The sha256 hash writer doesn't implement WriteString.
(See https://github.com/golang/go/issues/38776.)
As a consequence, we end up converting many strings to []byte.
Wrapping a bufio.Writer around the hash writer lets us
avoid these conversions by using WriteString.
Using a bufio.Writer is, perhaps surprisingly, almost as cheap as using unsafe.
The reason is that the sha256 writer does internal buffering,
but doesn't do any when handed larger writers.
Using a bufio.Writer merely shifts the data copying from one buffer
to a different one.
Using a concrete type for Print and print cuts 10% off of the execution time.
name old time/op new time/op delta
Hash-8 15.3µs ± 0% 11.5µs ± 0% -24.84% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
Hash-8 2.82kB ± 0% 1.98kB ± 0% -29.57% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
Hash-8 140 ± 0% 82 ± 0% -41.43% (p=0.000 n=10+10)
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
The new deepprint package just walks a Go data structure and writes to
an io.Writer. It's not pretty like go-spew, etc.
We then use it to replace the use of UAPI (which we have a TODO to
remove) to generate signatures of data structures to detect whether
anything changed (without retaining the old copy).
This was necessary because the UAPI conversion ends up trying to do
DNS lookups which an upcoming change depends on not happening.
Josh Bleecher Snyder
Dmytro Shynkevych
Brad Fitzpatrick