:orphan:

Server
------

Setting up web a server on ESP8266 requires very little code and is surprisingly straightforward. This is thanks to functionality provided by the versatile ESP8266WiFi library.

The purpose of this example will be to prepare a web page that can be opened in a web browser. This page should show the current raw reading of ESP's analog input pin.

Table of Contents
-----------------

-  `The Object <#the-object>`__
-  `The Page <#the-page>`__
-  `Header First <#header-first>`__
-  `The Page is Served <#the-page-is-served>`__
-  `Get it Together <#put-it-together>`__
-  `Get it Run <#get-it-run>`__
-  `What Else? <#what-else>`__
-  `Conclusion <#conclusion>`__

The Object
~~~~~~~~~~

We will start off by creating a server object.

.. code:: cpp

    WiFiServer server(80);

The server responds to clients (in this case - web browsers) on port 80, which is a standard port web browsers talk to web servers.

The Page
~~~~~~~~

Then let's write a short function ``prepareHtmlPage()``, that will return a ``String`` class variable containing the contents of the web page. We will then pass this variable to server to pass it over to a client.

.. code:: cpp

    String prepareHtmlPage()
    {
      String htmlPage = 
         String("HTTP/1.1 200 OK\r\n") +
                "Content-Type: text/html\r\n" +
                "Connection: close\r\n" +  // the connection will be closed after completion of the response
                "Refresh: 5\r\n" +  // refresh the page automatically every 5 sec
                "\r\n" +
                "<!DOCTYPE HTML>" +
                "<html>" +
                "Analog input:  " + String(analogRead(A0)) +
                "</html>" +
                "\r\n";
      return htmlPage;
    }

The function does nothing fancy but just puts together a text header and `HTML <https://www.w3schools.com/html/>`__ contents of the page.

Header First
~~~~~~~~~~~~

The header is to inform client what type of contents is to follow and how it will be served:

::

    Content-Type: text/html
    Connection: close
    Refresh: 5

In our example the content type is ``text/html``, the connection will be closed after serving and the content should be requested by the client again every 5 seconds. The header is concluded with an empty line ``\r\n``. This is to distinguish header from the content to follow.

::

    <!DOCTYPE HTML>
    <html>
    Analog input:  [Value]
    </html>

The content contains two basic `HTML <https://www.w3schools.com/html/>`__ tags, one to denote HTML document type ``<!DOCTYPE HTML>`` and another to mark beginning ``<html>`` and end ``</html>`` of the document. Inside there is a raw value read from ESP's analog input ``analogRead(A0)`` converted to the ``String`` type.

.. code:: cpp

    String(analogRead(A0))

The Page is Served
~~~~~~~~~~~~~~~~~~

Serving of this web page will be done in the ``loop()`` where server is waiting for a new client to connect and send some data containing a request:

.. code:: cpp

    void loop()
    {
      WiFiClient client = server.available(); 
      if (client)
      {
        // we have a new client sending some request
      }
    }

Once a new client is connected, server will read the client's request and print it out on a serial monitor.

.. code:: cpp

    while (client.connected())
    {
      if (client.available())
      {
        String line = client.readStringUntil('\r');
        Serial.print(line);
      }
    }

Request from the client is marked with an empty new line. If we find this mark, we can send back the web page and exit ``while()`` loop using ``break``.

.. code:: cpp

    if (line.length() == 1 && line[0] == '\n')
    {
        client.println(prepareHtmlPage());
        break;
    }

The whole process is concluded by stopping the connection with client:

.. code:: cpp

    client.stop();

Put it Together
~~~~~~~~~~~~~~~

Complete sketch is presented below.

.. code:: cpp

    #include <ESP8266WiFi.h>

    const char* ssid = "********";
    const char* password = "********";

    WiFiServer server(80);


    void setup()
    {
      Serial.begin(115200);
      Serial.println();

      Serial.printf("Connecting to %s ", ssid);
      WiFi.begin(ssid, password);
      while (WiFi.status() != WL_CONNECTED)
      {
        delay(500);
        Serial.print(".");
      }
      Serial.println(" connected");

      server.begin();
      Serial.printf("Web server started, open %s in a web browser\n", WiFi.localIP().toString().c_str());
    }


    // prepare a web page to be send to a client (web browser)
    String prepareHtmlPage()
    {
      String htmlPage = 
         String("HTTP/1.1 200 OK\r\n") +
                "Content-Type: text/html\r\n" +
                "Connection: close\r\n" +  // the connection will be closed after completion of the response
                "Refresh: 5\r\n" +  // refresh the page automatically every 5 sec
                "\r\n" +
                "<!DOCTYPE HTML>" +
                "<html>" +
                "Analog input:  " + String(analogRead(A0)) +
                "</html>" +
                "\r\n";
      return htmlPage;
    }


    void loop()
    {
      WiFiClient client = server.available(); 
      // wait for a client (web browser) to connect
      if (client)
      {
        Serial.println("\n[Client connected]");
        while (client.connected())
        {
          // read line by line what the client (web browser) is requesting
          if (client.available())
          {
            String line = client.readStringUntil('\r');
            Serial.print(line);
            // wait for end of client's request, that is marked with an empty line
            if (line.length() == 1 && line[0] == '\n')
            {
              client.println(prepareHtmlPage());
              break;
            }
          }
        }
        delay(1); // give the web browser time to receive the data

        // close the connection:
        client.stop();
        Serial.println("[Client disonnected]");
      }
    }

Get it Run
~~~~~~~~~~

Update ``ssid`` and ``password`` in sketch to match credentials of your access point. Load sketch to ESP module and open a serial monitor. First you should see confirmation that module connected to the access point and the web server started.

::

    Connecting to sensor-net ........ connected
    Web server started, open 192.168.1.104 in a web browser

Enter provided IP address in a web browser. You should see the page served by ESP8266:

.. figure:: pictures/server-browser-output.png
   :alt: Output from server in a web browser

The page would be refreshed every 5 seconds. Each time this happens, you should see a request from the client (your web browser) printed out on the serial monitor:

::

    [Client connected]
    GET / HTTP/1.1
    Accept: text/html, application/xhtml+xml, */*
    Accept-Language: en-US
    User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
    Accept-Encoding: gzip, deflate
    Host: 192.168.1.104
    DNT: 1
    Connection: Keep-Alive
    [client disonnected]

What Else?
~~~~~~~~~~

Looking on `client examples <client-examples.rst>`__ you will quickly find out the similarities in protocol to the server. The protocol starts with a header that contains information what communication will be about. It contains what content type is communicated or accepted like ``text/html``. It states whether connection will be kept alive or closed after submission of the header. It contains identification of the sender like ``User-Agent: Mozilla/5.0 (Windows NT 6.1)``, etc.

Conclusion
~~~~~~~~~~

The above example shows that a web server on ESP8266 can be set up in almost no time. Such server can easily stand up requests from much more powerful hardware and software like a PC with a web browser. Check out other classes like `ESP8266WebServer <https://github.com/esp8266/Arduino/tree/master/libraries/ESP8266WebServer>`__ that let you program more advanced applications.

If you like to try another server example, check out `WiFiWebServer.ino <https://github.com/esp8266/Arduino/blob/master/libraries/ESP8266WiFi/examples/WiFiWebServer/WiFiWebServer.ino>`__, that provides functionality of toggling the GPIO pin on and off out of a web browser.

For the list of functions provided to implement and manage servers, please refer to the `Server Class <server-class.rst>`__ documentation.
