Add base64-decode operator

doc/operators.md

@@ -23,6 +23,7 @@
 - [awsparam](#-awsparam-)
 - [awssecret](#-awssecret-)
 - [base64](#-base64-)
+- [base64-decode](#-base64-decode-)
 
 Additionally, there are operators that are specific to merging arrays. For more detail
 see the [array merging documentation][array-merging]:
@@ -391,6 +392,22 @@ time base64 encoding of string literals specified directly, or by reference.
 
 [Example][base64-example]
 
+## (( base64-decode ))
+
+Usage: `(( base64-decode LITERAL|REFERENCE ... ))`
+
+The `(( base64-decode ))` operator allows for merge-time decoding of base64-encoded string literals specified
+directly, or by reference.
+
+Example:
+```yaml
+encoded_string_1: Zm9v
+decoded_string_1: (( base64-decode encoded_string_1 ))
+decoded_string_2: (( base64-decode "YmFy" ))
+decoded_properties_file_contents: (( concat "fookey=" decoded_string_1 "\nbarkey=" decoded_string_2 "\n" ))
+encoded_properties_file_contents: (( base64 decoded_properties_file_contents ))
+```
+
 [array-merging]:      https://github.com/geofffranks/spruce/blob/master/doc/array-merging.md
 [env-var]:            https://github.com/geofffranks/spruce/blob/master/doc/environment-variables-and-defaults.md
 [vault]:              https://vaultproject.io

op_base64_decode.go

@@ -0,0 +1,98 @@
+package spruce
+
+import (
+	"encoding/base64"
+	"fmt"
+
+	"github.com/starkandwayne/goutils/ansi"
+
+	"github.com/starkandwayne/goutils/tree"
+
+	. "github.com/geofffranks/spruce/log"
+)
+
+// Base64DecodeOperator ...
+type Base64DecodeOperator struct{}
+
+// Setup ...
+func (Base64DecodeOperator) Setup() error {
+	return nil
+}
+
+// Phase ...
+func (Base64DecodeOperator) Phase() OperatorPhase {
+	return EvalPhase
+}
+
+// Dependencies ...
+func (Base64DecodeOperator) Dependencies(_ *Evaluator, _ []*Expr, _ []*tree.Cursor, auto []*tree.Cursor) []*tree.Cursor {
+	return auto
+}
+
+// Run ...
+func (Base64DecodeOperator) Run(ev *Evaluator, args []*Expr) (*Response, error) {
+	DEBUG("running (( base64-decode ... )) operation at $.%s", ev.Here)
+	defer DEBUG("done with (( base64-decode ... )) operation at $%s\n", ev.Here)
+
+	if len(args) != 1 {
+		return nil, fmt.Errorf("base64-decode operator requires exactly one string or reference argument")
+	}
+
+	var contents string
+
+	arg := args[0]
+	i := 0
+	v, err := arg.Resolve(ev.Tree)
+	if err != nil {
+		DEBUG("  arg[%d]: failed to resolve expression to a concrete value", i)
+		DEBUG("     [%d]: error was: %s", i, err)
+		return nil, err
+	}
+
+	switch v.Type {
+	case Literal:
+		DEBUG("  arg[%d]: using string literal '%v'", i, v.Literal)
+		DEBUG("     [%d]: appending '%v' to resultant string", i, v.Literal)
+		if fmt.Sprintf("%T", v.Literal) != "string" {
+			return nil, ansi.Errorf("@R{tried to base64 decode} @c{%v}@R{, which is not a string scalar}", v.Literal)
+		}
+		contents = fmt.Sprintf("%v", v.Literal)
+
+	case Reference:
+		DEBUG("  arg[%d]: trying to resolve reference $.%s", i, v.Reference)
+		s, err := v.Reference.Resolve(ev.Tree)
+		if err != nil {
+			DEBUG("     [%d]: resolution failed\n    error: %s", i, err)
+			return nil, fmt.Errorf("unable to resolve `%s`: %s", v.Reference, err)
+		}
+
+		switch s.(type) {
+		case string:
+			DEBUG("     [%d]: appending '%s' to resultant string", i, s)
+			contents = fmt.Sprintf("%v", s)
+
+		default:
+			DEBUG("  arg[%d]: %v is not a string scalar", i, s)
+			return nil, ansi.Errorf("@R{tried to base64 decode} @c{%v}@R{, which is not a string scalar}", v.Reference)
+		}
+
+	default:
+		DEBUG("  arg[%d]: I don't know what to do with '%v'", i, arg)
+		return nil, fmt.Errorf("base64-decode operator only accepts string literals and key reference argument")
+	}
+	DEBUG("")
+
+	if decoded, err := base64.StdEncoding.DecodeString(contents); err == nil {
+		DEBUG("  resolved (( base64-decode ... )) operation to the string:\n    \"%s\"", string(decoded))
+		return &Response{
+			Type:  Replace,
+			Value: string(decoded),
+		}, nil
+	} else {
+		return nil, fmt.Errorf("unable to base64 decode string %s: %s", contents, err)
+	}
+}
+
+func init() {
+	RegisterOp("base64-decode", Base64DecodeOperator{})
+}

operator_test.go

@@ -1963,6 +1963,40 @@ meta:
 
 	})
 
+	Convey("Base64Decode Operator", t, func() {
+		op := Base64DecodeOperator{}
+		ev := &Evaluator{
+			Tree: YAML(
+				`meta:
+  sample: "U2FtcGxlIFRleHQgVG8gQmFzZTY0IEVuY29kZSBGcm9tIFJlZmVyZW5jZQ=="
+`),
+		}
+
+		Convey("can decode from a string literal", func() {
+			r, err := op.Run(ev, []*Expr{
+				str("U2FtcGxlIFRleHQgVG8gQmFzZTY0IEVuY29kZQ=="),
+			})
+			So(err, ShouldBeNil)
+			So(r, ShouldNotBeNil)
+
+			So(r.Type, ShouldEqual, Replace)
+			So(r.Value.(string), ShouldEqual, "Sample Text To Base64 Encode")
+		})
+
+		Convey("can decode from a reference", func() {
+			r, err := op.Run(ev, []*Expr{
+				ref("meta.sample"),
+			})
+
+			So(err, ShouldBeNil)
+			So(r, ShouldNotBeNil)
+
+			So(r.Type, ShouldEqual, Replace)
+
+			So(r.Value.(string), ShouldEqual, "Sample Text To Base64 Encode From Reference")
+		})
+	})
+
 	Convey("awsparam/awssecret operator", t, func() {
 		op := AwsOperator{variant: "awsparam"}
 		ev := &Evaluator{