write ros time to message indexes, clarify docstrings

rosbag.go

@@ -96,8 +96,8 @@ type ConnectionHeader struct {
 // to be decodable using the message_definition field of the connection record
 // associated with "connID".
 type Message struct {
-	Conn uint32 // ID for connection on which emssage arrived
-	Time uint64 // time at which the message was received
+	Conn uint32 // ID for connection on which message arrived
+	Time uint64 // time at which the message was received in nanoseconds
 	Data []byte // serialized message data in ROS serialization format
 }
 
@@ -107,8 +107,8 @@ type Message struct {
 // offset.
 type ChunkInfo struct {
 	ChunkPos  uint64            // offset of the chunk record
-	StartTime uint64            // timestamp of earliest message in the chunk
-	EndTime   uint64            // timestamp of latest message in the chunk
+	StartTime uint64            // timestamp of earliest message in the chunk in nanoseconds
+	EndTime   uint64            // timestamp of latest message in the chunk in nanoseconds
 	Count     uint32            // number of connections in the chunk
 	Data      map[uint32]uint32 // map of connID to message count
 }
@@ -118,11 +118,11 @@ type ChunkInfo struct {
 type IndexData struct {
 	Conn  uint32              // connection ID
 	Count uint32              // number of messages on *conn* in the preceding chunk
-	Data  []MessageIndexEntry // *count* repeating occurrences of timestamps (uint64) and message offsets (uint32)
+	Data  []MessageIndexEntry // *count* repeating occurrences of timestamps and message offsets
 }
 
 // MessageIndexEntry is an entry in the data section of an IndexData record.
 type MessageIndexEntry struct {
-	Time   uint64 // time at which the message was recorded
-	Offset uint32 // offset of the message, relative to the start of the chunk data that contains it
+	Time   uint64 // time at which the message was recorded in nanoseconds
+	Offset uint32 // byte offset of the message within the uncompressed chunk data
 }

writer.go

@@ -291,7 +291,7 @@ func (b *Writer) writeIndexData(indexData IndexData) error {
 	data := make([]byte, 12*len(indexData.Data))
 	offset := 0
 	for _, entry := range indexData.Data {
-		offset += putU64(data[offset:], entry.Time)
+		offset += putRostime(data[offset:], entry.Time)
 		offset += putU32(data[offset:], entry.Offset)
 	}
 

writer_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func testBagIsReadable(t *testing.T, rs io.Reader) {
@@ -133,6 +134,35 @@ func TestWriter(t *testing.T) {
 	}
 }
 
+func TestCorrectMessageIndexes(t *testing.T) {
+	buf := &bytes.Buffer{}
+	timestamp := uint64(10_000_000_020)
+	writer, err := NewWriter(buf)
+	require.NoError(t, err)
+	require.NoError(t, writer.WriteConnection(connection(13, "/chat")))
+	require.NoError(t, writer.WriteMessage(message(13, timestamp, []byte("hello"))))
+	require.NoError(t, writer.Close())
+
+	reader := bytes.NewBuffer(buf.Bytes())
+	_, err = reader.Read(make([]byte, len(Magic)))
+	require.NoError(t, err)
+
+	for {
+		op, record, err := ReadRecord(reader)
+		require.NoError(t, err)
+		if op != OpIndexData {
+			continue
+		}
+		index, err := ParseIndexData(record)
+		require.NoError(t, err)
+		assert.Equal(t, index.Conn, uint32(13))
+		require.Len(t, index.Data, 1)
+		entry := index.Data[0]
+		require.Equal(t, entry.Time, timestamp)
+		break
+	}
+}
+
 func TestWriterIsDeterministic(t *testing.T) {
 	hashes := []string{}