Problem with sending a POST request using the WiFiEsp library

Question

I'm using an ESP8266 version 1 with the WiFiEsp library to connect to WiFi, and that works just fine.

I'm setting up the device using the same code as in the example WebClientRepeating.

I need to send a POST request instead of a GET request, but I can't get it to work as I want. If I create my POST request like this, it works just fine:

if (client.connect(server, 3005)) {
  Serial.println("Connecting...");

  // send the HTTP POST request  
  client.println("POST /open/peripherals HTTP/1.1");
  client.println("Host: 192.168.10.137:3005");
  client.println("User-Agent: Arduino/1.0");
  client.println("Connection: close");
  client.println();

  // note the time that the connection was made
  lastConnectionTime = millis();
}
else {
  // if you couldn't make a connection
  Serial.println("Connection failed");
}

I get the response like this:

[WiFiEsp] Connecting to 192.168.10.137
Connecting...
HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: application/json; charset=utf-8
Content-Length: 19
ETag: W/"13-jSAaqMh5E3R94/b2aONzvg"
Date: Sun, 13 Nov 2016 10:20:58 GMT
Connection: close

{"temp":"Testdata"}

However, if I try to send some body data in the request it fails:

if (client.connect(server, 3005)) {
  Serial.println("Connecting...");

  // send the HTTP POST request  
  client.println("POST /open/peripherals HTTP/1.1");
  client.println("Host: 192.168.10.137:3005");
  client.println("User-Agent: Arduino/1.0");
  client.println("Connection: close");
  client.println("Content-Type: application/x-www-form-urlencoded");
  client.println("Content-Length: 16");
  client.println();
  client.println("temperature=22.7");

  // note the time that the connection was made
  lastConnectionTime = millis();
}
else {
  // if you couldn't make a connection
  Serial.println("Connection failed");
}

Then the response from serial output is:

[WiFiEsp] Connecting to 192.168.10.137
Connecting...
[WiFiEsp] >>> TIMEOUT >>>
[WiFiEsp] Data packet send error (1)
[WiFiEsp] Failed to write to socket 0
[WiFiEsp] Disconnecting  0

However, the POST request including the body is received by the Web server just fine, but the response sent to the Arduino I can't read because it shows me an error instead of a proper response. From my webserver the response for the POST call that works and the POST call that fails is the same.

Does anyone knows why this fails when I add Content-Type, Content-Length and some body data?

Thanks in advance!

score 2 · Answer 1 · answered Feb 12 '17 at 15:00

Your problem is the content you are sending. While this format works well e. g. in Python libraries, this library seems to have a problem with it. I solved it this way, when I happened to face this problem:

//all your other code, including the remaining HTTP-Request
String content = "{\"temperature\":\""+String(value)+"\"}";
client.println("Content-Length: 16"); //insert, well, your content length
client.println(content);

score 0 · Answer 2 · edited Jul 19 '18 at 11:07

One major problem seems to exists within the AT firmware of most ESP's. By default, the http headers it sends include "Connection: close". However, the firmware seems to be buggy and unable to cope with the server closing the connection after it sends the response. Thus, in order to be able to get a response back from the target server you need to have "Connection: keep-alive" instead. This means you must explicitly add this to your header since "Connection: close" will be added if nothing else is said. Also to make life easier for the WifiEsp library you could make sure your server returns an already well-known status string for the library like fx "SEND OK"… I'm doing this on a barometer logger that sends data to a MVC Web Api written in C# and it works perfect...

Here's my code:

String PostHeader = "POST http://" + server + ":" + String(port) + "/api/values HTTP/1.1\r\n";
PostHeader += "Connection: keep-alive\r\n";
PostHeader += "Content-Type: application/json; charset=utf-8\r\n";
PostHeader += "Host: " + server + ":" + String(port) + "\r\n";
PostHeader += "Content-Length: " + String(jsonString.length()) + "\r\n\r\n";
PostHeader += jsonString;
Serial.println(PostHeader);
client.connect(server.c_str(), port);
client.println(PostHeader);
client.stop();

And the full log looks like this:

POST http://192.168.10.197:8001/api/values HTTP/1.1
Connection: keep-alive
Content-Type: application/json; charset=utf-8
Host: 192.168.10.197:8001
Content-Length: 144

{"IpAddress":"192.168.10.230","MacAddress":"5c:cf:7f:d9:2f:c8","Temperature":34.6,"Pressure":1007,"Altitude":48.48573,"PressureAtSeaLevel":1007}

[WiFiEsp] Connecting to 192.168.10.197
[WiFiEsp] Disconnecting  3

In the file debug.h located in the WifiEsp library source code you could alter a define and get more output to your serial console. Open the file and change

#define _ESPLOGLEVEL_ 3

to

#define _ESPLOGLEVEL_ 4

Save the file and recompile/deploy your source code to your Arduino and you will get extensive information about all AT commands the library sends and what the library receives in return.

Problem with sending a POST request using the WiFiEsp library

2 Answers2

Linked