helper/resource: add UniqueId() helper

A generic function for provider resources to use to get a unique
identifier.

helper/resource/id.go

@@ -0,0 +1,25 @@
+package resource
+
+import (
+	"crypto/rand"
+	"encoding/base32"
+	"fmt"
+	"strings"
+)
+
+const UniqueIdPrefix = `terraform-`
+
+// Helper for a resource to generate a unique identifier
+//
+// This uses a simple RFC 4122 v4 UUID with some basic cosmetic filters
+// applied (remove padding, downcase) to help distinguishing visually between
+// identifiers.
+func UniqueId() string {
+	var uuid [16]byte
+	rand.Read(uuid[:])
+	return fmt.Sprintf("%s%s", UniqueIdPrefix,
+		strings.ToLower(
+			strings.Replace(
+				base32.StdEncoding.EncodeToString(uuid[:]),
+				"=", "", -1)))
+}

helper/resource/id_test.go

@@ -0,0 +1,25 @@
+package resource
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestUniqueId(t *testing.T) {
+	iterations := 10000
+	ids := make(map[string]struct{})
+	var id string
+	for i := 0; i < iterations; i++ {
+		id = UniqueId()
+
+		if _, ok := ids[id]; ok {
+			t.Fatalf("Got duplicated id! %s", id)
+		}
+
+		if !strings.HasPrefix(id, "terraform-") {
+			t.Fatalf("Unique ID didn't have terraform- prefix! %s", id)
+		}
+
+		ids[id] = struct{}{}
+	}
+}