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Use callbacks for bindings to enable async behavior #2

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merged 1 commit into from Mar 22, 2024
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Use callbacks for bindings to enable async behavior #2

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25 changes: 16 additions & 9 deletions gui/choc_WebView.h
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Expand Up @@ -135,7 +135,8 @@ class WebView
void navigate (const std::string& url);

/// A callback function which can be passed to bind().
using CallbackFn = std::function<choc::value::Value(const choc::value::ValueView& args)>;
using ReplyFn = std::function<void(choc::value::Value, std::string)>;
using CallbackFn = std::function<void(const choc::value::ValueView& args, ReplyFn&& reply)>;
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clarifying question: in this new world, all functions would be required to call reply (at their leisure), and not be required to return anything. is that right?

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Right!

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Non-blocking thought: I wonder if it's worth supporting both synchronous and async bind() calls. If this were to get upstreamed I think that would be necessary. Maybe have a separate bindWithAsyncReply() method.

That would make the implementation a little more complex, but you should be able to do something like:

// Pseudocode
using CallbackFn = std::function<choc::value::Value(const choc::value::ValueView& args)>;
using AsyncCallbackFn = std::function<void(const choc::value::ValueView& args, ReplyFn&& reply)>;
// ...
unordered_map<string, variant<CallbackFn, AsyncCallbackFn>> bindings;
// ...
invokeBinding() {
   if (holds_alternative<CallbackFn>(b)) {
       doSynchronousCallback();
    } else {
        doAsyncCallback();
    }
}

/// Binds a C++ function to a named javascript function that can be called
/// by code running in the browser.
void bind (const std::string& functionName, CallbackFn&& function);
Expand Down Expand Up @@ -1495,17 +1496,23 @@ inline void WebView::invokeBinding (const std::string& msg)

try
{
auto result = b->second (json["params"]);
b->second (json["params"], [=](choc::value::Value result, std::string const& errorMessage) {
if (!errorMessage.empty())
{
auto call = callbackItem + ".reject(" + choc::json::toString(choc::value::createString(errorMessage)) + "); delete " + callbackItem + ";";
evaluateJavascript (call);
return;
}

auto call = callbackItem + ".resolve(" + choc::json::toString (result) + "); delete " + callbackItem + ";";
auto call = callbackItem + ".resolve(" + choc::json::toString (result) + "); delete " + callbackItem + ";";
evaluateJavascript (call);
});
}
catch (const std::exception& e)
{
auto call = callbackItem + ".reject(" + choc::json::toString(choc::value::createString(e.what())) + "); delete " + callbackItem + ";";
evaluateJavascript (call);
return;
}
catch (const std::exception&)
{}

auto call = callbackItem + ".reject(); delete " + callbackItem + ";";
evaluateJavascript (call);
}
catch (const std::exception&)
{}
Expand Down