t128_tank: stream from the beginning if parsing the index fails

[gregschrock]

I95-62311

Description

There are a couple cases when reading the index file we might return an error indicating that it failed and why.

1. file doesn't exist isn't an error, but other failures to read are
2. failing to parse the content of the file

The intention here was to provide information, but not to fail. The default index should be used when these errors occur. However, the calling code was written to check for the error and "fail" if observed. Instead, the failure should be logged and the process should continue. The code is updated to behave as described.

Testing: https://github.com/Juniper-SSN/ssr/pull/18009

The index code for reference:

func (r *Reader) getIndex(indexPath string, defaultIndex index) (index, error) {
	if indexPath == "" {
		r.log.Debugf("index file path not provided, starting with default index %s", defaultIndex.string())
		return defaultIndex, nil
	}
	content, err := os.ReadFile(indexPath)
	if errors.Is(err, os.ErrNotExist) {
		r.log.Debugf("index file %s does not exist, starting with default index %s", indexPath, defaultIndex.string())
		return defaultIndex, nil

	} else if err != nil {
		return defaultIndex, fmt.Errorf("encountered error reading index file, starting with default index %s: %s", defaultIndex.string(), err)
	}
	newContent := strings.Split(string(content), "\n")[0]
	r.log.Debugf("found '%s' in index file", newContent)
	index, err := newIndex(newContent)
	if err != nil {
		return defaultIndex, fmt.Errorf("encountered error while parsing index file content, starting with default index %s: %s", defaultIndex.string(), err)
	}

	return index, nil
}

[shriyanshk128T]

Should we do some manual testing just to make sure this doesn't break anything?

[gregschrock]

Added testing here: https://github.com/Juniper-SSN/ssr/pull/18009