Support unencrypted signals use of alignment_stuffing

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+## [1.2.1] - 2021-09-09
+
+### Fixed
+
+* Fixed case where unencrypted signals with `alignment_stuffing` returned `ErrBufferUnderflow`.
+
 ## [1.2.0] - 2021-07-07
 
 ### Fixed

README.md

@@ -19,7 +19,7 @@ Get the module:
 
 ```shell
 $ go get github.com/Comcast/scte35-go
-go get: added github.com/Comcast/scte35-go v1.0.0
+go get: added github.com/Comcast/scte35-go v1.2.1
 ```
 
 ## Code Examples

pkg/scte35/scte35_test.go

@@ -402,7 +402,7 @@ func TestDecodeBase64(t *testing.T) {
 		{
 			name:   "Empty String",
 			binary: "",
-			err:    fmt.Errorf("splice_info_section: %w", scte35.ErrBufferOverflow),
+			err:    scte35.ErrBufferOverflow,
 		},
 		{
 			name:   "Invalid Base64 Encoding",
@@ -536,9 +536,23 @@ func TestDecodeBase64(t *testing.T) {
 			binary: "/DA4AAAAAAAAAP/wFAUABDEAf+//mWEhzP4Azf5gAQAAAAATAhFDVUVJAAAAAX+/AQIwNAEAAKeYO3Q=",
 			err:    fmt.Errorf("splice_info_section: %w", scte35.ErrCRC32Invalid),
 		},
+		{
+			name:   "Alignment Stuffing without Encryption",
+			binary: "/DAeAAAAAAAAAP///wViAA/nf18ACQAAAAAskJv+YPtE",
+			expected: scte35.SpliceInfoSection{
+				SpliceCommand: &scte35.SpliceInsert{
+					SpliceEventID:       1644171239,
+					Program:             &scte35.SpliceInsertProgram{},
+					SpliceImmediateFlag: true,
+					UniqueProgramID:     9,
+				},
+				Tier:    4095,
+				SAPType: 3,
+			},
+			legacy: true, // binary wont match because of stuffing
+		},
 	}
 
-
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {
 			// decode the binary

pkg/scte35/splice_info_section.go

@@ -122,6 +122,12 @@ func (sis *SpliceInfoSection) Decode(b []byte) (err error) {
 	if encryptedPacket {
 		sis.alignmentStuffing = int(r.LeftBits()) - 64
 		sis.ecrc32 = r.Bytes(4)
+	} else {
+		sis.alignmentStuffing = int(r.LeftBits()-32) / 8
+		if sis.alignmentStuffing < 0 {
+			return ErrBufferOverflow
+		}
+		r.Skip(uint(sis.alignmentStuffing * 8))
 	}
 	sis.crc32 = r.Bytes(4)
 
@@ -201,8 +207,8 @@ func (sis *SpliceInfoSection) Encode() ([]byte, error) {
 	}
 
 	// Encoding encrypted signals is untested.
+	iow.PutUint64(uint(sis.alignmentStuffing), 0) // alignment_stuffing
 	if sis.EncryptedPacket.EncryptionAlgorithm != EncryptionAlgorithmNone {
-		iow.PutUint64(uint(sis.alignmentStuffing), 0)          // alignment_stuffing
 		iow.PutUint32(32, calculateCRC32(buf[:iow.Index()/8])) // E_CRC_32
 	}