[WIZwiki_W7500ECO] HTTPClient with JSON parser

This post shows how to use HTTPClient parse JSON data in the ARMmbed platform.

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 accessing data in JSON format. However, JSON parser is too big for the low-end device as like an ARMmbed platform which has limited-resource. This post shows how to use HTTPClient parse JSON data in the 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 passing 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

https://www.hackster.io/embeddist/wizwiki-w7500eco-httpclient-with-json-parser-f96641