2016-05-03 01:39:04 +01:00
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Network - TCP sockets
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=====================
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The building block of most of the internet is the TCP socket. These sockets
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provide a reliable stream of bytes between the connected network devices.
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This part of the tutorial will show how to use TCP sockets in a few different
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cases.
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Star Wars Asciimation
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---------------------
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The simplest thing to do is to download data from the internet. In this case
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we will use the Star Wars Asciimation service provided by the blinkenlights.nl
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website. It uses the telnet protocol on port 23 to stream data to anyone that
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connects. It's very simple to use because it doesn't require you to
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authenticate (give a username or password), you can just start downloading data
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straight away.
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The first thing to do is make sure we have the socket module available::
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>>> import socket
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Then get the IP address of the server::
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>>> addr_info = socket.getaddrinfo("towel.blinkenlights.nl", 23)
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The ``getaddrinfo`` function actually returns a list of addresses, and each
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address has more information than we need. We want to get just the first valid
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address, and then just the IP address and port of the server. To do this use::
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>>> addr = addr_info[0][-1]
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If you type ``addr_info`` and ``addr`` at the prompt you will see exactly what
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information they hold.
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Using the IP address we can make a socket and connect to the server::
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>>> s = socket.socket()
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2016-05-08 07:24:24 +01:00
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>>> s.connect(addr)
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2016-05-03 01:39:04 +01:00
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Now that we are connected we can download and display the data::
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>>> while True:
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... data = s.recv(500)
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... print(str(data, 'utf8'), end='')
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...
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When this loop executes it should start showing the animation (use ctrl-C to
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interrupt it).
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You should also be able to run this same code on your PC using normal Python if
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you want to try it out there.
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HTTP GET request
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----------------
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The next example shows how to download a webpage. HTTP uses port 80 and you
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first need to send a "GET" request before you can download anything. As part
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of the request you need to specify the page to retrieve.
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Let's define a function that can download and print a URL::
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def http_get(url):
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_, _, host, path = url.split('/', 3)
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addr = socket.getaddrinfo(host, 80)[0][-1]
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s = socket.socket()
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s.connect(addr)
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s.send(bytes('GET /%s HTTP/1.0\r\nHost: %s\r\n\r\n' % (path, host), 'utf8'))
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while True:
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data = s.recv(100)
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if data:
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print(str(data, 'utf8'), end='')
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else:
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break
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Make sure that you import the socket module before running this function. Then
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you can try::
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>>> http_get('http://micropython.org/ks/test.html')
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This should retrieve the webpage and print the HTML to the console.
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Simple HTTP server
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------------------
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The following code creates an simple HTTP server which serves a single webpage
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that contains a table with the state of all the GPIO pins::
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import machine
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pins = [machine.Pin(i, machine.Pin.IN) for i in (0, 2, 4, 5, 12, 13, 14, 15)]
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html = """<!DOCTYPE html>
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<html>
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<head> <title>ESP8266 Pins</title> </head>
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<body> <h1>ESP8266 Pins</h1>
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<table border="1"> <tr><th>Pin</th><th>Value</th></tr> %s </table>
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</body>
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</html>
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"""
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import socket
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addr = socket.getaddrinfo('0.0.0.0', 80)[0][-1]
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s = socket.socket()
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s.bind(addr)
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s.listen(1)
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print('listening on', addr)
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while True:
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cl, addr = s.accept()
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print('client connected from', addr)
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cl_file = cl.makefile('rwb', 0)
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while True:
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line = cl_file.readline()
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if not line or line == b'\r\n':
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break
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rows = ['<tr><td>%s</td><td>%d</td></tr>' % (str(p), p.value()) for p in pins]
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response = html % '\n'.join(rows)
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cl.send(response)
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cl.close()
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