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internal/encoding/json: fix performance cliff when decoding large integers that will go out of range.

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For large positive integers, add check for number of decimal digits
before converting number to plain integer w/o exponent.

If exponent value is large, previous implementation may end up
constructing a large string with lots of zeroes that is not useful as it
will fail later on when called with strconv.Parse{Uint,Int} anyways.

Fixes golang/protobuf#1002.

Change-Id: I65bfad304401e076743853d7501786b7231b083b
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/213717
Reviewed-by: Damien Neil <dneil@google.com>
This commit is contained in:
Herbie Ong 2020-01-07 17:26:43 -08:00
parent b0c26f1868
commit b02b6d1da5
1 changed files with 8 additions and 0 deletions
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8
internal/encoding/json/number.go
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@ -239,6 +239,14 @@ func normalizeToIntString(n numberParts) (string, bool) {
return "", false return "", false
} }
// Make sure resulting digits are within max value limit to avoid
// unnecessarily constructing a large byte slice that may simply fail
// later on.
const maxDigits = 20 // Max uint64 value has 20 decimal digits.
if intpSize+exp > maxDigits {
return "", false
}
// Set cap to make a copy of integer part when appended. // Set cap to make a copy of integer part when appended.
num = n.intp[:len(n.intp):len(n.intp)] num = n.intp[:len(n.intp):len(n.intp)]
num = append(num, n.frac...) num = append(num, n.frac...)