CLI: Fix zero-valued frequencies (#381)

Fixes a bug introduced recently that caused frequencies in `info` output
to be zero due to unintentional shadowing of a global variable used for
the cat command.

Use of global variables is an artifact of cobra's CLI command code
generation. We can get away from that with a bit of refactoring but
haven't done so yet. As a stopgap, this commit also introduces a
convention of prefixing the globals with the name of the related
command.

go/cli/mcap/cmd/cat.go

@@ -26,10 +26,10 @@ import (
 )
 
 var (
-	topics     string
-	start      int64
-	end        int64
-	formatJSON bool
+	catTopics     string
+	catStart      int64
+	catEnd        int64
+	catFormatJSON bool
 )
 
 type DecimalTime uint64
@@ -175,12 +175,12 @@ var catCmd = &cobra.Command{
 			if err != nil {
 				log.Fatalf("Failed to create reader: %s", err)
 			}
-			topics := strings.FieldsFunc(topics, func(c rune) bool { return c == ',' })
-			it, err := reader.Messages(start*1e9, end*1e9, topics, false)
+			topics := strings.FieldsFunc(catTopics, func(c rune) bool { return c == ',' })
+			it, err := reader.Messages(catStart*1e9, catEnd*1e9, topics, false)
 			if err != nil {
 				log.Fatalf("Failed to read messages: %s", err)
 			}
-			err = printMessages(ctx, os.Stdout, it, formatJSON)
+			err = printMessages(ctx, os.Stdout, it, catFormatJSON)
 			if err != nil {
 				log.Fatalf("Failed to print messages: %s", err)
 			}
@@ -197,12 +197,12 @@ var catCmd = &cobra.Command{
 			if err != nil {
 				return fmt.Errorf("failed to create reader: %w", err)
 			}
-			topics := strings.FieldsFunc(topics, func(c rune) bool { return c == ',' })
-			it, err := reader.Messages(start*1e9, end*1e9, topics, true)
+			topics := strings.FieldsFunc(catTopics, func(c rune) bool { return c == ',' })
+			it, err := reader.Messages(catStart*1e9, catEnd*1e9, topics, true)
 			if err != nil {
 				return fmt.Errorf("failed to read messages: %w", err)
 			}
-			err = printMessages(ctx, os.Stdout, it, formatJSON)
+			err = printMessages(ctx, os.Stdout, it, catFormatJSON)
 			if err != nil {
 				return fmt.Errorf("failed to print messages: %w", err)
 			}
@@ -217,8 +217,8 @@ var catCmd = &cobra.Command{
 func init() {
 	rootCmd.AddCommand(catCmd)
 
-	catCmd.PersistentFlags().Int64VarP(&start, "start-secs", "", 0, "start time")
-	catCmd.PersistentFlags().Int64VarP(&end, "end-secs", "", math.MaxInt64, "end time")
-	catCmd.PersistentFlags().StringVarP(&topics, "topics", "", "", "comma-separated list of topics")
-	catCmd.PersistentFlags().BoolVarP(&formatJSON, "json", "", false, "print messages as JSON")
+	catCmd.PersistentFlags().Int64VarP(&catStart, "start-secs", "", 0, "start time")
+	catCmd.PersistentFlags().Int64VarP(&catEnd, "end-secs", "", math.MaxInt64, "end time")
+	catCmd.PersistentFlags().StringVarP(&catTopics, "topics", "", "", "comma-separated list of topics")
+	catCmd.PersistentFlags().BoolVarP(&catFormatJSON, "json", "", false, "print messages as JSON")
 }

go/cli/mcap/cmd/convert.go

@@ -20,11 +20,13 @@ var (
 	db3Magic = []byte{0x53, 0x51, 0x4c, 0x69, 0x74, 0x65, 0x20, 0x66, 0x6f, 0x72, 0x6d, 0x61, 0x74, 0x20, 0x33, 0x00}
 )
 
-var amentPrefixPath string
-var compression string
-var chunkSize int64
-var includeCRC bool
-var chunked bool
+var (
+	convertAmentPrefixPath string
+	convertCompression     string
+	convertChunkSize       int64
+	convertIncludeCRC      bool
+	convertChunked         bool
+)
 
 type FileType string
 
@@ -83,7 +85,7 @@ var convertCmd = &cobra.Command{
 		defer w.Close()
 
 		var compressionFormat mcap.CompressionFormat
-		switch compression {
+		switch convertCompression {
 		case "lz4":
 			compressionFormat = mcap.CompressionLZ4
 		case "zstd":
@@ -93,9 +95,9 @@ var convertCmd = &cobra.Command{
 		}
 
 		opts := &mcap.WriterOptions{
-			IncludeCRC:  includeCRC,
-			Chunked:     chunked,
-			ChunkSize:   chunkSize,
+			IncludeCRC:  convertIncludeCRC,
+			Chunked:     convertChunked,
+			ChunkSize:   convertChunkSize,
 			Compression: compressionFormat,
 		}
 
@@ -112,7 +114,7 @@ var convertCmd = &cobra.Command{
 				die("failed to open sqlite3: %s", err)
 			}
 
-			amentPath := amentPrefixPath
+			amentPath := convertAmentPrefixPath
 			prefixPath := os.Getenv("AMENT_PREFIX_PATH")
 			if prefixPath != "" {
 				amentPath += ":" + prefixPath
@@ -131,35 +133,35 @@ var convertCmd = &cobra.Command{
 func init() {
 	rootCmd.AddCommand(convertCmd)
 	convertCmd.PersistentFlags().StringVarP(
-		&amentPrefixPath,
+		&convertAmentPrefixPath,
 		"ament-prefix-path",
 		"",
 		"",
 		"(ros2 only) colon-separated list of directories to search for message definitions (e.g /opt/ros/galactic:/opt/ros/noetic)",
 	)
 	convertCmd.PersistentFlags().StringVarP(
-		&compression,
+		&convertCompression,
 		"compression",
 		"",
 		"zstd",
 		"chunk compression algorithm (supported: zstd, lz4, none)",
 	)
 	convertCmd.PersistentFlags().Int64VarP(
-		&chunkSize,
+		&convertChunkSize,
 		"chunk-size",
 		"",
 		8*1024*1024,
 		"chunk size to target",
 	)
 	convertCmd.PersistentFlags().BoolVarP(
-		&includeCRC,
+		&convertIncludeCRC,
 		"include-crc",
 		"",
 		true,
 		"include chunk CRC checksums in output",
 	)
 	convertCmd.PersistentFlags().BoolVarP(
-		&chunked,
+		&convertChunked,
 		"chunked",
 		"",
 		true,

go/cli/mcap/cmd/info.go

@@ -31,10 +31,11 @@ func printInfo(w io.Writer, info *mcap.Info) error {
 	buf := &bytes.Buffer{}
 	fmt.Fprintf(buf, "library: %s\n", info.Header.Library)
 	fmt.Fprintf(buf, "profile: %s\n", info.Header.Profile)
+	var start, end uint64
 	if info.Statistics != nil {
 		fmt.Fprintf(buf, "messages: %d\n", info.Statistics.MessageCount)
-		start := info.Statistics.MessageStartTime
-		end := info.Statistics.MessageEndTime
+		start = info.Statistics.MessageStartTime
+		end = info.Statistics.MessageEndTime
 		starttime := time.Unix(int64(start/1e9), int64(start%1e9))
 		endtime := time.Unix(int64(end/1e9), int64(end%1e9))
 		fmt.Fprintf(buf, "duration: %s\n", endtime.Sub(starttime))