>Put hard limits on the rate or total number of friend lookups per account, especially if a lookup fails.
Easy: distribute the search across accounts. Also you'd expect most of the lookups to fail (most people in your contacts won't be Snapchat users).
> Keep track of global lookups and lock down the global lookup rate if there is a large number of failure
Again, you expect a large number of failures.
> Disallow more than a few lookups for accounts that haven't sent or received any messages.
Using the find friends functionality is intended to get you started with Snapchat. When you haven't sent many/any messages is when it matters most.
> Require approval by the receiver for a lookup based on a phone number before the username is revealed.
Many users (myself included) would consider notifications of this volume to be spam.
>Charge money for phone number based lookups
I don't know anyone who would pay to use Snapchat.
>require some sort of identification
Yeah, because requiring strong identification totally makes privacy advocates happy.
> Only allow phone number based lookups from within the smartphone app, not via the API.
Smartphone app has to communicate with Snapchat somehow, so the functionality is going to have to be exposed via an API. iOS is closed enough that you might be able to securely authenticate the app to the API, but AFAIK you can't stop the user from getting the key out of an Android app if he has root.
I can't comment on Snapchat's competence overall, but none of your solutions actually work. This is a nontrivial problem.
Easy: distribute the search across accounts. Also you'd expect most of the lookups to fail (most people in your contacts won't be Snapchat users).
> Keep track of global lookups and lock down the global lookup rate if there is a large number of failure
Again, you expect a large number of failures.
> Disallow more than a few lookups for accounts that haven't sent or received any messages.
Using the find friends functionality is intended to get you started with Snapchat. When you haven't sent many/any messages is when it matters most.
> Require approval by the receiver for a lookup based on a phone number before the username is revealed.
Many users (myself included) would consider notifications of this volume to be spam.
>Charge money for phone number based lookups
I don't know anyone who would pay to use Snapchat.
>require some sort of identification
Yeah, because requiring strong identification totally makes privacy advocates happy.
> Only allow phone number based lookups from within the smartphone app, not via the API.
Smartphone app has to communicate with Snapchat somehow, so the functionality is going to have to be exposed via an API. iOS is closed enough that you might be able to securely authenticate the app to the API, but AFAIK you can't stop the user from getting the key out of an Android app if he has root.
I can't comment on Snapchat's competence overall, but none of your solutions actually work. This is a nontrivial problem.