teller

Teller is a daemon with the sole purpose of exposing an HTTP API that allows users to exchange a variety of currencies (BTC, ETH, etc.) for Skycoin (and others in the future).

frontend

Teller's frontend is exposed as an HTTP API.

/api/bind

This creates a new request in the backend and returns JSON output on the frontend. The user can then send their currency to the returned address and the process will begin.

http request

{
	"address": "...skycoin address...",
	"drop_currency": "BTC"
}

• address is the user's skycoin address where skycoin will be delivered
• drop_currency determines the type of drop_address to generate (what currency the user wants to deposit)

http response

{
	"drop_address": "...",
	"drop_currency": "BTC"
}

• drop_address is the address of type drop_currency for the user to send their currency to
• drop_currency is the same as sent in the request

/api/status

This gets the metadata of a request and returns it to the user.

http request

{
	"address": "...skycoin address...",
	"drop_address": "...",
	"drop_currency": "..."
}

• address is the user's skycoin address where skycoin will be sent
• drop_address denotes the address they want the status of
• drop_currency denotes the currency of the address they want the status of

http response

{
	"status": "...",
	"updated_at": 1519131184
}

• status is one of the following:
  • waiting_deposit - skycoin address is bound, no deposit seen yet
  • waiting_send - deposit detected, waiting to send sky to user
  • waiting_confirm - skycoin sent, waiting to confirm transaction
  • done - skycoin transaction confirmed
  • expired - drop expired
• updated_at is the unix time (seconds) when the request was last updated

backend

NOTE

Each component (scanner, sender, monitor) is just a Go package. They aren't separate processes or daemons, everything is included inside the teller daemon (single binary). The diagrams and information is just to aid in communication and development.

---

A request can be created from two sources:

• frontend http request
• on startup (reading unfinished requests from disk)

Each request goes through the following steps:

1. request.Status = waiting_deposit - waiting for the user to deposit
   • scanner watches request.Drop until deposit is detected
2. request.Status = waiting_send - waiting for sender to send skycoin to request.Address
   • sender gets skycoin and sends it to request.Address
   • sender updates request.TxId with skycoin transaction ID
3. request.Status = waiting_confirm - waiting for monitor to confirm skycoin transaction
   • monitor watches request.TxId until confirmed
4. request.Status = done - goroutine exits

The request is saved to disk between each transition. So, after step 1, after step 2, after step 3, and after step 4.

At any point, if the request has expired, request.Status will be set to expired and the request will be discarded.

request

type Request struct {
    // Address contains the users Skycoin address.
    Address Address
    // Currency denotes the currency the user wants to exchange. BTC, ETH, etc.
    Currency Currency
    // Drop denotes the address of type Currency for the user to deposit to.
    Drop Drop
    // Metadata contains important data for handling the request.
    Metadata *Metadata
}

type Metadata struct {
    // Status can be:
    //     * "waiting_deposit"
    //     * "waiting_send"
    //     * "waiting_confirm"
    //     * "done"
    //     * "expired"
    Status Status `json:"status"`
    // CreatedAt denotes the unix time when Request was created.
    CreatedAt int64 `json:"created_at"`
    // UpdatedAt denotes the unix time when Request was last updated.
    UpdatedAt int64 `json:"updated_at"`
    // TxId is empty until filled by Sender, then Monitor tracks transaction.
    TxId string `json:"tx_id"`
}

scanner

The scanner continuously checks the balance of request.Drop and returns when the balance is greater than zero (user made a deposit), or the request has expired (hours/days with no activity).

possible errors

• Getting balance of request.Drop from multicoin wallet service.

sender

The sender handles the request once a deposit has been detected. It calculates the equivalent skycoin amount to send based on the current value of request.Currency. The sender then gets skycoin from an exchange (using exchange api service), or from the OTC wallet. Then, a skycoin transaction is created (using multicoin wallet api) and injected (using multicoin wallet api). The request.TxId is filled with the skycoin transaction ID for monitor to watch.

possible errors

• Getting skycoin from exchange api service.
• Creating skycoin transaction from multicoin wallet service.
• Injecting skycoin transaction from multicoin wallet service.

monitor

The monitor handles the request once skycoin has been sent to the user. It watches request.TxId until the skycoin transaction has been confirmed on the network. After a certain number of tries, it will timeout and report the error.

possible errors

• Getting status of transaction from multicoin wallet service.