core/filemgr: use xxhash instead of sha512 for filenames

[calebdoxsey]

Summary

For envoy we use files as a DataSource whenever possible. When we have raw data we save it to a cache directory with a filename like tls-crt-xxx.pem. The hash of the filename is computed using the SHA512_256 of the bytes.

For this use case its not necessary to have a cryptographic hash. We can instead use xxhash which is much faster. Roughly 10x improvement:

// BenchmarkGetFileNameWithBytesHash-10    	   12331	     95284 ns/op	    1657 B/op	      63 allocs/op
// BenchmarkGetFileNameWithBytesHash-10    	  112304	      9472 ns/op	     112 B/op	       5 allocs/op

Related issues

• https://github.com/pomerium/internal/issues/1573

Checklist

• reference any related issues
• updated docs
• updated unit tests
• updated UPGRADING.md
• add appropriate tag (improvement / bug / etc)
• ready for review

[coveralls]

coverage: 63.99% (-0.03%) from 64.015% when pulling 9ac7f53 on cdoxsey/bytes-data-source-performance into 53573dc on main.

[wasaga]

does xxhash require cgo?

The package is written with optimized pure Go and also contains even faster assembly implementations for amd64 and arm64. If desired, the purego build tag opts into using the Go code even on those architectures.

[calebdoxsey]

Not as far as I know. I didn't add xxhash. We already use it. If we don't trust it I can replace it with something else everywhere we use it.

[wasaga]

I didn't notice it's an existing dependency