OAuth problems with Tweet app running on Google AppEngine


The Twitter app I am having problems with generates tweets from an Arduino device, passing them through a series of C++ and then Python apps on their way to Twitter. I am performing the required OAuth functions in the Python app running on the Google AppEngine.

I am having trouble passing my OAuth tokens to Twitter via an app (“arduino-tweet1.appspot.com”) running on Google AppEngine. My own error-checking code is telling me that OAuth is failing with a “Token is not set” code that is referring to the “self token” which I am inferring to be the “oauth_token” or Twitter access token I received when I registered my app with Twitter.

When setting up the app I was advised to set a “callback URL” of the form “http://arduino-tweet1.appspot.com/oauth/twitter/callback” which I entered OAuth Settings page as I did the initial registration.

First question: since this is not a website application where I am authorizing (other) users to read or post tweets (the keys are hardcoded as there is only one authorized user - me, or rather my Arduino device), is this callback URL necessary? Is it somehow interfering with the transfer of my access token to my OAuth process running on GAE? BTW, I do not have the path “…/oauth/twitter/callback” defined anywhere…this seems more like an example of a path I should have rather than an actual path that exists on the server where “arduino-tweet1.appspot.com” resides.

Second, the GAE app (written in Python) seems to be set up and deployed OK…it’s up and running, tests OK, and returns this output:

connecting …
HTTP/1.0 500 Internal Server Error
Content-Type: text/html; charset=utf-8
Cache-Control: no-cache
Expires: Fri, 01 Jan 1990 00:00:00 GMT
Vary: Accept-Encoding
Date: Mon, 16 Jul 2012 23:28:51 GMT
Server: Google Frontend

Error 500 - token is not set
failed : code 500

Are there any simple tests I can perform to see if the basics are indeed happening? Any ideas on where to start debugging? Thanks!

This excerpt is from a simple running on an Arduino:

// Your Token to Tweet (registered with Twitter app arduino-tweet1/)
Twitter twitter("xxxxxxxxxxxxxxxxxxxxxxxxx");
// Message to post
char msg[] = "Hello, World! I'm Arduino!";
if (twitter.post(msg)) {
    // Specify &Serial to output received response to Serial.
    // If no output is required, you can just omit the argument, e.g.
    // int status = twitter.wait();
    int status = twitter.wait(&Serial);
    if (status == 200) {
    } else {
      Serial.print("failed : code ");

This tweet is handled by a simple CPP library that formats a simple Twitter message (“bool Twitter::post(const char *msg)”) for the GAE to app to eventually handle:

#include <string.h>
#include "Twitter.h"

#define LIB_DOMAIN "arduino-tweet1.appspot.com"

#if defined(ARDUINO) && ARDUINO < 100
static uint8_t server[] = {0,0,0,0}; // IP address of LIB_DOMAIN
Twitter::Twitter(const char *token) : client(server, 80), token(token)
Twitter::Twitter(const char *token) : token(token)

bool Twitter::post(const char *msg)
#if defined(ARDUINO) && ARDUINO < 100
	DNSError err = EthernetDNS.resolveHostName(LIB_DOMAIN, server);
	if (err != DNSSuccess) {
		return false;
	parseStatus = 0;
	statusCode = 0;
#if defined(ARDUINO) && ARDUINO < 100
	if (client.connect()) {
	if (client.connect(LIB_DOMAIN, 80)) {
		client.println("POST http://" LIB_DOMAIN "/update HTTP/1.0");
		client.print("Content-Length: ");
	} else {
		return false;
	return true;

which in turn calls the following OAuth-based App which resides on Google AppEngine:


    'twitter': {
        'consumer_key': 'xxxxxxxxxxxxxxx',
        'consumer_secret': 'yyyyyyyyyyyyyyyyyyyy',

        'request_token_url': 'https://twitter.com/oauth/request_token',
        'access_token_url': 'https://twitter.com/oauth/access_token',
        'user_auth_url': 'http://twitter.com/oauth/authorize',

        'default_api_prefix': 'http://api.twitter.com/1',
        'default_api_suffix': '.json',


I have a iOS/Android app and seem to be Precisely the same problem here.