FJsonSerializer::Deserialize bug with TArray

Development Programming & Scripting C++
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1

Hello!
Straight to the point;
I’m serializing an object in C# to Json, It looks like this:

List<ServerListItem> ServerList;
string result = JsonConvert.SerializeObject(ServerList);

I then try to Deserialize the same string with FJsonSerializer like this:

    TArray<FWServer> servers;
	TArray<TSharedPtr<FJsonValue>> JsonParsed;
	TSharedRef<TJsonReader<TCHAR>> JsonReader = TJsonReaderFactory<TCHAR>::Create(someServers);
	if (FJsonSerializer::Deserialize(JsonReader, JsonParsed))
	{
		for (int i = 0; i < JsonParsed.Num(); ++i)
		{
			auto item = JsonParsed[i]->AsObject();
			FWServer s = FWServer();
			s.mIpAddress = item->GetStringField("ipAddress");
			s.mPort = item->GetNumberField("Port");
			s.mServerName = item->GetStringField("ServerName");
			servers.Add(s);
		}
	}

Where “someServers” is an FString with the exact same contents as “Result” from c#. With one element the deserialize returns true, with more than one element it returns false.

Thank you.

Matt.

2

Inside the JsonSerializer.h file it fails at line 194, claiming the EJsonNotation is an Error.
Any idea why?

3

I ended up hacking my way around it. It seems like Unreal’s Json converter can’t handle arrays atm. This is what I ended up doing;

TArray<FString> serverListSplit;
FString left, right, current;
current = someServers;
current.RemoveFromStart("["); current.RemoveFromEnd("]");
while (current.Split("}", &left, &right))
{
	left += "}";
	right.RemoveFromStart(",");
	current = right;
	serverListSplit.Add(left);
}

TArray<FWServer> servers;
for (int i = 0; i < serverListSplit.Num(); ++i)
{
	TSharedPtr<FJsonObject> JsonParsed = MakeShareable(new FJsonObject());
	TSharedRef<TJsonReader<TCHAR>> JsonReader = TJsonReaderFactory<TCHAR>::Create(serverListSplit[i]);
	if (FJsonSerializer::Deserialize(JsonReader, JsonParsed))
	{
		auto item = JsonParsed;

		FWServer s = FWServer();
		s.mIpAddress		= item->GetStringField("ipAddress");
		s.mPort			= item->GetNumberField("Port");
		s.mServerName	= item->GetStringField("ServerName");
	}
}
1 Like
4

Can you post the string generated in your C# code? This may be a bug in FJsonDeserializer. Arrays should be supported.

5

Sure thing! Looks like this:

[{ipAddress:"127.0.0.1","Port":"7777","ServerName":"Testing01"},
{ipAddress:"127.0.0.1","Port":"7777","ServerName":"Testing02"}]
6

This doesn’t work for json output like:
[{“size”:3},{“parts”:[“part1”,“part2”,“part3”]}]

Do you know how to solve this?

7

Nothing pops out at me, but it appears we are missing a test case with a root array with multiple items. I’ll pop that in, see if it repros and get a fix.

8

I’ve added test cases for various root array scenario and I wasn’t able to repro your issue.

I then tried to test with the string you provided above and noticed that the ‘ipAddress’ fields don’t have quotes around them. Our parser requires that all field names be quoted.

9

Thank you! Then there must be an error in how the standard c# JSON serializer serializes JSON. Odd!

Thanks again for taking your time and testing this.

10

Hello! I have the same problems:
If root node is array, i get " Error: JSON data is invalid"

[
  {
"id": 1,
"name": " 0",
"visible": 1,
"summary": "",
"summaryformat": 1,
"section": 0,
"hiddenbynumsections": 0,
"uservisible": true,
"modules": [
  {
"id": 1,
"url": "http://moodle.local/mod/lesson/view.php?id=1",
"name": "Размножение диаспоры уругвайских тушканчиков",
"instance": 1,
"contextid": 60,
"visible": 1,
"uservisible": true,
"visibleoncoursepage": 1,
"modicon": "http://moodle.local/theme/image.php/_s/boost/lesson/1618901170/icon",
"modname": "lesson",
"modplural": "Лекции",
"availability": null,
"indent": 0,
"onclick": "",
"afterlink": null,
"customdata": """",
"noviewlink": false,
"completion": 1,
"completiondata": {
"state": 0,
"timecompleted": 0,
"overrideby": null,
"valueused": false
}
}
],
},
  {
"id": 2,
"name": " 1",
"visible": 0,
"summary": "",
"summaryformat": 1,
"section": 1,
"hiddenbynumsections": 0,
"uservisible": true,
"modules": [],
}
]
11

I solved a problem, added code:

    FString dataString = Response->GetContentAsString();
    if (dataString[0] == '[')
    	{
    		dataString = FString("{\"root\":") +dataString + '}';
    	}
    // Process the string
    	if (!FromString(dataString)) {
    		OnGetResult.Broadcast(false, this, EJSONResult::JSONParsingFailed);
    		return;
    	}
//
//
//  
    bool UJsonFieldData::FromString(const FString& dataString) {
    
    
    	TSharedRef<TJsonReader<TCHAR>> JsonReader = TJsonReaderFactory<TCHAR>::Create(dataString);
    
    	// Deserialize the JSON data
    	bool isDeserialized = FJsonSerializer::Deserialize(JsonReader, Data);
    
    	if (!isDeserialized || !Data.IsValid()) {
    		UE_LOG(JSONQueryLog, Error, TEXT("JSON data is invalid! Input:\n'%s'!"), *dataString);
    		return false;
    	}
    
    	return true;
    }