Fix index out of range panic

AllenX2018 · AllenX2018 · commit 63af0e0b6f30 · 2020-06-15T17:28:24.000+08:00
Fix a bug shown at https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=23083. Credit to OSS-Fuzz.
diff --git a/parser.go b/parser.go
@@ -766,7 +766,7 @@ func Set(data []byte, setValue []byte, keys ...string) (value []byte, err error)
 		if endOffset == -1 {
 			firstToken := nextToken(data)
 			// We can't set a top-level key if data isn't an object
-			if len(data) == 0 || data[firstToken] != '{' {
+			if firstToken < 0 || data[firstToken] != '{' {
 				return nil, KeyPathNotFoundError
 			}
 			// Don't need a comma if the input is an empty object

Original file line number	Diff line number	Diff line change
`@@ -766,7 +766,7 @@ func Set(data []byte, setValue []byte, keys ...string) (value []byte, err error)`
`766`	`766`	`if endOffset == -1 {`
`767`	`767`	`firstToken := nextToken(data)`
`768`	`768`	`// We can't set a top-level key if data isn't an object`
`769`		`- if len(data) == 0 \|\| data[firstToken] != '{' {`
	`769`	`+ if firstToken < 0 \|\| data[firstToken] != '{' {`
`770`	`770`	`return nil, KeyPathNotFoundError`
`771`	`771`	`}`
`772`	`772`	`// Don't need a comma if the input is an empty object`