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/**
* This update handler stores information about ongoing synchronization
* attempts from distinct source replicas.
*
* Normally, u1db synchronization occurs during one POST request. In order to
* split that into many serial POST requests, we store the state of each sync
* in the server, using a document with id 'u1db_sync_state'. To identify
* each sync attempt, we use a sync_id sent by the client. If we ever receive
* a new sync_id, we trash current data for that source replica and start
* over.
*
* We expect the following in the document body:
*
* {
* 'source_replica_uid': '<source_replica_uid>',
* 'sync_id': '<sync_id>',
* 'seen_ids': [['<doc_id>', <at_gen>], ...], // optional
* 'changes_to_return': [ // optional
* 'gen': <gen>,
* 'trans_id': '<trans_id>',
* 'changes_to_return': [[<doc_id>', <gen>, '<trans_id>'], ...]
* ],
* }
*
* The format of the final document stored on server is:
*
* {
* '_id': '<str>',
* '_rev' '<str>',
* 'ongoing_syncs': {
* '<source_replica_uid>': {
* 'sync_id': '<sync_id>',
* 'seen_ids': [['<doc_id>', <at_gen>[, ...],
* 'changes_to_return': {
* 'gen': <gen>,
* 'trans_id': '<trans_id>',
* 'changes_to_return': [
* ['<doc_id>', <gen>, '<trans_id>'],
* ...,
* ],
* },
* },
* ... // info about other source replicas here
* }
* }
*/
function(doc, req) {
// prevent updates to alien documents
if (doc != null && doc['_id'] != 'u1db_sync_state')
return [null, 'invalid data'];
// create the document if it doesn't exist
if (!doc)
doc = {
'_id': 'u1db_sync_state',
'ongoing_syncs': {},
};
// parse and validate incoming data
var body = JSON.parse(req.body);
if (body['source_replica_uid'] == null)
return [null, 'invalid data'];
var source_replica_uid = body['source_replica_uid'];
if (body['sync_id'] == null)
return [null, 'invalid data'];
var sync_id = body['sync_id'];
// trash outdated sync data for that replica if that exists
if (doc['ongoing_syncs'][source_replica_uid] != null &&
doc['ongoing_syncs'][source_replica_uid]['sync_id'] != sync_id)
delete doc['ongoing_syncs'][source_replica_uid];
// create an entry for that source replica
if (doc['ongoing_syncs'][source_replica_uid] == null)
doc['ongoing_syncs'][source_replica_uid] = {
'sync_id': sync_id,
'seen_ids': {},
'changes_to_return': null,
};
// incoming meta-data values should be exclusive, so we count how many
// arrived and deny to accomplish the transaction if the count is high.
var incoming_values = 0;
var info = doc['ongoing_syncs'][source_replica_uid]
// add incoming seen id
if ('seen_id' in body) {
info['seen_ids'][body['seen_id'][0]] = body['seen_id'][1];
incoming_values += 1;
}
// add incoming changes_to_return
if ('changes_to_return' in body) {
info['changes_to_return'] = body['changes_to_return'];
incoming_values += 1;
}
if (incoming_values != 1)
return [null, 'invalid data'];
return [doc, 'ok'];
}
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