encoding/gob: clean up decoderMap after errBadType

When decoding an invalid typeId the associated *decEngine was not
removed from decoderMap. If the decoder was run again on the same input
a nil *decEngine was found in the map and assumed to be initialized,
resulting in a panic.

Fixes #9649

Change-Id: I5bb51808362a21c09228c2705a658f073e5b59b3
Reviewed-on: https://go-review.googlesource.com/3509
Reviewed-by: Rob Pike <r@golang.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/src/encoding/gob/decode.go b/src/encoding/gob/decode.go
index f1c597086d..3f34cbac57 100644
--- a/src/encoding/gob/decode.go
+++ b/src/encoding/gob/decode.go
@@ -1051,6 +1051,7 @@ func (dec *Decoder) compileIgnoreSingle(remoteId typeId) (engine *decEngine, err
 // compileDec compiles the decoder engine for a value.  If the value is not a struct,
 // it calls out to compileSingle.
 func (dec *Decoder) compileDec(remoteId typeId, ut *userTypeInfo) (engine *decEngine, err error) {
+	defer catchError(&err)
 	rt := ut.base
 	srt := rt
 	if srt.Kind() != reflect.Struct || ut.externalDec != 0 {
@@ -1163,8 +1164,9 @@ func (dec *Decoder) decodeValue(wireId typeId, value reflect.Value) {
 	value = decAlloc(value)
 	engine := *enginePtr
 	if st := base; st.Kind() == reflect.Struct && ut.externalDec == 0 {
+		wt := dec.wireType[wireId]
 		if engine.numInstr == 0 && st.NumField() > 0 &&
-			dec.wireType[wireId] != nil && len(dec.wireType[wireId].StructT.Field) > 0 {
+			wt != nil && len(wt.StructT.Field) > 0 {
 			name := base.Name()
 			errorf("type mismatch: no fields matched compiling decoder for %s", name)
 		}