Implement required:false for parameter of type File

[khyew]

See #1151

The Swagger/OpenAPI spec indicates that required: false can be used to make any API parameters optional. The current implementation of go-swagger completely ignores this when generating the BindRequest for parameters of type file. The result is that all file parameters are mandatory and clients that omit any results in a HTTP 500 returned by the middleware layer.

This pull request makes a change to the parameter.gotmpl template to handle nullable file parameters.

Here's the generated output for required: true (current behaviour):

type PostV1FeedbackParams struct {
…
        Attachment runtime.File
…
}

func (o *PostV1FeedbackParams) BindRequest(r *http.Request, route *middleware.MatchedRoute) error {
...
        attachment, attachmentHeader, err := r.FormFile("attachment")
        if err != nil {
                res = append(res, errors.New(400, "reading file %q failed: %v", "attachment", err))
        } else {
                o.Attachment = runtime.File{Data: attachment, Header: attachmentHeader}
        }
...
}

Here's the generated output for required: false with this new template:

type PostV1FeedbackParams struct {
…
        Attachment *runtime.File
…
}

func (o *PostV1FeedbackParams) BindRequest(r *http.Request, route *middleware.MatchedRoute) error {
...
        attachment, attachmentHeader, err := r.FormFile("attachment")
        if err != nil && err != http.ErrMissingFile {
                res = append(res, errors.New(400, "reading file %q failed: %v", "attachment", err))
        } else if err == http.ErrMissingFile {
                // no-op for missing but optional file parameter
        } else {
                o.Attachment = &runtime.File{Data: attachment, Header: attachmentHeader}
        }
...
}

[codecov]

Codecov Report

Merging #1154 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1154   +/-   ##
=======================================
  Coverage   69.27%   69.27%           
=======================================
  Files          21       21           
  Lines        7391     7391           
=======================================
  Hits         5120     5120           
  Misses       1801     1801           
  Partials      470      470

Impacted Files	Coverage Δ
generator/bindata.go	60.32% <100%> (ø)	⬆️

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