googleapis/mcp-toolbox · error

unable to parse row: %w

Error message

unable to parse row: %w

What it means

This error is returned when rows.Scan(values...) fails while iterating a result set in RunSQL. It means a row's data could not be converted into the driver's generic any holders — usually due to malformed/unsupported data types (e.g. certain binary, JSON, or temporal encodings), driver protocol corruption, or a connection drop mid-rowset.

Source

Thrown at internal/sources/cloudsqlmysql/cloud_sql_mysql.go:162

	}

	// 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. Examine the wrapped driver error; identify the offending column type and cast/convert it in SQL (e.g. CAST(col AS CHAR), TO_JSON for JSON columns).
2. Exclude or reshape problematic columns (avoid BLOB/GEOMETRY/BIT in tool outputs; select only needed text/numeric columns).
3. Raise max_allowed_packet / timeout settings if the row is being truncated mid-transfer.
4. Retry if transient (connection drop); upgrade go-sql-driver/mysql if a type-conversion bug matches.
5. Return explicit column lists instead of SELECT * to keep scanned types simple.

Example fix

// before
SELECT * FROM shape_data;
// after
SELECT id, ST_AsText(geom) AS geom_wkt, name FROM shape_data;

func validateScannableColumns(cols []string) error {
    risky := []string{"blob", "geometry", "point", "polygon", "linestring", "bit", "binary", "varbinary"}
    for _, c := range cols {
        lc := strings.ToLower(c)
        for _, r := range risky {
            if strings.Contains(lc, r) {
                return fmt.Errorf("column %q may have type %q which can fail generic row scanning; cast it in SQL (e.g. CAST/ST_AsText)", c, r)
            }
        }
    }
    return nil
}

func isScanTypeError(err error) bool {
    var mysqlErr *mysql.MySQLError
    if errors.As(err, &mysqlErr) {
        switch mysqlErr.Number {
        case 1301, 1306: // unsupported/truncated data
            return true
        }
    }
    msg := strings.ToLower(err.Error())
    return strings.Contains(msg, "unsupported scan") ||
        strings.Contains(msg, "converting") ||
        strings.Contains(msg, "unexpected type")
}

result, err := src.RunSQL(ctx, statement, params)
if err != nil {
    if strings.Contains(err.Error(), "unable to parse row") && isScanTypeError(err) {
        // Rewrite the statement casting exotic columns to text:
        // SELECT id, CAST(payload AS CHAR) AS payload FROM t
        return nil
    }
    return err
}

When it happens

Trigger: Calling RunSQL on a result set containing column values the generic scan targets cannot convert (driver-specific unsupported types), a row arriving over a broken connection, or NULL/type mismatch handling tripping the driver's scanner.

Common situations: Selecting unusual column types (BLOB, GEOMETRY, exotic collations, huge DECIMAL/BIT values), truncated packets from oversized rows (net_read_timeout / max_allowed_packet), instance restart mid-iteration, driver version incompatibilities with newer MySQL column types.

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

• unable to parse row: %w
• unable to create pool: %w
• unable to connect successfully: %w
• unable to execute query: %w
• unable to retrieve rows column name: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/78d30fac5ab91a60. Report an issue: GitHub.