hbbft/tests

Honey-badger tests

The hbbft crate comes with a toolkit for testing its various algorithms in simulated network environments.

Old vs new

The old testing code can be found inside the network module and .rs files in the tests subdirectory that are not prefixed with net_. The newer networking code is contained inside the net module and the remaining .rs files.

VirtualNet

Core of most tests is the net::VirtualNet struct, which simulates a network of nodes all running an instance of a distributed algorithm. Messages sent by these nodes are queued by the network. Every time the network is "cranked", a buffered message is delivered to its destination node and processed.

Virtual networks can also host an adversary that can affect faulty nodes (which are tracked automatically) or reorder queued messages.

To create a new network, the NetBuilder should be used:

// Create a network of 10 nodes, out of which 3 are faulty.
let mut net = NetBuilder::new(0..10)
    .num_faulty(3)
    .using(move |id, netinfo| {
        println!("Constructing new dynamic honey badger node #{}", id);

        DynamicHoneyBadger::builder().build(netinfo)
    }).build()
    .expect("could not construct test network");

Algorithms that return a Step upon construction should use using_step instead.

Sending input

Input can be sent to any node of the VirtualNet using the send_input method:

let input = ...;
let _step = net.send_input(123, input).expect("algorithm failed");

While the resulting step is returned, it needn't be processed to keep the network going, as its messages are automatically added to the queue.

Instead of targeting a node in particular, the same input can be sent to all nodes:

net.broadcast_input(input).expect("algorithm failed");

Cranking the network

The network advances through the crank() function, on every call

0. the adversary is given a chance to re-order the message queue,
1. the next message in the queue is delivered to its destination node (if the node is non-faulty) or the adversary (if the node is faulty),
2. all messages from the resulting step are queued again,
3. and the resulting step (or error) is returned.

If there were no messages to begin with, None is returned instead.

Cranking can be done manually:

let step = net.crank()
              .expect("expected at least one messages")
              .expect("algorithm error");

For convenience, an iterator interface is also available:

for res in net {
    let (node_id, step) = res.expect("algorithm error");
    // ...
}

This has the drawback that access to the network is not available between cranks, since it will be borrowed inside the for-loop. A common workaround is using a while loop instead:

while let Some(res) = net.crank() {
    let (node_id, step) = res.expect("algorithm error");
    // `net` can still be mutable borrowed here.
}

Tracing

By default, all network tests write traces of every network message into logfiles, named net-trace_*.txt. Each log stores one message per line, in the format of [SENDER] -> [RECEIVER]: MSG.

This behavior can be controlled using the HBBFT_TEST_TRACE environment variable; if set and equal to 0 or false, this functionality is disabled. Tracing is enabled by default.

The NetBuilder allows hard-coding the trace setting, any value passed will override environment environment settings:

let net = NetBuilder(0..10)
  .trace(false)   // Never log network messages.
  // ...

Checking outputs

As a convenience, all nodes capture any generated output during operation for inspection. The following code fragment demonstrates how to use this to verify the end result:

let first = net.correct_nodes().nth(0).unwrap().outputs();
assert!(net.nodes().all(|node| node.outputs() == first));

println!("End result: {:?}", first);