What causes "cannot parse array value: %s" in vitessio/vitess?

Inspect the wrapped inner error to find the offending element and fix the array contents

cannot parse array value: %s

Error message

cannot parse array value: %s

What it means

While parsing a JSON array, one of the element values failed to parse via parseValue; the underlying error is wrapped with 'cannot parse array value:'. This contextualizes a nested parse failure as belonging to an array element.

Source

Thrown at go/mysql/json/parser.go:492

	if s[0] == ']' {
		v := c.getValue()
		v.t = TypeArray
		v.a = v.a[:0]
		return v, s[1:], nil
	}

	a := c.getValue()
	a.t = TypeArray
	a.a = a.a[:0]
	for {
		var v *Value
		var err error

		s = skipWS(s)
		v, s, err = parseValue(s, c, depth)
		if err != nil {
			return nil, s, fmt.Errorf("cannot parse array value: %s", err)
		}
		a.a = append(a.a, v)

		s = skipWS(s)
		if len(s) == 0 {
			return nil, s, errors.New("unexpected end of array")
		}
		if s[0] == ',' {
			s = s[1:]
			continue
		}
		if s[0] == ']' {
			s = s[1:]
			return a, s, nil
		}
		return nil, s, errors.New("missing ',' after array value")
	}
}

View on GitHub (pinned to 01a25a7d17)

Solutions

Inspect the wrapped inner error to find the offending element and fix the array contents
Validate the full JSON with a standard parser before calling mysql.ParseJSON
Fix upstream serialization that produced the broken array

Example fix

// before
v, err := mysql.ParseJSON("[tru]")
// after
v, err := mysql.ParseJSON("[true]")

Defensive patterns

Strategy: try-catch

Validate before calling

if !json.Valid([]byte(input)) {
	return fmt.Errorf("invalid JSON array document: %q", input)
}

Try / catch

v, err := mysql.ParseJSON(input)
if err != nil {
	var inner string
	if strings.Contains(err.Error(), "cannot parse array value") {
		inner = strings.TrimPrefix(err.Error(), "cannot parse array value: ")
		// inspect inner cause, fix or reject the array element
	}
	return fmt.Errorf("array element bad (%s): %w", inner, err)
}

Prevention

Run json.Valid on the whole document before parsing
Generate arrays with encoding/json, not manual bracket building
Keep elements non-empty: never emit `[a,]` from templates

When it happens

Trigger: Parsing input like `[tru]`, `[1,]` where an element position contains an invalid value, or an array containing an oversized number.

Common situations: Malformed JSON documents from application concatenation; corrupted JSON values read from a MySQL JSON column or binlog; truncated array payloads.

Related errors

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/3aedc51e3383e459. Report an issue: GitHub.