encoding/json: properly handle extra objects with fixed size arrays

If a fixed size array is passed in as the decode target and the JSON
to decode has extra array elements that are objects, then previously
the decoder would return a "data changing underfoot" error.

Fixes #3717.

R=golang-dev, adg, rsc
CC=golang-dev
https://golang.org/cl/7490046

1 files changed, 10 insertions, 0 deletions

diff --git a/src/pkg/encoding/json/decode.go b/src/pkg/encoding/json/decode.go
index d34e10f838..722037c309 100644
--- a/src/pkg/encoding/json/decode.go
+++ b/src/pkg/encoding/json/decode.go
@@ -261,6 +261,16 @@ func (d *decodeState) value(v reflect.Value) {
 		}
 		d.scan.step(&d.scan, '"')
 		d.scan.step(&d.scan, '"')
+
+		n := len(d.scan.parseState)
+		if n > 0 && d.scan.parseState[n-1] == parseObjectKey {
+			// d.scan thinks we just read an object key; finish the object
+			d.scan.step(&d.scan, ':')
+			d.scan.step(&d.scan, '"')
+			d.scan.step(&d.scan, '"')
+			d.scan.step(&d.scan, '}')
+		}
+
 		return
 	}