expvar: don't crash if map value set to nil

Fixes #52719

Change-Id: Ib032193d00664090c47ae92e7d59674ec2d0165a
Reviewed-on: https://go-review.googlesource.com/c/go/+/408677
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

diff --git a/src/expvar/expvar.go b/src/expvar/expvar.go
index 5629f89353d1e5a950f4aa8774300b40da5c6abb..08cd05565d42495d3848308c0fa43ee144105a59 100644 (file)
--- a/src/expvar/expvar.go
+++ b/src/expvar/expvar.go
@@ -118,7 +118,12 @@ func (v *Map) String() string {
                if !first {
                        fmt.Fprintf(&b, ", ")
                }
-               fmt.Fprintf(&b, "%q: %v", kv.Key, kv.Value)
+               fmt.Fprintf(&b, "%q: ", kv.Key)
+               if kv.Value != nil {
+                       fmt.Fprintf(&b, "%v", kv.Value)
+               } else {
+                       fmt.Fprint(&b, "null")
+               }
                first = false
        })
        fmt.Fprintf(&b, "}")
@@ -224,7 +229,8 @@ func (v *Map) Do(f func(KeyValue)) {
        defer v.keysMu.RUnlock()
        for _, k := range v.keys {
                i, _ := v.m.Load(k)
-               f(KeyValue{k, i.(Var)})
+               val, _ := i.(Var)
+               f(KeyValue{k, val})
        }
 }
 

diff --git a/src/expvar/expvar_test.go b/src/expvar/expvar_test.go
index ba95a36066c390135b05bd1ba555069a0efad122..552bae8c64a62f9e6485f0c334f23cdb3684efae 100644 (file)
--- a/src/expvar/expvar_test.go
+++ b/src/expvar/expvar_test.go
@@ -261,6 +261,29 @@ func TestMapCounter(t *testing.T) {
        }
 }
 
+func TestMapNil(t *testing.T) {
+       RemoveAll()
+       const key = "key"
+       m := NewMap("issue527719")
+       m.Set(key, nil)
+       s := m.String()
+       var j any
+       if err := json.Unmarshal([]byte(s), &j); err != nil {
+               t.Fatalf("m.String() == %q isn't valid JSON: %v", s, err)
+       }
+       m2, ok := j.(map[string]any)
+       if !ok {
+               t.Fatalf("m.String() produced %T, wanted a map", j)
+       }
+       v, ok := m2[key]
+       if !ok {
+               t.Fatalf("missing %q in %v", key, m2)
+       }
+       if v != nil {
+               t.Fatalf("m[%q] = %v, want nil", key, v)
+       }
+}
+
 func BenchmarkMapSet(b *testing.B) {
        m := new(Map).Init()