fix(go): fix Go client to normalize request header keys using Header.Set

[Wuchieh]

Use http.Header.Set when writing headerParams to http.Header in the generated Go client.

Previously, generated code directly assigned values to the underlying http.Header map:

headers[h] = []string{v}

This bypasses the header name canonicalization provided by http.Header.Set and may result in inconsistent header casing or duplicate logical headers.

This change replaces direct map assignment with:

headers.Set(h, v)

Changes

• Use http.Header.Set when writing headerParams to http.Header.
• Ensure request header names are canonicalized consistently.
• Avoid inconsistent casing or duplicate logical headers caused by direct map assignment.
• Add/update regression tests to cover the expected header handling behavior.

Related Issue

Fixes #24765

PR checklist

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• Run the following to [build the project](https://github.com/openapitools/openapi-generator#14---build-projects) and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit

• If your PR is targeting a particular programming language, @mention the relevant [technical committee](https://github.com/openapitools/openapi-generator/#62---openapi-generator-technical-committee) members.

---

Summary by cubic

Normalizes request header keys in generated Go clients by using http.Header.Set instead of direct map assignment. This canonicalizes names and prevents duplicate logical headers.

• If headerParams contains case-variant duplicates, only one canonical header is sent; which value is kept depends on map iteration order.
• Regenerates Go samples and updates sample dependency snapshots (normalize go.mod Go versions to X.Y.0 and add missing go.sum entries like terraform-plugin-testing).

^{Written for commit 8e27634. Summary will update on new commits.}

[Wuchieh]

@lwj5 Please review it.

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}

[wing328]

please follow step 3 to update the samples so that CI can verify the change

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

[wing328]

please review the build failures when you've time, e.g. https://github.com/OpenAPITools/openapi-generator/actions/runs/32814668511/job/97700780542?pr=24766

[Wuchieh]

please review the build failures when you've time, e.g. https://github.com/OpenAPITools/openapi-generator/actions/runs/32814668511/job/97700780542?pr=24766

Okay, I'll take a look later to see what the issue is.

[cubic-dev-ai]

1 issue found across 24 files (changes from recent commits).

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/client/echo_api/go/client.go">

<violation number="1">
P2: This PR changes properly gofmt-formatted Go code into gofmt-invalid code: spaces inside call/signature parens, `var param,ok`, `dataMap,err :=`, `for i:=0;i<len;...`, and an over-indented `case`. The same non-gofmt text is now in the `client.mustache` template, so every generated Go client ships this. Keep generated Go output gofmt-clean (run `gofmt -w` on the template and regenerate, or write the template in gofmt style) or CI/`go vet`/gofmt checks and downstream users on the Go codebase will hit formatting failures.</violation>
</file>

<sub>Tip: Review your code locally with the cubic CLI to iterate faster.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: This PR changes properly gofmt-formatted Go code into gofmt-invalid code: spaces inside call/signature parens, var param,ok, dataMap,err :=, for i:=0;i<len;..., and an over-indented case. The same non-gofmt text is now in the client.mustache template, so every generated Go client ships this. Keep generated Go output gofmt-clean (run gofmt -w on the template and regenerate, or write the template in gofmt style) or CI/go vet/gofmt checks and downstream users on the Go codebase will hit formatting failures.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/echo_api/go/client.go, line 144:

<comment>This PR changes properly gofmt-formatted Go code into gofmt-invalid code: spaces inside call/signature parens, `var param,ok`, `dataMap,err :=`, `for i:=0;i<len;...`, and an over-indented `case`. The same non-gofmt text is now in the `client.mustache` template, so every generated Go client ships this. Keep generated Go output gofmt-clean (run `gofmt -w` on the template and regenerate, or write the template in gofmt style) or CI/`go vet`/gofmt checks and downstream users on the Go codebase will hit formatting failures.</comment>

<file context>
@@ -140,19 +141,19 @@ func typeCheckParameter(obj interface{}, expected string, name string) error {
 }
 
-func parameterValueToString(obj interface{}, key string) string {
+func parameterValueToString( obj interface{}, key string ) string {
 	if reflect.TypeOf(obj).Kind() != reflect.Ptr {
 		if actualObj, ok := obj.(interface{ GetActualInstanceValue() interface{} }); ok {
</file context>

Suggested change

	if len(headerParams) > 0 {
	func parameterValueToString(obj interface{}, key string) string {

[Wuchieh]

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

Please review it.

[Wuchieh]

@wing328 Hi, I found that the go test configuration in this project was incorrect, which caused the previous CI checks to fail. Could you please review and approve it? Thank you.

Incorrect files:

• samples/openapi3/client/petstore/go/auth_test.go
• samples/client/petstore/go/auth_test.go

[wing328]

UPDATE: merged #24791 to add an option useHttpHeaderSet