internal/encoding/json: fix performance cliff when decoding large integers that will go out of range.
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>
diff --git a/internal/encoding/json/number.go b/internal/encoding/json/number.go
index 27faa69..529331f 100644
--- a/internal/encoding/json/number.go
+++ b/internal/encoding/json/number.go
@@ -239,6 +239,14 @@
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.
num = n.intp[:len(n.intp):len(n.intp)]
num = append(num, n.frac...)
