This change allows to connect to the mail server that we were using before the app was restarted. Separate loop is listening for whisper events, and when we receive event that request was completed we will update time on a peer record.
Records are stored in leveldb. Body of the record is marshaled using json. At this point the only field is a timestamp when record was used.
This loop doesn't control connections, it only tracks what mail server we ended up using. It works asynchronously to connection management loop. Which tracks events that are related to connection state and expiry of the requests.
When app starts we look into the database and select the most recently used record. This record is added to connection management loop first. So if this server is available we will stick to using it. If we weren't able to connect to the same server in configured timeout (5s) we will try to connect to any other server from list of active servers.
closes: #1285
This change implements connection manager that monitors 3 types of events:
1. update of the selected mail servers
2. disconnect from a mail server
3. errors for requesting mail history
When selected mail servers provided we will try to connect with as many as possible, and later disconnect the surplus. For example if we want to connect with one mail server and 3 were selected, we try to connect with all (3), and later disconnect with 2. It will to establish connection with live mail server faster.
If mail server disconnects we will choose any other mail server from the list of selected. Unless we have only one mail server. In such case we don't have any other choice and we will leave things as is.
If request for history was expired we will disconnect such peer and try to find another one. We will follow same rules as described above.
We will have two components that will rely on this logic:
1. requesting history
If target peer is provided we will use that peer, otherwise we will request history from any selected mail server that is connected at the time of request.
2. confirmation from selected mail server
Confirmation from any selected mail server will bee used to send a feedback that envelope was sent.
I will add several extensions, but probably in separate PRs:
1. prioritize connection with mail server that was used before reboot
2. disconnect from mail servers if history request wasn't expired but failed.
3. wait some time in RequestsMessage RPC to establish connection with any mail server
Currently this feature is hidden, as certain changes will be necessary in status-react.
partially implements: https://github.com/status-im/status-go/issues/1285
Dmitry Shulyak