Catbird

A PostgreSQL-powered message queue and task execution engine. Catbird brings reliability and simplicity to background job processing by using your database as the single source of truth—no extra services to manage, just your database coordinating everything.

Why Catbird?

• Transactional by default: enqueue messages in the same DB transaction as your app writes; rollback means no message.
• Exactly-once within a visibility window: safe retries after crashes, no duplicate processing.
• Database as coordinator: horizontal workers, PostgreSQL handles distribution and state.
• Workflows as DAGs: dependencies, branching, and data passing between steps.
• Definition separate from implementation: define and start tasks and flows in one place, implement them elsewhere.
• Persistence and auditability: queues, runs, and results live in PostgreSQL.
• Resiliency baked in: retries, backoff, optional circuit breakers.
• Operational UX: web dashboard and tui for runs, queues, and workers.
• Optional real-time layer: opt-in pub/sub with SSE support for pushing events to browsers.

Quick Start

client := catbird.New(conn)
ctx := context.Background()

// Queues
err := client.CreateQueue(ctx, "my-queue")
err = client.Send(ctx, "my-queue", map[string]any{"user_id": 123}, catbird.SendOpts{
    ConcurrencyKey: "user-123",
})
messages, err := client.Read(ctx, "my-queue", 10, 30*time.Second)
for _, msg := range messages {
    err = client.Delete(ctx, "my-queue", msg.ID)
}

// Continuous reader: loops ReadPoll, ack on nil, nack on error
go client.Reader(ctx, "my-queue", 10, 30*time.Second,
    func(ctx context.Context, msg catbird.Message) error {
        return nil // ack (deletes message)
    },
)

// Delayed send
client.Send(ctx, "my_queue", map[string]any{"job": "cleanup"}, catbird.SendOpts{VisibleAt: time.Now().Add(30 * time.Minute)})

// Tasks and flows
task := catbird.NewTask("send-email").
    WithDescription("Send a transactional email to a user").Do(func(ctx context.Context, input string) (string, error) {
        return "sent", nil
    })

flow := catbird.NewFlow("double-add")
flow.AddStep(catbird.NewStep("double").Do(func(ctx context.Context, input int) (int, error) {
    return input * 2, nil
}))
flow.AddStep(catbird.NewStep("add").
    DependsOn("double").Do(func(ctx context.Context, input int, doubled int) (int, error) {
    return doubled + 1, nil
}))

worker := catbird.NewWorker(pool).
    AddTask(task).
    AddFlow(flow)
go worker.Start(ctx)

taskHandle, err := client.RunTask(ctx, "send-email", "hello")
var taskOut string
err = taskHandle.WaitForOutput(ctx, &taskOut)

flowHandle, err := client.RunFlow(ctx, "double-add", 10)
var flowOut int
err = flowHandle.WaitForOutput(ctx, &flowOut)

// Delayed execution
client.RunTask(ctx, "process-user", userID, catbird.RunTaskOpts{VisibleAt: time.Now().Add(5 * time.Minute)})
client.RunFlow(ctx, "order_processing", map[string]any{"order_id": 123}, catbird.RunFlowOpts{VisibleAt: time.Now().Add(30 * time.Second)})

// Priority (higher = claimed first, default 0)
client.RunTask(ctx, "send-email", email, catbird.RunTaskOpts{Priority: 10})

// Ensure definitions exist before usage; this is not necessary if you
// just want to run a worker, definitions will be created for you.
err := client.CreateTask(ctx, taskA)
err = client.CreateTask(ctx, taskB)
err = client.CreateFlow(ctx, flowA)
err = client.CreateFlow(ctx, flowB)

// Direct package-level usage (no Client), for example in a transaction:
taskHandle, err := catbird.RunTask(ctx, tx, "send-email", "hello")

Deduplication

Catbird uses a ConcurrencyKey to prevent overlapping runs of tasks and flows, and overlapping messages in queues.

// ConcurrencyKey: prevent overlap
_, err := client.RunTask(ctx, "process-user", userID, catbird.RunTaskOpts{
    ConcurrencyKey: fmt.Sprintf("user-%d", userID),
})

Behavior

• Deduplicates queued and started runs: a new run with the same key is rejected while one is active
• After completion or failure: the same key can be used again
• Return value on duplicate: RunTask()/RunFlow() return a handle to the existing run ID
• Failure retries: allows retries on failed runs
• No key = no deduplication: if you don't provide a key, duplicates are allowed
• Queue messages: Use ConcurrencyKey in SendOpts for message deduplication

Topic-Based Routing

err := client.CreateQueue(ctx, "user-events")
err = client.CreateQueue(ctx, "audit-log")

err = client.Bind(ctx, "user-events", "events.user.created")
err = client.Bind(ctx, "user-events", "events.*.updated")
err = client.Bind(ctx, "audit-log", "events.#")

_, err = client.Publish(ctx, "events.user.created", map[string]any{
    "user_id": 123,
    "email":   "user@example.com",
})
_, err = client.Unbind(ctx, "user-events", "events.*.updated")

Wildcard rules:

• * matches a single token (e.g., events.*.created matches events.user.created)
• # matches zero or more tokens at the end (e.g., events.user.# matches events.user and events.user.created.v1)
• # must appear as .# at the end of the pattern, or as # by itself
• Tokens are separated by . and can contain a-z, A-Z, 0-9, _, -

Event-Triggered Runs

Bind tasks or flows to topic patterns so that publishing a message automatically creates a run.

// Bind a task to a topic pattern
err = client.BindTask(ctx, "send_email", "events.email.*")

// Bind a flow to a topic pattern
err = client.BindFlow(ctx, "order_processing", "events.order.#")

// Publishing now also triggers task/flow runs
_, err = client.Publish(ctx, "events.email.welcome", map[string]any{
    "user_id": 123,
    "email":   "user@example.com",
}, catbird.PublishOpts{
    ConcurrencyKey: "user-123",
})

// Unbind when done
_, err = client.UnbindTask(ctx, "send_email", "events.email.*")
_, err = client.UnbindFlow(ctx, "order_processing", "events.order.#")

Task Execution

// Define task (scheduling is separate)
task := catbird.NewTask("send-email").Do(func(ctx context.Context, input EmailRequest) (EmailResponse, error) {
        return EmailResponse{SentAt: time.Now()}, nil
    },
        catbird.WithConcurrency(5),
        catbird.WithMaxRetries(3),
        catbird.WithFullJitterBackoff(500*time.Millisecond, 10*time.Second),
        catbird.WithCircuitBreaker(5, 30*time.Second),
    )

// Define a task with a condition (skipped when condition is false)
conditionalTask := catbird.NewTask("premium-processing").
    WithCondition("input.is_premium"). // Skipped if is_premium = false
    Do(func(ctx context.Context, input ProcessRequest) (string, error) {
        return "processed", nil
    })

// Create worker (requires *pgxpool.Pool)
worker := catbird.NewWorker(pool).
    WithLogger(slog.Default()).
    WithShutdownTimeout(10 * time.Second).
    AddTask(task).
    AddTask(conditionalTask)
go worker.Start(ctx)

// Run the task
handle, err := client.RunTask(ctx, "send-email", EmailRequest{
    To:      "user@example.com",
    Subject: "Hello",
})

// Get result
var result EmailResponse
err = handle.WaitForOutput(ctx, &result)

OnFail Handlers

On-fail handlers run after a task reaches a failed state (after its own retries). They execute with their own HandlerOpt retry and backoff settings, and receive the original input plus rich failure context.

OnFail semantics (tasks and flows):

• OnFail runs only after the main task/flow run reaches failed (after normal handler retries are exhausted).
• OnFail has independent retry/backoff via its own HandlerOpt values.
• A successful OnFail marks on-fail handling complete, but the original run remains failed.
• If OnFail retries are exhausted, on-fail handling remains failed and no further retries are scheduled.

task := catbird.NewTask("charge-payment").Do(func(ctx context.Context, input ChargeRequest) (ChargeResult, error) {
        return ChargeResult{}, fmt.Errorf("gateway timeout")
    }).
    OnFail(func(ctx context.Context, input ChargeRequest, failure catbird.TaskFailure) error {
        // Send alert, enqueue compensation, or record audit log.
        return nil
    },
        catbird.WithMaxRetries(3),
        catbird.WithFullJitterBackoff(200*time.Millisecond, 5*time.Second),
    )

Flow Execution

A flow is a directed acyclic graph (DAG) of steps that execute when their dependencies are satisfied.

Summary

• Steps with no dependencies start immediately; independent branches run in parallel.
• Flow output is selected by output priority (configured with OutputPriority(...) or inferred from terminal steps).
• Conditions can skip steps; downstream handlers must accept Optional[T] for any conditional dependency.
• A step with a signal waits for both its dependencies and the signal input.
• WaitForOutput() returns the selected flow output once the flow completes.

Examples: Workflows

flow := catbird.NewFlow("order-processing")
flow.AddStep(catbird.NewStep("validate").Do(func(ctx context.Context, order Order) (ValidationResult, error) {
    if order.Amount <= 0 {
        return ValidationResult{Valid: false, Reason: "Invalid amount"}, nil
    }
    return ValidationResult{Valid: true}, nil
}))
flow.AddStep(catbird.NewStep("charge").
    DependsOn("validate").Do(func(ctx context.Context, order Order, validated ValidationResult) (ChargeResult, error) {
    if !validated.Valid {
        return ChargeResult{}, fmt.Errorf("cannot charge invalid order")
    }
    return ChargeResult{
        TransactionID: "txn-" + order.ID,
        Amount:        order.Amount,
    }, nil
}))
flow.AddStep(catbird.NewStep("check-inventory").
    DependsOn("validate").Do(func(ctx context.Context, order Order, validated ValidationResult) (InventoryCheck, error) {
    return InventoryCheck{
        InStock: true,
        Qty:     order.Amount,
    }, nil
}))
flow.AddStep(catbird.NewStep("ship").
    DependsOn("charge", "check-inventory").Do(func(ctx context.Context, order Order, chargeResult ChargeResult, inventory InventoryCheck) (ShipmentResult, error) {
    if !inventory.InStock {
        return ShipmentResult{}, fmt.Errorf("out of stock")
    }
    return ShipmentResult{
        TrackingNumber: "TRK-" + chargeResult.TransactionID,
        EstimatedDays:  3,
    }, nil
}))

// Create worker
worker := catbird.NewWorker(pool).
    AddFlow(flow)
go worker.Start(ctx)

Example: Multi-branch Output Ownership

Flows can have multiple terminal steps.

flow := catbird.NewFlow("approval-or-escalation")
flow.OutputPriority("approve", "escalate")

flow.AddStep(catbird.NewStep("validate").Do(func(ctx context.Context, req Request) (Validation, error) {
    return Validation{Score: req.Score}, nil
}))
flow.AddStep(catbird.NewStep("approve").
    DependsOn("validate").
    WithCondition("validate.score gte 80").Do(func(ctx context.Context, req Request, v Validation) (Decision, error) {
    return Decision{Status: "approved"}, nil
}))
flow.AddStep(catbird.NewStep("escalate").
    DependsOn("validate").
    WithCondition("validate.score lt 80").Do(func(ctx context.Context, req Request, v Validation) (Decision, error) {
    return Decision{Status: "escalated"}, nil
}))

If you omit OutputPriority(...), Catbird uses terminal steps in definition order as the default priority.

flow := catbird.NewFlow("default-terminal-priority")
flow.AddStep(catbird.NewStep("a").Do(func(ctx context.Context, in int) (int, error) { return in, nil }))
flow.AddStep(catbird.NewStep("left").DependsOn("a").Do(func(ctx context.Context, in int, a int) (int, error) { return a + 1, nil }))
flow.AddStep(catbird.NewStep("right").DependsOn("a").Do(func(ctx context.Context, in int, a int) (int, error) { return a + 2, nil }))

// Effective priority: left, then right.

OnFail Handlers

On-fail handlers run after a flow reaches a failed state (after its own retries). They execute with their own HandlerOpt retry and backoff settings, and receive the original input plus rich failure context.

flow := catbird.NewFlow("order-processing")
flow.AddStep(catbird.NewStep("charge").Do(func(ctx context.Context, order Order) (string, error) {
    return "", fmt.Errorf("charge failed")
}))
flow.OnFail(func(ctx context.Context, order Order, failure catbird.FlowFailure) error {
    var failedInput Order
    if err := failure.FailedStepInputAs(&failedInput); err == nil {
        // failedInput has the step input that caused the error
    }

    var chargeResult ChargeResult
    if err := failure.OutputAs("charge", &chargeResult); err == nil {
        // access completed step output when available
    }

    return nil
})

Example: Signals & Human-in-the-Loop

Signals enable workflows that wait for external input before proceeding, such as approval workflows or webhooks.

flow := catbird.NewFlow("document_approval")
flow.AddStep(catbird.NewStep("submit").Do(func(ctx context.Context, doc Document) (string, error) {
    return doc.ID, nil
}))
flow.AddStep(catbird.NewStep("approve").
    DependsOn("submit").
    WithSignal().Do(func(ctx context.Context, doc Document, approval ApprovalInput, docID string) (ApprovalResult, error) {
    if !approval.Approved {
        return ApprovalResult{}, fmt.Errorf("approval denied by %s: %s", approval.ApproverID, approval.Notes)
    }
    return ApprovalResult{
        Status:     "approved",
        ApprovedBy: approval.ApproverID,
        Timestamp:  time.Now().Format(time.RFC3339),
    }, nil
}))
flow.AddStep(catbird.NewStep("publish").
    DependsOn("approve").Do(func(ctx context.Context, doc Document, approval ApprovalResult) (PublishResult, error) {
    return PublishResult{
        PublishedAt: time.Now().Format(time.RFC3339),
        URL:         "https://example.com/docs/" + approval.ApprovedBy,
    }, nil
}))

A step with both dependencies and a signal waits for both conditions: all dependencies must complete and the signal must be delivered before the step executes.

Example: Early Completion

Use CompleteEarly(ctx, output, reason) inside a flow step handler when you already have the final business output and want to stop remaining branches.

flow := catbird.NewFlow("fraud-check")
flow.AddStep(catbird.NewStep("quick_guard").Do(func(ctx context.Context, in Order) (string, error) {
    if in.IsKnownSafe {
        return "", catbird.CompleteEarly(ctx, Decision{Approved: true}, "known-safe fast path")
    }
    return "continue", nil
}))
flow.AddStep(catbird.NewStep("slow_analysis").Do(func(ctx context.Context, in Order) (string, error) {
    time.Sleep(2 * time.Second)
    return "done", nil
}))
flow.AddStep(catbird.NewStep("final").
    DependsOn("quick_guard", "slow_analysis").Do(func(ctx context.Context, in Order, guard string, analysis string) (Decision, error) {
    return Decision{Approved: guard == "continue" && analysis == "done"}, nil
}))

When early completion wins the race, the flow run becomes completed with the provided output, and in-flight sibling work is stopped cooperatively.

Map Steps

Map steps fan out array processing into per-item SQL-coordinated work and aggregate results back in item order.

• Define map steps with AddStep(NewStep("name").MapFlowInput()...) or AddStep(NewStep("name").MapStepOutput("source")...)
• Use MapFlowInput() to map over flow input (flow input must be a JSON array)
• Use MapStepOutput("step_name") to map over a dependency step output array
• Each mapped item runs as its own task, so retries happen per item instead of rerunning the whole step.
• To fold mapped item outputs without materializing a full []Out, add an explicit reducer step with AddStep(NewStep("name").ReduceStep("mapped_step").Do(fn)).

Map flow input

flow := catbird.NewFlow("double-input")
flow.AddStep(catbird.NewStep("double").
    MapFlowInput().
    Do(func(ctx context.Context, n int) (int, error) {
    return n * 2, nil
}))

handle, _ := client.RunFlow(ctx, "double-input", []int{1, 2, 3})
var out []int
_ = handle.WaitForOutput(ctx, &out)
// out == []int{2, 4, 6}

Map dependency output

flow := catbird.NewFlow("double-numbers")
flow.AddStep(catbird.NewStep("numbers").Do(func(ctx context.Context, _ string) ([]int, error) {
    return []int{1, 2, 3}, nil
}))
flow.AddStep(catbird.NewStep("double").
    MapStepOutput("numbers").
    Do(func(ctx context.Context, _ string, n int) (int, error) {
    return n * 2, nil
}))

// Reduce mapped outputs with an explicit reducer step
flow = catbird.NewFlow("double-numbers-reduced")
flow.AddStep(catbird.NewStep("numbers").Do(func(ctx context.Context, _ string) ([]int, error) {
    return []int{1, 2, 3}, nil
}))
flow.AddStep(catbird.NewStep("double").
    MapStepOutput("numbers").
    Do(func(ctx context.Context, _ string, n int) (int, error) {
    return n * 2, nil
}))
flow.AddStep(catbird.NewStep("sum").
    ReduceStep("double").
    Do(func(ctx context.Context, acc int, out int) (int, error) {
    return acc + out, nil
}))

Ignore Output

Use IgnoreOutput("step") when a step must wait for a dependency but doesn't need its output. The dependency's output is never aggregated or transmitted — important for map steps with large fan-outs. The handler omits the parameter for that dependency.

flow.AddStep(catbird.NewStep("finish").
    DependsOn("expensive-map").
    IgnoreOutput("expensive-map").
    Do(func(ctx context.Context, in Input) (string, error) {
    return "done", nil
}))

Generator Steps

Generator steps act like normal flow steps with an extra trailing yield callback for streaming items; yielded items are processed by a per-item handler.

• Define the step with flow.AddStep(NewStep("name").Generate(...).Do(...))
• Optionally add DependsOn(...) and/or WithSignal() like a normal step
• Provide a generator with signature func(context.Context, In[, Signal][, Dep1, Dep2, ...], func(ItemType) error) error
• Provide an item handler with signature func(context.Context, ItemType) (OutType, error)
• To fold yielded item outputs, add an explicit reducer step with AddStep(NewStep(...).ReduceStep("generator_step").Do(fn))
• Generator steps do not support MapFlowInput() or MapStepOutput()

flow := catbird.NewFlow("generate-double-sum")
flow.AddStep(catbird.NewStep("seed").Do(func(ctx context.Context, in int) (int, error) {
    return in, nil
}))
flow.AddStep(catbird.NewStep("generate").
    DependsOn("seed").
    Generate(func(ctx context.Context, in int, seed int, yield func(int) error) error {
    for i := 0; i < seed; i++ {
        if err := yield(i); err != nil {
            return err
        }
    }
    return nil
}).
    Do(func(ctx context.Context, item int) (int, error) {
    return item * 2, nil
}))
flow.AddStep(catbird.NewStep("sum").
    DependsOn("generate").Do(func(ctx context.Context, in int, generated []int) (int, error) {
    total := 0
    for _, v := range generated {
        total += v
    }
    return total, nil
}))

handle, _ := client.RunFlow(ctx, "generate-double-sum", 5)
var out int
_ = handle.WaitForOutput(ctx, &out)
// out == 20

Use an explicit reducer step when you want bounded generator output instead of storing all item outputs as []Out:

flow := catbird.NewFlow("generate-double-sum-reduced")
flow.AddStep(catbird.NewStep("generate").
    Generate(func(ctx context.Context, input int, yield func(int) error) error {
    for i := 0; i < input; i++ {
        if err := yield(i); err != nil {
            return err
        }
    }
    return nil
}).
    Do(func(ctx context.Context, item int) (int, error) {
    return item * 2, nil
}))
flow.AddStep(catbird.NewStep("sum").
    ReduceStep("generate").
    Do(func(ctx context.Context, acc int, out int) (int, error) {
    return acc + out, nil
}))

handle, _ := client.RunFlow(ctx, "generate-double-sum-reduced", 5)
var out int
_ = handle.WaitForOutput(ctx, &out)
// out == 20

Status Values

Status	Meaning	Used by
queued	Runnable and never picked up by a worker	Task runs, flow step runs, map item runs
waiting_for_dependencies	Not runnable yet because one or more dependencies are still incomplete	Flow step runs
waiting_for_signal	Dependencies are resolved, but required signal input has not been delivered yet	Flow step runs
waiting_for_map_tasks	Parent map/reducer step is waiting for spawned map item runs to finish	Flow step runs
started	Picked up by a worker at least once (including retries)	Task runs, flow runs, flow step runs, map item runs
completed	Finished successfully and output is available	Task runs, flow runs, flow step runs, map item runs
failed	Finished with an error	Task runs, flow runs, flow step runs, map item runs
skipped	Intentionally skipped (typically due to a condition evaluating false)	Task runs, flow step runs
canceling	Cancellation requested; run is transitioning to canceled	Task runs, flow runs
canceled	Run was canceled before completing normally	Task runs, flow runs

Advanced: Step Communication at Runtime

flow := catbird.NewFlow("parallel_watch_flow")
flow.AddStep(catbird.NewStep("long_job").Do(func(ctx context.Context, in Order) (string, error) {
    time.Sleep(500 * time.Millisecond)
    return "job-finished", nil
}))
flow.AddStep(catbird.NewStep("watch_job").Do(func(ctx context.Context, in Order) (string, error) {
    step, err := catbird.WaitForStep(ctx, "long_job", catbird.WaitOpts{PollInterval: 25 * time.Millisecond})
    if err != nil {
        return "", err
    }
    if !step.IsCompleted() {
        return "", fmt.Errorf("long_job ended with status=%s", step.Status)
    }
    return "watcher-confirmed:" + step.Status, nil
}))

This runs long_job and watch_job in parallel. watch_job blocks on WaitForStep(...) until long_job reaches a terminal state, then exits immediately.

flow := catbird.NewFlow("loop_until_peer_done")
flow.AddStep(catbird.NewStep("controller").Do(func(ctx context.Context, in string) (string, error) {
    time.Sleep(2 * time.Second)
    return "stop-now", nil
}))
flow.AddStep(catbird.NewStep("worker_loop").Do(func(ctx context.Context, in string) (string, error) {
    for {
        controller, err := catbird.GetStep(ctx, "controller")
        if err != nil {
            return "", err
        }
        if controller.IsDone() {
            return "loop-stopped:" + controller.Status, nil
        }

        select {
        case <-ctx.Done():
            return "", ctx.Err()
        case <-time.After(100 * time.Millisecond):
        }
    }
}))

This pattern keeps worker_loop alive until controller reaches any terminal state, then exits cleanly.

Scheduling

Tasks and flows can be scheduled with cron expressions using CreateTaskSchedule and CreateFlowSchedule. Schedules are stored in PostgreSQL and polled by workers — no external cron daemon needed.

// Schedule a task
client.CreateTaskSchedule(ctx, "send-email", "@hourly")

// Schedule with static input
client.CreateTaskSchedule(ctx, "send-report", "*/15 * * * *",
    catbird.WithInput(EmailRequest{To: "ops@example.com", Subject: "Report"}),
)

// Schedule a flow
client.CreateFlowSchedule(ctx, "order-processing", "0 2 * * *")

// Skip all missed ticks on recovery (no catch-up runs)
client.CreateTaskSchedule(ctx, "stats", "@hourly", catbird.WithSkipCatchUp())

// Replay every missed tick on recovery
client.CreateTaskSchedule(ctx, "billing", "0 * * * *", catbird.WithCatchUpAll())

Cron Syntax

Standard 5-field cron format: minute hour day-of-month month day-of-week

Field	Values	Wildcards
Minute	0-59	*, */N, N-M, N-M/S, comma-separated
Hour	0-23	same
Day of month	1-31	same
Month	1-12	same
Day of week	0-6 (0 = Sunday, 7 also accepted as Sunday)	same

When both day-of-month and day-of-week are restricted (not *), the date matches if either field matches (standard cron OR semantics).

Shorthand descriptors: @yearly / @annually, @monthly, @weekly, @daily / @midnight, @hourly.

All cron evaluation is in UTC.

Catch-Up Policies

When a worker restarts after downtime, the catch-up policy controls how missed ticks are handled:

Policy	Option	On recovery (5 missed ticks)	Enqueues
skip	WithSkipCatchUp()	Skip all missed ticks, jump to future	0 runs
one (default)	—	Enqueue one catch-up run (oldest), jump to future	1 run
all	WithCatchUpAll()	Replay every missed tick, one at a time	All runs

Conditional Execution

Both tasks and flow steps support conditional execution via WithCondition on the builder methods. If the condition evaluates to false (or a referenced field is missing), the task/step is marked skipped and its handler does not run.

Rules at a Glance

• Prefixes: tasks use input.*; flow steps use input.*, step_name.*, or signal.*.
• Operators: eq, ne, gt, gte, lt, lte, in, exists, contains, plus not <expr>.
• Optional outputs: if a step can be skipped, downstream handlers must accept Optional[T] for that dependency.
• Map steps: define with AddStep(NewStep("name")...), then use MapFlowInput() or MapStepOutput("step_name"); map source values must be arrays.
• No AND/OR: only one expression per task/step; compute a derived field upstream if needed.

Tasks with Conditions

Tasks can use conditions to skip execution based on input fields.

type ProcessRequest struct {
    UserID     int    `json:"user_id"`
    IsPremium  bool   `json:"is_premium"`
    Amount     int    `json:"amount"`
    Environment string `json:"environment"`
}

// Only process premium users
premiumTask := catbird.NewTask("premium_processing").
    WithCondition("input.is_premium"). // Skipped if is_premium = false
    Do(func(ctx context.Context, req ProcessRequest) (string, error) {
        return fmt.Sprintf("Processed premium user %d", req.UserID), nil
    })

// Run task - may be skipped based on input
client.RunTask(ctx, "premium_processing", ProcessRequest{UserID: 123, IsPremium: false})
// This task run will be skipped (is_premium = false)

Flows with Conditions

Flow steps can branch based on prior outputs. Use Optional[T] to handle skipped dependencies.

flow := catbird.NewFlow("payment_processing")
flow.OutputPriority("charge", "free_order")

flow.AddStep(catbird.NewStep("validate").Do(func(ctx context.Context, order Order) (ValidationResult, error) {
    return ValidationResult{Valid: order.Amount > 0}, nil
}))
flow.AddStep(catbird.NewStep("charge").
    DependsOn("validate").
    WithCondition("validate.valid").Do(func(ctx context.Context, order Order, validation ValidationResult) (FinalResult, error) {
    return FinalResult{Status: "charged", TxnID: "txn-123"}, nil
}))
flow.AddStep(catbird.NewStep("free_order").
    DependsOn("validate").
    WithCondition("not validate.valid").Do(func(ctx context.Context, order Order, validation ValidationResult) (FinalResult, error) {
    return FinalResult{Status: "free_order", TxnID: ""}, nil
}))

Resiliency

Catbird includes multiple resiliency layers for runtime failures. Handler-level retries are configured with HandlerOpt values such as WithMaxRetries(...) and WithFullJitterBackoff(...), and external calls can be protected with WithCircuitBreaker(failureThreshold, openTimeout) to avoid cascading outages. In worker database paths, PostgreSQL reads/writes are retried with bounded attempts and full-jitter backoff; retries stop immediately on context cancellation or deadline expiry.

For reducer-step workflows, retries are two-phase: item handlers retry first per item, then reducer-step finalization retries at the reducer step. If retries are exhausted in either phase, the parent step fails and task/flow OnFail handlers run with the same terminal failure semantics as non-reduced steps.

Be aware of side effects

Catbird deduplication (ConcurrencyKey) controls duplicate run creation, while handler retries can still re-attempt the same run after transient failures. For non-repeatable side effects (payments, email, webhooks), use idempotent write patterns or upstream idempotency keys so retry attempts remain safe.

Cancellation

Cancellation semantics:

• Cancellation is a distinct terminal outcome (canceled), separate from failed and completed.
• Task cancellation moves queued/started runs directly to canceled; already-terminal task runs are unchanged.
• Flow cancellation is two-phase: flow goes to canceling, queued child work is canceled, then flow becomes canceled after in-flight started work drains.
• Cancellation requests are idempotent: repeated requests are successful no-ops.
• A cancel request does not rewrite an already-terminal run.

External cancellation:

taskHandle, _ := client.RunTask(ctx, "send-email", "hello")
_, _ = client.CancelTaskRun(ctx, "send-email", taskHandle.ID, catbird.CancelOpts{Reason: "operator requested stop"})

flowHandle, _ := client.RunFlow(ctx, "order-processing", map[string]any{"order_id": 123})
_, _ = client.CancelFlowRun(ctx, "order-processing", flowHandle.ID, catbird.CancelOpts{Reason: "customer canceled order"})

Internal cancellation from handlers:

task := catbird.NewTask("validate-order").Do(func(ctx context.Context, input Order) (string, error) {
        if input.Amount <= 0 {
            if err := catbird.Cancel(ctx, catbird.CancelOpts{Reason: "invalid amount"}); err != nil {
                return "", err
            }
            return "", nil
        }
        return "ok", nil
    })

flow := catbird.NewFlow("order-processing")
flow.AddStep(catbird.NewStep("guard").Do(func(ctx context.Context, input Order) (string, error) {
    if input.Amount <= 0 {
        if err := catbird.Cancel(ctx, catbird.CancelOpts{Reason: "invalid amount"}); err != nil {
            return "", err
        }
        return "", nil
    }
    return "proceed", nil
}))

Wire: Real-Time Notifications

Wire is an optional real-time pub/sub layer — use it when you need to push events to browsers or react to notifications server-side. If you're only using queues, tasks, and flows, you can ignore Wire entirely.

Wire provides topic-matched event dispatch with SSE support and presence tracking. Notifications are ephemeral (at-most-once, no storage).

wire := catbird.NewWire(pool, secret)

// Listen: server-side callbacks on topic patterns
wire.Listen("order.*", func(ctx context.Context, topic, message string) {
    log.Println(topic, message)
})

// RenderSSE: transform events for SSE clients (acts as allowlist)
wire.RenderSSE("task.*.completed", func(r *http.Request, topic, message string) (catbird.SSEEvent, error) {
    return catbird.SSEEvent{Event: "task-done", Data: "<div>Task done</div>"}, nil
})

go wire.Start(ctx)

// Notify: local dispatch + pg_notify for cross-node delivery
wire.Notify(ctx, "order.created", `{"id": 123}`)

// SSE: app controls token retrieval
http.HandleFunc("/events", func(w http.ResponseWriter, r *http.Request) {
    token := r.URL.Query().Get("token")
    wire.ServeSSE(w, r, token)
})

Listen vs RenderSSE

Method	Runs on	Purpose
wire.Listen	Every node	Server-side side effects (logging, webhooks)
wire.RenderSSE	Node with SSE client	Transform for SSE push (e.g., JSON → HTML)

Topics without a renderer pass through as-is. Multiple renderers matching the same topic each produce an SSE event. Render handlers receive the SSE client's *http.Request for access to user context (auth, language, etc).

Notify

// Package-level: explicit Conn, works inside transactions (fires on commit)
catbird.Notify(ctx, tx, "order.progress", `{"step": 1}`)

// Client method: uses client's Conn
client.Notify(ctx, "order.created", `{"id": 123}`)

// Wire method: local dispatch + pg_notify for cross-node
wire.Notify(ctx, "order.created", `{"id": 123}`)

SSEEvent

SSEEvent controls the full SSE output: event name, data, and optional ID. It implements io.Writer, so templates can write directly to it:

// Typed helper — unmarshals JSON, gives full SSEEvent control
catbird.RenderSSE[TaskEvent](wire, "task.*", func(r *http.Request, topic string, data TaskEvent) (catbird.SSEEvent, error) {
    ev := catbird.SSEEvent{Event: "task-update", ID: topic}
    err := views.TaskCompleted(r, data).Render(r.Context(), &ev)
    return ev, err
})

Tokens & SSE

SSE connections are authorized via encrypted tokens that specify which topics the client can subscribe to:

token := wire.Token([]string{"order.*", "task.invoice.#"}, catbird.TokenOpts{
    Identity: "user-123",
    ValidFor: time.Hour,
})

Presence

Track which identities are connected to a topic (across all nodes):

identities, err := wire.Presence(ctx, "dashboard")

Handler Access to Conn

Handlers can access the database connection from context for transactional work:

task := catbird.NewTask("process-order").Do(func(ctx context.Context, input Order) (Result, error) {
    conn, _ := catbird.GetConn(ctx)
    tx, _ := conn.Begin(ctx)
    defer tx.Rollback(ctx)

    catbird.Send(ctx, tx, "audit", map[string]any{"order_id": input.ID})
    catbird.Notify(ctx, tx, "order.progress", `{"step": 1}`)  // fires on commit

    tx.Commit(ctx)
    return Result{}, nil
})

Naming Rules

• Queue, task, flow, and step names: Lowercase letters, digits, and underscores only (a-z, 0-9, _). Max 58 characters. Step names must be unique within a flow. Reserved step names: input, signal.
• Topics/Patterns: Letters (upper/lower), digits, dots, underscores, and hyphens (a-z, A-Z, 0-9, ., _, -, plus wildcards *, #).

Query Helpers

Use query builders when you want SQL + args directly (for pgx.Batch or custom execution):

• SendQuery(queue, body, opts)
• PublishQuery(topic, body, opts)
• RunTaskQuery(name, input, opts)
• RunFlowQuery(name, input, opts)

// Queue into a batch
var batch pgx.Batch
q1, args1, err := catbird.SendQuery("my-queue", map[string]any{"user_id": 123})
if err != nil {
    return err
}
batch.Queue(q1, args1...)

PostgreSQL API Reference

Catbird is built on PostgreSQL functions, so you can use the API directly from any language or tool with PostgreSQL support (psql, Python, Node.js, Ruby, etc.).

For the full SQL function reference and practical SQL examples (queues, tasks, workflows, and run monitoring), see the SQL API reference.

Dashboard

The dashboard provides a web UI for monitoring queues, tasks, flows, and workers. You can run it standalone with the cb CLI or embed it as an http.Handler.

go install github.com/ugent-library/catbird/cmd/cb@latest
export CB_CONN="postgres://user:pass@localhost:5432/mydb?sslmode=disable"
cb dashboard

The dashboard is a standard http.Handler and can be embedded in any Go web application:

import (
    "log/slog"
    "net/http"

    "github.com/ugent-library/catbird"
    "github.com/ugent-library/catbird/dashboard"
)

func main() {
    client := catbird.New(conn)
    dash := dashboard.New(dashboard.Config{
        Client:     client,
        Log:        slog.Default(), // Optional: provide custom logger
        PathPrefix: "",              // Optional: mount at a subpath (e.g., "/admin")
    })
    http.ListenAndServe(":8080", dash.Handler())
}

Terminal UI

The terminal UI provides an interactive dashboard-like view in your terminal.

go install github.com/ugent-library/catbird/cmd/cb@latest
export CB_CONN="postgres://user:pass@localhost:5432/mydb?sslmode=disable"
cb ui

You can also start it from the root command using interactive mode:

cb -i

Data Retention

Set a retention period on a task or flow definition to have cb_gc() automatically delete terminal runs older than that duration. GC runs opportunistically from the worker heartbeat and can also be triggered manually via client.GC(ctx) or the standalone purge helpers below.

gcInfo, err := client.GC(ctx)
if err != nil {
    // handle error
}

_ = gcInfo.ExpiredQueuesDeleted
_ = gcInfo.StaleWorkersDeleted
_ = gcInfo.TaskRunsPurged
_ = gcInfo.FlowRunsPurged

task := catbird.NewTask("send-email").
    RetentionPeriod(7 * 24 * time.Hour). // NULL by default = no cleanup
    Do(func(ctx context.Context, in EmailInput) (string, error) {
        return "sent", nil
    })

flow := catbird.NewFlow("order-processing")
flow.RetentionPeriod(90 * 24 * time.Hour)
flow.AddStep(catbird.NewStep("step1").Do(func(ctx context.Context, in OrderInput) (string, error) {
    return "done", nil
}))

• Task runs cleaned up: completed, failed, skipped, canceled older than the retention period
• Flow runs cleaned up: completed, failed, canceled older than the retention period; associated step runs and map tasks are removed automatically via cascade
• Non-terminal rows are never touched: queued, started, waiting_*, canceling are left alone

Purge helpers

For targeted or ad-hoc cleanup independent of the retention period:

// Delete task runs older than 30 days
taskPurged, err := client.PurgeTaskRuns(ctx, "send-email", 30*24*time.Hour)

// Delete flow runs older than 90 days
flowPurged, err := client.PurgeFlowRuns(ctx, "order-processing", 90*24*time.Hour)

_ = taskPurged
_ = flowPurged

External archiving

For SQL-based archiving patterns and example queries, see the External archiving section in the SQL API reference.

Migrations

If your application already uses Goose migrations, you can register Catbird's schema migration as a normal app migration:

Create a migration file such as 00003_add_catbird.go:

package migrations

import (
    "context"
    "database/sql"

    "github.com/pressly/goose/v3"
    "github.com/ugent-library/catbird"
)

func init() {
    goose.AddMigrationNoTxContext(addCatbirdUp, addCatbirdDown)
}

func addCatbirdUp(ctx context.Context, db *sql.DB) error {
    return catbird.MigrateUpTo(ctx, db, 13)
}

func addCatbirdDown(ctx context.Context, db *sql.DB) error {
    return catbird.MigrateDownTo(ctx, db, 0)
}

Keep an explicit pinned version (for example 13) in this migration file. Do not use catbird.SchemaVersion.

Documentation

• Go API Documentation
• SQL API Reference: SQL function reference and practical SQL usage examples
• Events Reference
• Testing Guide
• Copilot Instructions

Acknowledgments

SQL code is taken from or inspired by the excellent pgmq and pgflow projects.