Tidy upper part of info table (#967)

This aligns the spacing in the upper part of the "mcap info" output.

go/cli/mcap/cmd/info.go

@@ -8,6 +8,7 @@ import (
 	"math"
 	"os"
 	"sort"
+	"strings"
 	"time"
 
 	"github.com/foxglove/mcap/go/cli/mcap/utils"
@@ -48,14 +49,21 @@ func getDurationNs(start uint64, end uint64) float64 {
 	return float64(diff) * signMultiplier
 }
 
+func addRow(rows [][]string, field string, value string, args ...any) [][]string {
+	return append(rows, []string{field, fmt.Sprintf(value, args...)})
+}
+
 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)
+
+	header := [][]string{
+		{"library:", info.Header.Library},
+		{"profile:", info.Header.Profile},
+	}
 	var start, end uint64
 	durationInSeconds := float64(0)
 	if info.Statistics != nil {
-		fmt.Fprintf(buf, "messages: %d\n", info.Statistics.MessageCount)
+		header = addRow(header, "messages:", "%d", info.Statistics.MessageCount)
 		start = info.Statistics.MessageStartTime
 		end = info.Statistics.MessageEndTime
 		durationNs := getDurationNs(start, end)
@@ -65,18 +73,19 @@ func printInfo(w io.Writer, info *mcap.Info) error {
 		if math.Abs(durationNs) > math.MaxInt64 {
 			// time.Duration is an int64 nanosecond count under the hood, but end and start can
 			// be further apart than that.
-			fmt.Fprintf(buf, "duration: %.3fs\n", durationInSeconds)
+			header = addRow(header, "duration:", "%.3fs", durationInSeconds)
 		} else {
-			fmt.Fprintf(buf, "duration: %s\n", endtime.Sub(starttime))
+			header = addRow(header, "duration:", "%s", endtime.Sub(starttime))
 		}
 		if starttime.After(LongAgo) {
-			fmt.Fprintf(buf, "start: %s (%s)\n", starttime.Format(time.RFC3339Nano), decimalTime(starttime))
-			fmt.Fprintf(buf, "end: %s (%s)\n", endtime.Format(time.RFC3339Nano), decimalTime(endtime))
+			header = addRow(header, "start:", "%s (%s)", starttime.Format(time.RFC3339Nano), decimalTime(starttime))
+			header = addRow(header, "end:", "%s (%s)", endtime.Format(time.RFC3339Nano), decimalTime(endtime))
 		} else {
-			fmt.Fprintf(buf, "start: %s\n", decimalTime(starttime))
-			fmt.Fprintf(buf, "end: %s\n", decimalTime(endtime))
+			header = addRow(header, "start:", "%s", decimalTime(starttime))
+			header = addRow(header, "end:", "%s", decimalTime(endtime))
 		}
 	}
+	utils.FormatTable(buf, header)
 	if len(info.ChunkIndexes) > 0 {
 		compressionFormatStats := make(map[mcap.CompressionFormat]struct {
 			count            int
@@ -121,13 +130,17 @@ func printInfo(w io.Writer, info *mcap.Info) error {
 			}
 		}
 	}
+
+	maxChanIDWidth := digits(uint64(chanIDs[len(chanIDs)-1])) + 3
 	for _, chanID := range chanIDs {
 		channel := info.Channels[chanID]
 		schema := info.Schemas[channel.SchemaID]
 		channelMessageCount := info.Statistics.ChannelMessageCounts[chanID]
 		frequency := 1e9 * float64(channelMessageCount) / float64(end-start)
+		width := digits(uint64(chanID)) + 2
+		padding := strings.Repeat(" ", maxChanIDWidth-width)
 		row := []string{
-			fmt.Sprintf("\t(%d) %s", channel.ID, channel.Topic),
+			fmt.Sprintf("\t(%d)%s%s", channel.ID, padding, channel.Topic),
 		}
 		if info.Statistics != nil {
 			row = append(row, fmt.Sprintf("%*d msgs (%.2f Hz)", maxCountWidth, channelMessageCount, frequency))

go/cli/mcap/utils/utils.go

@@ -1,13 +1,15 @@
 package utils
 
 import (
+	"bufio"
 	"bytes"
 	"context"
 	"encoding/json"
 	"fmt"
 	"io"
 	"os"
 	"regexp"
+	"strings"
 
 	"cloud.google.com/go/storage"
 	"github.com/foxglove/mcap/go/mcap"
@@ -104,14 +106,21 @@ func WithReader(ctx context.Context, filename string, f func(remote bool, rs io.
 }
 
 func FormatTable(w io.Writer, rows [][]string) {
-	tw := tablewriter.NewWriter(w)
+	buf := &bytes.Buffer{}
+	tw := tablewriter.NewWriter(buf)
 	tw.SetBorder(false)
 	tw.SetAutoWrapText(false)
 	tw.SetAlignment(tablewriter.ALIGN_LEFT)
 	tw.SetHeaderAlignment(tablewriter.ALIGN_LEFT)
 	tw.SetColumnSeparator("")
 	tw.AppendBulk(rows)
 	tw.Render()
+	// This tablewriter puts a leading space on the lines for some reason, so
+	// remove it.
+	scanner := bufio.NewScanner(buf)
+	for scanner.Scan() {
+		fmt.Fprintln(w, strings.TrimLeft(scanner.Text(), " "))
+	}
 }
 
 func inferWriterOptions(info *mcap.Info) *mcap.WriterOptions {