CkPython

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

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

import sys
import chilkat

success = False

# 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 = chilkat.CkFileAccess()
accessToken = fac.readEntireTextFile("qa_data/tokens/firebaseToken.txt","utf-8")
if (fac.get_LastMethodSuccess() == False):
    print(fac.lastErrorText())
    sys.exit()

rest = chilkat.CkRest()

# 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 = rest.Connect("chilkat.firebaseio.com",443,True,True)
if (success == False):
    print(rest.lastErrorText())
    sys.exit()

authGoogle = chilkat.CkAuthGoogle()
authGoogle.put_AccessToken(accessToken)
rest.SetAuthGoogle(authGoogle)

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

responseBody = rest.fullRequestNoBody("GET","/.json")

# A 307 redirect response is expected.
if (rest.get_ResponseStatusCode() != 307):
    print("Unexpected response code: " + str(rest.get_ResponseStatusCode()))
    print(responseBody)
    print("Failed.")
    sys.exit()

# Get the redirect URL
urlStr = rest.lastRedirectUrl()
url = chilkat.CkUrl()
url.ParseUrl(urlStr)

print("redirect URL domain: " + url.host())
print("redirect URL path: " + url.path())
print("redirect URL query params: " + url.query())
print("redirect URL path with query params: " + url.pathWithQueryParams())

# Our text/event-stream will be obtained from the redirect URL...
rest2 = chilkat.CkRest()

success = rest2.Connect(url.host(),443,True,True)
if (success != True):
    print(rest2.lastErrorText())
    sys.exit()

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):
    print(rest2.lastErrorText())
    sys.exit()

# 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 = rest2.ReadResponseHeader()
if (responseStatusCode < 0):
    print(rest2.lastErrorText())
    sys.exit()

# 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):
    print("Response Code: " + str(responseStatusCode))
    print("Response Status Text: " + rest2.responseStatusText())
    print("Response Header: " + rest2.responseHeader())
    responseBody = rest2.readRespBodyString()
    if (rest2.get_LastMethodSuccess() == True):
        print("Error Response Body: " + responseBody)

    print("Failed.")
    sys.exit()

# 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 = chilkat.CkJsonObject()

# 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..
eventStream = chilkat.CkStream()

# This sse object will be used as a helper to parse the server-sent event stream.
sse = chilkat.CkServerSentEvent()

# task is a CkTask
task = rest2.ReadRespBodyStreamAsync(eventStream,True)
task.Run()

# For this example, we'll just read a few events, and then cancel the
# async task.
count = 0
while (count < 3) and (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.
    eventStr = eventStream.readUntilMatch("\r\n\r\n")
    if (eventStream.get_LastMethodSuccess() != True):
        print(eventStream.lastErrorText())
        # Force the loop to exit by setting the count to a high number.
        count = 99999
    else:
        print("Event: [" + eventStr + "]")

        # We have an event. Let's update our local copy of the JSON database.
        success = sse.LoadEvent(eventStr)
        if (success != True):
            print("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):
                print("Failed to apply event: " + sse.eventName() + ": " + sse.data())
            else:
                print("Successfully applied event: " + sse.eventName() + ": " + sse.data())

    count = count + 1

# Make sure the background task is cancelled if still running.
task.Cancel()

# Examine the JSON database after applying events..
jsonDb.put_EmitCompact(False)
print("----")
print(jsonDb.emit())