ESP8266 official library post request returns 400

Question

Every time I try the post request I get a 400 error but the JSON and URL are identical to those that I used on an online API tester and it worked every time there. I am running this program in the official Arduino IDE and most of this code was taken from the ESP8266 official library here: https://github.com/esp8266/Arduino/blob/master/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.h

if (http.begin(client, host)) { // HTTP
 http.addHeader("Content-Type", "application/json");
 // Serial.print("[HTTP] GET...\n");
 // start connection and send HTTP header
 // int httpCode = http.GET();
 String request = "{ \"temperature\": 27.0, \"humidity\": 43 }";
 Serial.print("[HTTP] POST...\n");
 int httpCode = http.POST(request);

• Juraj: and the value of host?
• pythonhelpthrow: client is an instance of the WiFiClient object and host is a variable declared to the url with my private key included.
• Juraj: error code 400 is "Bad request" and it is a HTTP response from the server
• pythonhelpthrow: Right, but I'm trying to figure out what the inconsistency is between my code and the API tester I used. The JSON and URL are identical.
• Juraj: only other thing you provide is host in sketch

Answer 1

400 is a HTTP error "Bad request" sent by the HTTP server. Possible reasons for this error are malformed HTTP request line, malformed HTTP request headers, missing empty line after the last HTTP header and a request to 'secure' port without encryption.

In your case the HttpClient library constructs the HTTP request so there should be no error. Only thing you supply for the request is the URL in your case it is the variable host. As we cleared in comments, your URL started with https. The HttpClient library parsed the url, detected the https protocol and used the secure port 443. But the underlying networking Client object was not SSL so it didn't encrypt the request.

• pythonhelpthrow: Thank you for your help!
• jezmck: I appreciate the explanation of what went wrong, but how can we make it work?
• Juraj: @jezmck in this case it would be using the WiFiSecureClient as shown in the BasicHttpsClient example