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(VB.NET) Firebase Receive Server-Sent Events (text/event-stream)
Demonstrates how to start receiving server-sent events and update your JSON database with each event.
Important: A problem in reading the response text/event-stream was found and fixed after the release of Chilkat v188.8.131.52. This example is valid for Chilkat v184.108.40.206 and greater. (At the time of this writing, which is 18-Sep-2017, Chilkat v220.127.116.11 is not yet released. A .70 pre-release can be obtained by sending a request to firstname.lastname@example.org.)
' --------------------------------------------------------------------------------------------- ' Important: A problem in reading the response text/event-stream was found and fixed after the release of Chilkat v18.104.22.168. ' This example is valid for Chilkat v22.214.171.124 and greater. ' (At the time of this writing, which is 18-Sep-2017, Chilkat v126.96.36.199 is not yet released. ' A .70 pre-release can be obtained by sending a request to email@example.com.) ' --------------------------------------------------------------------------------------------- ' 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. Dim fac As New Chilkat.FileAccess Dim accessToken As String = fac.ReadEntireTextFile("qa_data/tokens/firebaseToken.txt","utf-8") If (fac.LastMethodSuccess <> True) Then Debug.WriteLine(fac.LastErrorText) Exit Sub End If Dim rest As New Chilkat.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. Dim success As Boolean = rest.Connect("chilkat.firebaseio.com",443,True,True) If (success <> True) Then Debug.WriteLine(rest.LastErrorText) Exit Sub End If Dim authGoogle As New Chilkat.AuthGoogle authGoogle.AccessToken = accessToken rest.SetAuthGoogle(authGoogle) rest.AddHeader("Accept","text/event-stream") rest.AddHeader("Cache-Control","no-cache") Dim responseBody As String = rest.FullRequestNoBody("GET","/.json") ' A 307 redirect response is expected. If (rest.ResponseStatusCode <> 307) Then Debug.WriteLine("Unexpected response code: " & rest.ResponseStatusCode) Debug.WriteLine(responseBody) Debug.WriteLine("Failed.") Exit Sub End If ' Get the redirect URL Dim url As Chilkat.Url = rest.RedirectUrl() If (rest.LastMethodSuccess <> True) Then Debug.WriteLine(rest.LastErrorText) Exit Sub End If Debug.WriteLine("redirect URL domain: " & url.Host) Debug.WriteLine("redirect URL path: " & url.Path) Debug.WriteLine("redirect URL query params: " & url.Query) Debug.WriteLine("redirect URL path with query params: " & url.PathWithQueryParams) ' Our text/event-stream will be obtained from the redirect URL... Dim rest2 As New Chilkat.Rest success = rest2.Connect(url.Host,443,True,True) If (success <> True) Then Debug.WriteLine(rest2.LastErrorText) Exit Sub End If 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) Then Debug.WriteLine(rest2.LastErrorText) Exit Sub End If ' 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. Dim responseStatusCode As Integer = rest2.ReadResponseHeader() If (responseStatusCode < 0) Then Debug.WriteLine(rest2.LastErrorText) Exit Sub End If ' 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) Then Debug.WriteLine("Response Code: " & responseStatusCode) Debug.WriteLine("Response Status Text: " & rest2.ResponseStatusText) Debug.WriteLine("Response Header: " & rest2.ResponseHeader) responseBody = rest2.ReadRespBodyString() If (rest2.LastMethodSuccess = True) Then Debug.WriteLine("Error Response Body: " & responseBody) End If Debug.WriteLine("Failed.") Exit Sub End If ' For this example, our JSON database will be empty at the beginning. ' The incoming events (put and patch) will be applied to this database. Dim jsonDb As New Chilkat.JsonObject ' Make sure to set the JSON path delimiter to "/". The default is "." and this ' is not compatible with Firebase paths. jsonDb.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.. Dim eventStream As New Chilkat.Stream ' This sse object will be used as a helper to parse the server-sent event stream. Dim sse As New Chilkat.ServerSentEvent Dim task As Chilkat.Task = rest2.ReadRespBodyStreamAsync(eventStream,True) task.Run() ' For this example, we'll just read a few events, and then cancel the ' async task. Dim count As Integer = 0 While (count < 3) And (task.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. Dim eventStr As String = eventStream.ReadUntilMatch(vbCrLf & vbCrLf) If (eventStream.LastMethodSuccess <> True) Then Debug.WriteLine(eventStream.LastErrorText) ' Force the loop to exit by setting the count to a high number. count = 99999 Else Debug.WriteLine("Event: [" & eventStr & "]") ' We have an event. Let's update our local copy of the JSON database. success = sse.LoadEvent(eventStr) If (success <> True) Then Debug.WriteLine("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 = jsonDb.FirebaseApplyEvent(sse.EventName,sse.Data) If (success <> True) Then Debug.WriteLine("Failed to apply event: " & sse.EventName & ": " & sse.Data) Else Debug.WriteLine("Successfully applied event: " & sse.EventName & ": " & sse.Data) End If End If End If count = count + 1 End While ' Make sure the background task is cancelled if still running. task.Cancel() ' Examine the JSON database after applying events.. jsonDb.EmitCompact = False Debug.WriteLine("----") Debug.WriteLine(jsonDb.Emit())
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