Satellite API

A lightning app (Lapp) based on c-lightning. Presents an API to submit messages for global broadcast over Blockstream Satellite with payments via Bitcoin Lightning.

Contents

• Setup
• Run
• Example Applications
• REST API
  • POST /order
  • POST /order/:uuid/bump
  • GET /order/:uuid
  • GET /order/:uuid/sent_message
  • DELETE /order/:uuid
  • GET /orders/pending
  • GET /orders/queued
  • GET /orders/sent
  • GET /info
  • GET /subscribe/:channels
• Debugging
  • Queue Page
• Future Work

Setup

The Satellite API comprises a RESTful API server and a transmitter daemon. The API server speaks JSON and is used for creating and managing message transmission orders and for processing lightning-charge payment callbacks. The transmitter daemon continuously dequeues paid messages and coordinates the corresponding satellite transmissions.

The Blockstream Satellite API is dependent on lightning-charge, which itself is dependent on c-lightning and bitcoin. The Satellite API server communicates with the Bitcoin Lightning Charge (BLC) stack to handle the Bitcoin Lightning payment required for each transmission order.

Run

A docker-compose script is available to bring up the Satellite API server, the transmitter daemon, and the other dependencies (BLC and Redis). To launch the container stack, run:

docker-compose up

Example Applications

The Blockstream Satellite command-line interface (CLI) has commands to submit messages to the Satellite API for global broadcasting. It also has commands to receive those messages through an actual satellite receiver or a simulated/demo receiver for testing. Please refer to the CLI documentation. Alternatively, if you are interested in implementing the communication with the Satellite API from scratch, the referred CLI can be used as a reference. The source code is available on the Satellite repository.

REST API

Each call to an API endpoint responds with a JSON object, whether the call is successful or results in an error.

The code samples below assume that you've set SATELLITE_API in your shell to the public base URL of your server.

POST /order

Place an order for a message transmission. The body of the POST must provide a bid in millisatoshis and a message, provided either as a message parameter string or as an HTTP form-based file upload. If the bid is below an allowed minimum millisatoshis per byte, a BID_TOO_SMALL (102) error is returned.

For example, to place an order to transmit the message "Hello world" with an initial bid of 10,000 millisatoshi, issue an HTTP POST request like this:

curl -F "bid=10000" -F "message=Hello World" $SATELLITE_API/order

Or, to place an order to transmit the file hello_world.png with an initial bid of 10,000 millisatoshi, issue an HTTP POST request like this:

curl -F "bid=10000" -F "file=@/path/to/upload/file/hello_world.png" $SATELLITE_API/order

If successful, the response includes the JSON Lightning invoice as returned by Lightning Charge's POST /invoice and an authentication token that can be used to modify the order. Within the metadata of the Lightning invoice, metadata is included providing: the bid (in millisatoshis), the SHA256 digest of the uploaded message file, and a UUID for the order.

{"auth_token":"d784e322dad7ec2671086ce3ad94e05108f2501180d8228577fbec4115774750","uuid":"409348bc-6af0-4999-b715-4136753979df","lightning_invoice":{"id":"N0LOTYc9j0gWtQVjVW7pK","msatoshi":"514200","description":"BSS Test","rhash":"5e5c9d111bc76ce4bf9b211f12ca2d9b66b81ae9839b4e530b16cedbef653a3a","payreq":"lntb5142n1pd78922pp5tewf6ygmcakwf0umyy039j3dndntsxhfswd5u5ctzm8dhmm98gaqdqdgff4xgz5v4ehgxqzjccqp286gfgrcpvzl04sdg2f9sany7ptc5aracnd6kvr2nr0e0x5ajpmfhsjkqzw679ytqgnt6w4490jjrgcvuemz790salqyz9far68cpqtgq3q23el","expires_at":1541642146,"created_at":1541641546,"metadata":{"sha256_message_digest":"0e2bddf3bba1893b5eef660295ef12d6fc72870da539c328cf24e9e6dbb00f00","uuid":"409348bc-6af0-4999-b715-4136753979df"},"status":"unpaid"}}

Error codes that can be returned by this endpoint include: BID_TOO_SMALL (102), MESSAGE_FILE_TOO_SMALL (117), MESSAGE_FILE_TOO_LARGE (118), MESSAGE_MISSING (126).

POST /order/:uuid/bump

Increase the bid for an order sitting in the transmission queue. The bid_increase must be provided in the body of the POST. A Lightning invoice is returned for it and, when it is paid, the increase is added to the current bid. An auth_token must also be provided. For example, to increase the bid on the order placed above by 100,000 millisatoshis, issue a POST like this:

curl -v -F "bid_increase=100000" -F "auth_token=d784e322dad7ec2671086ce3ad94e05108f2501180d8228577fbec4115774750" $SATELLITE_API/order/409348bc-6af0-4999-b715-4136753979df/bump

Response object is in the same format as for POST /order.

As shown below for DELETE, the auth_token may alternatively be provided using the X-Auth-Token HTTP header.

Error codes that can be returned by this endpoint include: INVALID_AUTH_TOKEN (109), ORDER_NOT_FOUND (104).

GET /order/:uuid

Retrieve an order by UUID. Must provide the corresponding auth token to prove that it is yours.

curl -v -H "X-Auth-Token: 5248b13a722cd9b2e17ed3a2da8f7ac6bd9a8fe7130357615e074596e3d5872f" $SATELLITE_API/order/409348bc-6af0-4999-b715-4136753979df

Error codes that can be returned by this endpoint include: INVALID_AUTH_TOKEN (109), ORDER_NOT_FOUND (104).

DELETE /order/:uuid

To cancel an order, issue an HTTP DELETE request to the API endpoint /order/:uuid/ providing the UUID of the order. An auth_token must also be provided. For example, to cancel the order above, issue a request like this:

curl -v -X DELETE -F "auth_token=5248b13a722cd9b2e17ed3a2da8f7ac6bd9a8fe7130357615e074596e3d5872f" $SATELLITE_API/order/409348bc-6af0-4999-b715-4136753979df

The auth_token may be provided as a parameter in the DELETE body as above or may be provided using the X-Auth-Token HTTP header, like this:

curl -v -X DELETE -H "X-Auth-Token: 5248b13a722cd9b2e17ed3a2da8f7ac6bd9a8fe7130357615e074596e3d5872f" $SATELLITE_API/order/409348bc-6af0-4999-b715-4136753979df

Error codes that can be returned by this endpoint include: INVALID_AUTH_TOKEN (109), ORDER_NOT_FOUND (104), ORDER_CANCELLATION_ERROR (120).

GET /orders/pending

Retrieve a list of 20 orders awaiting payment ordered by creation time. For pagination, optionally specify a before parameter (in ISO 8601 format) that specifies that the 20 orders immediately prior to the given time be returned.

curl $SATELLITE_API/orders/pending

curl $SATELLITE_API/orders/pending?before=2019-01-16T18:13:46-08:00

The response is a JSON array of records (one for each queued message). The revealed fields for each record include: uuid, bid, bid_per_byte, message_size, message_digest, status, created_at, started_transmission_at, and ended_transmission_at.

GET /orders/queued

Retrieve a list of paid but unsent orders in descending order of bid-per-byte. Both pending orders and the order currently being transmitted are returned. Optionally, accepts a parameter specifying how many queued orders to return.

curl $SATELLITE_API/orders/queued

curl $SATELLITE_API/orders/queued?limit=18

The response is a JSON array of records (one for each queued message). The revealed fields for each record include: uuid, bid, bid_per_byte, message_size, message_digest, status, created_at, started_transmission_at, and ended_transmission_at.

GET /orders/sent

Retrieves a list of up to 20 sent orders in reverse chronological order. For pagination, optionally specify a before parameter (in ISO 8601 format) that specifies that the 20 orders immediately before the given time be returned.

curl $SATELLITE_API/orders/sent

curl $SATELLITE_API/orders/sent?before=2019-01-16T18:13:46-08:00

The response is a JSON array of records (one for each queued message). The revealed fields for each record include: uuid, bid, bid_per_byte, message_size, message_digest, status, created_at, started_transmission_at, and ended_transmission_at.

GET /info

Returns information about the c-lightning node where satellite API payments are terminated. The response is a JSON object consisting of the node ID, port, IP addresses, and other information useful for opening payment channels. For example:

{"id":"032c6ba19a2141c5fee6ac8b6ff6cf24456fd4e8e206716a39af3300876c3a4835","port":42259,"address":[],"version":"v0.5.2-2016-11-21-1937-ge97ee3d","blockheight":434,"network":"regtest"}

GET /subscribe/:channels

Subscribe to one or more server-sent events channels. The channels parameter is a comma-separated list of event channels. Currently, only one channel is available: transmissions, to which an event is pushed each time a message transmission begins and ends. Event data includes a JSON representation of the order, including its current status.

curl $SATELLITE_API/subscribe/:channels

Error codes that can be returned by this endpoint include: CHANNELS_EQUALITY (124).

Debugging

Queue Page

A simple table view of queued, pending and sent messages is available at $SATELLITE_API/queue.html. This page can be used for debugging and as an example for building a web front-end to the satellite API.

Future Work

• Configure Flask-Limiter or similar to block and throttle abusive requests.
• Support bids priced in fiat currencies.
• Report the top bid_per_byte, queue depth, and estimated time to transmit in the response of POST /order.