Minimize allocations writing User-Agent header

[mattrobenolt]

The fmt.Sprintf stood out again in my profiling as a relatively hot path, and through the lifetime of an application, this value will not change. So we can generate this header value at init() time and avoid the extra memory allocation as well on each request.

Before submitting your PR: Please read through the contribution guide at https://github.com/bufbuild/connect-go/blob/main/.github/CONTRIBUTING.md

[mattrobenolt]

I'm not sure if you'd want to exclude these linter failures since this pattern is already used elsewhere, and doing this any other way would also require a global variable. (with a sync.Once)

[bufdev]

Also just a comment, we/I hate force pushes on PRs because it overwrites review context...I only mention it as I assume you're going to be a long-time contributor and figured worth getting on same page :-)

[mattrobenolt]

Also just a comment, we/I hate force pushes on PRs because it overwrites review context

👍

Would you typically then squash merge? As long as it's squashed, that's fine with me.

[pkwarren]

Would you typically then squash merge? As long as it's squashed, that's fine with me.

Yep - that's the only option on most/all of our repos.

[pkwarren]

LGTM. Will wait for @akshayjshah/@bufdev to merge.

[akshayjshah]

LGTM.

I'd prefer to stop here - we're eating a slice allocation every time we write this header, but I don't want a global []string here. (I say this because long ago I tried to optimize away all the slice allocations, but the safety tradeoffs weren't worth it for a Buf-supported library.)