encoding/json: panic for nil map key types implementing TextMarshaler #33675
Description
What version of Go are you using (go version)?
$ go version go version go1.12.8 darwin/amd64
Does this issue reproduce with the latest release?
Yes.
What operating system and processor architecture are you using (go env)?
go env Output
$ go env GOARCH="amd64" GOBIN="" GOCACHE="/Users/will/Library/Caches/go-build" GOEXE="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="darwin" GOOS="darwin" GOPATH="/Users/will/go" GOPROXY="" GORACE="" GOROOT="/usr/local/opt/go/libexec" GOTMPDIR="" GOTOOLDIR="/usr/local/opt/go/libexec/pkg/tool/darwin_amd64" GCCGO="gccgo" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="" CGO_CFLAGS="-g -O2" CGO_CPPFLAGS="" CGO_CXXFLAGS="-g -O2" CGO_FFLAGS="-g -O2" CGO_LDFLAGS="-g -O2" PKG_CONFIG="pkg-config" GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/rw/cyt9bjxx34qglfg2jsfm27jr0000gn/T/go-build363570579=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
Given the following program that use a map key type implementing the encoding.TextMarshaler interface, when the key is nil, the code panic.
https://play.golang.org/p/KcDK-mOPbqe
What did you expect to see?
Expected a json.UnsupportedValueError, or the key to be encoded as an empty string.
What did you see instead?
Following panic stack trace.
Taken from playground output.
panic: value method net.IP.MarshalText called using nil *IP pointer [recovered]
panic: value method net.IP.MarshalText called using nil *IP pointer
goroutine 1 [running]:
encoding/json.(*encodeState).marshal.func1(0x44af48, 0x5d4c)
/usr/local/go/src/encoding/json/encode.go:302 +0xc0
panic(0x1275a0, 0x40c2c0)
/usr/local/go/src/runtime/panic.go:522 +0x240
net.(*IP).MarshalText(0x0, 0x134040, 0x0, 0x1, 0xeed34048, 0x0, 0x1, 0x128d80)
<autogenerated>:1 +0xa0
encoding/json.(*reflectWithString).resolve(0x4301e0, 0x2, 0x2, 0x0)
/usr/local/go/src/encoding/json/encode.go:871 +0x420
encoding/json.mapEncoder.encode(0x15a05c, 0x4540c0, 0x1235c0, 0x43e360, 0x15, 0x120100)
/usr/local/go/src/encoding/json/encode.go:690 +0x4a0
encoding/json.(*encodeState).reflectValue(0x4540c0, 0x1235c0, 0x43e360, 0x15, 0x120100, 0x207a60)
/usr/local/go/src/encoding/json/encode.go:334 +0xa0
encoding/json.(*encodeState).marshal(0x4540c0, 0x1235c0, 0x43e360, 0x100, 0x0, 0x0)
/usr/local/go/src/encoding/json/encode.go:306 +0x100
encoding/json.Marshal(0x1235c0, 0x43e360, 0x40a0f0, 0x5d4c, 0x444260, 0x43e280, 0x0, 0x5d4c)
/usr/local/go/src/encoding/json/encode.go:160 +0x60
main.main()
/tmp/sandbox157275249/prog.go:15 +0x1a0
The (encodeWithString).resolve method does not check if a reflect.Value of kind Ptr is nil before doing the type assertion to encoding.TextMarshaler with the result of the (reflect.Value).Interface call.
After adding the following check after line 869 of encoding/json/encode.go:
if w.v.Kind() == reflect.Ptr && w.v.IsNil() {
return nil
}I now get this output:
{"":"","127.0.0.1":"localhost"}
Am I missing something regarding nil keys in maps ?