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expression: check max_allowed_packet constraint for function insert #7502

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merged 6 commits into from
Aug 29, 2018
Merged

expression: check max_allowed_packet constraint for function insert #7502

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086bbaf
expression: check max_allowed_packet constraint for function insert
eurekaka Aug 27, 2018
04fa228
modifications according to comments:
eurekaka Aug 28, 2018
558bc71
Merge branch 'master' into str_udf_overflow_insert
zz-jason Aug 28, 2018
28a5ba4
Merge branch 'master' into str_udf_overflow_insert
Aug 28, 2018
99faa60
calcute accurate bytes consumed by the result string
eurekaka Aug 28, 2018
b27aa83
Merge branch 'master' into str_udf_overflow_insert
Aug 29, 2018
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30 changes: 26 additions & 4 deletions expression/builtin_string.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3170,21 +3170,30 @@ func (c *insertFunctionClass) getFunction(ctx sessionctx.Context, args []Express
bf.tp.Flen = mysql.MaxBlobWidth
SetBinFlagOrBinStr(args[0].GetType(), bf.tp)
SetBinFlagOrBinStr(args[3].GetType(), bf.tp)

valStr, _ := ctx.GetSessionVars().GetSystemVar(variable.MaxAllowedPacket)
maxAllowedPacket, err := strconv.ParseUint(valStr, 10, 64)
if err != nil {
return nil, errors.Trace(err)
}

if types.IsBinaryStr(args[0].GetType()) {
sig = &builtinInsertBinarySig{bf}
sig = &builtinInsertBinarySig{bf, maxAllowedPacket}
} else {
sig = &builtinInsertSig{bf}
sig = &builtinInsertSig{bf, maxAllowedPacket}
}
return sig, nil
}

type builtinInsertBinarySig struct {
baseBuiltinFunc
maxAllowedPacket uint64
}

func (b *builtinInsertBinarySig) Clone() builtinFunc {
newSig := &builtinInsertBinarySig{}
newSig.cloneFrom(&b.baseBuiltinFunc)
newSig.maxAllowedPacket = b.maxAllowedPacket
return newSig
}

Expand Down Expand Up @@ -3216,18 +3225,26 @@ func (b *builtinInsertBinarySig) evalString(row chunk.Row) (string, bool, error)
}

if length > strLength-pos+1 || length < 0 {
return str[0:pos-1] + newstr, false, nil
length = strLength - pos + 1
}

if uint64(strLength-length+int64(len(newstr))) > b.maxAllowedPacket {
b.ctx.GetSessionVars().StmtCtx.AppendWarning(errWarnAllowedPacketOverflowed.GenByArgs("insert", b.maxAllowedPacket))
return "", true, nil
}

return str[0:pos-1] + newstr + str[pos+length-1:], false, nil
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should we check whether len(str[0:pos-1] + newstr + str[pos+length-1:]) > b. maxAllowedPacket ?

}

type builtinInsertSig struct {
baseBuiltinFunc
maxAllowedPacket uint64
}

func (b *builtinInsertSig) Clone() builtinFunc {
newSig := &builtinInsertSig{}
newSig.cloneFrom(&b.baseBuiltinFunc)
newSig.maxAllowedPacket = b.maxAllowedPacket
return newSig
}

Expand Down Expand Up @@ -3260,7 +3277,12 @@ func (b *builtinInsertSig) evalString(row chunk.Row) (string, bool, error) {
}

if length > runeLength-pos+1 || length < 0 {
return string(runes[0:pos-1]) + newstr, false, nil
length = runeLength - pos + 1
}

if uint64(runeLength-length)*uint64(mysql.MaxBytesOfCharacter)+uint64(len(newstr)) > b.maxAllowedPacket {
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What if the number of bytes of some character is less than MaxBytesOfCharacter? Will this raise warning while it should not?

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Yes, this false-negative case exists, but to compute the exact bytes of these characters, we may need the charset info of the string, and then compute the length of specific characters for this charset, which incurs too much overhead, I guess that is why we use MaxBytesOfCharacter in other functions such as builtinLpadSig::evalString. @zz-jason should we compute the exact bytes for the string?

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maybe we can build the string first, and use len() to compute the consumed bytes, but is it possible that panic is raised in building the string because it is too large? I think the purpose of max_allowed_packet check here is to prevent this kind of panic to some extent.

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in MySQL, the byte count for lpad is calculated by:

byte_count = count * collation.collation->mbmaxlen;

as for the insert function, seems MySQL calculates the exact bytes for the string:

  /*
    There is one exception not handled (intentionaly) by the character set
    aggregation code. If one string is strong side and is binary, and
    another one is weak side and is a multi-byte character string,
    then we need to operate on the second string in terms on bytes when
    calling ::numchars() and ::charpos(), rather than in terms of characters.
    Lets substitute its character set to binary.
  */
  if (collation.collation == &my_charset_bin) {
    res->set_charset(&my_charset_bin);
    res2->set_charset(&my_charset_bin);
  }

  /* start and length are now sufficiently valid to pass to charpos function */
  start = res->charpos((int)start);
  length = res->charpos((int)length, (uint32)start);

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Why first build it? It just constitutes of three parts, so sum them would be enough.

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seems there isn't a convenient and efficient way to calculate the byte count of a []rune. @tiancaiamao any idea?

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@zz-jason zz-jason Aug 28, 2018 •
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another method is to write a utf-8 code point iterator like this: https://gist.github.com/zz-jason/078110974bb931b7f8e3432775ecfd05, we can iterate on the origin []byte, find the code point located at pos and pos+length, and the count the bytes for each []rune prefix.

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oh you are right... updated

b.ctx.GetSessionVars().StmtCtx.AppendWarning(errWarnAllowedPacketOverflowed.GenByArgs("insert", b.maxAllowedPacket))
return "", true, nil
}
return string(runes[0:pos-1]) + newstr + string(runes[pos+length-1:]), false, nil
}
Expand Down
45 changes: 45 additions & 0 deletions expression/builtin_string_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1425,6 +1425,51 @@ func (s *testEvaluatorSuite) TestRpadSig(c *C) {
c.Assert(terror.ErrorEqual(errWarnAllowedPacketOverflowed, lastWarn.Err), IsTrue, Commentf("err %v", lastWarn.Err))
}

func (s *testEvaluatorSuite) TestInsertBinarySig(c *C) {
colTypes := []*types.FieldType{
{Tp: mysql.TypeVarchar},
{Tp: mysql.TypeLonglong},
{Tp: mysql.TypeLonglong},
{Tp: mysql.TypeVarchar},
}
resultType := &types.FieldType{Tp: mysql.TypeVarchar, Flen: 3}

args := []Expression{
&Column{Index: 0, RetType: colTypes[0]},
&Column{Index: 1, RetType: colTypes[1]},
&Column{Index: 2, RetType: colTypes[2]},
&Column{Index: 3, RetType: colTypes[3]},
}

base := baseBuiltinFunc{args: args, ctx: s.ctx, tp: resultType}
insert := &builtinInsertBinarySig{base, 3}

input := chunk.NewChunkWithCapacity(colTypes, 2)
input.AppendString(0, "abc")
input.AppendString(0, "abc")
input.AppendInt64(1, 3)
input.AppendInt64(1, 3)
input.AppendInt64(2, -1)
input.AppendInt64(2, -1)
input.AppendString(3, "d")
input.AppendString(3, "de")

res, isNull, err := insert.evalString(input.GetRow(0))
c.Assert(res, Equals, "abd")
c.Assert(isNull, IsFalse)
c.Assert(err, IsNil)

res, isNull, err = insert.evalString(input.GetRow(1))
c.Assert(res, Equals, "")
c.Assert(isNull, IsTrue)
c.Assert(err, IsNil)

warnings := s.ctx.GetSessionVars().StmtCtx.GetWarnings()
c.Assert(len(warnings), Equals, 1)
lastWarn := warnings[len(warnings)-1]
c.Assert(terror.ErrorEqual(errWarnAllowedPacketOverflowed, lastWarn.Err), IsTrue, Commentf("err %v", lastWarn.Err))
}

func (s *testEvaluatorSuite) TestInstr(c *C) {
defer testleak.AfterTest(c)()
tbl := []struct {
Expand Down