Merge pull request #442 from fujiwara/layer_arn-func

Add layer_arn function.

README.md

@@ -557,6 +557,31 @@ The `caller_identity` function returns an object containing the following fields
 
 This object is the same as the result of [GetCallerIdentity](https://docs.aws.amazon.com/STS/latest/APIReference/API_GetCallerIdentity.html) API.
 
+#### Resolve Lambda layer ARN
+
+The `layer_arn` template/Jsonnet function resolves the Lambda layer ARN.
+
+```json
+{
+  "Layers": [
+    "{{ layer_arn `my-layer` `latest` }}"
+  ]
+}
+```
+
+```jsonnet
+local layer_arn = std.native('layer_arn');
+{
+  Layers: [
+    layer_arn('my-layer', 'latest'),
+  ],
+}
+```
+
+The `layer_arn` function takes two string arguments: `LayerName` and `Version`.
+- `LayerName` is the name of the Lambda layer.
+- `Version` is the version of the Lambda layer. If `Version` is empty or `latest`, the latest version is used. Otherwise, the specified version is used.
+
 #### Lookup resource attributes in tfstate ([Terraform state](https://www.terraform.io/docs/state/index.html))
 
 When `--tfstate` option set to an URL to `terraform.tfstate`, tfstate template function enabled.

lambroll.go

@@ -191,10 +191,16 @@ func New(ctx context.Context, opt *Option) (*App, error) {
 		loader.Funcs(prefixedFuncs)
 	}
 
+	// load caller identity functions
 	callerIdentity := newCallerIdentity(v2cfg)
 	nativeFuncs = append(nativeFuncs, callerIdentity.JsonnetNativeFuncs(ctx)...)
 	loader.Funcs(callerIdentity.FuncMap(ctx))
 
+	// load layer functions
+	layerArnResolver := newLayerArnResolver(v2cfg)
+	nativeFuncs = append(nativeFuncs, layerArnResolver.JsonnetNativeFuncs(ctx)...)
+	loader.Funcs(layerArnResolver.FuncMap(ctx))
+
 	app := &App{
 		callerIdentity:   callerIdentity,
 		profile:          profile,

layer.go

@@ -0,0 +1,84 @@
+package lambroll
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"text/template"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/service/lambda"
+	"github.com/google/go-jsonnet"
+	"github.com/google/go-jsonnet/ast"
+)
+
+type LayerArnResolver struct {
+	svc *lambda.Client
+}
+
+func newLayerArnResolver(cfg aws.Config) *LayerArnResolver {
+	return &LayerArnResolver{
+		svc: lambda.NewFromConfig(cfg),
+	}
+}
+
+func (r *LayerArnResolver) resolve(ctx context.Context, name, version string) (string, error) {
+	switch version {
+	case "latest", "":
+		out, err := r.svc.ListLayerVersions(ctx, &lambda.ListLayerVersionsInput{
+			LayerName: &name,
+			MaxItems:  aws.Int32(1),
+		})
+		if err != nil {
+			return "", fmt.Errorf("failed to list layer versions: %w", err)
+		}
+		if len(out.LayerVersions) == 0 {
+			return "", fmt.Errorf("layer_arn: layer %s not found", name)
+		}
+		return *out.LayerVersions[0].LayerVersionArn, nil
+	default:
+		v, err := strconv.ParseInt(version, 10, 64)
+		if err != nil {
+			return "", fmt.Errorf("layer_arn: version must be a string of number or 'latest'")
+		}
+		out, err := r.svc.GetLayerVersion(ctx, &lambda.GetLayerVersionInput{
+			LayerName:     &name,
+			VersionNumber: &v,
+		})
+		if err != nil {
+			return "", fmt.Errorf("failed to get layer version %s:%s %w", name, version, err)
+		}
+		return *out.LayerVersionArn, nil
+	}
+}
+
+func (r *LayerArnResolver) JsonnetNativeFuncs(ctx context.Context) []*jsonnet.NativeFunction {
+	return []*jsonnet.NativeFunction{
+		{
+			Name:   "layer_arn",
+			Params: []ast.Identifier{"name", "version"},
+			Func: func(params []any) (any, error) {
+				if len(params) != 2 {
+					return nil, fmt.Errorf("layer_arn: invalid number of arguments")
+				}
+				name, ok := params[0].(string)
+				if !ok {
+					return nil, fmt.Errorf("layer_arn: name must be a string")
+				}
+				version, ok := params[1].(string)
+				if !ok {
+					return nil, fmt.Errorf("layer_arn: version must be a string")
+				}
+				return r.resolve(ctx, name, version)
+			},
+		},
+	}
+}
+
+func (r *LayerArnResolver) FuncMap(ctx context.Context) template.FuncMap {
+	return template.FuncMap{
+		"layer_arn": func(name, version string) (string, error) {
+			return r.resolve(ctx, name, version)
+		},
+	}
+}