[BUG] Description

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

OpenAPI specs with the body marked as not required for a post request, results in code that when called will trigger a segmentation fault because it is treated as always required.

The workaround is to provide an empty body, however it's both a surpri

openapi-generator version

Version: 5.2.0

OpenAPI declaration file content or url

openapi: 3.0.2
info:
  version: v1
  title: Simple Example of Bug
paths:
  "/v1/application/{id}/lifecycle/{action}":
    post:
      parameters:
        - name: id
          in: path
          description: ID of application
          required: true
          schema:
            type: string
        - name: action
          in: path
          description: action to take on the application
          required: true
          schema:
            type: string
            enum:
              - activate
              - deactivate
      requestBody:
        content:
          application/json:
            schema:
              type: string
              description: "No request body"
      responses:
        "204":
          description: "Deactivated successfully"
        "403":
          description: Forbidden

Generation Details

docker run --user $(id -u):$(id -g) --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:v5.2.0 generate -i /local/openapi.yaml -g go -o /local/client --package-name client
output

[main] INFO  o.o.codegen.DefaultGenerator - Generating with dryRun=false
[main] INFO  o.o.c.ignore.CodegenIgnoreProcessor - Output directory (/local/client) does not exist, or is inaccessible. No file (.openapi-generator-ignore) will be evaluated.
[main] INFO  o.o.codegen.DefaultGenerator - OpenAPI Generator: go (client)
[main] INFO  o.o.codegen.DefaultGenerator - Generator 'go' is considered stable.
[main] INFO  o.o.c.languages.AbstractGoCodegen - Environment variable GO_POST_PROCESS_FILE not defined so Go code may not be properly formatted. To define it, try `export GO_POST_PROCESS_FILE="/usr/local/bin/gofmt -w"` (Linux/Mac)
[main] INFO  o.o.c.languages.AbstractGoCodegen - NOTE: To enable file post-processing, 'enablePostProcessFile' must be set to `true` (--enable-post-process-file for CLI).
[main] INFO  o.o.codegen.utils.URLPathUtils - 'host' (OAS 2.0) or 'servers' (OAS 3.0) not defined in the spec. Default to [http://localhost] for server URL [http://localhost/]
[main] INFO  o.o.codegen.utils.URLPathUtils - 'host' (OAS 2.0) or 'servers' (OAS 3.0) not defined in the spec. Default to [http://localhost] for server URL [http://localhost/]
[main] WARN  o.o.codegen.DefaultCodegen - Empty operationId found for path: post /v1/application/{id}/lifecycle/{action}. Renamed to auto-generated operationId: v1ApplicationIdLifecycleActionPost
[main] INFO  o.o.codegen.utils.URLPathUtils - 'host' (OAS 2.0) or 'servers' (OAS 3.0) not defined in the spec. Default to [http://localhost] for server URL [http://localhost/]
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/api_default.go
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/docs/DefaultApi.md
[main] INFO  o.o.codegen.utils.URLPathUtils - 'host' (OAS 2.0) or 'servers' (OAS 3.0) not defined in the spec. Default to [http://localhost] for server URL [http://localhost/]
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/api/openapi.yaml
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/README.md
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/git_push.sh
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/.gitignore
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/configuration.go
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/client.go
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/response.go
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/go.mod
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/go.sum
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/.travis.yml
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/utils.go
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/.openapi-generator-ignore
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/.openapi-generator/VERSION
[main] INFO  o.o.codegen.TemplateManager - writing file /local/client/.openapi-generator/FILES
################################################################################
# Thanks for using OpenAPI Generator.                                          #
# Please consider donation to help us maintain this project 🙏                 #
# https://opencollective.com/openapi_generator/donate                          #
################################################################################

Steps to reproduce

1. create directory to run under (test)
2. create file openapi.yaml containing the above yaml
3. run the generator as described:
   docker run --user $(id -u):$(id -g) --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:v5.2.0 generate -i /local/openapi.yaml -g go -o /local/client --package-name client
4. adjust the generated go.mod in the client directory
   sed -i -e 's:module .*:module github.com/test/test/client:' client/go.mod
5. initialize a go mod in the current directory containing the following:

   module github.com/test/test
   
   go 1.16
   
   require github.com/test/test/client v0.1.0
   
   replace github.com/test/test/client => ./client
   

6. Run go mod download && go mod vendor
7. add the following as main.go in the current directory:

   package main
   
   import (
   	"context"
   	"fmt"
   	"os"
   
   	"github.com/test/test/client"
   )
   
   func main() {
   	fmt.Println("vim-go")
   	cfg := client.NewConfiguration()
   	app := client.NewAPIClient(cfg).DefaultApi
   	_, err := app.V1ApplicationIdLifecycleActionPost(context.Background(), "some-id", "deactivate").Execute()
   	if err != nil {
   		os.Exit(1)
   	}
   }
   

8. Attempt to execute using go run:

   go run ./main.go 
   vim-go
   panic: runtime error: invalid memory address or nil pointer dereference
   [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x67df26]
   
   goroutine 1 [running]:
   github.com/test/test/client.setBody(0x69cda0, 0x0, 0x701fb6, 0x10, 0xc00011db40, 0x2800000014, 0x7f8500000028)
   	/home/baileybd/git/github.com/test/test/vendor/github.com/test/test/client/client.go:432 +0x126
   github.com/test/test/client.(*APIClient).prepareRequest(0xc00000e0f0, 0x75e1b0, 0xc0000180a8, 0xc00001e420, 0x2c, 0x6fe8f0, 0x4, 0x69cda0, 0x0, 0xc00011da18, ...)
   	/home/baileybd/git/github.com/test/test/vendor/github.com/test/test/client/client.go:214 +0x19ad
   github.com/test/test/client.(*DefaultApiService).V1ApplicationIdLifecycleActionPostExecute(0xc00000e0f8, 0x75e1b0, 0xc0000180a8, 0xc00000e0f8, 0x6ff72e, 0x7, 0x7004d9, 0xa, 0x0, 0xc00004e710, ...)
   	/home/baileybd/git/github.com/test/test/vendor/github.com/test/test/client/api_default.go:107 +0x4f6
   github.com/test/test/client.ApiV1ApplicationIdLifecycleActionPostRequest.Execute(...)
   	/home/baileybd/git/github.com/test/test/vendor/github.com/test/test/client/api_default.go:44
   main.main()
   	/home/baileybd/git/github.com/test/test/main.go:15 +0x29e
   exit status 2
   

Related issues/PRs

Appears #4701 is attempting to fix the same issue for Java

Suggest a fix

I believe the fix is to modify the following code:
https://github.com/OpenAPITools/openapi-generator/blob/56e7f811bc634eea50576e3445180eb8d2e6f598/modules/openapi-generator/src/main/resources/go/api.mustache#L297-L300

To look something like:

{{#bodyParams}}
{{#required}}
	localVarPostBody = r.{{paramName}}
{{/required}}
{{^required}}
	if r.{{paramName}} != nil {
		localVarPostBody = r.{{paramName}}
	}
{{/required}}
{{/bodyParams}}

Applying the following diff to master prevents the segmentation fault:

diff --git modules/openapi-generator/src/main/resources/go/api.mustache modules/openapi-generator/src/main/resources/go/api.mustache
index 4a94d6aaf59..b4c7b90afb6 100644
--- modules/openapi-generator/src/main/resources/go/api.mustache
+++ modules/openapi-generator/src/main/resources/go/api.mustache
@@ -296,7 +296,14 @@ func (a *{{{classname}}}Service) {{nickname}}Execute(r {{#structPrefix}}{{&class
 {{/formParams}}
 {{#bodyParams}}
        // body params
+{{#required}}
        localVarPostBody = r.{{paramName}}
+{{/required}}
+{{^required}}
+       if r.{{paramName}} != nil {
+               localVarPostBody = r.{{paramName}}
+       }
+{{/required}}
 {{/bodyParams}}
 {{#authMethods}}
 {{#isApiKey}}

However I suspect this is incomplete and there is likely other files that would have to be updated based on the corresponding Java PR #4701

Start with modules/openapi-generator/src/main/resources/go/api.mustache around the body parameter handling, then reproduce the nil-body crash using the supplied OpenAPI YAML and Go generation command. Compare the generated api_default.go and client.go behavior with the related Java issue/PR; done means optional request bodies no longer dereference nil and the regression is covered.