Understanding prepare() RuntimeError on StreamResponse object

[mdublin]

I am attempting to build a really simple server endpoint that streams some byte data (supposed to response to a Range request from a client) using an instance of the web.StreamResponse class. I know in the older versions, start() is required before write(), but is prepare() meant to replace start() ?

# simple func to provide byte data
def bytesource():
    videofile = open('bytedump.txt', 'rb')
    byteload = videofile.read()
    return byteload[10:2000] 

# basic view intended to provide byte data
async def bytedata(request):
    stream = web.StreamResponse(status=200, reason='OK')

    stream.headers['Content-Type'] = 'text/html; charset=utf-8'
    stream.headers['Cache-Control'] = 'no-cache'
    stream.headers['Connection'] = 'keep-alive'
    stream.headers['Accept-Ranges'] = 'bytes'

    #stream.start(request)
    #stream._start(request)
    #stream.prepare(request)

    msg= bytesource()
    stream.write(msg)

    stream.write_eof()
    return stream

If I uncomment out stream.prepare(request), I get back:

RuntimeError: Cannot call write() before start()

If I try stream.start(request) I obviously get:

AttributeError: 'StreamResponse' objet has no attribute 'start'

Finally however, if I try: stream._start(request) everything works, and I get my byte data response sent to the client, and everything is ok.

But clearly, I am not meant to use a private class method here, right? What am I doing wrong or what am I missing in my understanding of how to implement such a view correctly?

Thank you for any help you can provide.

[fafhrd91]

I updated exception text,

here is reference to stream response http://aiohttp.readthedocs.io/en/stable/web_reference.html#streamresponse

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