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encoding/json: detect cyclic maps and slices

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Now reports an error if cyclic maps and slices are to be encoded
instead of an infinite recursion. This case wasn't handled in CL 187920.

Fixes #40745.

Change-Id: Ia34b014ecbb71fd2663bb065ba5355a307dbcc15
GitHub-Last-Rev: 6f874944f4
GitHub-Pull-Request: golang/go#40756
Reviewed-on: https://go-review.googlesource.com/c/go/+/248358
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Trust: Daniel Martí <mvdan@mvdan.cc>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
lujjjh 2020-09-17 14:39:13 +00:00 • committed by Daniel Martí
parent 25a33daa2b
commit 428509402b
2 changed files with 53 additions and 1 deletions
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27
src/encoding/json/encode.go
View file

@ -779,6 +779,16 @@ func (me mapEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
e.WriteString("null")
return
}
if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
// We're a large number of nested ptrEncoder.encode calls deep;
// start checking if we've run into a pointer cycle.
ptr := v.Pointer()
if _, ok := e.ptrSeen[ptr]; ok {
e.error(&UnsupportedValueError{v, fmt.Sprintf("encountered a cycle via %s", v.Type())})
}
e.ptrSeen[ptr] = struct{}{}
defer delete(e.ptrSeen, ptr)
}
e.WriteByte('{')
// Extract and sort the keys.
@ -801,6 +811,7 @@ func (me mapEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
me.elemEnc(e, v.MapIndex(kv.v), opts)
}
e.WriteByte('}')
e.ptrLevel--
}
func newMapEncoder(t reflect.Type) encoderFunc {
@ -857,7 +868,23 @@ func (se sliceEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
e.WriteString("null")
return
}
if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
// We're a large number of nested ptrEncoder.encode calls deep;
// start checking if we've run into a pointer cycle.
// Here we use a struct to memorize the pointer to the first element of the slice
// and its length.
ptr := struct {
ptr uintptr
len int
}{v.Pointer(), v.Len()}
if _, ok := e.ptrSeen[ptr]; ok {
e.error(&UnsupportedValueError{v, fmt.Sprintf("encountered a cycle via %s", v.Type())})
}
e.ptrSeen[ptr] = struct{}{}
defer delete(e.ptrSeen, ptr)
}
se.arrayEnc(e, v, opts)
e.ptrLevel--
}
func newSliceEncoder(t reflect.Type) encoderFunc {