fix: retrieve vert.x versions from generator

Fixes #62

pkg/hal/cli/component/create.go

@@ -1,6 +1,7 @@
 package component
 
 import (
+	"encoding/json"
 	"fmt"
 	"github.com/spf13/cobra"
 	"halkyon.io/api/component/v1beta1"
@@ -35,7 +36,7 @@ var runtimes = map[string]halkyonRuntime{
 	},
 	"vert.x": {
 		name:      "vert.x",
-		versions:  []string{"3.8.4", "3.7.1"},
+		versions:  <-getVertXVersions(),
 		generator: `https://start.vertx.io/starter.zip?vertxVersion={{.RV}}&groupId={{.G}}&artifactId={{.A}}&packageName={{.P}}`,
 	},
 	"thorntail": {
@@ -252,6 +253,38 @@ func (o *createOptions) getChildDirNames() []string {
 	return childDirs
 }
 
+func getVertXVersions() chan []string {
+	versions := make(chan []string)
+	go func() {
+		resp := io.HttpGet("https://start.vertx.io", "metadata", nil)
+		type version struct {
+			Number     string
+			Exclusions []string
+		}
+
+		var objMap map[string]*json.RawMessage
+		err := json.Unmarshal(resp, &objMap)
+		if err != nil {
+			versions <- []string{"couldn't retrieve vert.x metadata: " + err.Error()}
+		}
+
+		var versionObjs []version
+		err = json.Unmarshal(*objMap["versions"], &versionObjs)
+		if err != nil {
+			versions <- []string{"couldn't retrieve vert.x metadata: " + err.Error()}
+		}
+
+		vers := make([]string, 0, len(versionObjs))
+		for _, v := range versionObjs {
+			vers = append(vers, v.Number)
+		}
+
+		versions <- vers
+	}()
+
+	return versions
+}
+
 func getRuntimeNames() []string {
 	result := make([]string, 0, len(runtimes))
 	for k := range runtimes {