Merged feature/104 into master (with tests).

container/mts/mpegts.go

@@ -180,6 +180,7 @@ func FindPat(d []byte) ([]byte, int, error) {
 var (
 	errInvalidLen     = errors.New("MPEG-TS data not of valid length")
 	errCouldNotFind   = errors.New("could not find packet with given PID")
+	errNotConsecutive = errors.New("could not find consecutive PIDs")
 )
 
 // FindPid will take a clip of MPEG-TS and try to find a packet with given PID - if one
@@ -221,26 +222,24 @@ func LastPid(d []byte, pid uint16) (pkt []byte, i int, err error) {
 // along with optional metadata if present. Commonly used to find a
 // PAT immediately followed by a PMT.
 func IndexPid(d []byte, pids ...uint16) (idx int, m map[string]string, err error) {
-	prev := 0
+	idx = -1
 	for _, pid := range pids {
-		pkt, i, _err := FindPid(d, pid)
+		if len(d) < PacketSize {
+			return idx, m, errInvalidLen
+		}
+		pkt, i, err := FindPid(d, pid)
 		if err != nil {
-			err = errors.Wrap(_err, "could not find PID")
-			return
+			return idx, m, errCouldNotFind
 		}
 		if pid == PmtPid {
 			m, _ = metaFromPMT(pkt)
 		}
-		if prev == 0 {
+		if idx == -1 {
 			idx = i
-			prev = i
-			continue
+		} else if i != 0 {
+			return idx, m, errNotConsecutive
 		}
-		if i != prev+PacketSize {
-			err = errors.New("PIDs not consecutive")
-			return
-		}
-		prev = i
+		d = d[i+PacketSize:]
 	}
 	return
 }

container/mts/mpegts_test.go

@@ -491,6 +491,26 @@ func TestSegmentForMeta(t *testing.T) {
 		if !reflect.DeepEqual(want, got) {
 			t.Errorf("did not get expected result for test %v\nGot: %v\nWant: %v\n", testn, got, want)
 		}
+
+		// Now test IndexPid.
+		i, m, err := IndexPid(clip.Bytes(), PatPid, PmtPid)
+		if err != nil {
+			t.Fatalf("IndexPid failed with error: %v", err)
+		}
+		if i != 0 {
+			t.Fatalf("IndexPid unexpected index; got %d, expected 0", i)
+		}
+		if m["n"] != "1" {
+			t.Fatalf("IndexPid unexpected metadata; got %s, expected 1", m["n"])
+		}
+	}
+
+	// Finally, test IndexPid error handling.
+	for _, d := range [][]byte{[]byte{}, make([]byte, PacketSize/2), make([]byte, PacketSize)} {
+		_, _, err := IndexPid(d, PatPid, PmtPid)
+		if err == nil {
+			t.Fatalf("IndexPid expected error")
+		}
 	}
 }