rvitorper/go-bt: Minimalist BT implementation in Go · GitHub

go-bt is a Behavior Tree library for Go.

Designed for background workers, game AI, mundane task automation, and asynchronous logic.

Instead of time.Sleep or infinite while loops, go-bt uses a cooperative multitasking model. Nodes return state instantly, yielding control back to the supervisor.

1. Stateless Nodes: Nodes (Sequence, Selector, etc.) do not hold runtime state. All temporal memory and execution states live entirely within the generic BTContext[T].
2. The Magic Numbers: Every node’s Run method returns exactly one of three integers:
   • 1 (Success): The task is done and successful.
   • 0 (Running): The task needs more time (e.g., waiting on I/O, or sleeping). It yields the thread.
   • -1 (Failure): The task failed.
3. First-Class Context: BTContext[T] directly embeds Go’s standard context.Context, ensuring your trees natively respect global cancellation tokens and timeouts.
4. Time-Travel Testing: The engine uses an injected clock directly on the context, allowing you to instantly test a 5-minute Timeout or Sleep node in your unit tests without actually waiting.

go-bt provides a minimalist set of core nodes that can be combined to create any logical control flow:

• Composites: Selector (Stateless Priority / Fallback), Sequence (Stateless AND gate), MemSequence (Stateful chronological execution)
• Decorators: Inverter (NOT gate), Optional (Swallows failures), Timeout, Retry, Repeat
• Leaves: Condition (Instant memory read), Action (Execution), Sleep (Non-blocking wait)

Your blackboard is the custom state your tree will read and manipulate. Because the library uses Go Generics, it can be any struct.

type WorkerState struct 🔥

You can use the go-bt nodes to assemble your logic. This example asserts that the worker is connected before attempting to process tasks:

package main

import (
    "time"
    "context"
    "go-bt/core"
    "go-bt/composite"
    "go-bt/leaf"
)

func BuildWorkerTree(cancel context.CancelFunc) core.Command[WorkerState] {
   return composite.NewSelector(
      composite.NewSequence(
         composite.NewSelector(
            leaf.NewCondition(func(blackboard *WorkerState) bool {
               // Assert connected
               // Here you'd check whether the connection is valid, etc.
               return blackboard.IsConnected
            }),
            leaf.NewAction(func(ctx *core.BTContext[WorkerState]) int {
               // Make a network connection
               // Here you'd actually connect to a database
               ctx.Blackboard.IsConnected = true
               return 1
            }),
         ),
         leaf.NewAction(func(ctx *core.BTContext[WorkerState]) int {
            // Process Tasks if connected
            if ctx.Blackboard.PendingTasks <= 0 {
               cancel()
               return 1
            }
            ctx.Blackboard.PendingTasks--
            return 1
         }),
      ),
   )
}

go-bt provides a concurrent, panic-safe Supervisor to drive your tree. It spins up in the background and continuously ticks the logic without blocking your main application thread.

func main() {
   state := &WorkerState{IsConnected: false, PendingTasks: 2}
   
   // Initialize the context with a global cancellation token
   ctx, cancel := context.WithCancel(context.Background())
   btCtx := core.NewBTContext(ctx, state)
   tree := BuildWorkerTree(cancel)
   
   // Create a Supervisor that ticks every 100ms
   supervisor := core.NewSupervisor(tree, 100*time.Millisecond, func(err any) {
   println("Tree panicked, safely recovered:", err)
   })
   
   // Start the daemon in the background
   wg := supervisor.Start(btCtx)
   
   // Wait for the global context to be cancelled
   wg.Wait()
}

You can check examples in the example directory.

Testing temporal logic (like Sleep or Timeout) in CI/CD pipelines usually results in slow, flaky tests. go-bt solves this by exposing the Now function directly on the BTContext.

In your tests, simply replace the standard clock with a mock closure. This allows you to artificially advance time by hours or days in a single microsecond, instantly triggering your Timeout or Sleep node’s success/failure states to assert structural correctness.