fix: csharp get file name from content disposition

[fghpdf]

Summary

Download a file can't get the file name from the header, content-disposition.

The generator will generate the FileParameter class, and the code doesn't handle this type.

And also, according to RFC 2616, the HTTP headers are case insensitive.

OpenAPI Example

openapi: 3.0.0
info:
  title: Swagger Petstore - OpenAPI 3.1
  description: |-
  version: 1.0.11
servers:
  - url: http://localhost:8080
tags:
  - name: file
    description: A Restful API to manage files
paths:
  /files/${fileId}:
    get:
      tags:
        - file
      description: Download an existing file by Id
      operationId: downloadFile
      parameters:  
        - in: path
          name: fileId
          schema:
            type: string
            format: uuid
          required: true
      responses:
        '200':
          description: Successful operation
          content:
            application/octet-stream:
              schema:
                type: string
                format: binary

OpenAPI CLI Command

openapi-generator-cli generate -g csharp --additional-properties=library=httpclient --additional-properties=targetFramework=net6.0 -i file.yaml 

Expect

Get file name: example.txt

Actual

Get file name: 'no_name_provided'

Server

If you want to have a quick test, you can use this Golang code:

package main

import (
	"github.com/gin-gonic/gin"
	"log"
	"path/filepath"
)

func main() {
	r := gin.Default()
	r.GET("/files/:fileId", func(c *gin.Context) {
		fileId := c.Param("fileId")
		log.Println(fileId)
		filePath := filepath.Join("./", "example.txt")
		c.Writer.Header().Set("Access-Control-Allow-Origin", "*")
		c.Writer.Header().Set("Access-Control-Allow-Credentials", "true")
		c.Writer.Header().Set("Access-Control-Allow-Headers", "Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization, accept, origin, Cache-Control, X-Requested-With")
		c.Writer.Header().Set("Access-Control-Allow-Methods", "POST, OPTIONS, GET, PUT")
		c.Header("Content-Disposition", "attachment; filename=example.txt")
		c.Header("Content-Type", "application/octet-stream")
		c.File(filePath)
	})
	r.Run() // listen and serve on 0.0.0.0:8080 (for windows "localhost:8080")
}

PR checklist

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[fghpdf]

@wing328 I appreciate the extra details you added.

[wing328]

@fghpdf thanks for the PR.

Have you tested the fix locally to confirm it works for your use cases?

[fghpdf]

@fghpdf thanks for the PR.

Have you tested the fix locally to confirm it works for your use cases?

Sure, I tried this case locally:

[Fact]
public void UpdatePetTest()
{
    FileParameter file = instance.DownloadFile(Guid.NewGuid());
    _output.WriteLine(file.Name);
    Assert.Equal("example.txt", file.Name);
}

And this PR can solve this issue.

[wing328]

ok. let's give it a try