Transform Uploads to Streams before calling action

[dylanwulf]

Hello 👋 I am currently working on accepting file uploads with moleculer-apollo-server. In the process, I discovered a couple pain points which I would like to propose solutions for. These changes will result in a minor API change.

Problem 1

In ApolloServer.js, the processRequest function is being imported from v10 of graphql-upload. The output from the processRequest function then ends up passing through the GraphQLUpload scalar implementation, which is re-exported from apollo-server-core in index.js. The problem is that apollo-server-core is using v8 of graphql-upload. Since the output of v10 processRequest does not match the expected input of v8 GraphQLUpload, the action ends up receiving the wrong data.

Proposed solution to Problem 1

In index.js, we could re-export GraphQLUpload from the graphql-upload package instead of from apollo-server-core. This should ensure that both processRequest and GraphQLUpload are coming from the same version of graphql-upload.

Problem 2

When uploading a file, the action receives a parameter in the following format (assuming Problem 1 has been fixed):

{
  filename: string
  encoding: string
  mimetype: string
  createReadStream: function
}

Calling the createReadStream function will return a readable Stream which can be used to read the contents of the uploaded file. Unfortunately since functions are not serializable, file uploads do not work across the transporter.

Proposed solution to Problem 2

Moleculer supports passing streams to actions, so in service.js createActionResolver, we could transform the file upload into a stream before calling the action. This should allow file uploads to actions in separate nodes.
Since we have no way to tell which arguments are uploads, we could allow the consumer to specify the name of the argument which is expected to be a file upload (I named this option fileUploadArg).
Unfortunately this solution creates a couple sub-problems, discussed below.

Subproblem 2.1

When a stream is passed to an action, that action cannot accept any other parameters. So we can get the file contents to the action, but filename, encoding, and mimetype get lost.

Proposed solution to Subproblem 2.1

We can put filename, encoding, and mimetype into ctx.meta so that the action still has access to that data (I used a property called ctx.meta.$fileInfo).

Subproblem 2.2

graphql-upload allows uploading multiple files in a single mutation. But moleculer actions can only receive a single stream.

Proposed solution to Subproblem 2.2

If the fileUploadArg is an array, then we can call the action once per array element, and combine the results into a result array. This would allow multiple file uploads in a single mutation.

Thank you!

[shawnmcknight]

This proposal looks good to me with the exception of my few notes. Please make sure to update the TS types (I think only the GraphQL upload is affected) also.

[shawnmcknight]

This looks really solid. Thank you for including the examples and documentation. I just had one note to relocate the placement of the export.

[icebob]

Thank you very much for your PR! Particularly, you've added example & update docs with example. Great job!

[icebob]

@shawnmcknight I've approved it. If you also approve, please merge it.

[shawnmcknight]

Excellent! Merging!

[shawnmcknight]

@icebob When you have an opportunity, can you publish a new version for this?

This is a partial breaking change due to the export of a different version of GraphQL upload which elicits different behavior from the object that is resolved. The new transformation to a stream logic is opt-in, but an existing consumer would see different behavior due to how the graphql-upload version differs from how the version exported from apollo-core worked.

[icebob]

Released as 0.3.0: https://github.com/moleculerjs/moleculer-apollo-server/releases/tag/v0.3.0