fix(go-server): allow zero values for required request body fields

[halfcrazy]

fix #20496

Previously, AssertXxxRequired used IsZeroValue on all required fields,
so legitimate request bodies with present-but-zero primitives were rejected
(e.g. {"n": 0}, {"complete": false}, {"name": ""}).
This PR validates primitive required fields by JSON key presence in
a generated UnmarshalJSON, matching the approach already used by go-client.
Complex required fields (nested models, arrays, maps) and embedded allOf
parent fields continue to be checked via AssertXxxRequired.

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cc @antihax (2017/11) @grokify (2018/07) @kemokemo (2018/09) @jirikuncar (2021/01) @ph4r5h4d (2021/04) @lwj5 (2023/04)

---

Summary by cubic

Allows zero values for required fields in go-server JSON bodies by validating JSON key presence in generated UnmarshalJSON, matching go-client. Missing required keys now raise RequiredError; file upload handling and tests were tightened.

• Bug Fixes
  • Models add UnmarshalJSON to check required key presence (incl. embedded allOf), honor nullable required fields, and reject unknown keys; supports inline oneOf.
  • allOf parents are embedded in children. Assert helpers only check complex fields and embedded parents; primitive checks moved to JSON key presence.
  • Controllers surface RequiredError from body decode (incl. optional bodies) instead of a generic parsing error.
  • Standardized RequiredError text to "field '%s' is required.".
  • File uploads: controllers defer-close uploaded file(s); temp files are rewound, left open for callers, and cleaned up on errors.
  • Tests and samples: added samples/server/others/go-server/required-zero-value and an inline-oneOf required test; CI runs it and uses go test -mod=mod ./... -v.

^{Written for commit 3f18d44. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found and verified against the latest diff

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="samples/server/petstore/go-chi-server/go/model_order.go">

<violation number="1" location="samples/server/petstore/go-chi-server/go/model_order.go:16">
P3: This generated Go sample is not `gofmt`-formatted after adding the imports; Go tooling will reorder the stdlib import block. Suggest running `gofmt` so regenerated samples match normal Go formatting.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P3: This generated Go sample is not gofmt-formatted after adding the imports; Go tooling will reorder the stdlib import block. Suggest running gofmt so regenerated samples match normal Go formatting.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/server/petstore/go-chi-server/go/model_order.go, line 16:

<comment>This generated Go sample is not `gofmt`-formatted after adding the imports; Go tooling will reorder the stdlib import block. Suggest running `gofmt` so regenerated samples match normal Go formatting.</comment>

<file context>
@@ -13,6 +13,8 @@ package petstoreserver
 
 import (
 	"time"
+	"bytes"
+	"encoding/json"
 )
</file context>

[halfcrazy]

#4031 (comment)

[cubic-dev-ai]

3 issues found across 87 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="samples/openapi3/server/petstore/go/go.mod">

<violation number="1" location="samples/openapi3/server/petstore/go/go.mod:12">
P2: Go version mismatch: module declares `go 1.18` but chi v5.2.2 requires `go 1.20` (from its go.mod `go` directive). `go mod tidy` / `go build` with Go 1.18 may fail or produce unexpected behavior. Consider either bumping the module's `go` directive to at least 1.20 or pinning to a chi version compatible with Go 1.18.</violation>
</file>

<file name="samples/server/others/go-server/required-zero-value/go/api.go">

<violation number="1" location="samples/server/others/go-server/required-zero-value/go/api.go:19">
P3: DefaultAPIRouter interface is defined but never implemented or referenced. The controller dispatches via Routes()/OrderedRoutes() on the Router interface from routers.go, and NewRouter accepts Router, not DefaultAPIRouter. This type is dead code.</violation>
</file>

<file name="modules/openapi-generator/src/main/resources/go-server/model.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/go-server/model.mustache:72">
P2: Unknown JSON properties remain silently accepted despite the strict decoder. The generated presence unmarshaller filters them out before `DisallowUnknownFields`, and models without required fields bypass this path entirely; validate keys before filtering or decode the original payload with the strict decoder.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P3: DefaultAPIRouter interface is defined but never implemented or referenced. The controller dispatches via Routes()/OrderedRoutes() on the Router interface from routers.go, and NewRouter accepts Router, not DefaultAPIRouter. This type is dead code.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/server/others/go-server/required-zero-value/go/api.go, line 19:

<comment>DefaultAPIRouter interface is defined but never implemented or referenced. The controller dispatches via Routes()/OrderedRoutes() on the Router interface from routers.go, and NewRouter accepts Router, not DefaultAPIRouter. This type is dead code.</comment>

<file context>
@@ -0,0 +1,26 @@
+)
+
+// DefaultAPIRouter defines the required methods for binding the api requests to a responses for the DefaultAPI
+type DefaultAPIRouter interface {
+	Update(http.ResponseWriter, *http.Request)
+}
</file context>