xdr: Add a custom marshaller for claim predicate timestamp

[tamirms]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot, or all or doc if the changes are broad or impact many
  packages.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've updated the relevant CHANGELOG (here for Horizon) if
  needed with deprecations, added features, breaking changes, and DB schema changes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

What

Add a custom marshaller for representing the AbsBefore timestamp.

Why

Currently, claimable balances which have a AbsBefore timestamp beyond year 9999 causes Horizon ingestion to crash. The crash is due to the fact that the time.Parse() implementation does not support parsing strings that far into the future.

Known limitations

• Using a regexp to get around the fact that time.Parse() doesn't accept time.Time instances with years outside the range of 0000..9999 range is a bit hacky
• Perhaps it would be cleaner to represent AbsBefore as a unix timestamp integer. However, doing such a change now would break the API and it would require changes downstream in the SDK implementations.

[bartekn]

We should check len(b), otherwise it will panic for len(b) < 2.

[leighmcculloch]

💡 I think we're doing more lifting than we need to do with the parsing we're doing here. Checking null, and looking for quotes is all work that the json package will do for us. We also don't need to parse out the full date with a regex manually given that the time package will do that for us. I think we should leverage json.Unmarshal if we can, so that we reduce our chance of not handling edge cases as much as possible.

This is one approach:

Suggested change

	if string(b) == "null" {
	return nil
	}
	if b[0] != '"' || b[len(b)-1] != '"' {
	return fmt.Errorf("%s does not begin and end with double quotes", b)
	}
	trimmed := string(b[1 : len(b)-1])
	m := reISO8601.FindStringSubmatch(trimmed)
	if len(m) != 4 {
	return fmt.Errorf("UnmarshalJSON: cannot parse %s", trimmed)
	}
	// No need to check for errors since the regexp guarantees the matches
	// are valid integers
	year, _ := strconv.Atoi(m[1])
	month, _ := strconv.Atoi(m[2])
	day, _ := strconv.Atoi(m[3])
	ts, err := time.Parse(time.RFC3339, "2006-01-02"+trimmed[len(m[0]):])
	if err != nil {
	return errors.Wrap(err, "Could not extract time")
	}
	t.Time = time.Date(year, time.Month(month), day, ts.Hour(), ts.Minute(), ts.Second(), ts.Nanosecond(), ts.Location())
	return nil
	var s *string
	err := json.Unmarshal(data, &s)
	if err != nil {
	return err
	}
	if s == nil {
	return nil
	}
	parts := strings.SplitN(*s, "-", 2)
	year, err := strconv.ParseInt(parts[0], 10, 64)
	if err != nil {
	return err
	}
	rest, err := time.Parse(time.RFC3339, "0000-"+parts[1])
	if err != nil {
	return err
	}
	t.Time = rest.AddDate(int(year), 0, 0)
	return nil

[tamirms]

unfortunately splitting on the first "-" doesn't work on timestamps which have a negative year