HTTP POST using Arduino ESP8266 SparkFun Shield

Question

I'm trying to send a POST HTTP to a local server running node.js. The GET request works well. The POST using Postman (local) works well, I don't have any firewall. But I can't run it with Arduino.

The code I'm using is a simple SparkFun Client example in which I only changed GET to POST:

void clientDemo() {
  // To use the ESP8266 as a TCP client, use the 
  // ESP8266Client class. First, create an object:
  ESP8266Client client;

  // ESP8266Client connect([server], [port]) is used to 
  // connect to a server (const char * or IPAddress) on
  // a specified port.
  // Returns: 1 on success, 2 on already connected,
  // negative on fail (-1=TIMEOUT, -3=FAIL).
  int retVal = client.connect(destServer, 5000);
  if (retVal == -1) {
    Serial.println(F("Time out"));
    return;
  } else if(retVal == -3) {
    Serial.println(F("Fail connection"));
    return;
  } else if(retVal == 1) {
    Serial.println("Connected with server!");
  }

  // print and write can be used to send data to a connected
  // client connection.
  client.print(httpPost);

  // available() will return the number of characters
  // currently in the receive buffer.
  while (client.available())
    Serial.write(client.read()); // read() gets the FIFO char

  // connected() is a boolean return value - 1 if the 
  // connection is active, 0 if it's closed.
  if (client.connected())
    client.stop(); // stop() closes a TCP connection.
}

And the httpPost is:

const String httpPost = "POST /meteo HTTP/1.1\n"
                        "Host: 192.168.0.131:5000\n"
                        "User-Agent: Arduino/1.0\n"
                        "Connection: close\n"
                        "Content-Type: application/x-www-form-urlencoded;\n"
                          "windspeedmph=0&winddir=0&humidity=0&temp=0&pressure=0\n";

All I get in the serial monitor is "Connected with server!"...

What am I doing wrong?

Community · Accepted Answer · 2017-05-23 12:13:53Z

1

There needs to be an empty line between the headers and body:

const String httpPost =   "POST /meteo HTTP/1.1\r\n"
                          "Host: 192.168.0.131:5000\r\n"
                          "User-Agent: Arduino/1.0\r\n"
                          "Connection: close\r\n"
                          "Content-Type: application/x-www-form-urlencoded;\r\n"
                          "\r\n"
                          "windspeedmph=0&winddir=0&humidity=0&temp=0&pressure=0\n";

Also by standard you should use \r\n for line breaks and not just \n.
HTTP header line break style

edited May 23, 2017 at 12:13

CommunityBot

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answered Dec 23, 2015 at 2:51

gre_gor

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1 Comment

wiwo Over a year ago

Unfortunately it does not help. Still only "Connected with server!" and nothing more. I don't even see any POST attempts in logs.

Andrei Lobov · Accepted Answer · 2016-12-07 12:25:18Z

1

In my case it was also important to specify Content-Length field. Then the application started to work as it should. Without the Content-Length field no data was visible on the receiver side. The Content-Length specifies the length of the payload, in your case the length of the string: "windspeedmph=0&winddir=0&humidity=0&temp=0&pressure=0\n".

answered Dec 7, 2016 at 12:25

Andrei Lobov

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