Support the new return arg type "file"

[bajtos]

In strongloop/strong-remoting#284, we added support for new return type "file":

MyModel.download = function(cb) {
  // this can be for example http.request()
  getTheStreamBody(function(err, stream) {
    if (err) return cb(err);
    // stream can be any of: string, buffer, ReadableStream (e.g. http.IncomingMessage)
    cb(null, stream, 'application/octet-stream');
  });
}

MyModel.remoteMethod('download', {
  isStatic: true,
  returns: [
    { arg: 'body', type: 'file', root: true },
    { arg: 'Content-Type', type: 'string', http: { target: 'header' } },
  ],
});

Now we need to extend swagger-spec generator to support his new file and map it to swagger type "file".

Nice to have: support return arguments mapped as http.target:header too.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been closed due to continued inactivity. Thank you for your understanding. If you believe this to be in error, please contact one of the code owners, listed in the CODEOWNERS file at the top-level of this repository.

[eisverticker]

the file loopback type is still not documented and the loopback-cli does not support that type either
see loopback type documentation

[bajtos]

A status update/summary for anybody discovering this issue (cc @eisverticker @bschrammIBM). As I understand it, our support for "file" type is partial only.

At the side of remote method output ("returns" arguments):

• Add support for "file" return args strong-remoting#284 modified our runtime to allow remote methods to return a single "file" type argument that's mapped to the response body.
• loopback-swagger was not updated yet to support this new type, this very issue Support the new return arg type "file" #34 is keeping track of that feature. Because it hasn't received enough priority and attention, it was automatically closed by our stale-bot, even though it has not been implemented.
• Improve schema generation for return object #28 modified our swagger-spec generator to recognize ReadableStream (used by PersistedModel.createChangeStream) as an allowed return type and emit "file" in the swagger spec.

At the side of remote method inputs ("accepts" arguments):

• Add support for file type #34 #90 modifies swagger spec generator to recognize "file" type inputs
• however, our runtime does not support "file" inputs yet - see Allow remote methods to accept uploaded files loopback#3266

Actionable items for volunteers wanting to help us to make "file" support happen:

• Modify swagger spec generator to recognize "file" return types, as described at the top of this GH issue (this should be fairly easy).
• Improve strong-remoting to support "file" uploads (Allow remote methods to accept uploaded files loopback#3266). This is a pretty advanced task requiring quite a bit of knowledge about how HTTP requests work in Node.js and how are file uploads represented in HTTP messages. The code in loopback-component-storage's upload function is a good source of inspiration.