HTTPClient for Arduino

Overview

An Arduino HTTP Client that uses the Arduino Ethernet Library to make HTTP requests and handle responses.

Usage

Creating a HTTP Client

HTTP Client works with the Arduino Ethernet Library. Before you can create a HTTP client you must initialize your ethernet connection with something like:

Ethernet.begin(mac, ip);

For details on this see http://arduino.cc/en/Reference/ServerBegin

To create a client (in this example for pachube) you can simply call one of the constructors:

//  The address of the server you want to connect to (pachube.com):
byte server[] = { 173,203,98,29 }; 
HTTPClient client("api.pachube.com",server);

which is equivalent to

HTTPClient client("api.pachube.com",server,80);

Now you are ready to go.

Making a request

HTTP client supports three types of requests:

1. GET requests to get some data from a URL
2. POST requests to transfer a larger amount of data to a server
3. PUT requests as sepcified by REST APIs

DELETE requests have not yet been implemented.

All request take a number of parameters (depending on the request type):

• The URI - a string (char*) containing the uri - which is normally everything following the hostname of a URL for http://arduino.cc/en/Reference/HomePage it would be Reference/HomePage
• Optional parameters as key value pairs. Parameters are appended to a URL like http://myhost/the/uri?parameter-name=parameter-value&other=parameter parameters are values of the struct http_client_parameter. It is easiest to do this like:

http_client_parameter parameters[] = {
  { "key","afad32216dd2aa83c768ce51eef041d69a90a6737b2187dada3bb301e4c48841" }
  ,{ NULL,NULL }
};

• For POST and PUT request a string with additional data can be passed as a string. The data has to be in memory. Future Versions may have future features.
• For all requests additional headers can be specified. It works exactly the same was as uri parameters:

http_client_parameter pachube_api_header[] = {
  { "X-PachubeApiKey","afad32216dd2aa83c768ce51eef041d69a90a6737b2187dada3bb301e4c48841" }
  ,{ NULL,NULL }
};

Even though the HTTPClient supports HTTP 1.1 request no keep alive requests are supported currently.

Handling a response

The result code of a HTTP request can be read with getLastReturnCode(). It returns a integer containing the return code. 200 indicates that everything was ok. For further details refer to http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

The result of a request is a stream (aka FILE*) by that you can read the data without the need to keep the whole answer in memory - which would fail for most HTML pages.

FILE* streams are a bit more unusual the normal Arduino streams. They have been choosen since you can use all the nice fprintff and fscanf routines of avr-libc.

After reading the response from the stream it has to be closed with the method:

closeStream(stream)

DO NOT FORGET IT. Each stream has some data attached and if you forget to close the stream you get a memory leak, slowly filling up the precious memory of the Arduino.

Debug mode

The HTTPClient has also a debug mode which can be switched on and off by using debug() with parameter 0 as no debug and anything else Ð e.g. -1 Ð as enabling debug output. By default the debug code is disabled. If debug is enabled the complete request and response is printed out on the serial connection. Very useful if your request does not work.

Contributions

• Thanks to colagrosso for fixing the URL encoding
• Thanks to hex705 for properly porting it to Arduino 1.0

Copyright and license

HTTPClient is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

HTTPClient is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with HTTPClient. If not, see http://www.gnu.org/licenses/.