https://github.com/googleapis/googleapis/blob/master/google/... is a more complete version of this. It supports resumable uploads, and the download can start from an offset within a file, allowing you to download only part of the file instead of the whole.

Another version of this is to use grpc to communicate the "metadata" of a download file, and then "side" load the file using a side channel with http (or some other light-weight copy methods). Gitlab uses this to transfer Git packfiles and serve git fetch requests iirc https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/sidec...

Building on sluongng's point about schema evolution: we ended up in a weird middle ground on a project where we used gRPC for metadata and presigned S3 URLs for the actual bytes.

The metadata schema changed constantly (new compression formats, different checksum algorithms, retry policies). Having protobufs for that was genuinely useful. But trying to pipe multi-gigabyte files through gRPC streams was painful. Memory pressure, connection timeouts on slow clients, debugging visibility was terrible.

S3 presigned URLs are the boring answer, but they work. Your object storage handles the hard parts (resumability, CDN integration, the actual bytes), and your gRPC service handles the interesting parts (authentication, metadata, business logic).

I would add a further advantage of plain HTTP (REST) compared to gRPC. Splitting the response into blocks and having the client request the next block, as in the gRPC solution, causes round-trip delays. The server can't send the second block of data until the client requests it, so the server is essentially idle until the client has received all packets of the first block, parsed them and generated the next request.

In contrast, while HTTP/2 does impose framing of streams, that framing is done entirely server-side. If all one end has to send to the other is a single stream, it'll be DATA frame after DATA frame for the same stream. The client is not required to acknowledge anything. (At least, nothing above the TCP layer!)

It probably wasn't noticeable in this experiment as, if I'm reading it correctly, the server and client were on the same box, but if you were separated by any significant distance, plain HTTP should be noticeably faster.

I've done this before, using Google's semi-standard ByteStream messages. It works, but is a bit of work, and I really don't love how you're building on top of a protocol that completely solves streaming contents of arbitrary size, which gRPC drops, and you have to reinvent again in the application layer.

I know it's not easy to solve given how protobuf-centric it is, but this is the worst piece of gRPC for me. The 4MB limit is a terrible size, it's big enough to rarely hit in test cases but small enough it can hit you in production. If you control it all you can just lift that number to something arbitrarily big to avoid most things just failing (although you probably don't want to use that as an actual solution for streaming files of any size), but in practice a lot of "serious" setups end up contorting themselves remarkably to try to avoid that limit.

Perhaps worth mentioning: https://github.com/stapelberg/rsync-over-grpc.

Method signatures in gRPC present a pandora's box of questions: https://matttproud.com/blog/posts/grpc-method-discipline.htm....

The questions aren't unique to gRPC, however; gRPC forces you to confront them early and explicitly IMO, which is not a bad thing.

I have PTSD from Google Protobufs. Sometimes the cost of a less-efficient protocol or traditional REST is worth it over an overengineered solution. Protobufs can be fine, but it's largely overkill. Debugging with protobuf was the price we paid for an "efficient" protocol

And then a C programmer comes in and slams sendfile. That’s the main advantage of HTTP/1.1. Of course TLS throws a wrench in it, but once kTLS is actually good (ahem), it’ll work.

In all seriousness, don’t do large file transfers over gRPC, except in a pinch for small files. As soon as e.g API gateways are introduced in the mix, stuff can go south very quickly: increased allocation, GC pressure, network usage, etc. Just use presigned S3 URLs.

Apparently the correct spelling is "transferring".