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Joe Tsai 81d9214ff6 expvar: emit valid JSON strings
Map.String and expvarHandler used the %q flag with fmt.Fprintf
to escape Go strings, which does so according to the Go grammar,
which is not always compatible with JSON strings.

Rather than calling json.Marshal for every string,
which will always allocate, declare a local appendJSONQuote
function that does basic string escaping.
Also, we declare an unexported appendJSON method on every
concrete Var type so that the final JSON output can be
constructed with far fewer allocations.

The resulting logic is both more correct and also much faster.
This does not alter the whitespace style of Map.String or expvarHandler,
but may alter the representation of JSON strings.

Performance:

	name         old time/op    new time/op    delta
	MapString    5.10µs ± 1%    1.56µs ± 1%  -69.33%  (p=0.000 n=10+9)

	name         old alloc/op   new alloc/op   delta
	MapString    1.21kB ± 0%    0.66kB ± 0%  -45.12%  (p=0.000 n=10+10)

	name         old allocs/op  new allocs/op  delta
	MapString      37.0 ± 0%       7.0 ± 0%  -81.08%  (p=0.000 n=10+10)

Fixes #59040

Change-Id: I46a2125f43550b91d52019e5edc003d9dd19590f
Reviewed-on: https://go-review.googlesource.com/c/go/+/476336
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
2023-08-19 23:26:49 +00:00
.github .github: fix templates with multiple labels 2023-07-31 18:28:27 +00:00
api encoding: add AppendEncode and AppendDecode 2023-08-17 16:23:42 +00:00
doc spec: correct type parameter name used in example 2023-08-18 20:44:48 +00:00
lib/time lib/time: update to 2023c/2023c 2023-05-03 20:14:11 +00:00
misc misc/wasm: switch default WASI runtime 2023-07-26 14:30:35 +00:00
src expvar: emit valid JSON strings 2023-08-19 23:26:49 +00:00
test cmd/compile: enable -d=zerocopy by default 2023-08-18 11:59:42 +00:00
.gitattributes
.gitignore internal/platform,cmd/dist: export the list of supported platforms 2023-06-22 19:44:52 +00:00
codereview.cfg codereview.cfg: add codereview.cfg for master branch 2021-02-19 18:44:53 +00:00
CONTRIBUTING.md doc: normalize proposal-process links 2023-03-29 22:00:27 +00:00
go.env cmd/go: additional doc-inspired tests and bug fixes 2023-06-06 19:18:46 +00:00
LICENSE
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README.md README: update from CC-BY-3.0 to CC-BY-4.0 2022-11-02 20:14:56 +00:00
SECURITY.md SECURITY.md: replace golang.org with go.dev 2022-04-26 19:59:47 +00:00

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