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package jwt
import (
"encoding/json"
"fmt"
"math"
"strconv"
"time"
)
// TimePrecision sets the precision of times and dates within this library. This
// has an influence on the precision of times when comparing expiry or other
// related time fields. Furthermore, it is also the precision of times when
// serializing.
//
// For backwards compatibility the default precision is set to seconds, so that
// no fractional timestamps are generated.
var TimePrecision = time.Second
// MarshalSingleStringAsArray modifies the behavior of the ClaimStrings type,
// especially its MarshalJSON function.
//
// If it is set to true (the default), it will always serialize the type as an
// array of strings, even if it just contains one element, defaulting to the
// behavior of the underlying []string. If it is set to false, it will serialize
// to a single string, if it contains one element. Otherwise, it will serialize
// to an array of strings.
var MarshalSingleStringAsArray = true
// NumericDate represents a JSON numeric date value, as referenced at
// https://datatracker.ietf.org/doc/html/rfc7519#section-2.
type NumericDate struct {
time.Time
}
// NewNumericDate constructs a new *NumericDate from a standard library time.Time struct.
// It will truncate the timestamp according to the precision specified in TimePrecision.
func NewNumericDate(t time.Time) *NumericDate {
return &NumericDate{t.Truncate(TimePrecision)}
}
// newNumericDateFromSeconds creates a new *NumericDate out of a float64 representing a
// UNIX epoch with the float fraction representing non-integer seconds.
func newNumericDateFromSeconds(f float64) *NumericDate {
round, frac := math.Modf(f)
return NewNumericDate(time.Unix(int64(round), int64(frac*1e9)))
}
// MarshalJSON is an implementation of the json.RawMessage interface and serializes the UNIX epoch
// represented in NumericDate to a byte array, using the precision specified in TimePrecision.
func (date NumericDate) MarshalJSON() (b []byte, err error) {
var prec int
if TimePrecision < time.Second {
prec = int(math.Log10(float64(time.Second) / float64(TimePrecision)))
}
truncatedDate := date.Truncate(TimePrecision)
// For very large timestamps, UnixNano would overflow an int64, but this
// function requires nanosecond level precision, so we have to use the
// following technique to get round the issue:
//
// 1. Take the normal unix timestamp to form the whole number part of the
// output,
// 2. Take the result of the Nanosecond function, which returns the offset
// within the second of the particular unix time instance, to form the
// decimal part of the output
// 3. Concatenate them to produce the final result
seconds := strconv.FormatInt(truncatedDate.Unix(), 10)
nanosecondsOffset := strconv.FormatFloat(float64(truncatedDate.Nanosecond())/float64(time.Second), 'f', prec, 64)
output := append([]byte(seconds), []byte(nanosecondsOffset)[1:]...)
return output, nil
}
// UnmarshalJSON is an implementation of the json.RawMessage interface and
// deserializes a [NumericDate] from a JSON representation, i.e. a
// [json.Number]. This number represents an UNIX epoch with either integer or
// non-integer seconds.
func (date *NumericDate) UnmarshalJSON(b []byte) (err error) {
var (
number json.Number
f float64
)
if err = json.Unmarshal(b, &number); err != nil {
return fmt.Errorf("could not parse NumericData: %w", err)
}
if f, err = number.Float64(); err != nil {
return fmt.Errorf("could not convert json number value to float: %w", err)
}
n := newNumericDateFromSeconds(f)
*date = *n
return nil
}
// ClaimStrings is basically just a slice of strings, but it can be either
// serialized from a string array or just a string. This type is necessary,
// since the "aud" claim can either be a single string or an array.
type ClaimStrings []string
func (s *ClaimStrings) UnmarshalJSON(data []byte) (err error) {
var value interface{}
if err = json.Unmarshal(data, &value); err != nil {
return err
}
var aud []string
switch v := value.(type) {
case string:
aud = append(aud, v)
case []string:
aud = ClaimStrings(v)
case []interface{}:
for _, vv := range v {
vs, ok := vv.(string)
if !ok {
return ErrInvalidType
}
aud = append(aud, vs)
}
case nil:
return nil
default:
return ErrInvalidType
}
*s = aud
return
}
func (s ClaimStrings) MarshalJSON() (b []byte, err error) {
// This handles a special case in the JWT RFC. If the string array, e.g.
// used by the "aud" field, only contains one element, it MAY be serialized
// as a single string. This may or may not be desired based on the ecosystem
// of other JWT library used, so we make it configurable by the variable
// MarshalSingleStringAsArray.
if len(s) == 1 && !MarshalSingleStringAsArray {
return json.Marshal(s[0])
}
return json.Marshal([]string(s))
}
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