gecko/content/xbl/src/nsXBLProtoImplField.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsIAtom.h"
#include "nsString.h"
#include "nsJSUtils.h"
#include "jsapi.h"
#include "nsUnicharUtils.h"
#include "nsReadableUtils.h"
#include "nsXBLProtoImplField.h"
#include "nsIScriptContext.h"
#include "nsIURI.h"
#include "nsXBLSerialize.h"
#include "nsXBLPrototypeBinding.h"
#include "mozilla/dom/BindingUtils.h"

using namespace mozilla;
using namespace mozilla::dom;

nsXBLProtoImplField::nsXBLProtoImplField(const PRUnichar* aName, const PRUnichar* aReadOnly)
  : mNext(nullptr),
    mFieldText(nullptr),
    mFieldTextLength(0),
    mLineNumber(0)
{
  MOZ_COUNT_CTOR(nsXBLProtoImplField);
  mName = NS_strdup(aName);  // XXXbz make more sense to use a stringbuffer?
  
  mJSAttributes = JSPROP_ENUMERATE;
  if (aReadOnly) {
    nsAutoString readOnly; readOnly.Assign(aReadOnly);
    if (readOnly.LowerCaseEqualsLiteral("true"))
      mJSAttributes |= JSPROP_READONLY;
  }
}


nsXBLProtoImplField::nsXBLProtoImplField(const bool aIsReadOnly)
  : mNext(nullptr),
    mFieldText(nullptr),
    mFieldTextLength(0),
    mLineNumber(0)
{
  MOZ_COUNT_CTOR(nsXBLProtoImplField);

  mJSAttributes = JSPROP_ENUMERATE;
  if (aIsReadOnly)
    mJSAttributes |= JSPROP_READONLY;
}

nsXBLProtoImplField::~nsXBLProtoImplField()
{
  MOZ_COUNT_DTOR(nsXBLProtoImplField);
  if (mFieldText)
    nsMemory::Free(mFieldText);
  NS_Free(mName);
  NS_CONTENT_DELETE_LIST_MEMBER(nsXBLProtoImplField, this, mNext);
}

void 
nsXBLProtoImplField::AppendFieldText(const nsAString& aText)
{
  if (mFieldText) {
    nsDependentString fieldTextStr(mFieldText, mFieldTextLength);
    nsAutoString newFieldText = fieldTextStr + aText;
    PRUnichar* temp = mFieldText;
    mFieldText = ToNewUnicode(newFieldText);
    mFieldTextLength = newFieldText.Length();
    nsMemory::Free(temp);
  }
  else {
    mFieldText = ToNewUnicode(aText);
    mFieldTextLength = aText.Length();
  }
}

// XBL fields are represented on elements inheriting that field a bit trickily.
// Initially the element itself won't have a property for the field.  When an
// attempt is made to access the field, the element's resolve hook won't find
// it.  But the XBL prototype object, in the prototype chain of the element,
// will resolve an accessor property for the field on the XBL prototype object.
// That accessor, when used, will then (via InstallXBLField below) reify a
// property for the field onto the actual XBL-backed element.
//
// The accessor property is a plain old property backed by a getter function and
// a setter function.  These properties are backed by the FieldGetter and
// FieldSetter natives; they're created by XBLResolve.  The precise field to be
// reified is identified using two extra slots on the getter/setter functions.
// XBLPROTO_SLOT stores the XBL prototype object that provides the field.
// FIELD_SLOT stores the name of the field, i.e. its JavaScript property name.
//
// This two-step field installation process -- reify an accessor on the
// prototype, then have that reify an own property on the actual element -- is
// admittedly convoluted.  Better would be for XBL-backed elements to be proxies
// that could resolve fields onto themselves.  But given that XBL bindings are
// associated with elements mutably -- you can add/remove/change -moz-binding
// whenever you want, alas -- doing so would require all elements to be proxies,
// which isn't performant now.  So we do this two-step instead.
static const uint32_t XBLPROTO_SLOT = 0;
static const uint32_t FIELD_SLOT = 1;

bool
ValueHasISupportsPrivate(const JS::Value &v)
{
  if (!v.isObject()) {
    return false;
  }

  const DOMClass* domClass = GetDOMClass(&v.toObject());
  if (domClass) {
    return domClass->mDOMObjectIsISupports;
  }

  JSClass* clasp = ::JS_GetClass(&v.toObject());
  const uint32_t HAS_PRIVATE_NSISUPPORTS =
    JSCLASS_HAS_PRIVATE | JSCLASS_PRIVATE_IS_NSISUPPORTS;
  return (clasp->flags & HAS_PRIVATE_NSISUPPORTS) == HAS_PRIVATE_NSISUPPORTS;
}

// Define a shadowing property on |this| for the XBL field defined by the
// contents of the callee's reserved slots.  If the property was defined,
// *installed will be true, and idp will be set to the property name that was
// defined.
static JSBool
InstallXBLField(JSContext* cx,
                JS::Handle<JSObject*> callee, JS::Handle<JSObject*> thisObj,
                jsid* idp, bool* installed)
{
  *installed = false;

  // First ensure |this| is a reasonable XBL bound node.
  //
  // FieldAccessorGuard already determined whether |thisObj| was acceptable as
  // |this| in terms of not throwing a TypeError.  Assert this for good measure.
  MOZ_ASSERT(ValueHasISupportsPrivate(JS::ObjectValue(*thisObj)));

  // But there are some cases where we must accept |thisObj| but not install a
  // property on it, or otherwise touch it.  Hence this split of |this|-vetting
  // duties.
  nsISupports* native =
    nsContentUtils::XPConnect()->GetNativeOfWrapper(cx, thisObj);
  if (!native) {
    // Looks like whatever |thisObj| is it's not our nsIContent.  It might well
    // be the proto our binding installed, however, where the private is the
    // nsXBLDocumentInfo, so just baul out quietly.  Do NOT throw an exception
    // here.
    //
    // We could make this stricter by checking the class maybe, but whatever.
    return true;
  }

  nsCOMPtr<nsIContent> xblNode = do_QueryInterface(native);
  if (!xblNode) {
    xpc::Throw(cx, NS_ERROR_UNEXPECTED);
    return false;
  }

  // Now that |this| is okay, actually install the field.  Some of this
  // installation work could have been done in XBLResolve, but this splitting
  // of work seems simplest to implement and friendliest regarding lifetimes
  // and potential cycles.

  // Because of the possibility (due to XBL binding inheritance, because each
  // XBL binding lives in its own global object) that |this| might be in a
  // different compartment from the callee (not to mention that this method can
  // be called with an arbitrary |this| regardless of how insane XBL is), and
  // because in this method we've entered |this|'s compartment (see in
  // Field[GS]etter where we attempt a cross-compartment call), we must enter
  // the callee's compartment to access its reserved slots.
  nsXBLPrototypeBinding* protoBinding;
  nsDependentJSString fieldName;
  {
    JSAutoCompartment ac(cx, callee);

    js::Rooted<JSObject*> xblProto(cx);
    xblProto = &js::GetFunctionNativeReserved(callee, XBLPROTO_SLOT).toObject();

    JS::Value name = js::GetFunctionNativeReserved(callee, FIELD_SLOT);
    JSFlatString* fieldStr = JS_ASSERT_STRING_IS_FLAT(name.toString());
    fieldName.init(fieldStr);

    MOZ_ALWAYS_TRUE(JS_ValueToId(cx, name, idp));

    JS::Value slotVal = ::JS_GetReservedSlot(xblProto, 0);
    protoBinding = static_cast<nsXBLPrototypeBinding*>(slotVal.toPrivate());
    MOZ_ASSERT(protoBinding);
  }

  nsXBLProtoImplField* field = protoBinding->FindField(fieldName);
  MOZ_ASSERT(field);

  // This mirrors code in nsXBLProtoImpl::InstallImplementation
  nsIScriptGlobalObject* global = xblNode->OwnerDoc()->GetScriptGlobalObject();
  if (!global) {
    return true;
  }

  nsCOMPtr<nsIScriptContext> context = global->GetContext();
  if (!context) {
    return true;
  }

  nsresult rv = field->InstallField(context, thisObj, protoBinding->DocURI(),
                                    installed);
  if (NS_SUCCEEDED(rv)) {
    return true;
  }

  if (!::JS_IsExceptionPending(cx)) {
    xpc::Throw(cx, rv);
  }
  return false;
}

bool
FieldGetterImpl(JSContext *cx, JS::CallArgs args)
{
  const JS::Value &thisv = args.thisv();
  MOZ_ASSERT(ValueHasISupportsPrivate(thisv));

  js::Rooted<JSObject*> thisObj(cx, &thisv.toObject());

  bool installed = false;
  js::Rooted<JSObject*> callee(cx, &args.calleev().toObject());
  js::Rooted<jsid> id(cx);
  if (!InstallXBLField(cx, callee, thisObj, id.address(), &installed)) {
    return false;
  }

  if (!installed) {
    args.rval().setUndefined();
    return true;
  }

  js::Rooted<JS::Value> v(cx);
  if (!JS_GetPropertyById(cx, thisObj, id, v.address())) {
    return false;
  }
  args.rval().set(v);
  return true;
}

static JSBool
FieldGetter(JSContext *cx, unsigned argc, JS::Value *vp)
{
  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
  return JS::CallNonGenericMethod<ValueHasISupportsPrivate, FieldGetterImpl>
                                 (cx, args);
}

bool
FieldSetterImpl(JSContext *cx, JS::CallArgs args)
{
  const JS::Value &thisv = args.thisv();
  MOZ_ASSERT(ValueHasISupportsPrivate(thisv));

  js::Rooted<JSObject*> thisObj(cx, &thisv.toObject());

  bool installed = false;
  js::Rooted<JSObject*> callee(cx, &args.calleev().toObject());
  js::Rooted<jsid> id(cx);
  if (!InstallXBLField(cx, callee, thisObj, id.address(), &installed)) {
    return false;
  }

  if (installed) {
    js::Rooted<JS::Value> v(cx,
                            args.length() > 0 ? args[0] : JS::UndefinedValue());
    if (!::JS_SetPropertyById(cx, thisObj, id, v.address())) {
      return false;
    }
  }
  args.rval().setUndefined();
  return true;
}

static JSBool
FieldSetter(JSContext *cx, unsigned argc, JS::Value *vp)
{
  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
  return JS::CallNonGenericMethod<ValueHasISupportsPrivate, FieldSetterImpl>
                                 (cx, args);
}

JSBool
XBLResolve(JSContext *cx, JSHandleObject obj, JSHandleId id, unsigned flags,
           JSMutableHandleObject objp)
{
  objp.set(NULL);

  if (!JSID_IS_STRING(id)) {
    return true;
  }

  nsXBLPrototypeBinding* protoBinding =
    static_cast<nsXBLPrototypeBinding*>(::JS_GetReservedSlot(obj, 0).toPrivate());
  MOZ_ASSERT(protoBinding);

  // If the field's not present, don't resolve it.  Also don't resolve it if the
  // field is empty; see also nsXBLProtoImplField::InstallField which also must
  // implement the not-empty requirement.
  nsDependentJSString fieldName(id);
  nsXBLProtoImplField* field = protoBinding->FindField(fieldName);
  if (!field || field->IsEmpty()) {
    return true;
  }

  // We have a field: now install a getter/setter pair which will resolve the
  // field onto the actual object, when invoked.
  js::Rooted<JSObject*> global(cx, JS_GetGlobalForObject(cx, obj));

  js::Rooted<JSObject*> get(cx);
  get = ::JS_GetFunctionObject(js::NewFunctionByIdWithReserved(cx, FieldGetter,
                                                               0, 0, global,
                                                               id));
  if (!get) {
    return false;
  }
  js::SetFunctionNativeReserved(get, XBLPROTO_SLOT, JS::ObjectValue(*obj));
  js::SetFunctionNativeReserved(get, FIELD_SLOT,
                                JS::StringValue(JSID_TO_STRING(id)));

  js::Rooted<JSObject*> set(cx);
  set = ::JS_GetFunctionObject(js::NewFunctionByIdWithReserved(cx, FieldSetter,
                                                               1, 0, global,
                                                               id));
  if (!set) {
    return false;
  }
  js::SetFunctionNativeReserved(set, XBLPROTO_SLOT, JS::ObjectValue(*obj));
  js::SetFunctionNativeReserved(set, FIELD_SLOT,
                                JS::StringValue(JSID_TO_STRING(id)));

  if (!::JS_DefinePropertyById(cx, obj, id, JS::UndefinedValue(),
                               JS_DATA_TO_FUNC_PTR(JSPropertyOp, get.get()),
                               JS_DATA_TO_FUNC_PTR(JSStrictPropertyOp, set.get()),
                               field->AccessorAttributes())) {
    return false;
  }

  objp.set(obj);
  return true;
}

nsresult
nsXBLProtoImplField::InstallField(nsIScriptContext* aContext,
                                  JSObject* aBoundNode,
                                  nsIURI* aBindingDocURI,
                                  bool* aDidInstall) const
{
  NS_PRECONDITION(aBoundNode,
                  "uh-oh, bound node should NOT be null or bad things will "
                  "happen");

  *aDidInstall = false;

  // Empty fields are treated as not actually present.
  if (IsEmpty()) {
    return NS_OK;
  }

  nsAutoMicroTask mt;

  // EvaluateString and JS_DefineUCProperty can both trigger GC, so
  // protect |result| here.
  nsresult rv;

  nsAutoCString uriSpec;
  aBindingDocURI->GetSpec(uriSpec);
  
  JSContext* cx = aContext->GetNativeContext();
  NS_ASSERTION(!::JS_IsExceptionPending(cx),
               "Shouldn't get here when an exception is pending!");
  
  // compile the literal string
  nsCOMPtr<nsIScriptContext> context = aContext;

  JSAutoRequest ar(cx);
  jsval result = JSVAL_NULL;

  JS::CompileOptions options(cx);
  options.setFileAndLine(uriSpec.get(), mLineNumber)
         .setVersion(JSVERSION_LATEST)
         .setUserBit(true); // Flag us as XBL
  rv = context->EvaluateString(nsDependentString(mFieldText,
                                                 mFieldTextLength),
                               *aBoundNode, options,
                               /* aCoerceToString = */ false,
                               &result);
  if (NS_FAILED(rv)) {
    return rv;
  }


  // Define the evaluated result as a JS property
  nsDependentString name(mName);
  if (!::JS_DefineUCProperty(cx, aBoundNode,
                             reinterpret_cast<const jschar*>(mName), 
                             name.Length(), result, nullptr, nullptr,
                             mJSAttributes)) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  *aDidInstall = true;
  return NS_OK;
}

nsresult
nsXBLProtoImplField::Read(nsIScriptContext* aContext,
                          nsIObjectInputStream* aStream)
{
  nsAutoString name;
  nsresult rv = aStream->ReadString(name);
  NS_ENSURE_SUCCESS(rv, rv);
  mName = ToNewUnicode(name);

  rv = aStream->Read32(&mLineNumber);
  NS_ENSURE_SUCCESS(rv, rv);

  nsAutoString fieldText;
  rv = aStream->ReadString(fieldText);
  NS_ENSURE_SUCCESS(rv, rv);
  mFieldTextLength = fieldText.Length();
  if (mFieldTextLength)
    mFieldText = ToNewUnicode(fieldText);

  return NS_OK;
}

nsresult
nsXBLProtoImplField::Write(nsIScriptContext* aContext,
                           nsIObjectOutputStream* aStream)
{
  XBLBindingSerializeDetails type = XBLBinding_Serialize_Field;

  if (mJSAttributes & JSPROP_READONLY) {
    type |= XBLBinding_Serialize_ReadOnly;
  }

  nsresult rv = aStream->Write8(type);
  NS_ENSURE_SUCCESS(rv, rv);
  rv = aStream->WriteWStringZ(mName);
  NS_ENSURE_SUCCESS(rv, rv);
  rv = aStream->Write32(mLineNumber);
  NS_ENSURE_SUCCESS(rv, rv);

  return aStream->WriteWStringZ(mFieldText ? mFieldText : EmptyString().get());
}