feat: a few ARM template string functions

changes/unreleased/Added-20230629-110316.yaml

@@ -0,0 +1,3 @@
+kind: Added
+body: Add support for a few ARM template string functions
+time: 2023-06-29T11:03:16.471829+01:00

go.mod

@@ -33,6 +33,7 @@ require (
 	github.com/spf13/cobra v1.6.1
 	github.com/spf13/pflag v1.0.5
 	github.com/stretchr/testify v1.8.0
+	github.com/vincent-petithory/dataurl v1.0.0
 	github.com/zclconf/go-cty v1.12.1
 	github.com/zclconf/go-cty-yaml v1.0.2
 	golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e

go.sum

@@ -509,6 +509,8 @@ github.com/tchap/go-patricia/v2 v2.3.1 h1:6rQp39lgIYZ+MHmdEq4xzuk1t7OdC35z/xm0BG
 github.com/tchap/go-patricia/v2 v2.3.1/go.mod h1:VZRHKAb53DLaG+nA9EaYYiaEx6YztwDlLElMsnSHD4k=
 github.com/ulikunitz/xz v0.5.10 h1:t92gobL9l3HE202wg3rlk19F6X+JOxl9BBrCCMYEYd8=
 github.com/ulikunitz/xz v0.5.10/go.mod h1:nbz6k7qbPmH4IRqmfOplQw/tblSgqTqBwxkY0oWt/14=
+github.com/vincent-petithory/dataurl v1.0.0 h1:cXw+kPto8NLuJtlMsI152irrVw9fRDX8AbShPRpg2CI=
+github.com/vincent-petithory/dataurl v1.0.0/go.mod h1:FHafX5vmDzyP+1CQATJn7WFKc9CvnvxyvZy6I1MrG/U=
 github.com/vmihailenco/msgpack v3.3.3+incompatible/go.mod h1:fy3FlTQTDXWkZ7Bh6AcGMlsjHatGryHQYUTf1ShIgkk=
 github.com/vmihailenco/msgpack/v4 v4.3.12 h1:07s4sz9IReOgdikxLTKNbBdqDMLsjPKXwvCazn8G65U=
 github.com/vmihailenco/msgpack/v4 v4.3.12/go.mod h1:gborTTJjAo/GWTqqRjrLCn9pgNN+NXzzngzBKDPIqw4=

pkg/input/arm/eval.go

@@ -31,10 +31,15 @@ type Function func(e *EvaluationContext, args ...interface{}) (interface{}, erro
 
 func BuiltinFunctions() map[string]Function {
 	return map[string]Function{
-		"concat":        concatImpl,
-		"resourceGroup": resourceGroupImpl,
-		"resourceId":    resourceIDImpl,
-		"variables":     variablesImpl,
+		"base64":          oneStringArg(base64Impl),
+		"base64ToString":  oneStringArg(base64ToStringImpl),
+		"concat":          concatImpl,
+		"dataUri":         oneStringArg(dataURIImpl),
+		"dataUriToString": oneStringArg(dataURIToStringImpl),
+		"first":           oneStringArg(firstImpl),
+		"resourceGroup":   resourceGroupImpl,
+		"resourceId":      resourceIDImpl,
+		"variables":       variablesImpl,
 	}
 }
 

pkg/input/arm/functions_string.go

@@ -14,10 +14,45 @@
 
 package arm
 
-import "fmt"
+import (
+	"encoding/base64"
+	"fmt"
 
-// Note that concat can operate on arrays too, we just haven't implemented
-// support for this yet.
+	"github.com/vincent-petithory/dataurl"
+)
+
+// Functions from https://learn.microsoft.com/en-us/azure/azure-resource-manager/templates/template-functions-string#base64
+
+func oneStringArg(f func(string) (interface{}, error)) Function {
+	return func(e *EvaluationContext, args ...interface{}) (interface{}, error) {
+		strargs, err := assertAllType[string](args...)
+		if err != nil {
+			return nil, err
+		}
+		if len(strargs) != 1 {
+			return nil, fmt.Errorf("expected 1 arg, got %d", len(strargs))
+		}
+		return f(strargs[0])
+	}
+}
+
+func base64Impl(arg string) (interface{}, error) {
+	return base64.StdEncoding.EncodeToString([]byte(arg)), nil
+}
+
+func base64ToStringImpl(arg string) (interface{}, error) {
+	decoded, err := base64.StdEncoding.DecodeString(arg)
+	if err != nil {
+		return nil, fmt.Errorf("error decoding base64: %w", err)
+	}
+	return string(decoded), nil
+}
+
+// TODO base64ToJson returns an object. We can implement this when we introduce
+// object variable support.
+
+// TODO concat can operate on arrays too, we just haven't implemented support
+// for this yet.
 func concatImpl(e *EvaluationContext, args ...interface{}) (interface{}, error) {
 	res := ""
 	for _, arg := range args {
@@ -29,3 +64,29 @@ func concatImpl(e *EvaluationContext, args ...interface{}) (interface{}, error)
 	}
 	return res, nil
 }
+
+// TODO contains can operate on arrays and objects, and returns a boolean. We
+// haven't implemented support for these types yet.
+
+func dataURIImpl(arg string) (interface{}, error) {
+	return dataurl.EncodeBytes([]byte(arg)), nil
+}
+
+func dataURIToStringImpl(arg string) (interface{}, error) {
+	decoded, err := dataurl.DecodeString(arg)
+	if err != nil {
+		return nil, fmt.Errorf("error decoding dataUri: %w", err)
+	}
+	return string(decoded.Data), nil
+}
+
+// TODO empty returns a boolean, a type we haven't implemented support for yet
+// TODO endsWith returns a boolean, a type we haven't implemented support for yet
+
+// TODO first can also operate on arrays, a type we haven't implemented support
+// for yet
+func firstImpl(arg string) (interface{}, error) {
+	return string([]rune(arg)[0]), nil
+}
+
+// TODO implement format after adding integer and boolean type support

pkg/input/arm/functions_string_test.go

@@ -0,0 +1,62 @@
+// © 2022-2023 Snyk Limited All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package arm
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestBase64(t *testing.T) {
+	res, err := base64Impl("foo")
+	require.NoError(t, err)
+	require.Equal(t, "Zm9v", res)
+}
+
+func TestBase64ToString(t *testing.T) {
+	res, err := base64ToStringImpl("Zm9v")
+	require.NoError(t, err)
+	require.Equal(t, "foo", res)
+}
+
+func TestConcat(t *testing.T) {
+	res, err := concatImpl(nil, "foo", "bar")
+	require.NoError(t, err)
+	require.Equal(t, "foobar", res)
+}
+
+func TestDataURI(t *testing.T) {
+	res, err := dataURIImpl("Hello")
+	require.NoError(t, err)
+
+	// Behaves slightly differently than the example in https://learn.microsoft.com/en-us/azure/azure-resource-manager/templates/template-functions-string#TestDataURI
+	// Note the absence of a hyphen in "data:text/plain;charset=utf8;base64,SGVsbG8="
+	// It's not clear whether or not this is a problem, it depends on how tolerant
+	// of different representations of charset names Azure is.
+	require.Equal(t, "data:text/plain;charset=utf-8;base64,SGVsbG8=", res)
+}
+
+func TestDataURIToString(t *testing.T) {
+	res, err := dataURIToStringImpl("data:;base64,SGVsbG8sIFdvcmxkIQ==")
+	require.NoError(t, err)
+	require.Equal(t, "Hello, World!", res)
+}
+
+func TestFirst(t *testing.T) {
+	res, err := firstImpl("Hello")
+	require.NoError(t, err)
+	require.Equal(t, "H", res)
+}