Making a http POST request using Arduino

Question

I am trying to post information to an API on a web project that I have created and hosted. I am not sure what the exact format is for the HTTP POST request. Every time I try I get HTTP 400 errors with the message that there is "an invalid verb".

Sample Code:

byte server[] = {"our IP"}
..
..

client(server, 80)
..
..
client.println("POST /Api/AddParking/3");

It connects to the IP address supplied without any problems, but all I get back in the above mentioned HTTP error code 400. I am not sure if I was supposed to include a HTTP version after my POST or and Content-Length or any other information.

Answer 1

Sending hand-crafted HTTP packets can be a bit tricky because they are extremely picky about the format used. I highly recommend reading through the HTTP protocol if you have the time because it explains the syntax and fields required. In particular you should look at section 5 "Request".

With regards to your code, you do need to specify the HTTP version after the POST URI and I believe you also need to specify the "Host" header. On top of that you need to be sure to have a carriage-return line-feed (CRLF) at the end of each line. So, your packet should look something like:

POST /Api/AddParking/3 HTTP/1.1
Host: www.yourhost.com

Answer 2

The original question is already answered, but just for reference for people passing by via Google; here is a more complete example how to post data to a webserver with an Arduino:

IPAddress server(10,0,0,138);
String PostData = "someDataToPost";

if (client.connect(server, 80)) {
  client.println("POST /Api/AddParking/3 HTTP/1.1");
  client.println("Host: 10.0.0.138");
  client.println("User-Agent: Arduino/1.0");
  client.println("Connection: close");
  client.print("Content-Length: ");
  client.println(PostData.length());
  client.println();
  client.println(PostData);
}