perf: Copy files instead of sending over HTTP if Wave app and Wave server are running on the same machine. #982

[mturoci]

This is a rough proposal for further discussion. If approved, will finish the rest of the sync/async upload methods.

Rationale: When uploading files, we send them over HTTP with serialization/deserialization overhead that slows the whole method. However, most of the Wave apps run both Wave server (waved) and Wave app on the same machine which means a simple file copy should be enough.

Perf testing

HTTPX 0.16.1 is the original version from the time of creating issue #982.

File size	HTTPX 0.16.1	HTTPX 0.23.1 (latest - Mac)	cp (Mac)	robocopy (Windows)	xcopy (Windows)	HTTPX 0.23.1 (latest - Windows)
1GB	~8.5s	~4.3s	~14ms	~50ms	~800ms	~5.8s
10 GB	10min timeout	~40s	~10ms	~150ms	~75s	10min timeout

Although we have public/private dirs, the concept of serving files and figuring out what is the correct URL can be troublesome for non-software engineering users so I would suggest keeping the current q.site.upload as is.

This change would impact most (if not all) Wave users who use q.site.upload.

Wdyt @lo5?

Closes #982

[lo5]

The implementation looks good.

However, because the implementation unconditionally resorts to copy-if-local, it's possible we might hit some unforeseen OS permissions/config where the copying might fail.

Possible safeguards are:
A. Fallback to HTTP if local copy fails (try-except).
B. Enable copy-if-local behavior only if an env var is set.
C. Enable copy-if-local by default, but allow disabling behavior if an env var is set (provides an escape hatch if existing installations get hosed).

Thoughts?

[mturoci]

Thanks for the suggestions @lo5! A combination of A and C seems like the way to go for me. Will do.

[mturoci]

The PR is done.

• Tested against both Windows and Unix.
• Made async (to not block the main thread).

@lo5 can you please let me know what you think about naming? (H2O_WAVE_NO_COPY_UPLOAD, H2O_WAVE_WAVED_DIR). Once resolved, can be merged.

[lo5]

Names look fine. Minor changes to the docs.