(MFC) Firebase Receive Server-Sent Events (text/event-stream)

Demonstrates how to start receiving server-sent events and update your JSON database with each event.

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkFileAccess.h>
#include <CkRest.h>
#include <CkAuthGoogle.h>
#include <CkUrl.h>
#include <CkJsonObject.h>
#include <CkStream.h>
#include <CkServerSentEvent.h>
#include <CkTask.h>

void ChilkatSample(void)
    {
    CkString strOut;

    // Demonstrates how to begin receiving server-sent events, and to update
    // your JSON database for each event.

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // This example assumes a JWT authentication token, if required, has been previously obtained.
    // See Get Firebase Access Token from JSON Service Account Private Key for sample code.

    // Load the previously obtained Firebase access token into a string.
    CkFileAccess fac;
    const char *accessToken = fac.readEntireTextFile("qa_data/tokens/firebaseToken.txt","utf-8");
    if (fac.get_LastMethodSuccess() != true) {
        strOut.append(fac.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    CkRest rest;

    // Make the initial connection (without sending a request yet).
    // Once connected, any number of requests may be sent.  It is not necessary to explicitly
    // call Connect before each request.  
    bool success = rest.Connect("chilkat.firebaseio.com",443,true,true);
    if (success != true) {
        strOut.append(rest.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    CkAuthGoogle authGoogle;
    authGoogle.put_AccessToken(accessToken);
    rest.SetAuthGoogle(authGoogle);

    rest.AddHeader("Accept","text/event-stream");
    rest.AddHeader("Cache-Control","no-cache");

    const char *responseBody = rest.fullRequestNoBody("GET","/.json");

    // A 307 redirect response is expected.
    if (rest.get_ResponseStatusCode() != 307) {
        strOut.append("Unexpected response code: ");
        strOut.appendInt(rest.get_ResponseStatusCode());
        strOut.append("\r\n");
        strOut.append(responseBody);
        strOut.append("\r\n");
        strOut.append("Failed.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Get the redirect URL
    CkUrl *url = rest.RedirectUrl();
    if (rest.get_LastMethodSuccess() != true) {
        strOut.append(rest.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    strOut.append("redirect URL domain: ");
    strOut.append(url->host());
    strOut.append("\r\n");
    strOut.append("redirect URL path: ");
    strOut.append(url->path());
    strOut.append("\r\n");
    strOut.append("redirect URL query params: ");
    strOut.append(url->query());
    strOut.append("\r\n");
    strOut.append("redirect URL path with query params: ");
    strOut.append(url->pathWithQueryParams());
    strOut.append("\r\n");

    // Our text/event-stream will be obtained from the redirect URL...
    CkRest rest2;

    success = rest2.Connect(url->host(),443,true,true);
    if (success != true) {
        strOut.append(rest2.lastErrorText());
        strOut.append("\r\n");
        delete url;
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    rest2.AddHeader("Accept","text/event-stream");
    rest2.AddHeader("Cache-Control","no-cache");

    // Add the redirect query params to the request
    rest2.AddQueryParams(url->query());

    // In our case, we don't actually need the auth query param,
    // so remove it.
    rest2.RemoveQueryParam("auth");

    // Send the request.  (We are only sending the request here.
    // We are not yet getting the response because the response
    // will be a text/event-stream.)
    success = rest2.SendReqNoBody("GET",url->path());
    if (success != true) {
        strOut.append(rest2.lastErrorText());
        strOut.append("\r\n");
        delete url;
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    delete url;

    // Read the response header.  
    // We want to first get the response header to see if it's a successful
    // response status code.  If not, then the response will not be a text/event-stream
    // and we should read the response body normally.
    int responseStatusCode = rest2.ReadResponseHeader();
    if (responseStatusCode < 0) {
        strOut.append(rest2.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // If successful, a 200 response code is expected.
    // If the reponse code is not 200, then read the response body and fail..
    if (responseStatusCode != 200) {
        strOut.append("Response Code: ");
        strOut.appendInt(responseStatusCode);
        strOut.append("\r\n");
        strOut.append("Response Status Text: ");
        strOut.append(rest2.responseStatusText());
        strOut.append("\r\n");
        strOut.append("Response Header: ");
        strOut.append(rest2.responseHeader());
        strOut.append("\r\n");
        responseBody = rest2.readRespBodyString();
        if (rest2.get_LastMethodSuccess() == true) {
            strOut.append("Error Response Body: ");
            strOut.append(responseBody);
            strOut.append("\r\n");
        }

        strOut.append("Failed.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // For this example, our JSON database will be empty at the beginning.
    // The incoming events (put and patch) will be applied to this database.
    CkJsonObject jsonDb;

    // Make sure to set the JSON path delimiter to "/".  The default is "." and this
    // is not compatible with Firebase paths.
    jsonDb.put_DelimiterChar("/");

    // At this point, we've received the response header.  Now it's time to begin
    // receiving the event stream.  We'll start a background thread to read the 
    // stream.  (Our main application (foreground) thread can cancel it at any time.)  
    // While receiving in the background thread, our foreground thread can read the stream
    // as it desires..
    CkStream eventStream;

    // This sse object will be used as a helper to parse the server-sent event stream.
    CkServerSentEvent sse;

    CkTask *task = rest2.ReadRespBodyStreamAsync(eventStream,true);
    task->Run();

    // For this example, we'll just read a few events, and then cancel the
    // async task.
    int count = 0;
    while ((count < 3) && (task->get_Finished() == false)) {

        // Get the next event, which is a series of text lines ending with
        // a blank line. 
        // Note: This method blocks the calling thread until a message arrives.
        // a program might instead periodically check the availability of
        // data via the stream's DataAvailable property, and then do the read.

        // An alternative to writing a while loop to read the event stream
        // would be to setup some sort of timer event in your program (using whatever timer functionality
        // is provided in a programming language/environment), to periodically check the eventStream's
        // DataAvailable property and consume the incoming event.
        const char *eventStr = eventStream.readUntilMatch("\r\n\r\n");
        if (eventStream.get_LastMethodSuccess() != true) {
            strOut.append(eventStream.lastErrorText());
            strOut.append("\r\n");
            // Force the loop to exit by setting the count to a high number.
            count = 99999;
        }
        else {
            strOut.append("Event: [");
            strOut.append(eventStr);
            strOut.append("]");
            strOut.append("\r\n");

            // We have an event. Let's update our local copy of the JSON database.
            success = sse.LoadEvent(eventStr);
            if (success != true) {
                strOut.append("Failed to load sse event: ");
                strOut.append(eventStr);
                strOut.append("\r\n");
            }
            else {
                // Now we can easily access the event name and data, and apply it to our JSON database:
                success = jsonDb.FirebaseApplyEvent(sse.eventName(),sse.data());
                if (success != true) {
                    strOut.append("Failed to apply event: ");
                    strOut.append(sse.eventName());
                    strOut.append(": ");
                    strOut.append(sse.data());
                    strOut.append("\r\n");
                }
                else {
                    strOut.append("Successfully applied event: ");
                    strOut.append(sse.eventName());
                    strOut.append(": ");
                    strOut.append(sse.data());
                    strOut.append("\r\n");
                }

            }

        }

        count = count + 1;
    }

    // Make sure the background task is cancelled if still running.
    task->Cancel();

    delete task;

    // Examine the JSON database after applying events..
    jsonDb.put_EmitCompact(false);
    strOut.append("----");
    strOut.append("\r\n");
    strOut.append(jsonDb.emit());
    strOut.append("\r\n");


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }