feat: add pubsub go example (#2960)

Fixes #2956

examples/go/cron/README.md

@@ -0,0 +1,7 @@
+# FTL cron example
+
+Cron jobs will be scheduled on deploy. Expect:
+```
+info:cron: Frequent cron job triggered.
+info:cron: Hourly cron job triggered.
+```

examples/go/pubsub/README.md

@@ -0,0 +1,12 @@
+# FTL pubsub example
+
+Run using:
+```sh
+ftl call pubsub.orderPizza '{"type":"veggie","customer":"bob"}'
+```
+
+Expect:
+```
+info:pubsub: Cooking pizza: {99 veggie bob}
+info:pubsub: Delivering pizza: {99 veggie bob}
+```

examples/go/pubsub/dispatch.go

@@ -0,0 +1,38 @@
+package pubsub
+
+import (
+	"context"
+
+	"github.com/TBD54566975/ftl/go-runtime/ftl" // Import the FTL SDK.
+	"golang.org/x/exp/rand"
+)
+
+type OrderPizzaRequest struct {
+	Type     ftl.Option[string] `json:"type"`
+	Customer string             `json:"customer"`
+}
+
+type OrderPizzaResponse struct {
+	ID int `json:"id"`
+}
+
+//ftl:verb export
+func OrderPizza(ctx context.Context, req OrderPizzaRequest) (OrderPizzaResponse, error) {
+	randomID := rand.Intn(1000)
+	p := Pizza{
+		ID:       randomID,
+		Type:     req.Type.Default("cheese"),
+		Customer: req.Customer,
+	}
+	ftl.LoggerFromContext(ctx).Infof("Ordering pizza with ID: %d", randomID)
+	NewOrderTopic.Publish(ctx, p)
+	return OrderPizzaResponse{ID: randomID}, nil
+}
+
+var _ = ftl.Subscription(PizzaReadyTopic, "deliverPizzaSub")
+
+//ftl:subscribe deliverPizzaSub
+func DeliverPizza(ctx context.Context, pizza Pizza) error {
+	ftl.LoggerFromContext(ctx).Infof("Delivering pizza: %v", pizza)
+	return nil
+}

examples/go/pubsub/ftl.toml

@@ -0,0 +1,2 @@
+module = "pubsub"
+language = "go"

examples/go/pubsub/go.mod

@@ -0,0 +1,51 @@
+module ftl/pubsub
+
+go 1.23.0
+
+replace github.com/TBD54566975/ftl => ../../..
+
+require (
+	github.com/TBD54566975/ftl v0.0.0-00010101000000-000000000000
+	golang.org/x/exp v0.0.0-20240909161429-701f63a606c0
+)
+
+require (
+	connectrpc.com/connect v1.16.2 // indirect
+	connectrpc.com/grpcreflect v1.2.0 // indirect
+	connectrpc.com/otelconnect v0.7.1 // indirect
+	github.com/XSAM/otelsql v0.34.0 // indirect
+	github.com/alecthomas/atomic v0.1.0-alpha2 // indirect
+	github.com/alecthomas/concurrency v0.0.2 // indirect
+	github.com/alecthomas/participle/v2 v2.1.1 // indirect
+	github.com/alecthomas/types v0.16.0 // indirect
+	github.com/alessio/shellescape v1.4.2 // indirect
+	github.com/benbjohnson/clock v1.3.5 // indirect
+	github.com/danieljoos/wincred v1.2.0 // indirect
+	github.com/deckarep/golang-set/v2 v2.6.0 // indirect
+	github.com/go-logr/logr v1.4.2 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/godbus/dbus/v5 v5.1.0 // indirect
+	github.com/hashicorp/cronexpr v1.1.2 // indirect
+	github.com/jackc/pgpassfile v1.0.0 // indirect
+	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
+	github.com/jackc/pgx/v5 v5.7.1 // indirect
+	github.com/jackc/puddle/v2 v2.2.2 // indirect
+	github.com/jpillora/backoff v1.0.0 // indirect
+	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/multiformats/go-base36 v0.2.0 // indirect
+	github.com/puzpuzpuz/xsync/v3 v3.4.0 // indirect
+	github.com/swaggest/jsonschema-go v0.3.72 // indirect
+	github.com/swaggest/refl v1.3.0 // indirect
+	github.com/zalando/go-keyring v0.2.5 // indirect
+	go.opentelemetry.io/otel v1.30.0 // indirect
+	go.opentelemetry.io/otel/metric v1.30.0 // indirect
+	go.opentelemetry.io/otel/trace v1.30.0 // indirect
+	golang.org/x/crypto v0.27.0 // indirect
+	golang.org/x/mod v0.21.0 // indirect
+	golang.org/x/net v0.29.0 // indirect
+	golang.org/x/sync v0.8.0 // indirect
+	golang.org/x/sys v0.25.0 // indirect
+	golang.org/x/text v0.18.0 // indirect
+	google.golang.org/protobuf v1.34.2 // indirect
+)

examples/go/pubsub/kitchen.go

@@ -0,0 +1,27 @@
+package pubsub
+
+import (
+	"context"
+
+	"github.com/TBD54566975/ftl/go-runtime/ftl" // Import the FTL SDK.
+)
+
+//ftl:export
+var NewOrderTopic = ftl.Topic[Pizza]("newOrderTopic")
+
+//ftl:export
+var PizzaReadyTopic = ftl.Topic[Pizza]("pizzaReadyTopic")
+
+var _ = ftl.Subscription(NewOrderTopic, "cookPizzaSub")
+
+type Pizza struct {
+	ID       int
+	Type     string
+	Customer string
+}
+
+//ftl:subscribe cookPizzaSub
+func CookPizza(ctx context.Context, pizza Pizza) error {
+	ftl.LoggerFromContext(ctx).Infof("Cooking pizza: %v", pizza)
+	return PizzaReadyTopic.Publish(ctx, pizza)
+}