Add support for "file" return args

[bajtos]

1. Fix handling of return args with http.target:header. Arguments mapped to a response http header should not be included in the response body.

2. Allow users to specify { type: 'file', root: true } for the single argument that will be sent directly as the response body.

The following values are supported for file the file argument:

• String
• Buffer
• ReadableStream (anything that exposes .pipe() method)

Example usage:

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' } },
  ],
});

Fix strongloop/loopback#2063
Connect to strongloop/loopback#213
Connect to #35

/to @ritch please review
/cc @raymondfeng @STRML

[bajtos]

I have simplified and reworked this feature. Instead of adding a new flag, I added a new type called "file":

{
  returns: { arg: 'body', type: 'file', root: true }
}

This way the feature is focused on developer's intention (I want to return a raw file response) instead of implementation details (I want to skip json/xml encoding and send the value in raw form). This should make it easier for consumers of remoting metadata (e.g. loopback-swagger) to correctly handle this case.

[ritch]

We should add a note to these docs: http://apidocs.strongloop.com/strong-remoting/#sharedmethod about the new file type.

Otherwise LGTM 👍

[bajtos]

We should add a note to these docs: http://apidocs.strongloop.com/strong-remoting/#sharedmethod about the new file type.

Added, see 0d4ea21

I'd like to document this feature in more details as part of #35, I'll probably create a new "doc" story for that.

[raymondfeng]

It's a great feature. What about accepts? If one of the args is file, we should only handle the content-type multipart/form-data. See http://swagger.io/specification/

[bajtos]

It's a great feature. What about accepts? If one of the args is file, we should only handle the content-type multipart/form-data. See http://swagger.io/specification/

@raymondfeng sounds good, please open a new issue to keep track of this feature request.