Runtime panic with CloseNotify

[yugui]

The integration test sometimes fails with a runtime panic.

e.g. https://travis-ci.org/gengo/grpc-gateway/jobs/111913217

$ env GLOG_logtostderr=1 go test -v github.com/gengo/grpc-gateway/...
=== RUN   TestIntegration
E0226 02:27:10.407340    5251 a_bit_of_everything.go:67] nested:<name:"hoge" amount:10 > nested:<name:"fuga" amount:20 > float_value:1.5 double_value:2.5 int64_value:4294967296 uint64_value:9223372036854775807 int32_value:-2147483648 fixed64_value:9223372036854775807 fixed32_value:4294967295 bool_value:true string_value:"strprefix/foo" uint32_value:4294967295 sfixed32_value:2147483647 sfixed64_value:-4611686018427387904 sint32_value:2147483647 sint64_value:4611686018427387903 
E0226 02:27:10.407661    5251 a_bit_of_everything.go:67] nested:<name:"hoge" amount:10 > nested:<name:"fuga" amount:20 > float_value:1.5 double_value:2.5 int64_value:4294967296 uint64_value:9223372036854775807 int32_value:-2147483648 fixed64_value:9223372036854775807 fixed32_value:4294967295 bool_value:true string_value:"strprefix/bar" uint32_value:4294967295 sfixed32_value:2147483647 sfixed64_value:-4611686018427387904 sint32_value:2147483647 sint64_value:4611686018427387903 
E0226 02:27:10.407774    5251 a_bit_of_everything.go:67] nested:<name:"hoge" amount:10 > nested:<name:"fuga" amount:20 > float_value:1.5 double_value:2.5 int64_value:4294967296 uint64_value:9223372036854775807 int32_value:-2147483648 fixed64_value:9223372036854775807 fixed32_value:4294967295 bool_value:true string_value:"strprefix/baz" uint32_value:4294967295 sfixed32_value:2147483647 sfixed64_value:-4611686018427387904 sint32_value:2147483647 sint64_value:4611686018427387903 
E0226 02:27:10.407873    5251 a_bit_of_everything.go:67] nested:<name:"hoge" amount:10 > nested:<name:"fuga" amount:20 > float_value:1.5 double_value:2.5 int64_value:4294967296 uint64_value:9223372036854775807 int32_value:-2147483648 fixed64_value:9223372036854775807 fixed32_value:4294967295 bool_value:true string_value:"strprefix/qux" uint32_value:4294967295 sfixed32_value:2147483647 sfixed64_value:-4611686018427387904 sint32_value:2147483647 sint64_value:4611686018427387903 
E0226 02:27:10.407969    5251 a_bit_of_everything.go:67] nested:<name:"hoge" amount:10 > nested:<name:"fuga" amount:20 > float_value:1.5 double_value:2.5 int64_value:4294967296 uint64_value:9223372036854775807 int32_value:-2147483648 fixed64_value:9223372036854775807 fixed32_value:4294967295 bool_value:true string_value:"strprefix/quux" uint32_value:4294967295 sfixed32_value:2147483647 sfixed64_value:-4611686018427387904 sint32_value:2147483647 sint64_value:4611686018427387903 
panic: net/http: CloseNotify called after ServeHTTP finished
goroutine 89 [running]:
panic(0x87f8e0, 0xc82036c150)
    /home/travis/.gimme/versions/go/src/runtime/panic.go:483 +0x3f3
net/http.(*response).CloseNotify(0xc820360270, 0x0)
    /home/travis/.gimme/versions/go/src/net/http/server.go:1535 +0x9d
github.com/gengo/grpc-gateway/examples/examplepb.RegisterABitOfEverythingServiceHandler.func9.1(0x7fe8ab5313a0, 0xc820360270, 0xc82036c070)
    /home/travis/gopath/src/github.com/gengo/grpc-gateway/examples/examplepb/a_bit_of_everything.pb.gw.go:658 +0x27
created by github.com/gengo/grpc-gateway/examples/examplepb.RegisterABitOfEverythingServiceHandler.func9
    /home/travis/gopath/src/github.com/gengo/grpc-gateway/examples/examplepb/a_bit_of_everything.pb.gw.go:660 +0x132
FAIL    github.com/gengo/grpc-gateway/examples  0.149s
?       github.com/gengo/grpc-gateway/examples/examplepb    [no test files]
?       github.com/gengo/grpc-gateway/examples/server   [no test files]
?       github.com/gengo/grpc-gateway/examples/sub  [no test files]
?       github.com/gengo/grpc-gateway/protoc-gen-grpc-gateway   [no test files]

[kazegusuri]

I've noticed this in my env.