googleapis/mcp-toolbox · error

unable to parse row: %w

Error message

unable to parse row: %w

What it means

This error wraps a failure from database/sql's rows.Scan() while reading a result row in the MySQL source's RunSQL tool. The Go MySQL driver could not copy a column value from the current row into the destination buffer (rawValues). It almost always indicates a value/type mismatch between what the driver returned and what the scan destinations expect, and the wrapped error names the offending column.

Source

Thrown at internal/sources/mysql/mysql.go:160

	}

	// create an array of values for each column, which can be re-used to scan each row
	rawValues := make([]any, len(cols))
	values := make([]any, len(cols))
	for i := range rawValues {
		values[i] = &rawValues[i]
	}

	colTypes, err := results.ColumnTypes()
	if err != nil {
		return nil, fmt.Errorf("unable to get column types: %w", err)
	}

	out := []any{}
	for results.Next() {
		err := results.Scan(values...)
		if err != nil {
			return nil, fmt.Errorf("unable to parse row: %w", err)
		}
		row := orderedmap.Row{}
		for i, name := range cols {
			val := rawValues[i]
			if val == nil {
				row.Add(name, nil)
				continue
			}

			convertedValue, err := mysqlcommon.ConvertToType(colTypes[i], val)
			if err != nil {
				return nil, fmt.Errorf("errors encountered when converting values: %w", err)
			}
			row.Add(name, convertedValue)
		}
		out = append(out, row)
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Read the wrapped error to identify the failing column and cast/convert it in SQL (e.g. CAST(col AS CHAR), HEX() for binary).
2. Upgrade the github.com/go-sql-driver/mysql dependency to the latest version.
3. Test the same query with a plain MySQL client to confirm the data itself is valid.
4. If BIT columns are the cause, select them as col+0 or CAST(col AS UNSIGNED).

Example fix

// before
SELECT flags FROM permissions;
// after
SELECT CAST(flags AS UNSIGNED) AS flags FROM permissions;

// Validate the query result types before running through the tool:
rows, err := db.QueryContext(ctx, "SELECT flags FROM permissions LIMIT 1")
if err != nil { return err }
ctypes, err := rows.ColumnTypes()
if err != nil { return err }
for _, ct := range ctypes {
    fmt.Println(ct.Name(), ct.DatabaseTypeName()) // flag exotic types (BIT, GEOMETRY) and CAST them in SQL
}

out, err := toolboxClient.InvokeTool(ctx, "run-sql", params)
if err != nil {
    var parseErr *parseRowError // or match on the wrapped driver error
    if strings.Contains(err.Error(), "unable to parse row") {
        // inspect wrapped cause, adjust SQL casts, and retry once
    }
    return err
}

When it happens

Trigger: Executing a query via the mysql run-sql tool whose result contains a value the driver cannot scan into the []byte/raw destination (e.g. certain BIT, unusual geometry, or corrupted binary values), or a driver/serve version mismatch causing column type descriptors the scanner cannot handle.

Common situations: Selecting exotic column types (BIT(M>1), GEOMETRY, malformed JSON), querying a proxy or older MySQL/MariaDB server with divergent protocol types, or data truncated by server-side max_allowed_packet issues.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• errors encountered when converting values: %w
• unable to parse row: %w
• unable to create pool: %w
• unable to connect successfully: %w
• unable to execute query: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/48824e869058aa3e. Report an issue: GitHub.