# Redis Store
> An Interledger.rs store backed by Redis

## Recommended Configuration

See [./redis-example.conf].

## Internal Organization

### Account Details

Account IDs are unsigned 64-bit integers. The `next_account_id` stores the integer that should be used for the next account added to the store.

Static account details as well as balances are stored as hash maps under the keys `accounts:X`, where X is the account ID.

#### Balances

For each account, the store tracks a `balance` (as a signed 64-bit integer) that represents the **net** position with that account holder. 
A positive balance indicates the operator of the store has an outstanding liability (owes money) to that account holder. 
A negative balance represents an asset (the account holder owes money to the operator).

The store also tracks `prepaid_amount`, which represents the amount that the account holder has pre-funded (in incoming settlements) above what they owe for ILP packets they have sent.
This is tracked separately from the `balance` to avoid the ["settling back and forth forever" problem](https://forum.interledger.org/t/what-should-positive-negative-balances-represent/501/26).

The `asset_code` and `asset_scale` for each of the accounts' balances can be found in the Account Details hash map. 
Note that this means that accounts' balances are not directly comparable (for example if account 1's `balance` is 100 and account 2's `balance` is 1000, this does not necessarily mean that we owe accountholder 2 more than accountholder 1, because these values represent completely different assets).

#### Incoming / Outgoing Auth Tokens

Auth tokens are encrypted in the following manner:
- The encryption/decryption key is generated as `hmac_sha256(store_secret, "ilp_store_redis_encryption_key")`
- Tokens are encrypted using the AES-256-GCM symmetric encryption scheme using 12-byte randomly generated nonces
- The nonce is appended to the encrypted output (which includes the auth tag) and stored in the DB

### Routing Table

The current routing table is stored as a hash map under the key `routes:current`. The routing table maps ILP address prefixes to the account ID of the "next hop" that the packet should be forwarded to.

Statically configured routes are stored as a hash map of prefix to account ID under the key `routes:static`. These will take precedence over any routes added directly to the current routing table.

### Exchange Rates

Exchange rates are stored as a hash map of currency code to rate under the key `rates:current`.

### Rate Limiting

This store uses [`redis-cell`](https://github.com/brandur/redis-cell) for rate limiting. This means that the module MUST be loaded when the Redis server is started.

`redis-cell` is used for both packet- and value throughput-based rate limiting. The limits are set on each account in the Account Details.