From 58396853ca2e8b1b6e4c67a97016d3b949964b9f Mon Sep 17 00:00:00 2001
From: Alec Thomas <aat@tbd.email>
Date: Wed, 4 Dec 2024 12:17:51 +1100
Subject: [PATCH] feat: add routing table package (#3613)

This is a prototype routing package that syncs routes from the schema.
It will no doubt need adjustment.
---
 internal/routing/routing.go      | 70 ++++++++++++++++++++++++++++++++
 internal/routing/routing_test.go | 48 ++++++++++++++++++++++
 2 files changed, 118 insertions(+)
 create mode 100644 internal/routing/routing.go
 create mode 100644 internal/routing/routing_test.go

diff --git a/internal/routing/routing.go b/internal/routing/routing.go
new file mode 100644
index 0000000000..8374239d51
--- /dev/null
+++ b/internal/routing/routing.go
@@ -0,0 +1,70 @@
+package routing
+
+import (
+	"context"
+	"net/url"
+
+	"github.com/alecthomas/atomic"
+	"github.com/alecthomas/types/optional"
+
+	"github.com/TBD54566975/ftl/internal/log"
+	"github.com/TBD54566975/ftl/internal/model"
+	"github.com/TBD54566975/ftl/internal/schema"
+	"github.com/TBD54566975/ftl/internal/schema/schemaeventsource"
+)
+
+type RouteTable struct {
+	// Routes keyed by module name. TODO: this should be keyed by deployment key.
+	routes *atomic.Value[map[string]*url.URL]
+}
+
+func New(ctx context.Context, changes schemaeventsource.EventSource) *RouteTable {
+	r := &RouteTable{
+		routes: atomic.New(extractRoutes(ctx, changes.View())),
+	}
+	go r.run(ctx, changes)
+	return r
+}
+
+func (r *RouteTable) run(ctx context.Context, changes schemaeventsource.EventSource) {
+	for {
+		select {
+		case <-ctx.Done():
+			return
+
+		case event := <-changes.Events():
+			routes := extractRoutes(ctx, event.Schema())
+			r.routes.Store(routes)
+		}
+	}
+}
+
+// Get returns the URL for the given deployment or None if it doesn't exist.
+func (r *RouteTable) Get(deployment model.DeploymentKey) optional.Option[*url.URL] {
+	routes := r.routes.Load()
+	return optional.Zero(routes[deployment.Payload.Module])
+}
+
+// GetForModule returns the URL for the given module or None if it doesn't exist.
+func (r *RouteTable) GetForModule(module string) optional.Option[*url.URL] {
+	routes := r.routes.Load()
+	return optional.Zero(routes[module])
+}
+
+func extractRoutes(ctx context.Context, schema *schema.Schema) map[string]*url.URL {
+	logger := log.FromContext(ctx)
+	out := make(map[string]*url.URL, len(schema.Modules))
+	for _, module := range schema.Modules {
+		if module.Runtime == nil || module.Runtime.Deployment == nil {
+			continue
+		}
+		rt := module.Runtime.Deployment
+		u, err := url.Parse(rt.Endpoint)
+		if err != nil {
+			logger.Warnf("Failed to parse endpoint URL for module %q: %v", module.Name, err)
+			continue
+		}
+		out[module.Name] = u
+	}
+	return out
+}
diff --git a/internal/routing/routing_test.go b/internal/routing/routing_test.go
new file mode 100644
index 0000000000..994cce357a
--- /dev/null
+++ b/internal/routing/routing_test.go
@@ -0,0 +1,48 @@
+package routing
+
+import (
+	"context"
+	"net/url"
+	"testing"
+	"time"
+
+	"github.com/alecthomas/assert/v2"
+	"github.com/alecthomas/types/must"
+	"github.com/alecthomas/types/optional"
+
+	"github.com/TBD54566975/ftl/internal/log"
+	"github.com/TBD54566975/ftl/internal/schema"
+	"github.com/TBD54566975/ftl/internal/schema/schemaeventsource"
+)
+
+func TestRouting(t *testing.T) {
+	events := schemaeventsource.NewUnattached()
+	events.Publish(schemaeventsource.EventUpsert{
+		Module: &schema.Module{
+			Name: "time",
+			Runtime: &schema.ModuleRuntime{
+				Deployment: &schema.ModuleRuntimeDeployment{
+					Endpoint: "http://time.ftl",
+				},
+			},
+		},
+	})
+
+	rt := New(log.ContextWithNewDefaultLogger(context.TODO()), events)
+	assert.Equal(t, optional.Some(must.Get(url.Parse("http://time.ftl"))), rt.GetForModule("time"))
+	assert.Equal(t, optional.None[*url.URL](), rt.GetForModule("echo"))
+
+	events.Publish(schemaeventsource.EventUpsert{
+		Module: &schema.Module{
+			Name: "echo",
+			Runtime: &schema.ModuleRuntime{
+				Deployment: &schema.ModuleRuntimeDeployment{
+					Endpoint: "http://echo.ftl",
+				},
+			},
+		},
+	})
+
+	time.Sleep(time.Millisecond * 250)
+	assert.Equal(t, optional.Some(must.Get(url.Parse("http://echo.ftl"))), rt.GetForModule("echo"))
+}