StreamableFile overrides Content-Type header

[dzunftmeister-evorhei]

Feature Request

Is your feature request related to a problem? Please describe.

StreamableFile set a fixed content-type header of application/octet-stream, even if you set an other like response.header('content-type', 'image/svg')

https://github.com/dzunftmeister-evorhei/nest-streamablefile-res-issue
nest run start:dev
http://localhost:3000/fileTestInline

Describe the solution you'd like

there should be a possibility to set the content-type header to get inline view of files working
e.g. new StreamableFile(file, {contentType: 'image/svg'})

Teachability, Documentation, Adoption, Migration Strategy

What is the motivation / use case for changing the behavior?

[micalevisk]

This happen due to the following lines

nest/packages/platform-express/adapters/express-adapter.ts

Lines 32 to 35 in 72a88d5

	if (body instanceof StreamableFile) {
	response.setHeader('Content-Type', 'application/octet-stream');
	return body.getStream().pipe(response);
	}

And the commit message of b862e9c made by @jmcdo29 states this behavior.

But this behaves differently from fastify, which under the hood sets to application/octet-stream only if there's no content-type (I guess)

nest/packages/platform-fastify/adapters/fastify-adapter.ts

Lines 147 to 151 in 72a88d5

	if (body instanceof StreamableFile) {
	body = body.getStream();
	}
	return fastifyReply.send(body);
	}

[dzunftmeister-evorhei]

then we could do something like this for express ...
if (!response.getHeader('Content-Type')) { response.setHeader('Content-Type', 'application/octet-stream'); }

[kamilmysliwiec]

Lets track this here #7589