ArduinoJson/examples/JsonHttpClient/JsonHttpClient.ino

// Sample Arduino Json Web Client
// Downloads and parse http://jsonplaceholder.typicode.com/users/1
//
// Copyright Benoit Blanchon 2014-2016
// MIT License
//
// Arduino JSON library
// https://github.com/bblanchon/ArduinoJson
// If you like this project, please add a star!

#include <ArduinoJson.h>
#include <SPI.h>
#include <Ethernet.h>

EthernetClient client;

const char* server = "jsonplaceholder.typicode.com";  // server's address
const char* resource = "/users/1";                    // http resource
const unsigned long BAUD_RATE = 9600;                 // serial connection speed
const unsigned long HTTP_TIMEOUT = 10000;  // max respone time from server
const size_t MAX_CONTENT_SIZE = 512;       // max size of the HTTP response

// The type of data that we want to extract from the page
struct UserData {
  char name[32];
  char company[32];
};

// ARDUINO entry point #1: runs once when you press reset or power the board
void setup() {
  initSerial();
  initEthernet();
}

// ARDUINO entry point #2: runs over and over again forever
void loop() {
  if (connect(server)) {
    if (sendRequest(server, resource) && skipResponseHeaders()) {
      char response[MAX_CONTENT_SIZE];
      readReponseContent(response, sizeof(response));

      UserData userData;
      if (parseUserData(response, &userData)) {
        printUserData(&userData);
      }
    }
    disconnect();
  }
  wait();
}

// Initialize Serial port
void initSerial() {
  Serial.begin(BAUD_RATE);
  while (!Serial) {
    ;  // wait for serial port to initialize
  }
  Serial.println("Serial ready");
}

// Initialize Ethernet library
void initEthernet() {
  byte mac[] = {0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};
  if (!Ethernet.begin(mac)) {
    Serial.println("Failed to configure Ethernet");
    return;
  }
  Serial.println("Ethernet ready");
  delay(1000);
}

// Open connection to the HTTP server
bool connect(const char* hostName) {
  Serial.print("Connect to ");
  Serial.println(hostName);

  bool ok = client.connect(hostName, 80);

  Serial.println(ok ? "Connected" : "Connection Failed!");
  return ok;
}

// Send the HTTP GET request to the server
bool sendRequest(const char* host, const char* resource) {
  Serial.print("GET ");
  Serial.println(resource);

  client.print("GET ");
  client.print(resource);
  client.println(" HTTP/1.0");
  client.print("Host: ");
  client.println(server);
  client.println("Connection: close");
  client.println();

  return true;
}

// Skip HTTP headers so that we are at the beginning of the response's body
bool skipResponseHeaders() {
  // HTTP headers end with an empty line
  char endOfHeaders[] = "\r\n\r\n";

  client.setTimeout(HTTP_TIMEOUT);
  bool ok = client.find(endOfHeaders);

  if (!ok) {
    Serial.println("No response or invalid response!");
  }

  return ok;
}

// Read the body of the response from the HTTP server
void readReponseContent(char* content, size_t maxSize) {
  size_t length = client.readBytes(content, maxSize);
  content[length] = 0;
  Serial.println(content);
}

// Parse the JSON from the input string and extract the interesting values
// Here is the JSON we need to parse
// {
//   "id": 1,
//   "name": "Leanne Graham",
//   "username": "Bret",
//   "email": "Sincere@april.biz",
//   "address": {
//     "street": "Kulas Light",
//     "suite": "Apt. 556",
//     "city": "Gwenborough",
//     "zipcode": "92998-3874",
//     "geo": {
//       "lat": "-37.3159",
//       "lng": "81.1496"
//     }
//   },
//   "phone": "1-770-736-8031 x56442",
//   "website": "hildegard.org",
//   "company": {
//     "name": "Romaguera-Crona",
//     "catchPhrase": "Multi-layered client-server neural-net",
//     "bs": "harness real-time e-markets"
//   }
// }
bool parseUserData(char* content, struct UserData* userData) {
  // Compute optimal size of the JSON buffer according to what we need to parse.
  // This is only required if you use StaticJsonBuffer.
  const size_t BUFFER_SIZE =
      JSON_OBJECT_SIZE(8)     // the root object has 8 elements
      + JSON_OBJECT_SIZE(5)   // the "address" object has 5 elements
      + JSON_OBJECT_SIZE(2)   // the "geo" object has 2 elements
      + JSON_OBJECT_SIZE(3);  // the "company" object has 3 elements

  // Allocate a temporary memory pool on the stack
  StaticJsonBuffer<BUFFER_SIZE> jsonBuffer;
  // If the memory pool is too big for the stack, use this instead:
  // DynamicJsonBuffer jsonBuffer;

  JsonObject& root = jsonBuffer.parseObject(content);

  if (!root.success()) {
    Serial.println("JSON parsing failed!");
    return false;
  }

  // Here were copy the strings we're interested in
  strcpy(userData->name, root["name"]);
  strcpy(userData->company, root["company"]["name"]);
  // It's not mandatory to make a copy, you could just use the pointers
  // Since, they are pointing inside the "content" buffer, so you need to make
  // sure it's still in memory when you read the string

  return true;
}

// Print the data extracted from the JSON
void printUserData(const struct UserData* userData) {
  Serial.print("Name = ");
  Serial.println(userData->name);
  Serial.print("Company = ");
  Serial.println(userData->company);
}

// Close the connection with the HTTP server
void disconnect() {
  Serial.println("Disconnect");
  client.stop();
}

// Pause for a 1 minute
void wait() {
  Serial.println("Wait 60 seconds");
  delay(60000);
}