Function decodeErrorContext

pkg/util/json/parser.go:290–321

decodeErrorContext returns input context for an error encountered during decoding. There is quite a bit of code here, but debugging faulty JSON is hard, so take extra care to produce nice error message, with good context information.

(err error, s string, pos int)

// There is quite a bit of code here, but debugging faulty JSON is hard, so
// take extra care to produce nice error message, with good context information.
func decodeErrorContext(err error, s string, pos int) error {
	if len(s) == 0 {
		return errors.Wrap(err, "while decoding empty string")
	}

	const contextSize = 16
	ctxStart := pos - contextSize
	if ctxStart < 0 {
		ctxStart = 0
	}
	ctxEnd := pos + contextSize
	if ctxEnd > len(s) {
		ctxEnd = len(s)
	}

	var leftPad, rightPad string
	if pos > ctxStart {
		leftPad = strings.Repeat(".", pos-ctxStart)
	}
	if ctxEnd > pos {
		rightPad = strings.Repeat(".", ctxEnd-pos-1)
	}

	return errors.Wrapf(err,
		"while decoding %d bytes at offset %d:\n"+
			"...|%s|...\n"+
			"...|%s^%s|...",
		len(s), pos,
		s[ctxStart:ctxEnd],
		leftPad, rightPad,
	)
}

// unsafeGetBytes returns []byte in the underlying string,
// without incurring copy.