Published November 8, 2015 © GPL3+

[WIZwiki_W7500ECO] HTTPClient with JSON parser

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

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

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

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

Code

#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

 // 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");

#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

 // 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");

Credits

Soohwan Kim

6 projects • 7 followers

Embedded System, ARM mbed, Arduino, TCP/IP, SoC, Open Source Hardware