WebSockets sending JSON data

[Mis1eader-dev]

Is your feature request related to a problem? Please describe. Currently websocket connections can only send const string& and const char*, for it to send const Json::Value& we have to stringify it first, and then send it over the const string& overload. The problem is, there is only one public method exposed by Json::Value to construct a stringified JSON, that is Json::Value::toStyledString. But it outputs a prettified version of the JSON, with indents. There is Json::StreamWriter, but that is a lot of manual work.

Describe the solution you'd like A public overloaded method for drogon::WebSocketConnection taking in a const Json::Value&, to stringify efficiently, just like how drogon::HttpResponse::newHttpJsonResponse(json) generates an efficient stringified version of the JSON.

[hwc0919]

I write a format function for Json::Value myself. I think this is the one of the unfriendly places of jsoncpp. nlohmann json has a dump() method, which is really good.

I personally don't want to add any more Jsoncpp relative apis into framework. It really sucks, in both api design and performance. Perhaps we will get rid of it in future.

[Mis1eader-dev]

Perhaps we can write a middle layer API that reveives the const Json::Value& and spits out a dumped JSON string, this way we know where it has been referenced and can change its signature easily

[hwc0919]

@Mis1eader-dev You are right.

This is my version of 'parse' and 'dump'.

The dump api is simple, but I don't know if it is a standard practice to use a static builder...

The parse api is still ugly... There are so many different ways to handle errors, and we don't have a standard for that.

I don't feel like forcing others to use my way, so I won't want to write this PR :see_no_evil:. I'll leave it to someone who wants.

#include <json/reader.h>
#include <json/writer.h>

std::string jsonToString(const Json::Value & json)
{
    static const Json::StreamWriterBuilder & builder = []() -> Json::StreamWriterBuilder & {
        static Json::StreamWriterBuilder builder;
        builder["commentStyle"] = "None";
        builder["indentation"] = "";
        return builder;
    }();
    return writeString(builder, json);
}

bool stringToJson(const std::string & doc, Json::Value * root, Json::String * errs)
{
    return stringToJson(&doc[0], &doc[0] + doc.size(), root, errs);
}

bool stringToJson(char const * beginDoc, char const * endDoc, Json::Value * root, Json::String * errs)
{
    static Json::CharReaderBuilder & builder = []() -> Json::CharReaderBuilder & {
        static Json::CharReaderBuilder builder;
        builder["collectComments"] = false;
        return builder;
    }();
    std::unique_ptr<Json::CharReader> jsonReader(builder.newCharReader());
    return jsonReader->parse(beginDoc, endDoc, root, errs);
}

[Mis1eader-dev]

Why no PR? It's better to have something than not have JSON for WebSockets We can copy the logic written in the HttpResponse implementation for JSON responses and make a drogon::json middle layer containing both strToJson and jsonToStr methods For strToJson we'll use the logic of HttpRequest JSON parsing