Is this Google Endpoints error on the server or client?

Question

I've been learning Google Endpoints from the tutorial at https://developers.google.com/appengine/docs/java/endpoints/. I got the Endpoint successfully deployed to Google App Engine and I managed to build a simple iPhone app that calls the Endpoint. However, my iPhone app gets the following error when it tries to call the Endpoint:

Error Message

error NSError * domain: @"com.google.GTLJSONRPCErrorDomain" - code: -32099 0x00000001094518a0

_userInfo __NSDictionaryI * 3 key/value pairs 0x00000001094452b0

[0] (null) @"error" : @"java.lang.IndexOutOfBoundsException: Index: 0, Size: 0"
[1] (null) @"NSLocalizedFailureReason" : @"(java.lang.IndexOutOfBoundsException: Index: 0, Size: 0)"
[2] (null) @"GTLStructuredError" : (no summary)

iPhone API Caller (in Objective-C running in Xcode Debugger)

- (IBAction)myButton:(id)sender {
    NSInteger myId;
    if (self.mySwitch.isOn) {
        myId = 0;
    }
    else {
        myId = 1;
    }
    GTLQueryHelloworld *query = [GTLQueryHelloworld queryForGreetingsGetGreetingWithIdentifier:myId];
    [self.helloWorldService executeQuery:query completionHandler:^(GTLServiceTicket *ticket, id object, NSError *error) {
        if (!error) {
            [self.myLabel setText:object];
        }
        else {
            [self.myLabel setText:[error description]];  // This line gets called 
        }
    }];
}

I found the same error message reported in Youtube video upload fails after 100 % progress for some users with Backend Error code:-32099 but that pertained to calling YouTube and it was eventually closed as a bug that was fixed. So I don't think it's related.

I believe the bug is on the client side because I put some logging on the server (Java) and it does not appear to get called:

public class Greetings {
    private static final Logger log = Logger.getLogger(Greetings.class.getName());

    public static ArrayList<HelloGreeting> greetings = new ArrayList<HelloGreeting>();

    static {
            log.setLevel(Level.INFO);
            greetings.add(new HelloGreeting("hello world!"));
            greetings.add(new HelloGreeting("goodbye world!"));
    }

        public HelloGreeting getGreeting(@Named("id") Integer id) {
            log.info("HelloGreeting called with getGreeting");
            log.info("getGreeting id " + id);
            return greetings.get(id);
    }

I don't see "HelloGreeting called with getGreeting" in my Google server logs, all I see is the log message indicating that my Endpoint project was successfully deployed:

21:56:45.639 Endpoints: https://1-war-dot-firstendpointproject.appspot.com/_ah/api/helloworld@v1 Saved

I've also confirmed I can successfully test the helloworld.greetings.getGreeting API from the deployed API explorer for my project:

https://1-war-dot-firstendpointproject.appspot.com/_ah/api/explorer

When I call the API from the Explorer it generates a log message:

24.130.150.54 - - [19/Jun/2014:21:17:45 -0700] "POST /_ah/spi/com.google.appengine.samples.helloendpoints.Greetings.getGreeting HTTP/1.1" 200 93 "https://1-war-dot-firstendpointproject.appspot.com/ah/api/static/proxy.html?jsh=m%3B%2F%2Fscs%2Fapps-static%2F_%2Fjs%2Fk%3Doz.gapi.en.htta44JhPmg.O%2Fm%3D__features__%2Fam%3DAQ%2Frt%3Dj%2Fd%3D1%2Fz%3Dzcms%2Frs%3DAItRSTPk1CJ1YqUCyb-H-zhkQTjKPZwvbQ" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/537.75.14" "1-war-dot-firstendpointproject.appspot.com" ms=17 cpu_ms=87 cpm_usd=0.000010 instance=00c61b117ce13f56d6eb483511c2c1bcd24241 app_engine_release=1.9.6

It does not generate "HelloGreeting called with getGreeting" but I suspect that is because I have not configured the logger. At any rate, when my client calls the Endpoint I get no log message at all. Since the API explorer call at least generates 1 log message, I suspect the problem is on the client.

Questions:

1] Is the error I'm seeing generated on the client or the server side?

2] Do you know what array this error is refering to?

3] What are some techniques for debugging a connection problem like this?

Thanks for your help StackOverflowers!

Michael

Answer 1

I think what's going on is as the following: The server runs into an unexpected situation (specifically: it throws an unhanded IndexOutOfBoundsException), hence it cannot return the kind of JSON that the generated client stub expects in its HTTP response (specifically: it returns HTTP status 500 instead of 2xx). The client stub reports this as NSError with domain com.google.GTLJSONRPCErrorDomain and code 32099. The JSON-RPC 2.0 spec defines this error code as "reserved for implementation-defined server-errors".

It would seem that the best way to handle this is add appropriate exception handling either on the server- or client-side, depending on what exactly caused the unexpected situation on the server. An IndexOutOfBoundsException is most likely for the server to handle, as it may stem from an application-level bug.

So to answer the verbatim question: the (original) error is on the server. BTW, unlike the OP I do see related JUL logging output in the Google Developers Console.

Answer 2

I looked at your endpoint and successfully called it in the explorer and with curl. I am pretty sure that the problem is in the client and the server doesn't understand the request.

If you are sure you are calling the client correctly, I would try regenerating it. Perhaps there has been a bugfix since the last time you generated.