• Compress the HTML with gzip and use the compressed file instead. You must specify

  Content-Encoding" : "gzip"

  in the response header for this to work

Add a program that controls the user programmable LED on the CPU via the WEB. Use two buttons to switch the LED on or off and an image to show its current state.

Exercise 5: Server Side Events

In case of AJAX it is the client (browser) who repeatedly asks for new measurement, and it is therefore the browser who determines the timing. Often however, the server should send its data as soon as they are ready. This can be achieved with "server side events". Please see this tutorial for more details: https://www.w3schools.com/html/html5_serversentevents.asp]].

Modify exercise 4 to use server side events instead of AJAX for the communication between server and browser.

Exercise 6: Web Sockets

While AJAX and server side events depend on the cmd/response protocole off HTML, web sockets use the own protocol and provide full duplex communication.
See https://www.tutorialspoint.com/websockets/index.htm for more details.

First study the websocket examples given in the microdot examples section and then rewrite exercise 4/5 using web sockets.

Exercise 2: microdot

https://microdot.readthedocs.io/en/latest/

Both, picoweb and microdot are already included in the microPython firmware:

• Modify the hello.py example from microdot to display your own WEB page
• Separate the HTML code into a separate file and upload it to the "html" folder on the ESP32. Create this folder if it does not exist yet.
• Compress the HTML with gzip and use the compressed file instead. You must specify
  Content-Encoding" : "gzip"
  for this to work

• https://www.w3schools.com/js/DEFAULT.asp
• https://www.w3schools.com/xml/ajax_intro.asp

To improve your program even further, you can plot the incoming measurements with the Highcharts JavaScript library.

Exercise 2: picoweb

Download picoweb and its example programms from gitthub: https://github.com/pfalcon/picoweb.

You can find several tutorials on picoweb on the Internet:

• https://www.dfrobot.com/blog-742.html
• https://techtutorialsx.com/2017/09/01/esp32-micropython-http-webserver-with-picoweb

For more information on the use of picoweb you will have to study the examples distributed with the github repository or picoweb itself. The examples demonstrate most of picoweb's features.

Re-write the example from exercise 1 using the picoweb framework. Now the HTML page is separated from the code and must be stored in a separate file. Upload this file to the ESP32 into a folder named html. Create the folder if it does not exist yet. You may also compress the HTML file with gzip and transfer the compressed file to the browser thus limiting the size of the message that must be sent.

Exercise 3: Provide Measurement Data on the WEB Page

Exercise 4: Ajax

Print the incoming HTTP request, which will look similar to this:

The request starts with "Content Get / HTTP/1.1"

The page seen by the browser will look similar to this:

utemplates

picoweb

This is how your WEB site for SHT30 measurements might look like (screen dump of the solution script):

Exercise 3: Ajax

The above exercise has a major flaw: For each measurement you must reload the entire page. It would be much nicer it the WEB page could be updated whenever a new measurement comes in.

Version 1:

The server then starts listening for incoming an connection request and establishes a connection by accepting it.

s.listen(5) print("Starting the Hello World WEB server on IP address ",ipaddr,"port 80")
while True: 
    conn,addr=s.accept()      print("GOT a connection from %s" % str(addr))

Finally it reads an http request from the connection and answers with its Hello World page:

    request=conn.recv(1024)
    print("Content %s" % str(request))
    request=str(request)     response=html      conn.send(response)      conn.close()

html is the http string to be sent.

Please check https://docs.micropython.org/en/latest/library/usocket.html for more details.

Version 2:

In the second version we will separate the HTML text from the server and store it in the html directory (to be creatd with ampy) on the ESP32. Now we can use a ready made Web server for MicroPython, picoweb to serve the page.

Version 3:

If we do not use an external SD card, then space for the HTML pages is rather limited. It may therefore be interesting to use gzip compresses pages. Modify your picoweb server to use gzipped HTML.

Exercise 2: Provide Measurement Data on the WEB Page

Modify the WEB server to provide temperature and humidity measured with the SHT30.

A WEB Server and the HTTP Protocol

Exercise 1: Write a Hello World WEB Server

Let's start simple and produce a WB server that simply sends "Hello World!" to the browser when called.

-- Uli Raich - 2020-05-27

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