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httpx.Parse fails to unmarshal interface{} field with mixed string/number values #5721
Description
Describe the bug
httpx.Parse fails to parse a request body that contains an interface{} field when the actual JSON value can be either a string or a number. The same request works perfectly with json.NewDecoder(r.Body).Decode(&req), indicating that the JSON is valid and the structure definition is correct.
To Reproduce
- Define the following API types:
type UpdateReq struct {
Id uint64 `json:"id"`
Items []DataItem `json:"datas,optional"`
}
type DataItem struct {
Value interface{} `json:"value,omitempty"` // can be string or number
ValueType int `json:"valueType"` // 0 for string, 1 for number
}- Handler code that uses httpx.Parse:
func UpdateDataHandler(svcCtx *svc.ServiceContext) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
var req types.UpdateReq
if err := httpx.Parse(r, &req); err != nil {
httpx.ErrorCtx(r.Context(), w, err)
return
}
// ... business logic
}
}- Send a POST request with the following JSON body (no query or form parameters):
{
"id": "123",
"datas": [
{
"value": "1",
"valueType": 0
},
{
"value": 2,
"valueType": 1
}
]
}- The error returned is:
type mismatch for field "datas[0].value"
Use the following method to resolve successfully
func UpdateDataHandler(svcCtx *svc.ServiceContext) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
var req types.UpdateReq
if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
httpx.ErrorCtx(r.Context(), w, err)
return
}
// ... business logic
}
}Environments
go-zero version: v1.10.2
goctl version: v1.10.1
Go version: 1.24.0
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junnhwan commentedon Aug 11, 2026
Hi, I would like to work on this issue. I reproduced the failure locally: UnmarshalJsonReader returns 'type mismatch for field "datas[0].value"' when an interface{} field receives mixed string/number JSON values.
Root cause: the mapping unmarshaler has no handling for empty-interface fields. In processFieldPrimitive, an interface{} field matches neither the same-kind branch nor the json.Number branch, so it always falls through to newTypeMismatchError.
I'm preparing a minimal fix so interface{} fields receive the raw decoded JSON value (strings stay strings, numbers stay json.Number because jsonx uses UseNumber), plus a regression test. I'll open a PR once the change is ready.
fix(mapping): support unmarshaling into interface{} fields for mixed …