feat(core): add file send capability

[jmcdo29]

Fastify has the built in capbility to send files without
any extra code. Express can send files via stream.pipe(res)
if the file is a stream, and as such, the
Content-Type header is set to application/octet-stream
in the ExpressAdapter if a stream or Buffer is detected.

fix #5263

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[X] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior?

Files are not currently supported by Express and Fastify

Issue Number: #5263

What is the new behavior?

Fastify and Express Adapters now both support sending files via streams and Buffers.

Does this PR introduce a breaking change?

[ ] Yes
[X] No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 0646adc6-5d7d-4efd-a4d6-05e8e76f2a14

• 4 of 11 (36.36%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.1%) to 94.621%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/common/file-stream/streamable-file.ts	2	9	22.22%

Totals
Change from base Build dc31867d-4641-4462-b640-88e523413104:	-0.1%
Covered Lines:	5084
Relevant Lines:	5373

---

💛 - Coveralls

[kamilmysliwiec]

I've just realized that this may actually introduce a breaking change. Very rare case, but what if someone has a class that contains a custom pipe() method defined. Although this object is intended to be serialized as any other DTO, Nest would try to pipe a stream.

To avoid a breaking change, perhaps we can define a new, dedicated wrapper class that you could use as follows new ResponseStream(stream) (or any other, better name) and then just check with instanceof instead of checking for pipe method

[jmcdo29]

I've just realized that this may actually introduce a breaking change. Very rare case, but what if someone has a class that contains a custom pipe() method defined. Although this object is intended to be serialized as any other DTO, Nest would try to pipe a stream.

To avoid a breaking change, perhaps we can define a new, dedicated wrapper class that you could use as follows new ResponseStream(stream) (or any other, better name) and then just check with instanceof instead of checking for pipe method

Oh wow, very good catch, hadn't thought of that. As Fastify already handles streams and buffers, would this change only affect Express, or should we make a similar change (using this new class) for Fastify as well, to keep parity between the engines?

[kamilmysliwiec]

As Fastify already handles streams and buffers, would this change only affect Express, or should we make a similar change (using this new class) for Fastify as well, to keep parity between the engines?

Well, I guess we can just add a new wrapper class and mention it in the docs as a "cross-platform" supported solution. As you pointed out above, since Fastify already handles streams and buffers, using this class won't be required (but still, it gives some ++ in case one wants to switch to another HTTP engine at some point).

[jmcdo29]

Circling back around to this: what about StreamableFile as a class name? That or NestStreamable or NestFile? Something that specifies it's to be used with the framework.

Also, where in the code would this go? I assume @nestjs/common, but not sure where from there. http?

[kamilmysliwiec]

StreamableFile sounds good :)

I assume @nestjs/common, but not sure where from there. HTTP?

We might need a new folder for this. I'm open to any ideas. classes seems to be somewhat too generic

[jmcdo29]

All right, I'll get back to work on this PR when I've got some time and we can discuss what changes might need to be made when I update the PR

[jmcdo29]

All right, added in the StreamableFile class and I think it's working as expected. Let me know what you think and if I should get to work on the docs.

[kamilmysliwiec]

Looks great! @jmcdo29 can you please resolve conflicts + create a PR to the docs with this feature? I'm not sure what would be the best chapter to add it though (maybe FIle Upload although the name may be a little bit confusing)

[jmcdo29]

What if we add a section to the Controllers page about Streaming Files? Though, that page is getting pretty cluttered. Maybe a new Technique?

[jmcdo29]

Merge conflicts are fixed. Kafka test failed (as usual)

[kamilmysliwiec]

LGTM, thanks!