need to handle "ER_WARN_ALLOWED_PACKET_OVERFLOWED" for some string functions

[zz-jason]

Take this as an example:

select rpad('hello', 18446744073709551617, '1');

In MySQL, the result is NULL and a warning about "Result of rpad() was larger than max_allowed_packet" is returned:

MySQL(localhost:3306) > select rpad('hello', 18446744073709551617, '1');
+------------------------------------------+
| rpad('hello', 18446744073709551617, '1') |
+------------------------------------------+
| NULL                                     |
+------------------------------------------+
1 row in set, 3 warnings (0.01 sec)

MySQL(localhost:3306) > show warnings;
+---------+------+---------------------------------------------------------------------------+
| Level   | Code | Message                                                                   |
+---------+------+---------------------------------------------------------------------------+
| Warning | 1292 | Truncated incorrect DECIMAL value: '18446744073709551617'                 |
| Warning | 1292 | Truncated incorrect DECIMAL value: '18446744073709551617'                 |
| Warning | 1301 | Result of rpad() was larger than max_allowed_packet (4194304) - truncated |
+---------+------+---------------------------------------------------------------------------+
3 rows in set (0.00 sec)

MySQL(localhost:3306) > select version();
+-----------+
| version() |
+-----------+
| 5.7.22    |
+-----------+
1 row in set (0.00 sec)

In TiDB, this query results in a "lost connection" and the panic is "runtime error: makeslice: len out of range", and the panic stack is:

2018/07/25 16:33:10.027 conn.go:427: [error] lastCmd select rpad('hello', 18446744073709551617, '1'), runtime error: makeslice: len out of range, goroutine 743 [running]:
github.com/pingcap/tidb/server.(*clientConn).Run.func1(0xc43bbea000, 0xc4203bddff)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/server/conn.go:425 +0x10e
panic(0x1d54500, 0x2024180)
        /Users/jianzhang.zj/opt/goroot/src/runtime/panic.go:505 +0x229
strings.Repeat(0xc43c64253d, 0x1, 0x7ffffffffffffffb, 0xc4203bca18, 0x1)
        /Users/jianzhang.zj/opt/goroot/src/strings/strings.go:543 +0x83
github.com/pingcap/tidb/expression.(*builtinRpadSig).evalString(0xc422664f40, 0x0, 0x0, 0x0, 0x17f2c44, 0xc422664f40, 0x205eb00, 0xc43e274000)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/expression/builtin_string.go:1959 +0x38c
github.com/pingcap/tidb/expression.(*ScalarFunction).EvalString(0xc43d1e0aa0, 0x205eb00, 0xc43e274000, 0x0, 0x0, 0x0, 0x0, 0x0, 0xc4203bcca8, 0x1741c17)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/expression/scalar_function.go:216 +0x4c
github.com/pingcap/tidb/expression.(*ScalarFunction).Eval(0xc43d1e0aa0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/expression/scalar_function.go:188 +0x481
github.com/pingcap/tidb/expression.foldConstant(0x205df00, 0xc43d1e0aa0, 0x1e18b60, 0xc43c642501, 0xc43d1e0aa0)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/expression/constant_fold.go:102 +0x5e2
github.com/pingcap/tidb/expression.FoldConstant(0x205df00, 0xc43d1e0aa0, 0xc43c642518, 0x4)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/expression/constant_fold.go:33 +0x35
github.com/pingcap/tidb/expression.NewFunction(0x205eb00, 0xc43e274000, 0xc43c642518, 0x4, 0xc43c6406c0, 0xc422664ec0, 0x3, 0x4, 0x1e18aa0, 0xc422664ec0, ...)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/expression/scalar_function.go:98 +0x341
github.com/pingcap/tidb/plan.(*expressionRewriter).funcCallToExpression(0xc421a80d00, 0xc43c8e87e0)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/expression_rewriter.go:1198 +0x174
github.com/pingcap/tidb/plan.(*expressionRewriter).Leave(0xc421a80d00, 0x20313e0, 0xc43c8e87e0, 0x2048e40, 0xc438357e40, 0x1aa0b01)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/expression_rewriter.go:746 +0x86a
github.com/pingcap/tidb/ast.(*FuncCallExpr).Accept(0xc43c8e87e0, 0x202cae0, 0xc421a80d00, 0x1a2fd5c, 0x205e800, 0xc421a80c80)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/ast/functions.go:363 +0x1bf
github.com/pingcap/tidb/plan.(*planBuilder).rewriteExprNode(0xc43b7e3e00, 0xc421a80d00, 0x2048740, 0xc43c8e87e0, 0xc4203bd301, 0x1010559, 0xc422664e40, 0x40, 0x38, 0x1dedf60, ...)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/expression_rewriter.go:132 +0x54
github.com/pingcap/tidb/plan.(*planBuilder).rewriteWithPreprocess(0xc43b7e3e00, 0x2048740, 0xc43c8e87e0, 0x205e800, 0xc421a80c80, 0x0, 0x1eba401, 0x0, 0x0, 0x0, ...)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/expression_rewriter.go:104 +0x12b
github.com/pingcap/tidb/plan.(*planBuilder).rewrite(0xc43b7e3e00, 0x2048740, 0xc43c8e87e0, 0x205e800, 0xc421a80c80, 0x0, 0x1, 0x0, 0x0, 0x0, ...)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/expression_rewriter.go:80 +0x96
github.com/pingcap/tidb/plan.(*planBuilder).buildProjection(0xc43b7e3e00, 0x205e800, 0xc421a80c80, 0xc42402e6e0, 0x1, 0x1, 0x0, 0x1, 0x1, 0x1e17360)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/logical_plan_builder.go:572 +0x220
github.com/pingcap/tidb/plan.(*planBuilder).buildSelect(0xc43b7e3e00, 0xc4210bb4a0, 0x0, 0x0)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/logical_plan_builder.go:1664 +0x309
github.com/pingcap/tidb/plan.(*planBuilder).build(0xc43b7e3e00, 0x2031ca0, 0xc4210bb4a0, 0xc421a293b0, 0x205eb00)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/planbuilder.go:155 +0x603
github.com/pingcap/tidb/plan.Optimize(0x205eb00, 0xc43e274000, 0x2031ca0, 0xc4210bb4a0, 0x2048fc0, 0xc421a293b0, 0x2a7bd00, 0x0, 0x0, 0x2f)
        /Users/jianzhang.zj/opt/gopath/src/github.com/pingcap/tidb/plan/optimize
2018/07/25 16:33:10.027 server.go:316: [info] con:1 close connection

What we need to do is not allocate a buffer larger than "max_allowed_packet" for these string functions:

• to_base64 @supernan1994 expression: handle max_allowed_packet warnings for to_base64 function. #7266
• from_base64 @supernan1994 expression: handle max_allowed_packet warnings for from_base64 function. #7409
• concat @amyangfei expression: add max_allowed_packet check in concat/concat_ws #11137
• concat_ws @amyangfei expression: add max_allowed_packet check in concat/concat_ws #11137
• replace
• insert @eurekaka expression: check max_allowed_packet constraint for function insert #7502
• repeat @hhxcc expression: handle max_allowed_packet warnings for repeat function. #7181
• space @hhxcc expression: handle max_allowed_packet warnings for space function. #7210
• rpad @zz-jason expression: handle max_allowed_packet warnings for pad functions #7171
• lpad @zz-jason expression: handle max_allowed_packet warnings for pad functions #7171
• cast
• export_set
• quote

All the above functions implemented in MySQL are located in the "sql/item_strfunc.cc" file, you can grep the function name to see specific implementations.

All the above functions can be found in TiDB from the source file "expression/builtin.go".

[supernan1994]

I wanna take to_base64 and from_base64, I will start when #7171 is merged

[zz-jason]

@supernan1994 Thanks for your participating! We'll merge #7171 as soon as possible 😄

[zz-jason]

@supernan1994 friendly ping, #7171 has been merged.

[supernan1994]

@zz-jason Got it!