Add support for multipart uploads

[evanfuller]

Tika appears to support multipart file uploads via the endpoint POST /tika/form, as documented here.

It would be great to add this support so that we could use the client for uploading large files without having to hold the buffer with all bytes in memory.

[tbpg]

This seems reasonable to me (another endpoint to support). But, I'm not sure I understand this part:

hold the buffer with all bytes in memory.

An io.Reader doesn't need to be stored in memory, right? Or is this an issue under the hood with how the request is handled?

[evanfuller]

@tbpg I'm basing my intuition off of this medium post.

The gist would be that if we want multipart support, we need some in-memory buffer to pass to multipart.NewWriter() when building requests, but in the (first) experiment the author conducted, Go just naively built a buffer in-memory containing the entire file. Later in the post, the author makes an improvement by using an io.Pipe instead so that the entire file is not held in memory just for the request.

Admittedly, I did not attempt to replicate the findings of this post, so it could be possible that Go has improved buffering for large requests like this, but I'm not sure.

[tbpg]

Gotcha. That seems reasonable to me. I think we'd have to play with what the exact API is for the tika package. In general, I'd like to leave as much of the creation of the io.Reader to the caller. But, it might be too cumbersome to expect someone to use the multipart package?

[evanfuller]

Yeah, point definitely taken on trying to be implementation/caller-agnostic. That said, the docs for this particular endpoint suggest that it is specifically for use with multipart uploads.

[k7en]

Hello
I'm trying to extract meta-information and body text of a large file and it's consuming a lot of memory and I came here in search of a solution. I would like to communicate to Tika's API using the Multpart method.
Do you know what the situation is now with this Issue?
If you know how to solve this problem, I'd appreciate some advice.
BRGDS.

[tbpg]

I'm very open to a PR here. Warning, we might need to modify the interface a little bit, keeping it as minimal as possible while enabling you to do what you need to do.