googleapis/mcp-toolbox · error

unable to unmarshal json data %s

Error message

unable to unmarshal json data %s

What it means

json.Unmarshal failed on the []byte value of a JSON-typed column in RunSQL — the bytes stored in the TiDB JSON column are not valid JSON, so they cannot be decoded into a Go value.

Source

Thrown at internal/sources/tidb/tidb.go:163

			val := rawValues[i]
			if val == nil {
				vMap[name] = nil
				continue
			}

			// mysql driver return []uint8 type for "TEXT", "VARCHAR", and "NVARCHAR"
			// we'll need to cast it back to string
			switch colTypes[i].DatabaseTypeName() {
			case "JSON":
				// unmarshal JSON data before storing to prevent double
				// marshaling
				byteVal, ok := val.([]byte)
				if !ok {
					return nil, fmt.Errorf("expected []byte for JSON column, but got %T", val)
				}
				var unmarshaledData any
				if err := json.Unmarshal(byteVal, &unmarshaledData); err != nil {
					return nil, fmt.Errorf("unable to unmarshal json data %s", val)
				}
				vMap[name] = unmarshaledData
			case "TEXT", "VARCHAR", "NVARCHAR":
				byteVal, ok := val.([]byte)
				if !ok {
					return nil, fmt.Errorf("expected []byte for text-like column, but got %T", val)
				}
				vMap[name] = string(byteVal)
			default:
				vMap[name] = val
			}
		}
		out = append(out, vMap)
	}

	if err := results.Err(); err != nil {
		return nil, fmt.Errorf("errors encountered during row iteration: %w", err)
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Inspect the raw column value shown in the error
2. Fix the malformed JSON stored in the row
3. Cast the column to CHAR in the query if it is not truly JSON

When it happens

Trigger: Thrown at internal/sources/tidb/tidb.go:163 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/8bf88670ec8914b1. Report an issue: GitHub.