Move NTP function to ntp package and add ToTime32

Moves all NTP related functions to the NTP package and adds a function
to recover a time.Time from a uint32 encoded NTP timestamp.

internal/ntp/ntp.go

@@ -20,6 +20,11 @@ func ToNTP(t time.Time) uint64 {
 	return uint64(integerPart)<<32 | uint64(fractionalPart)
 }
 
+// ToNTP32 converts a time.Time object to a uint32 NTP timestamp
+func ToNTP32(t time.Time) uint32 {
+	return uint32((ToNTP(t) >> 16) & 0xFFFFFFFF)
+}
+
 // ToTime converts a uint64 NTP timestamps to a time.Time object
 func ToTime(t uint64) time.Time {
 	seconds := (t & 0xFFFFFFFF00000000) >> 32
@@ -28,3 +33,12 @@ func ToTime(t uint64) time.Time {
 
 	return time.Unix(0, 0).Add(-2208988800 * time.Second).Add(d)
 }
+
+// ToTime32 converts a uint32 NTP timestamp to a time.Time object, using the
+// highest 16 bit of the reference to recover the lost bits. The low 16 bits are
+// not recovered.
+func ToTime32(t uint32, reference time.Time) time.Time {
+	referenceNTP := ToNTP(reference) & 0xFFFF000000000000
+	tu64 := ((uint64(t) << 16) & 0x0000FFFFFFFF0000) | referenceNTP
+	return ToTime(tu64)
+}

internal/ntp/ntp_test.go

@@ -11,7 +11,7 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestNTPTimeConverstion(t *testing.T) {
+func TestNTPToTimeConverstion(t *testing.T) {
 	for i, cc := range []struct {
 		ts time.Time
 	}{
@@ -24,6 +24,7 @@ func TestNTPTimeConverstion(t *testing.T) {
 	} {
 		t.Run(fmt.Sprintf("TimeToNTP/%v", i), func(t *testing.T) {
 			assert.InDelta(t, cc.ts.UnixNano(), ToTime(ToNTP(cc.ts)).UnixNano(), float64(time.Millisecond.Nanoseconds()))
+			assert.InDelta(t, cc.ts.UnixNano(), ToTime32(ToNTP32(cc.ts), cc.ts).UnixNano(), float64(time.Millisecond.Nanoseconds()))
 		})
 	}
 }
@@ -50,3 +51,38 @@ func TestTimeToNTPConverstion(t *testing.T) {
 		})
 	}
 }
+
+func TestNTPTime32(t *testing.T) {
+	zero := time.Date(1900, time.January, 1, 0, 0, 0, 0, time.UTC)
+	notSoLongAgo := time.Date(2022, time.May, 5, 14, 48, 20, 0, time.UTC)
+	for i, cc := range []struct {
+		input    time.Time
+		expected uint32
+	}{
+		{
+			input:    zero,
+			expected: 0,
+		},
+		{
+			input:    zero.Add(time.Second),
+			expected: 1 << 16,
+		},
+		{
+			input:    notSoLongAgo,
+			expected: uint32(uint(notSoLongAgo.Sub(zero).Seconds())&0xffff) << 16,
+		},
+		{
+			input:    zero.Add(400 * time.Millisecond),
+			expected: 26214,
+		},
+		{
+			input:    zero.Add(1400 * time.Millisecond),
+			expected: 1<<16 + 26214,
+		},
+	} {
+		t.Run(fmt.Sprintf("%v", i), func(t *testing.T) {
+			res := ToNTP32(cc.input)
+			assert.Equalf(t, cc.expected, res, "%b != %b", cc.expected, res)
+		})
+	}
+}

pkg/rfc8888/recorder.go

@@ -6,6 +6,7 @@ package rfc8888
 import (
 	"time"
 
+	"github.com/pion/interceptor/internal/ntp"
 	"github.com/pion/rtcp"
 )
 
@@ -44,7 +45,7 @@ func (r *Recorder) BuildReport(now time.Time, maxSize int) *rtcp.CCFeedbackRepor
 	report := &rtcp.CCFeedbackReport{
 		SenderSSRC:      r.ssrc,
 		ReportBlocks:    []rtcp.CCFeedbackReportBlock{},
-		ReportTimestamp: ntpTime32(now),
+		ReportTimestamp: ntp.ToNTP32(now),
 	}
 
 	maxReportBlocks := (maxSize - 12 - (8 * len(r.streams))) / 2
@@ -65,14 +66,3 @@ func (r *Recorder) BuildReport(now time.Time, maxSize int) *rtcp.CCFeedbackRepor
 
 	return report
 }
-
-func ntpTime32(t time.Time) uint32 {
-	// seconds since 1st January 1900
-	s := (float64(t.UnixNano()) / 1000000000.0) + 2208988800
-
-	integerPart := uint32(s)
-	fractionalPart := uint32((s - float64(integerPart)) * 0xFFFFFFFF)
-
-	// higher 32 bits are the integer part, lower 32 bits are the fractional part
-	return uint32(((uint64(integerPart)<<32 | uint64(fractionalPart)) >> 16) & 0xFFFFFFFF)
-}

pkg/rfc8888/recorder_test.go

@@ -4,7 +4,6 @@
 package rfc8888
 
 import (
-	"fmt"
 	"testing"
 	"time"
 
@@ -161,38 +160,3 @@ func TestRecorder(t *testing.T) {
 		}
 	})
 }
-
-func TestNTPTime32(t *testing.T) {
-	zero := time.Date(1900, time.January, 1, 0, 0, 0, 0, time.UTC)
-	notSoLongAgo := time.Date(2022, time.May, 5, 14, 48, 20, 0, time.UTC)
-	for i, cc := range []struct {
-		input    time.Time
-		expected uint32
-	}{
-		{
-			input:    zero,
-			expected: 0,
-		},
-		{
-			input:    zero.Add(time.Second),
-			expected: 1 << 16,
-		},
-		{
-			input:    notSoLongAgo,
-			expected: uint32(uint(notSoLongAgo.Sub(zero).Seconds())&0xffff) << 16,
-		},
-		{
-			input:    zero.Add(400 * time.Millisecond),
-			expected: 26214,
-		},
-		{
-			input:    zero.Add(1400 * time.Millisecond),
-			expected: 1<<16 + 26214,
-		},
-	} {
-		t.Run(fmt.Sprintf("%v", i), func(t *testing.T) {
-			res := ntpTime32(cc.input)
-			assert.Equalf(t, cc.expected, res, "%b != %b", cc.expected, res)
-		})
-	}
-}