Semnodime/aiohttp_demo.py

## aiohttp_demo.py
"""Small demo of a single async request utilizing the aiohttp framework. The point is to understand what is going on."""
import aiohttp
import asyncio


async def main():
    async with aiohttp.ClientSession() as session:
        # session.get() returns a context manager that can be used by `await` and `async with`
        _req_context_manager = session.get('http://localhost:10000')
        # print(_req_context_manager)
        # it is recommended to use the `async with … as …:` similarly to how you would use `with … as …:` for files.
        # you can use `async with` to automatically close the request when done or when exceptions occur
        async with _req_context_manager as response:
            # print(response)
            while True:
                print('Attempting to read content stream…')
                a = await response.content.read(10)
                print('Data: %r' % a)
                if not a:
                    break

            # .text() has to be used with `await` in order to be truly executed
            # it only returns a ClientResponse.text
            print('TEXT()________', response.text())  # <generator object ClientResponse.text at …>
            # once you await this co-routine it loads all response content into memory and tries to return decoded text
            if True:
                print('AWAIT TEXT()__', repr((await response.text())[:20]))  # '<!doctype html>\n<!--'
                # Accessing .text() automatically closes the response
                # If you use .content.read() without `async with … as …:` make sure to close the request manually!

            # you can also access the binary (already deflated but not decoded) content directly for streaming
            # the .content is no function!
            # it is a StreamReader
            flow_control_stream_reader = response.content
            print('CONTENT', flow_control_stream_reader)  # <StreamReader 2225 bytes>
            # it has an asynchronous .read() which returns the co-routine that can be used by `await`
            print('CONTENT.read(10)_____', flow_control_stream_reader.read(20))  # <generator object …>
            # so if you `await` .content.read() you read from the content buffer of the response
            print('AWAIT CONTENT.read(10)', await flow_control_stream_reader.read(20))  # b''
            # since we called await .text() on the response we already emptied and closed the read stream
            # you can confirm this behaviour by deactivating the `if True:…` some lines above
            # then .content.read(10) will read 10 bytes: b'<!doctype html>\n<!--'


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())
    # The console output with python3.6 is the following (with censored memory addresses):
    r'''
    <aiohttp.client._RequestContextManager object at …>
    <ClientResponse(https://www.python.org/) [200 OK]>
    <CIMultiDictProxy('Server': 'nginx', 'Content-Type': 'text/html; charset=utf-8', 'X-Frame-Options': 'SAMEORIGIN', 'X-Xss-Protection': '1; mode=block', 'X-Clacks-Overhead': 'GNU Terry Pratchett', 'Via': '1.1 varnish', 'Content-Length': '49060', 'Accept-Ranges': 'bytes', 'Date': 'Tue, 25 Sep 2018 10:11:21 GMT', 'Via': '1.1 varnish', 'Age': '2002', 'Connection': 'keep-alive', 'X-Served-By': 'cache-iad2134-IAD, cache-hhn1520-HHN', 'X-Cache': 'HIT, HIT', 'X-Cache-Hits': '1, 4', 'X-Timer': 'S1537870282.892255,VS0,VE0', 'Vary': 'Cookie', 'Strict-Transport-Security': 'max-age=63072000; includeSubDomains')>

    TEXT()________ <generator object ClientResponse.text at …>
    CONTENT <StreamReader 2225 bytes>
    CONTENT.read(10)_____ <generator object FlowControlStreamReader.read at …>
    AWAIT TEXT()__ '<!doctype html>\n<!--'
    AWAIT CONTENT.read(10) b''

    Process finished with exit code 0
    '''
	"""Small demo of a single async request utilizing the aiohttp framework. The point is to understand what is going on."""
	import aiohttp
	import asyncio


	async def main():
	async with aiohttp.ClientSession() as session:
	# session.get() returns a context manager that can be used by `await` and `async with`
	_req_context_manager = session.get('http://localhost:10000')
	# print(_req_context_manager)
	# it is recommended to use the `async with … as …:` similarly to how you would use `with … as …:` for files.
	# you can use `async with` to automatically close the request when done or when exceptions occur
	async with _req_context_manager as response:
	# print(response)
	while True:
	print('Attempting to read content stream…')
	a = await response.content.read(10)
	print('Data: %r' % a)
	if not a:
	break

	# .text() has to be used with `await` in order to be truly executed
	# it only returns a ClientResponse.text
	print('TEXT()________', response.text()) # <generator object ClientResponse.text at …>
	# once you await this co-routine it loads all response content into memory and tries to return decoded text
	if True:
	print('AWAIT TEXT()__', repr((await response.text())[:20])) # '<!doctype html>\n<!--'
	# Accessing .text() automatically closes the response
	# If you use .content.read() without `async with … as …:` make sure to close the request manually!

	# you can also access the binary (already deflated but not decoded) content directly for streaming
	# the .content is no function!
	# it is a StreamReader
	flow_control_stream_reader = response.content
	print('CONTENT', flow_control_stream_reader) # <StreamReader 2225 bytes>
	# it has an asynchronous .read() which returns the co-routine that can be used by `await`
	print('CONTENT.read(10)_____', flow_control_stream_reader.read(20)) # <generator object …>
	# so if you `await` .content.read() you read from the content buffer of the response
	print('AWAIT CONTENT.read(10)', await flow_control_stream_reader.read(20)) # b''
	# since we called await .text() on the response we already emptied and closed the read stream
	# you can confirm this behaviour by deactivating the `if True:…` some lines above
	# then .content.read(10) will read 10 bytes: b'<!doctype html>\n<!--'


	if __name__ == '__main__':
	loop = asyncio.get_event_loop()
	loop.run_until_complete(main())
	# The console output with python3.6 is the following (with censored memory addresses):
	r'''
	<aiohttp.client._RequestContextManager object at …>
	<ClientResponse(https://www.python.org/) [200 OK]>
	<CIMultiDictProxy('Server': 'nginx', 'Content-Type': 'text/html; charset=utf-8', 'X-Frame-Options': 'SAMEORIGIN', 'X-Xss-Protection': '1; mode=block', 'X-Clacks-Overhead': 'GNU Terry Pratchett', 'Via': '1.1 varnish', 'Content-Length': '49060', 'Accept-Ranges': 'bytes', 'Date': 'Tue, 25 Sep 2018 10:11:21 GMT', 'Via': '1.1 varnish', 'Age': '2002', 'Connection': 'keep-alive', 'X-Served-By': 'cache-iad2134-IAD, cache-hhn1520-HHN', 'X-Cache': 'HIT, HIT', 'X-Cache-Hits': '1, 4', 'X-Timer': 'S1537870282.892255,VS0,VE0', 'Vary': 'Cookie', 'Strict-Transport-Security': 'max-age=63072000; includeSubDomains')>

	TEXT()________ <generator object ClientResponse.text at …>
	CONTENT <StreamReader 2225 bytes>
	CONTENT.read(10)_____ <generator object FlowControlStreamReader.read at …>
	AWAIT TEXT()__ '<!doctype html>\n<!--'
	AWAIT CONTENT.read(10) b''

	Process finished with exit code 0
	'''