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I have a complete implementation of a protocol where four messages are exchanged between the client (a native Android application) and the server (a standalone Java server) in the following way using a persistent connection through Java sockets:

(client->server): message1

(server->client); message2

(client->server): message3

(server->client): message4

Between sending each message, both client and server have to do heavy mathematical (cryptographic) operations (pairing-based computations over elliptic curves).

This project works properly in my local development machine using sockets and mantaining opened this socket from message1 to the message4 between the Android app and the Java server. Now, I need to do the same with Google AppEngine, but since it does not allow opening sockets, I do not know how can I do it. I already checked the Channel and XMPP APIs, but I do not know whether my use-case applies to that APIs. Is it the right method using Channel and XMPP APIs from AppEngine? Is it possible to emulate the functionality implemented in my local machine through sockets on AppEngine?

Thank you for your response.

apaspai
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  • Can you add some details regarding your requirements? It is very hard to advice anything without requirements. Probably Channel API will work for you if your client can handle JavaScript. – Kirill Lebedev Jan 14 '13 at 21:34
  • My client application is a native Android app. The protocol needs to do heavy mathematical computation before to send both message1 and message3. Therefore, I do not know whether it is useful to handle JavaScript. I just modified my initial question. Thanks – apaspai Jan 15 '13 at 10:10

1 Answers1

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Google App Engine doesn't support persistent connections.

You will need to significantly re-design your protocol to run over HTTP.

As an example, message1 can be sent over an HTTP request, message2 can be returned with the matching HTTP response. At that point, your socket connection ends.

You'll have to issue a second HTTP request to open a new socket with message3, and you can return message4 with the second HTTP response.

You can "connect" the first and second HTTP request by using an HTTP session. A session is basically an id with extra data stored on the server side. You'd create the session in the first HTTP request, and pass it as a parameter to the second HTTP request. The server can look up the session id and the associated data when processing the second request.

You can find more info about sessions on SO: How to use session on Google app engine

The XMPP API will not help you, it's for communicating between the GAE server-side code and other XMPP clients that use HTTP as a communcation protocol.

The Channel API can be used to send data from the server->client, but it's actually implemented as an HTTP long poll. Multiple long HTTP requests are used, and you are not guaranteed to have a single socket that stays open; multiple sockets are opened and closed in the process. It will be more complicated that what I described above, and more expensive.

Community
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dragonx
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  • According to your answer, I have to deal with HTTP sessions. Thank you for your time and your response, it will be very helpful for me. – apaspai Jan 16 '13 at 18:17