[WIZwiki_W7500ECO] HTTPClient with JSON parser

JSON is easy for machines to parse and generate which is based on a subset of the JavaScript Programming Language. Currently many Web Services allow to access data in JSON format. However, JSON parser is too big for low-end device as like a ARMmbed platform which has limited-resource. This post shows how to use HTTPClient parse Json data in ARMmbed platform.

Preparation materials

1. Software
   • JSON Parser: MbedJSONValue libs
   • Ethernet Networking : WIZnetInterface
   • HTTP Server with JSON : Fraka6 Blog - No Free Lunch: The simplest python server example ;)

2. Hardware

   • WIZwiki-W7500ECONET: WIZwiki-W7500 + ECO Shield Ethernet
     

     • ARMmbed Board: WIZwiki-W7500ECO
       

     • Ethernet Shield: ECO Shield Ethernet
       

Simplest python JSON server on PC

• Reference : fraka6.blogsopot.kr: The simplest python server example

• Modify Server IP address & port on ron_handler

  def run(port=8000): #set port
  
    print('http server is starting...')
    #ip and port of server
    #server_address = ('127.0.0.1', port)
    server_address = ('192.168.0.223', port)#set port
    httpd = HTTPServer(server_address, Handler)
    print('http server is running...listening on port %s' %port)
    httpd.serve_forever()
  

• Modify JSON form in do_GET handler

  #handle GET command
  def do_GET(self):
    if format == 'html':
        self.send_response(200)
        self.send_header("Content-type", "text/plain")
        self.send_header('Content-type','text-html')
        self.end_headers()
        self.wfile.write("body")
    elif format == 'json':
        #self.request.sendall(json.dumps({'path':self.path}))
        #self.request.sendall(json.dumps({'pi':3.14}))
        self.request.sendall(json.dumps({'name':'John snow', 'age': 30, 'gender':'male'}))
    else:
        self.request.sendall("%s\t%s" %('path', self.path))
    return
  

• Excute json_server
  

• Test by using curl

    $>curl ip_address:port_number
  

  

Make main.cc

• Source Code@https://developer.mbed.org/users/embeddist/code/Simple_HTTPClient_JSON/wiki/Homepage

1. Network Configration for WIZwiki-W7500ECO

    // Enter a MAC address for your controller below.
    uint8_t mac_addr[6] = {0x00, 0x08, 0xDC, 0x00, 0x01, 0x02};
   
    printf("initializing Ethernet\r\n");
    // initializing MAC address
    eth.init(mac_addr, "192.168.0.34", "255.255.255.0", "192.168.0.1");
   
    // Check Ethenret Link
    if(eth.link() == true)   printf("- Ethernet PHY Link-Done \r\n");
    else printf("- Ethernet PHY Link- Fail\r\n");
   
    // Start Ethernet connecting: Trying to get an IP address using DHCP
    if (eth.connect()<0)    printf("Fail - Ethernet Connecing");
   

2. TCP connect to simple python JSON server

    sock.connect("192.168.0.223", 8000); // "destination IP address", destination port number
   

3. Make Get form in HTTP format

    snprintf(http_tx_msg, http_tx_msg_sz,  "GET / HTTP/1.1\r\nHost: 192.168.0.223:8000\r\nUser-Agent: WIZwiki-W7500ECO\r\nConection: close\r\n\r\n");
   

4. TCP Send Get form

    sock.send_all(http_tx_msg, http_tx_msg_sz-1); // tx_buf, tx_buf_size
   

5. TCP Recv data in JSON format

    while ( (returnCode = sock.receive(http_rx_msg, http_rx_msg_sz-1)) > 0) {
            http_rx_msg[returnCode] = '\0';
            printf("Received %d chars from server:\n\r%s\n", returnCode, http_rx_msg);
        }
   

6. Do JSON parse

    parse(parser, http_rx_msg);
   

7. Output the parsed data

    // parsing "string" in string type
    printf("name =%s\r\n" , parser["name"].get<string>().c_str());
    // parsing "age" in integer type
    printf("age =%d\r\n" , parser["age"].get<int>());
    // parsing "gender" in string type
    printf("gender =%s\r\n" , parser["gender"].get<string>().c_str());
   

Demo. HTTPClient with JSON parser

1. Network config.
2. Confirm Received JSON data
3. Print-out the pasing data
   

Packet Capture

1. TCP-Connection
2. Target board sends GET Form to simple python JSON server
3. simple python JSON server sends JSON data to Target board