Correct EBP group ID parsing to read 7-bit ID field

Code would previously include the extension flag bit in the group ID, causing literal group ID comparisons to incorrectly fail. Also correct ebp.StreamSyncSignal() to search all available group IDs and not only the second.
Comcast · Aug 15, 2022 · 62fa5de · 62fa5de
1 parent 4c4c4eb
commit 62fa5de
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Showing 6 changed files with 130 additions and 24 deletions.
diff --git a/ebp/baseebp.go b/ebp/baseebp.go
@@ -146,10 +146,10 @@ func (ebp *baseEbp) SetIsEmpty(value bool) {
 // but Stream Sync and SCTE-35 were the only two ever to get implemented. MK was the only Transcoder to implement SCTE-35 within the
 // Grouping ID section and we never leveraged that data on any downstream devices.
 func (ebp *baseEbp) StreamSyncSignal() uint8 {
-	// The first byte is Grouping ID, the second byte is the sync signal
-	if len(ebp.Grouping) == 2 && ebp.Grouping[0] == 0x80 {
-		return ebp.Grouping[1]
+	for _, groupID := range ebp.Grouping {
+		if groupID == StreamSynchronized || groupID == StreamNotSynchronized {
+			return groupID
+		}
 	}
-
 	return InvalidStreamSyncSignal
 }
diff --git a/ebp/cablelabsebp.go b/ebp/cablelabsebp.go
@@ -122,12 +122,15 @@ func readCableLabsEbp(data []byte) (ebp *cableLabsEbp, err error) {
 
 	if ebp.GroupingFlag() {
 		var group byte
-		group = data[index]
+		var groupExtFlag bool
+		groupExtFlag = data[index]&0x80 != 0
+		group = data[index] & 0x7F
 		ebp.Grouping = append(ebp.Grouping, group)
 		index += uint8(1)
 
-		for group&0x80 != 0 {
-			group = data[index]
+		for groupExtFlag {
+			groupExtFlag = data[index]&0x80 != 0
+			group = data[index] & 0x7F
 			ebp.Grouping = append(ebp.Grouping, group)
 			index += uint8(1)
 		}
@@ -182,11 +185,15 @@ func (ebp *cableLabsEbp) Data() []byte {
 
 	if ebp.GroupingFlag() {
 		for i := range ebp.Grouping {
-			ebp.Grouping[i] |= 0x80 // set flag because this is not the last ID
-			if i == len(ebp.Grouping)-1 {
-				ebp.Grouping[i] &= 0x7F // last index does not have this flag set
+			var group byte
+			if i < len(ebp.Grouping)-1 {
+				// add the ext flag for all but the last group
+				group = ebp.Grouping[i] | 0x80
+			} else {
+				// last group - no ext flag
+				group = ebp.Grouping[i]
 			}
-			binary.Write(data, ebpEncoding, ebp.Grouping[i])
+			binary.Write(data, ebpEncoding, group)
 		}
 	}
 

diff --git a/ebp/cablelabsebp_test.go b/ebp/cablelabsebp_test.go
@@ -1,7 +1,7 @@
 /*
 MIT License
 
-Copyright 2016 Comcast Cable Communications Management, LLC
+# Copyright 2016 Comcast Cable Communications Management, LLC
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -110,3 +110,49 @@ func TestCableLabsEBP(t *testing.T) {
 		)
 	}
 }
+
+func TestParseCableLabsEBPWithMultipleGroups(t *testing.T) {
+	var ebpBytes = []byte{0xdf, 0x11, 0x45, 0x42, 0x50, 0x30, 0x98, 0x80, 0xa3, 0xfe, 0x1d, 0xe6, 0xa1, 0x45, 0x18, 0xb8, 0x51, 0x00, 0x00}
+	ebp, err := readCableLabsEbp(ebpBytes)
+	if err != nil {
+		t.Logf("failed to parse CableLabs-style EBP: #{err}")
+		t.FailNow()
+	}
+	if ebp.StreamSyncSignal() != StreamSynchronized {
+		t.Errorf("Wrong stream sync signal (expected 0x1D, got #{ebp.StreamSyncSignal()})")
+	}
+	var expectedGroups = []uint8{0x00, 0x23, 0x7E, 0x1D}
+	if len(ebp.Grouping) != len(expectedGroups) {
+		t.Logf("Wrong number of group IDs (expected #{len(expectedGroups)}, got #{len(ebp.Grouping)}")
+		t.FailNow()
+	}
+	for i, gid := range expectedGroups {
+		other := ebp.Grouping[i]
+		if gid != other {
+			t.Errorf("Wrong group ID (expected #{gid}, got #{other})")
+		}
+	}
+}
+
+func TestParseCableLabsEBPWithSyncInMiddle(t *testing.T) {
+	var ebpBytes = []byte{0xdf, 0x12, 0x45, 0x42, 0x50, 0x30, 0x98, 0x80, 0xa3, 0xfe, 0x9d, 0x05, 0xe6, 0xa1, 0x45, 0x18, 0xb8, 0x51, 0x00, 0x00}
+	ebp, err := readCableLabsEbp(ebpBytes)
+	if err != nil {
+		t.Logf("failed to parse CableLabs-style EBP: #{err}")
+		t.FailNow()
+	}
+	if ebp.StreamSyncSignal() != StreamSynchronized {
+		t.Errorf("Wrong stream sync signal (expected 0x1D, got #{ebp.StreamSyncSignal()})")
+	}
+	var expectedGroups = []uint8{0x00, 0x23, 0x7E, 0x1D, 0x05}
+	if len(ebp.Grouping) != len(expectedGroups) {
+		t.Logf("Wrong number of group IDs (expected #{len(expectedGroups)}, got #{len(ebp.Grouping)}")
+		t.FailNow()
+	}
+	for i, gid := range expectedGroups {
+		other := ebp.Grouping[i]
+		if gid != other {
+			t.Errorf("Wrong group ID (expected #{gid}, got #{other})")
+		}
+	}
+}
diff --git a/v2/ebp/baseebp.go b/v2/ebp/baseebp.go
@@ -146,10 +146,10 @@ func (ebp *baseEbp) SetIsEmpty(value bool) {
 // but Stream Sync and SCTE-35 were the only two ever to get implemented. MK was the only Transcoder to implement SCTE-35 within the
 // Grouping ID section and we never leveraged that data on any downstream devices.
 func (ebp *baseEbp) StreamSyncSignal() uint8 {
-	// The first byte is Grouping ID, the second byte is the sync signal
-	if len(ebp.Grouping) == 2 && ebp.Grouping[0] == 0x80 {
-		return ebp.Grouping[1]
+	for _, groupID := range ebp.Grouping {
+		if groupID == StreamSynchronized || groupID == StreamNotSynchronized {
+			return groupID
+		}
 	}
-
 	return InvalidStreamSyncSignal
 }
diff --git a/v2/ebp/cablelabsebp.go b/v2/ebp/cablelabsebp.go
@@ -122,12 +122,15 @@ func readCableLabsEbp(data []byte) (ebp *cableLabsEbp, err error) {
 
 	if ebp.GroupingFlag() {
 		var group byte
-		group = data[index]
+		var groupExtFlag bool
+		groupExtFlag = data[index]&0x80 != 0
+		group = data[index] & 0x7F
 		ebp.Grouping = append(ebp.Grouping, group)
 		index += uint8(1)
 
-		for group&0x80 != 0 {
-			group = data[index]
+		for groupExtFlag {
+			groupExtFlag = data[index]&0x80 != 0
+			group = data[index] & 0x7F
 			ebp.Grouping = append(ebp.Grouping, group)
 			index += uint8(1)
 		}
@@ -182,11 +185,15 @@ func (ebp *cableLabsEbp) Data() []byte {
 
 	if ebp.GroupingFlag() {
 		for i := range ebp.Grouping {
-			ebp.Grouping[i] |= 0x80 // set flag because this is not the last ID
-			if i == len(ebp.Grouping)-1 {
-				ebp.Grouping[i] &= 0x7F // last index does not have this flag set
+			var group byte
+			if i < len(ebp.Grouping)-1 {
+				// add the ext flag for all but the last group
+				group = ebp.Grouping[i] | 0x80
+			} else {
+				// last group - no ext flag
+				group = ebp.Grouping[i]
 			}
-			binary.Write(data, ebpEncoding, ebp.Grouping[i])
+			binary.Write(data, ebpEncoding, group)
 		}
 	}
 

diff --git a/v2/ebp/cablelabsebp_test.go b/v2/ebp/cablelabsebp_test.go
@@ -1,7 +1,7 @@
 /*
 MIT License
 
-Copyright 2016 Comcast Cable Communications Management, LLC
+# Copyright 2016 Comcast Cable Communications Management, LLC
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -110,3 +110,49 @@ func TestCableLabsEBP(t *testing.T) {
 		)
 	}
 }
+
+func TestParseCableLabsEBPWithMultipleGroups(t *testing.T) {
+	var ebpBytes = []byte{0xdf, 0x11, 0x45, 0x42, 0x50, 0x30, 0x98, 0x80, 0xa3, 0xfe, 0x1d, 0xe6, 0xa1, 0x45, 0x18, 0xb8, 0x51, 0x00, 0x00}
+	ebp, err := readCableLabsEbp(ebpBytes)
+	if err != nil {
+		t.Logf("failed to parse CableLabs-style EBP: #{err}")
+		t.FailNow()
+	}
+	if ebp.StreamSyncSignal() != StreamSynchronized {
+		t.Errorf("Wrong stream sync signal (expected 0x1D, got #{ebp.StreamSyncSignal()})")
+	}
+	var expectedGroups = []uint8{0x00, 0x23, 0x7E, 0x1D}
+	if len(ebp.Grouping) != len(expectedGroups) {
+		t.Logf("Wrong number of group IDs (expected #{len(expectedGroups)}, got #{len(ebp.Grouping)}")
+		t.FailNow()
+	}
+	for i, gid := range expectedGroups {
+		other := ebp.Grouping[i]
+		if gid != other {
+			t.Errorf("Wrong group ID (expected #{gid}, got #{other})")
+		}
+	}
+}
+
+func TestParseCableLabsEBPWithSyncInMiddle(t *testing.T) {
+	var ebpBytes = []byte{0xdf, 0x12, 0x45, 0x42, 0x50, 0x30, 0x98, 0x80, 0xa3, 0xfe, 0x9d, 0x05, 0xe6, 0xa1, 0x45, 0x18, 0xb8, 0x51, 0x00, 0x00}
+	ebp, err := readCableLabsEbp(ebpBytes)
+	if err != nil {
+		t.Logf("failed to parse CableLabs-style EBP: #{err}")
+		t.FailNow()
+	}
+	if ebp.StreamSyncSignal() != StreamSynchronized {
+		t.Errorf("Wrong stream sync signal (expected 0x1D, got #{ebp.StreamSyncSignal()})")
+	}
+	var expectedGroups = []uint8{0x00, 0x23, 0x7E, 0x1D, 0x05}
+	if len(ebp.Grouping) != len(expectedGroups) {
+		t.Logf("Wrong number of group IDs (expected #{len(expectedGroups)}, got #{len(ebp.Grouping)}")
+		t.FailNow()
+	}
+	for i, gid := range expectedGroups {
+		other := ebp.Grouping[i]
+		if gid != other {
+			t.Errorf("Wrong group ID (expected #{gid}, got #{other})")
+		}
+	}
+}