistics(IsolatePtr ptr);
@@ -171,6 +172,9 @@ extern ValuePtr PromiseResolverGetPromise(ValuePtr ptr);
 int PromiseResolverResolve(ValuePtr ptr, ValuePtr val_ptr);
 int PromiseResolverReject(ValuePtr ptr, ValuePtr val_ptr);
 int PromiseState(ValuePtr ptr);
+ValuePtr PromiseThen(ValuePtr ptr, int callback_ref);
+ValuePtr PromiseThen2(ValuePtr ptr, int on_fulfilled_ref, int on_rejected_ref);
+ValuePtr PromiseCatch(ValuePtr ptr, int callback_ref);
 extern ValuePtr PromiseResult(ValuePtr ptr);
 
 extern RtnValue FunctionCall(ValuePtr ptr, int argc, ValuePtr argv[]);