encoding/json: reduce allocations by Decoder for \uXXXX

[schmichael]

What version of Go are you using (go version)?

go version go1.8.3 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/schmichael/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build241021771=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

Looked at how json.Decoder parsed Unicode escape sequences.

What did you expect to see?

Not strconv

What did you see instead?

strconv

I'm working on a patch to decoder.go:getu4() to convert Unicode escape sequences to their underlying rune without round tripping the data through a string to use strconv. Should save an allocation.

[gopherbot]

CL https://golang.org/cl/44738 mentions this issue.