cmd, ui: Move size parsing code and make it more robust

internal/ui/format.go

@@ -3,7 +3,10 @@ package ui
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"math/bits"
+	"strconv"
 	"time"
 )
 
@@ -56,6 +59,44 @@ func FormatSeconds(sec uint64) string {
 	return fmt.Sprintf("%d:%02d", min, sec)
 }
 
+// ParseBytes parses a size in bytes from s. It understands the suffixes
+// B, K, M, G and T for powers of 1024.
+func ParseBytes(s string) (int64, error) {
+	if s == "" {
+		return 0, errors.New("expected size, got empty string")
+	}
+
+	numStr := s[:len(s)-1]
+	var unit uint64 = 1
+
+	switch s[len(s)-1] {
+	case 'b', 'B':
+		// use initialized values, do nothing here
+	case 'k', 'K':
+		unit = 1024
+	case 'm', 'M':
+		unit = 1024 * 1024
+	case 'g', 'G':
+		unit = 1024 * 1024 * 1024
+	case 't', 'T':
+		unit = 1024 * 1024 * 1024 * 1024
+	default:
+		numStr = s
+	}
+	value, err := strconv.ParseInt(numStr, 10, 64)
+	if err != nil {
+		return 0, err
+	}
+
+	hi, lo := bits.Mul64(uint64(value), unit)
+	value = int64(lo)
+	if hi != 0 || value < 0 {
+		return 0, fmt.Errorf("ParseSize: %q: %w", numStr, strconv.ErrRange)
+	}
+
+	return value, nil
+}
+
 func ToJSONString(status interface{}) string {
 	buf := new(bytes.Buffer)
 	err := json.NewEncoder(buf).Encode(status)