I would like to pass a protobuf message from Javascript to a C++
WebAssembly module.
I do receive, and can successfully parse the simpler protobuf messages on
the C++ side, however, protobuf is failing to parse the less-simple
protobuf messages.
Here is the code that I am using :
```
goog.module('protobufMessageGenerator');
goog.require('proto.my_proto.MyMessage'); function generateMyMessage() {
var msg = new proto.my_proto.MyMessage() var internal = new
proto.my_proto.MyMessageInternal() internal.setAccentColor("#CC1D24")
internal.setLogo("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")
msg.setInternal(internal) return msg }
```
Using the google-closure-compiler, I compile this protobuf message
generator to pure Javascript. I use this code to pass the message to the
C++ WebAssembly module :
```
function sendMessage() {
Module.self().setMyMessage(module$contents$protobufMessageGenerator_generateMyMessage().serializeBinary())
} sendMessage()
```
I receive the message on the C++ side using this code :
```
void JavascriptPublicInterface::setMyMessage(const QString &myMessage) { if
(_myMessage != myMessage) { _myMessage = myMessage; emit
myMessageChanged(); } } void
JavascriptPublicInterface::setMyMessageEMS(const std::string &myMessage) {
setMyMessage(QString::fromStdString(myMessage)); } //... void
startListeningToMyMessage(std::function<void(euf_proto::MyMessage
myMessage)> listener) { const auto changedListener = [listener]() { const
auto newMyMessageString = JavascriptPublicInterface::self()->myMessage();
my_proto::MyMessage myMessagePb; if
(myMessagePb.ParseFromString(newMyMessageString.toStdString())) { qDebug()
<< "C++ : Successfully parsed new MyMessage: " << newMyMessageString; }
else { qDebug() << "C++ : Failed to parse new MyMessage: " <<
newMyMessageString; } qDebug() << "MyMessage received: " <<
QString::fromStdString(myMessagePb.DebugString()); listener(myMessagePb);
}; if (!QObject::connect(JavascriptPublicInterface::self(),
&JavascriptPublicInterface::myMessageChanged, changedListener)) { throw
std::runtime_error("Failed to connect to JavascriptPublicInterface
myMessageChanged"); } }
```
In the Javascript console I see : "C++ : Failed to parse new MyMessage: ..."
I guess that it can be related to the fact that Javascript is using UTF-16
and C++ is using UTF-8 encoding (because the messages that are UTF-8 only
can be successfully parsed), so I tried to fix the sending and receiving
like this:
```
//For more info see :
https://emscripten.org/docs/api_reference/emscripten.h.html?highlight=stringtoutf8
function convertUtf16ToUtf8(input) { var uint8Arr = input var jsString =
String.fromCharCode.apply(null, uint8Arr) var lengthBytes =
lengthBytesUTF8(jsString)+1 var stringOnWasmHeap = _malloc(lengthBytes)
stringToUTF8(jsString, stringOnWasmHeap, lengthBytes) return
stringOnWasmHeap } function sendMessage() { var myMessage =
convertUtf16ToUtf8(module$contents$protobufMessageGenerator_generateMyMessage().serializeBinary())
Module.self().setMyMessage(myMessage) _free(myMessage) } sendMessage()
```
And I modified the parsing on the C++ side like this :
```
void JavascriptPublicInterface::setMyMessageEMS(const int pointer) { const
char* msg = (char*)pointer; setMyMessage(QString::fromStdString(msg)); }
```
But I still get this error : "C++ : Failed to parse new MyMessage: ..."
How could I fix this?
(I am using protobuf 3.19.1 (same version on both the Javascript and the
C++ side).)
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