/*
Enforces the global google books API limit of 1 request / user / second.
Since all our requests look alike (we are all the same user, identified by an API key), we need to queue the requests up, and wait for a slot. This is
done up to a maximum of wait time of 30 seconds, then a timeout abort is reported.
*/
func lookupISBNGlobal(ctx appengine.Context, country string, isbn isbn13.ISBN13) (*data.BookMetaData, error) {
limiter := rate.New(ctx, 1*time.Second)
var callErr error
var result *data.BookMetaData
closure := func() {
result, callErr = lookupISBN(ctx, country, isbn)
}
if limitErr := limiter.Queue(globalAPIQueueLockKey, 30*time.Second, closure); limitErr == nil {
return result, callErr
} else {
return nil, limitErr
}
}
/**
Retrieves ISBN metadata from google books. The method enforces a limit of 1 lookup per 15 seconds.
If a user exceeds this limit, the request is denied, and ErrAPIRejected is returned.
*/
func LookupISBN(ctx appengine.Context, country string, isbn isbn13.ISBN13) (*data.BookMetaData, error) {
key := "lock:" + user.Current(ctx).ID
limiter := rate.New(ctx, 15*time.Second)
var callErr error
var result *data.BookMetaData
closure := func() {
result, callErr = lookupISBNGlobal(ctx, country, isbn)
}
if limitErr := limiter.Queue(key, 10*time.Second, closure); limitErr == nil {
return result, callErr
} else {
return nil, ErrorAPIRejected
}
}