(PureBasic) 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 PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkJsonObject.pb"
IncludeFile "CkTask.pb"
IncludeFile "CkFileAccess.pb"
IncludeFile "CkUrl.pb"
IncludeFile "CkStream.pb"
IncludeFile "CkAuthGoogle.pb"
IncludeFile "CkRest.pb"
IncludeFile "CkServerSentEvent.pb"

Procedure ChilkatExample()

    ; 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.
    fac.i = CkFileAccess::ckCreate()
    If fac.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    accessToken.s = CkFileAccess::ckReadEntireTextFile(fac,"qa_data/tokens/firebaseToken.txt","utf-8")
    If CkFileAccess::ckLastMethodSuccess(fac) <> 1
        Debug CkFileAccess::ckLastErrorText(fac)
        CkFileAccess::ckDispose(fac)
        ProcedureReturn
    EndIf

    rest.i = CkRest::ckCreate()
    If rest.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; 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.  
    success.i = CkRest::ckConnect(rest,"chilkat.firebaseio.com",443,1,1)
    If success <> 1
        Debug CkRest::ckLastErrorText(rest)
        CkFileAccess::ckDispose(fac)
        CkRest::ckDispose(rest)
        ProcedureReturn
    EndIf

    authGoogle.i = CkAuthGoogle::ckCreate()
    If authGoogle.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkAuthGoogle::setCkAccessToken(authGoogle, accessToken)
    CkRest::ckSetAuthGoogle(rest,authGoogle)

    CkRest::ckAddHeader(rest,"Accept","text/event-stream")
    CkRest::ckAddHeader(rest,"Cache-Control","no-cache")

    responseBody.s = CkRest::ckFullRequestNoBody(rest,"GET","/.json")

    ; A 307 redirect response is expected.
    If CkRest::ckResponseStatusCode(rest) <> 307
        Debug "Unexpected response code: " + Str(CkRest::ckResponseStatusCode(rest))
        Debug responseBody
        Debug "Failed."
        CkFileAccess::ckDispose(fac)
        CkRest::ckDispose(rest)
        CkAuthGoogle::ckDispose(authGoogle)
        ProcedureReturn
    EndIf

    ; Get the redirect URL
    url.i = CkRest::ckRedirectUrl(rest)
    If CkRest::ckLastMethodSuccess(rest) <> 1
        Debug CkRest::ckLastErrorText(rest)
        CkFileAccess::ckDispose(fac)
        CkRest::ckDispose(rest)
        CkAuthGoogle::ckDispose(authGoogle)
        ProcedureReturn
    EndIf

    Debug "redirect URL domain: " + CkUrl::ckHost(url)
    Debug "redirect URL path: " + CkUrl::ckPath(url)
    Debug "redirect URL query params: " + CkUrl::ckQuery(url)
    Debug "redirect URL path with query params: " + CkUrl::ckPathWithQueryParams(url)

    ; Our text/event-stream will be obtained from the redirect URL...
    rest2.i = CkRest::ckCreate()
    If rest2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkRest::ckConnect(rest2,CkUrl::ckHost(url),443,1,1)
    If success <> 1
        Debug CkRest::ckLastErrorText(rest2)
        CkUrl::ckDispose(url)

        CkFileAccess::ckDispose(fac)
        CkRest::ckDispose(rest)
        CkAuthGoogle::ckDispose(authGoogle)
        CkRest::ckDispose(rest2)
        ProcedureReturn
    EndIf

    CkRest::ckAddHeader(rest2,"Accept","text/event-stream")
    CkRest::ckAddHeader(rest2,"Cache-Control","no-cache")

    ; Add the redirect query params to the request
    CkRest::ckAddQueryParams(rest2,CkUrl::ckQuery(url))

    ; In our case, we don't actually need the auth query param,
    ; so remove it.
    CkRest::ckRemoveQueryParam(rest2,"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 = CkRest::ckSendReqNoBody(rest2,"GET",CkUrl::ckPath(url))
    If success <> 1
        Debug CkRest::ckLastErrorText(rest2)
        CkUrl::ckDispose(url)

        CkFileAccess::ckDispose(fac)
        CkRest::ckDispose(rest)
        CkAuthGoogle::ckDispose(authGoogle)
        CkRest::ckDispose(rest2)
        ProcedureReturn
    EndIf

    CkUrl::ckDispose(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.
    responseStatusCode.i = CkRest::ckReadResponseHeader(rest2)
    If responseStatusCode < 0
        Debug CkRest::ckLastErrorText(rest2)
        CkFileAccess::ckDispose(fac)
        CkRest::ckDispose(rest)
        CkAuthGoogle::ckDispose(authGoogle)
        CkRest::ckDispose(rest2)
        ProcedureReturn
    EndIf

    ; 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
        Debug "Response Code: " + Str(responseStatusCode)
        Debug "Response Status Text: " + CkRest::ckResponseStatusText(rest2)
        Debug "Response Header: " + CkRest::ckResponseHeader(rest2)
        responseBody = CkRest::ckReadRespBodyString(rest2)
        If CkRest::ckLastMethodSuccess(rest2) = 1
            Debug "Error Response Body: " + responseBody
        EndIf

        Debug "Failed."
        CkFileAccess::ckDispose(fac)
        CkRest::ckDispose(rest)
        CkAuthGoogle::ckDispose(authGoogle)
        CkRest::ckDispose(rest2)
        ProcedureReturn
    EndIf

    ; For this example, our JSON database will be empty at the beginning.
    ; The incoming events (put and patch) will be applied to this database.
    jsonDb.i = CkJsonObject::ckCreate()
    If jsonDb.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

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

    ; 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..
    eventStream.i = CkStream::ckCreate()
    If eventStream.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; This sse object will be used as a helper to parse the server-sent event stream.
    sse.i = CkServerSentEvent::ckCreate()
    If sse.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    task.i = CkRest::ckReadRespBodyStreamAsync(rest2,eventStream,1)
    CkTask::ckRun(task)

    ; For this example, we'll just read a few events, and then cancel the
    ; async task.
    count.i = 0
    While (count < 3) AND (CkTask::ckFinished(task) = 0)

        ; 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.
        eventStr.s = CkStream::ckReadUntilMatch(eventStream,Chr(13) + Chr(10) + Chr(13) + Chr(10))
        If CkStream::ckLastMethodSuccess(eventStream) <> 1
            Debug CkStream::ckLastErrorText(eventStream)
            ; Force the loop to exit by setting the count to a high number.
            count = 99999
        Else
            Debug "Event: [" + eventStr + "]"

            ; We have an event. Let's update our local copy of the JSON database.
            success = CkServerSentEvent::ckLoadEvent(sse,eventStr)
            If success <> 1
                Debug "Failed to load sse event: " + eventStr
            Else
                ; Now we can easily access the event name and data, and apply it to our JSON database:
                success = CkJsonObject::ckFirebaseApplyEvent(jsonDb,CkServerSentEvent::ckEventName(sse),CkServerSentEvent::ckData(sse))
                If success <> 1
                    Debug "Failed to apply event: " + CkServerSentEvent::ckEventName(sse) + ": " + CkServerSentEvent::ckData(sse)
                Else
                    Debug "Successfully applied event: " + CkServerSentEvent::ckEventName(sse) + ": " + CkServerSentEvent::ckData(sse)
                EndIf

            EndIf

        EndIf

        count = count + 1
    Wend

    ; Make sure the background task is cancelled if still running.
    CkTask::ckCancel(task)

    CkTask::ckDispose(task)

    ; Examine the JSON database after applying events..
    CkJsonObject::setCkEmitCompact(jsonDb, 0)
    Debug "----"
    Debug CkJsonObject::ckEmit(jsonDb)


    CkFileAccess::ckDispose(fac)
    CkRest::ckDispose(rest)
    CkAuthGoogle::ckDispose(authGoogle)
    CkRest::ckDispose(rest2)
    CkJsonObject::ckDispose(jsonDb)
    CkStream::ckDispose(eventStream)
    CkServerSentEvent::ckDispose(sse)


    ProcedureReturn
EndProcedure