From 26f5d6791453fbd06ca36f5b823d8ea1f987e45d Mon Sep 17 00:00:00 2001
From: Garrett Johnson <garrett@segment.io>
Date: Tue, 20 Oct 2015 09:06:52 -0400
Subject: [PATCH] Add uuid interpolation function

---
 config/interpolate_funcs.go                   | 24 +++++++++++
 config/interpolate_funcs_test.go              | 42 ++++++++++++++++++-
 .../docs/configuration/interpolation.html.md  |  5 +++
 3 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/config/interpolate_funcs.go b/config/interpolate_funcs.go
index 5322e46c4f2b..9201f61a153b 100644
--- a/config/interpolate_funcs.go
+++ b/config/interpolate_funcs.go
@@ -12,6 +12,7 @@ import (
 	"strings"
 
 	"github.com/hashicorp/terraform/config/lang/ast"
+	"github.com/hashicorp/terraform/helper/resource"
 	"github.com/mitchellh/go-homedir"
 )
 
@@ -33,6 +34,7 @@ func init() {
 		"split":        interpolationFuncSplit(),
 		"base64encode": interpolationFuncBase64Encode(),
 		"base64decode": interpolationFuncBase64Decode(),
+		"uuid": interpolationFuncUuid(),
 	}
 }
 
@@ -442,3 +444,25 @@ func interpolationFuncBase64Decode() ast.Function {
 		},
 	}
 }
+
+// interpolationFuncUuid implements an uuid v4 generator with an optional 
+// prefix string. Refer to pkg helper/resource/id for implementation details
+// of the uuid generator.
+func interpolationFuncUuid() ast.Function {
+	return ast.Function{
+		Variadic:     true,
+		VariadicType: ast.TypeString,
+		ReturnType: ast.TypeString,
+		Callback: func(args []interface{}) (interface{}, error) {
+			var prefix string
+
+			if len(args) == 1 {
+				if v, ok := args[0].(string); ok {
+					prefix = v
+				}
+			}
+
+			return resource.PrefixedUniqueId(prefix), nil
+		},
+	}
+}
diff --git a/config/interpolate_funcs_test.go b/config/interpolate_funcs_test.go
index cafdf05640d9..f4311b695c7e 100644
--- a/config/interpolate_funcs_test.go
+++ b/config/interpolate_funcs_test.go
@@ -6,7 +6,7 @@ import (
 	"os"
 	"reflect"
 	"testing"
-
+	"strings"
 	"github.com/hashicorp/terraform/config/lang"
 	"github.com/hashicorp/terraform/config/lang/ast"
 )
@@ -644,6 +644,46 @@ func TestInterpolateFuncBase64Decode(t *testing.T) {
 	})
 }
 
+func TestInterpolateUuid(t *testing.T) {
+	cases := []struct{
+		Input string
+		Result int
+		Prefix string
+		Vars map[string]ast.Variable
+	}{
+		{`${uuid()}`, 26, "", map[string]ast.Variable{}},
+		{`${uuid("")}`, 26, "", map[string]ast.Variable{}},
+		{`${uuid("lb-")}`, 29, "lb-", map[string]ast.Variable{}},
+	}
+
+	// defaults
+	for i, tc := range cases {
+		ast, err := lang.Parse(tc.Input)
+		if err != nil {
+			t.Fatalf("Case #%d: input: %#v\nerr: %s", i, tc.Input, err)
+		}
+
+		out, _, err := lang.Eval(ast, langEvalConfig(tc.Vars))
+		if err != nil {
+			t.Fatalf("Case #%d: input: %#v\nerr: %s", i, tc.Input, err)
+		}
+
+		t.Logf("%s=%s", tc.Input, out)
+
+
+		if len(out.(string)) != tc.Result {
+			err = fmt.Errorf("expected input length (%d) to equal (%d)", len(out.(string)), tc.Result)
+			t.Fatalf("Case #%d: input: %#v\nerr: %s", i, tc.Input, err)
+		}
+
+		if !strings.HasPrefix(out.(string), tc.Prefix) {
+			err = fmt.Errorf("expected prefix %s", tc.Prefix)
+			t.Fatalf("Case #%d: input: %#v\nerr: %s", i, tc.Input, err)
+		}
+
+	}
+}
+
 type testFunctionConfig struct {
 	Cases []testFunctionCase
 	Vars  map[string]ast.Variable
diff --git a/website/source/docs/configuration/interpolation.html.md b/website/source/docs/configuration/interpolation.html.md
index 28d03790d700..7b9f93d7704c 100644
--- a/website/source/docs/configuration/interpolation.html.md
+++ b/website/source/docs/configuration/interpolation.html.md
@@ -74,6 +74,11 @@ are documented below.
 
 The supported built-in functions are:
 
+  * `uuid(string)` - Returns a uuid string, with an optional prefix. This 
+  uses a RFC 4122 v4 UUID with some basic cosmetic filters 
+  applied (base32, remove padding, downcase) to make visually distinguishing 
+  identifiers easier. This is the format used internally.
+
   * `base64decode(string)` - Given a base64-encoded string, decodes it and
     returns the original string.