CORS issue: res.set_header() not working

[dk9966]

server.cc:

void runServer(Database &database)
{
    // Generate server object
    httplib::Server svr;

    //other svr.get, svr.post in between

    svr.Put("/city", [&database](const httplib::Request &req, httplib::Response &res)
            {

                // Parse request body and define repsonse object
                nlohmann::json requestBody = nlohmann::json::parse(req.body), response;

                // Ensure all required fields are present
                if (requireFields(res, requestBody, {"id", "field", "value"}, response))
                {
                    // Extract fields
                    std::string id = requestBody["id"];
                    std::string field = requestBody["field"];
                    std::string value = requestBody["value"];
                    // Call helper function
                    // Fill in response object
                    database.UpdateCity(id, field, value);
                    response["response"]["success"] = true;
                }

                // Stringify response and set as response

                res.set_header("Access-Control-Allow-Origin", "*");
                res.set_content(response.dump(), "text/json");
                database.PrintTables();
            });
}

App.js:

const printDB = (event) => {
    if (event.key === "Enter") {
      fetch("http://localhost:8080/city", {
        method: "PUT",
        headers: {
          Accept: "application/json",
          "Content-Type": "application/json",
        },
        body: JSON.stringify({
          id: "NOmDpk5F3Bp1ZkOvTgpe",
          field: "CITY_NAME",
          value: "nyc",
        }),
      });
    }
  };

Currently, the code in the server.cc works well using curl calls. However, when I have a client that sends a request to the server which updates the things in a database, there is a CORS issue that prevents the request from going through. I have tried using res.set_header("Access-Control-Allow-Origin", "*"); but the same error message keeps popping up. I'm not sure what I am missing at this point.

I have the res.set_header() line but the error message shows that it isn't detected. I've also searched in closed issues and didn't really get much help from that.

[yhirose]

Hope this helps.