speedracer 0.0.1

Conveniently access data

What is speedracer?

speedracer provides convenience classes for

• Subscribing to the Mission Data Broker (MDB)
• Authenticating to Autobahn APIs

Quickstart

Subscribing to the MDB

To subscribe to a dataset on the MDB

1. Provide the base URL of the MDB Account Server (MAS) when creating a Connection
2. Provide the dataset to the subscribe method

conn = Connection('https://mdb-account-server.com')
sub = await conn.subscribe('mydataset')
async for msg in sub:
    print(msg.data.decode())

Authenticating to Autobahn APIs

To authenticate to Autobahn's REST APIs

1. Create a JWTManager with the API Gateway's URL
2. Call the get_headers method to get an Authorization HTTP header

manager = JWTManager('https://api-gateway.com/getjwt')
headers = manager.get_headers()

If already subscribed to MDB, you can reuse your Connection's JWTManager

conn.jwt_manager.get_headers()

Advanced Usage

MDB

Callback

Instead of iterating over a Subscription, you can provide a callback that takes a message as an argument.

def cb(msg):
    print(msg.data.decode())

conn = Connection('https://mdb-account-server.com')
sub = await conn.subscribe('mydataset', callback=cb)

# Since subscribe does not block, call sub.wait to block
await sub.wait(messages=15)
await sub.wait(timeout=5)

Seek

To move the cursor of your Subscription, use seek.

# seek to message sequence 1
await sub.seek(start_sequence=1)

# seek to 5 minutes ago
await sub.seek(start_datetime=datetime.datetime.utcnow() - datetime.timedelta(minutes=5)

Offset

By default, subscribe starts with the oldest message. To start at the current time, specify offset.

sub = await conn.subscribe('mydataset', offset=Offset.NOW)

Low Latency

By default, Subscriptions fetch messages in batches of 10. If the server has less than 10 messages to send, it will wait a bit for new messages before returning the messages it does have. If that waiting is a problem, you may want to set batch_size to 1.

sub = await conn.subscribe('mydataset', batch_size=1)

Frequently Asked Questions

TLS Errors

TLS errors occur for 2 reasons

1. Not specifying client certificates
2. Not specifying a Certificate Authority

Client certificates

By default, speedracer looks for certificates in the user's home directory named cert.crt and cert.key. To specify a different path, pass cert=('./mycert.crt', './mycert.key').

conn = Connection('https://mdb-account-server.com', cert=('./mycert.crt', './mycert.key'))

manager = JWTManager('https://api-gateway.com/getjwt', cert=('./mycert.crt', './mycert.key'))

Certificate Authority

To specify a Certificate Authorty

conn = Connection('https://mdb-account-server.com', ca_bundle='ca.pem')

manager = JWTManager('https://api-gateway.com/getjwt', verify='./ca.pem')

JWTManager also supports verify=False, but Connection does not offer an insecure option.

Subscription not starting at specified offset

The MDB remembers your subscription's place. If your program restarts, the subscription will pick up where it left off. If that is not the behavior you want, then use the Subscription's seek method.