The Router only supports uploading a file if the file field name is "file"

[l-petrov]

Component(s)

router

Component version

0.158.0

wgc version

0.71.3

controlplane version

None

router version

0.158.0

What happened?

If possible, please create a PR with a failing test to illustrate the issue clearly.
Otherwise, please attach a minimum reproduction through a GitHub repository that includes
essential information such as the relevant subgraph SDLs.
Please also make sure that the instructions for the reproduction are clear, tested, and fully accurate.

Description

When attempting to upload a file through the Router, the name of the field in the schema must be file, as illustrated in the example provided:
https://cosmo-docs.wundergraph.com/router/file-upload
Any other name will result in the router passing null as the file data to the final federated GraphQL server.

This is because the httpclient package, which is part of the graphql-go-tools repository, has a hardcoded name for the file variables, which is file, as evident in the nethttpclient.go file.

func DoMultipartForm(
	client *http.Client, ctx context.Context, requestInput []byte, files []File, out *bytes.Buffer,
) (err error) {
	if len(files) == 0 {
		return errors.New("no files provided")
	}

	url, method, body, headers, queryParams, enableTrace := requestInputParams(requestInput)

	h := pool.Hash64.Get()
	defer pool.Hash64.Put(h)
	_, _ = h.Write(body)

	formValues := map[string]io.Reader{
		"operations": bytes.NewReader(body),
	}

	var fileMap string
	var tempFiles []*os.File
	for i, file := range files {
		if len(fileMap) == 0 {
			if len(files) == 1 {
				fileMap = fmt.Sprintf(`"%d" : ["variables.file"]`, i)
			} else {
				fileMap = fmt.Sprintf(`"%d" : ["variables.files.%d"]`, i, i)
			}
		} else {
			fileMap = fmt.Sprintf(`%s, "%d" : ["variables.files.%d"]`, fileMap, i, i)
		}
		key := fmt.Sprintf("%d", i)
		_, _ = h.WriteString(file.Path())
		temporaryFile, err := os.Open(file.Path())
		tempFiles = append(tempFiles, temporaryFile)
		if err != nil {
			return err
		}
		formValues[key] = bufio.NewReader(temporaryFile)
	}
....

Steps to Reproduce

1. Create a simple WunderGraph router that is federating a GraphQL server with a schema that has a query with a file upload query. Make sure the field of the file data is not named file
2. Try to upload a file to print the contents of the file at the GraphQL server as it was passed by WunderGraph router.

Expected Result

If this is by design it should be stated explicitly in the docs that you can upload files only using fields that are named file.
Other wise the expected result is that the file upload should work with any field name.

Actual Result

The destination GraphQL server receives a null file

Environment information

Environment

OS: MacOS 15.2
Package Manager: npm
Compiler(if manually compiled): (e.g., "go 14.2")

Router configuration

No response

Router execution config

No response

Log output

No response

Additional context

No response

[github-actions]

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[jensneuse]

Thanks for bringing this up. We'll take a look at improving the docs.