可以arduino发送重复的http请求，并从响应中获取和解析数据

Question

I want to use an Arduino for a project. What i want is arduino should send repeated http request (say every minute) with some data (most probably the IP address) to the server. And server will return a response with some data in JSON format and arduino should parse the data and write it to a text file. The data is some configuration parameters from the database. Can I do it with Arduino? I saw some posts saying that the repeated http request is not possible? any kind of help? A sample code will be really helpful. I am using Arduino mega with Ethernet shield.

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

// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

// Set the static IP address to use if the DHCP fails to assign
IPAddress ip(192, 168, 0, 177);
IPAddress myDns(192, 168, 0, 1);

// Initialize the Ethernet client library
// with the IP address and port of the server
// that you want to connect to (port 80 is default for HTTP):
EthernetClient client;
void setup(){
// Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }
 // start the Ethernet connection:
  Serial.println("Initialize Ethernet with DHCP:");
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
  // Check for Ethernet hardware present
    if (Ethernet.hardwareStatus() == EthernetNoHardware) {
      Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
      while (true) {
        delay(1); // do nothing, no point running without Ethernet hardware
      }
    }
    if (Ethernet.linkStatus() == LinkOFF) {
      Serial.println("Ethernet cable is not connected.");
    }
// try to congifure using IP address instead of DHCP:
    Ethernet.begin(mac, ip, myDns);
  } else {
    Serial.print("  DHCP assigned IP ");
    Serial.println(Ethernet.localIP());
  }

// give the Ethernet shield a second to initialize:
  delay(1000);
  Serial.print("connecting... ");
}


void loop(){

  if (Ethernet.begin(mac) !=0){
    HttpClient http; 
    http.begin("http://jsonplaceholder.typicode.com/comments?id=10"); //Specify the URL
    int httpCode = http.GET();                                        //Make the request
    if (httpCode > 0) { //Check for the returning code
        String payload = http.getString();
        Serial.println(httpCode);
        Serial.println(payload);
      } 
    else {
      Serial.println("Error on HTTP request");
    }
    http.end(); //Free the resources
  }
  delay(10000);  

    }

I tried the above code to send an http request. But getting an error no matching function for call to 'HttpClient::HttpClient()'

any suggestions would be really helpful.

Answer 1

You don't have any limitation for sending repeated requests except the timing for each request. Your code is fine except the part that making an HTTP request. The default Arduino library is a little complicated for handling HTTP requests (e.g there is no HttpClient.GET).

There are many high-level API out there that handles the requests for you and also can set various header types.

For example ArduinoHTTPClient is a good one. Just grab the library and check out examples. I rewrite your code based on that and you will get your JSON response body. Then you can simply use one of the JSON parsers like ArduinoJSON to parse results.

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

// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
byte mac[] = {0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};

// Set the static IP address to use if the DHCP fails to assign
IPAddress ip(192, 168, 0, 177);
IPAddress myDns(192, 168, 0, 1);

char serverAddress[] = "http://jsonplaceholder.typicode.com"; // server address
int port = 80;

EthernetClient EthClient;
HttpClient client = HttpClient(EthClient, serverAddress, port);

void setup()
{
    Serial.begin(9600);

    // start the Ethernet connection:
    Serial.println("Initialize Ethernet with DHCP:");
    if (Ethernet.begin(mac) == 0)
    {
        Serial.println("Failed to configure Ethernet using DHCP");
        // Check for Ethernet hardware present
        if (Ethernet.hardwareStatus() == EthernetNoHardware)
        {
            Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
            while (true)
            {
                delay(1); // do nothing, no point running without Ethernet hardware
            }
        }
        if (Ethernet.linkStatus() == LinkOFF)
        {
            Serial.println("Ethernet cable is not connected.");
        }
        // try to congifure using IP address instead of DHCP:
        Ethernet.begin(mac, ip, myDns);
    }
    else
    {
        Serial.print("  DHCP assigned IP ");
        Serial.println(Ethernet.localIP());
    }
}
void loop()
{
    Serial.println("making GET request");
    client.get("/comments?id=10");

    // read the status code and body of the response
    int statusCode = client.responseStatusCode();
    String response = client.responseBody();

    Serial.print("Status code: ");
    Serial.println(statusCode);
    Serial.print("Response: ");
    Serial.println(response);
    Serial.println("Wait five seconds");
    delay(5000);
}