Add support for decoding base64 strings without padding (#1604)

pkg/yqlib/decoder_base64.go

@@ -4,10 +4,33 @@ import (
 	"bytes"
 	"encoding/base64"
 	"io"
+	"strings"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
+type base64Padder struct {
+	count uint64
+	io.Reader
+}
+
+func (c *base64Padder) pad(buf []byte) (int, error) {
+	pad := strings.Repeat("=", int(4-c.count%4))
+	n, err := strings.NewReader(pad).Read(buf)
+	c.count += uint64(n)
+	return n, err
+}
+
+func (c *base64Padder) Read(buf []byte) (int, error) {
+	n, err := c.Reader.Read(buf)
+	c.count += uint64(n)
+
+	if err == io.EOF && c.count%4 != 0 {
+		return c.pad(buf)
+	}
+	return n, err
+}
+
 type base64Decoder struct {
 	reader       io.Reader
 	finished     bool
@@ -20,7 +43,7 @@ func NewBase64Decoder() Decoder {
 }
 
 func (dec *base64Decoder) Init(reader io.Reader) error {
-	dec.reader = reader
+	dec.reader = &base64Padder{Reader: reader}
 	dec.readAnything = false
 	dec.finished = false
 	return nil

pkg/yqlib/operator_encoder_decoder_test.go

@@ -310,6 +310,14 @@ var encoderDecoderOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!str)::\n",
 		},
 	},
+	{
+		description: "base64 missing padding test",
+		skipDoc:     true,
+		expression:  `"Y2F0cw" | @base64d`,
+		expected: []string{
+			"D0, P[], (!!str)::cats\n",
+		},
+	},
 	{
 		requiresFormat: "xml",
 		description:    "empty xml decode",