René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"strict-server: response types silently drop data for allOf-composed unions and properties + additionalProperties","articleBody":"PR #2332 fixed strict-server response types losing their model's `MarshalJSON`, closing #970 and #1665. Two shapes are still affected: the response is emitted as a defined type with no delegation, and `encoding/json` quietly serialises an incomplete body. No error, no compile failure — just a 200 with fields missing.\n\n## Environment\n\n- `oapi-codegen` **v2.8.0**\n- `oapi-codegen/runtime` v1.6.0\n- Go **1.26.4** (darwin/arm64)\n\n## Configuration\n\n```yaml\npackage: repro\ngenerate:\n  strict-server: true\n  gorilla-server: true\n  models: true\noutput-options:\n  skip-prune: true\n```\n\n## Minimal specification\n\n```yaml\nopenapi: \"3.0.0\"\ninfo:\n  title: allOf-composed union repro\n  version: \"1.0\"\npaths:\n  /thing:\n    get:\n      operationId: getThing\n      responses:\n        \"200\":\n          description: ok\n          content:\n            application/json:\n              schema: { $ref: \"#/components/schemas/Thing\" }\n  /bag:\n    get:\n      operationId: getBag\n      responses:\n        \"200\":\n          description: ok\n          content:\n            application/json:\n              schema: { $ref: \"#/components/schemas/Bag\" }\ncomponents:\n  schemas:\n    Base:\n      type: object\n      required: [id]\n      properties:\n        id: { type: string }\n    # case 1: union nested inside an allOf member\n    Thing:\n      allOf:\n        - $ref: \"#/components/schemas/Base\"\n        - oneOf:\n            - $ref: \"#/components/schemas/Cat\"\n            - $ref: \"#/components/schemas/Dog\"\n    Cat:\n      type: object\n      properties: { meow: { type: string } }\n    Dog:\n      type: object\n      properties: { woof: { type: string } }\n    # case 2: fixed properties alongside additionalProperties\n    Bag:\n      type: object\n      required: [kind]\n      properties:\n        kind: { type: string }\n      additionalProperties: true\n```\n\n## Current behaviour\n\nThe **models** are generated correctly. Both get a custom marshaller:\n\n```go\ntype Thing struct {\n\tId    string `json:\"id\"`\n\tunion json.RawMessage\n}\nfunc (t Thing) MarshalJSON() ([]byte, error) { ... }\n\ntype Bag struct {\n\tKind                 string                 `json:\"kind\"`\n\tAdditionalProperties map[string]interface{} `json:\"-\"`\n}\nfunc (a Bag) MarshalJSON() ([]byte, error) { ... }\n```\n\nThe **response types** do not, so nothing delegates to those marshallers:\n\n```go\ntype GetThing200JSONResponse Thing   // no MarshalJSON\ntype GetBag200JSONResponse Bag       // no MarshalJSON\n```\n\nThe generated visitor encodes the response value directly:\n\n```go\nfunc (response GetThing200JSONResponse) VisitGetThingResponse(w http.ResponseWriter) error {\n\tvar buf bytes.Buffer\n\tif err := json.NewEncoder(&buf).Encode(response); err != nil {\n\t\treturn err\n\t}\n\t...\n}\n```\n\nBecause `GetThing200JSONResponse` is a defined type it does not inherit `Thing`'s method, so `encoding/json` falls back to struct-field encoding and drops the unexported `union` field. Same for `Bag`, whose `AdditionalProperties` map is tagged `json:\"-\"`.\n\nServing each response through its generated visitor:\n\n| Response value | Actual (v2.8.0) | Expected |\n|---|---|---|\n| `Thing{Id: \"abc\"}` + `FromCat(Cat{Meow: \"purr\"})` | `{\"id\":\"abc\"}` | `{\"id\":\"abc\",\"meow\":\"purr\"}` |\n| `Bag{Kind: \"demo\", AdditionalProperties: {\"extra\": 42}}` | `{\"kind\":\"demo\"}` | `{\"extra\":42,\"kind\":\"demo\"}` |\n\n## Expected behaviour\n\nThe response type should delegate to the model's marshaller, exactly as #2332 already does for a response whose schema is directly a `oneOf`/`anyOf`.\n","author":{"url":"https://github.com/PieterVoorwinden","@type":"Person","name":"PieterVoorwinden"},"datePublished":"2026-09-02T09:51:01Z","url":"https://github.com/oapi-codegen/oapi-codegen/issues/2549"}