Fail to create table with some TiDB table info

[JaySon-Huang]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

A simplified case from https://asktug.com/t/topic/662946

> set sql_mode='';
> CREATE TABLE test ( id int(16) NOT NULL AUTO_INCREMENT, PRIMARY KEY (id));
> alter table test add column b longblob not null default '';

-- p.s. Note that `set sql_mode=""` is required or the SQL will get blocked like
> CREATE TABLE test ( id int(16) NOT NULL AUTO_INCREMENT, PRIMARY KEY (id));
> alter table test add column b longblob not null default '';
ERROR 1101 (42000): BLOB/TEXT/JSON column 'b' can't have a default value

Those SQLs will create a table with JSON info as below. Note that the column type of "b" is not null long blob, but its "default"/"origin_default" field is "" and "type.FLen" is -1.

{
	"cols": [{
		"comment": "",
		"default": null,
		"default_bit": null,
		"id": 1,
		"name": {
			"L": "id",
			"O": "id"
		},
		"offset": 0,
		"origin_default": null,
		"state": 5,
		"type": {
			"Charset": "binary",
			"Collate": "binary",
			"Decimal": 0,
			"Elems": null,
			"Flag": 515,
			"Flen": 16,
			"Tp": 3
		}
	}, {
		"comment": "",
		"default": "",
		"default_bit": null,
		"id": 15,
		"name": {
			"L": "b",
			"O": "b"
		},
		"offset": 12,
		"origin_default": "",
		"state": 5,
		"type": {
			"Charset": "binary",
			"Collate": "binary",
			"Decimal": 0,
			"Elems": null,
			"Flag": 4225,
			"Flen": -1,
			"Tp": 251
		}
	}],
	"comment": "",
	"id": 330,
	"index_info": [],
	"is_common_handle": false,
	"name": {
		"L": "test",
		"O": "test"
	},
	"partition": null,
	"pk_is_handle": true,
	"schema_version": 465,
	"state": 5,
	"update_timestamp":999 
}

However, if we run CREATE TABLE test ( id int(16) NOT NULL AUTO_INCREMENT, b longblob not null, PRIMARY KEY (id)); in TiDB, we can only get a JSON as below, which "default"/"origin_default" is null instead of "". And this won't make any error.

2. What did you expect to see? (Required)

Table create successfully

3. What did you see instead (Required)

TiFlash crashes with basic_string::_M_replace_aux

4. What is your TiFlash version? (Required)

v5.2.1

[JaySon-Huang]

When run into defaultValueToField with that table info json. The column "b" with "default" field is "" and "type.FLen" is -1, and line 161 will run into v.append(-1, , '\0') which cause error.

The unit test case: https://github.com/JaySon-Huang/tiflash/tree/add_4596_test

tiflash/dbms/src/Storages/Transaction/TiDB.cpp

Lines 153 to 164 in e235089

	case TypeString:
	{
	auto v = value.convert<String>();
	if (hasBinaryFlag())
	{
	// For binary column, we have to pad trailing zeros according to the specified type length.
	// User may define default value `0x1234` for a `BINARY(4)` column, TiDB stores it in a string "\u12\u34" (sized 2).
	// But it actually means `0x12340000`.
	v.append(flen - v.length(), '\0');
	}
	return v;
	}

[JaySon-Huang]

However, if we run CREATE TABLE test ( id int(16) NOT NULL AUTO_INCREMENT, b longblob not null, PRIMARY KEY (id)); in TiDB, we can only get a JSON as below, which "default"/"origin_default" is null instead of "". And this won't make any error.

{
	"cols": [{
		"comment": "",
		"default": null,
		"default_bit": null,
		"id": 1,
		"name": {
			"L": "id",
			"O": "id"
		},
		"offset": 0,
		"origin_default": null,
		"state": 5,
		"type": {
			"Charset": "binary",
			"Collate": "binary",
			"Decimal": 0,
			"Elems": null,
			"Flag": 515,
			"Flen": 16,
			"Tp": 3
		}
	}, {
		"comment": "",
		"default": null,
		"default_bit": null,
		"id": 2,
		"name": {
			"L": "b",
			"O": "b"
		},
		"offset": 1,
		"origin_default": null,
		"state": 5,
		"type": {
			"Charset": "binary",
			"Collate": "binary",
			"Decimal": 0,
			"Elems": null,
			"Flag": 4225,
			"Flen": -1,
			"Tp": 251
		}
	}],
	"comment": "",
	"id": 56,
	"index_info": [],
	"is_common_handle": false,
	"name": {
		"L": "test",
		"O": "test"
	},
	"partition": null,
	"pk_is_handle": true,
	"schema_version": 30,
	"state": 5,
	"tiflash_replica": {
		"Count": 0
	},
	"update_timestamp": 432338767854960649
}

[JaySon-Huang]

Mark it as a "moderate" bug since we can not reproduce it easily

[JaySon-Huang]

/assign @Lloyd-Pottiger