HTTPClient with JSON parser

details

Description

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

[WIZwiki_W7500ECO] HTTPClient with JSON parser

Components Required

Wizwiki W7500 ECO

Story

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

Software
- JSON Parser: MbedJSONValue libs
- Ethernet Networking : WIZnetInterface
- HTTP Server with JSON : Fraka6 Blog – No Free Lunch: The simplest python server example 😉
Hardware
- WIZwiki-W7500ECONET: WIZwiki-W7500 + ECO Shield Ethernet
  - ARMmbed Board: WIZwiki-W7500ECO
  - Ethernet Shield: ECO Shield Ethernet

Simplest python JSON server on PC

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

Execute json_server

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

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");

TCP connect to simple python JSON server

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

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");

TCP Send Get form

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

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);
     }

Do JSON parse
```
 parse(parser, http_rx_msg); 
```

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

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

Packet Capture

TCP-Connection
Target board sends GET Form to simple python JSON server
simple python JSON server sends JSON data to Target board

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