x/net/http/httpguts: add parser/accessors for Link header

[arnottcr]

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

$ go version
go version go1.12.4 linux/amd64

Does this issue reproduce with the latest release?

yes

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

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/user/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/user/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build550614768=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I am consuming an API that implements pagination via the link header, see RFC5988.

What did you expect to see?

I hoped that the std lib would have implemented a parser for this bespoke syntax. This could even be done lazily to prevent overhead.

What did you see instead?

I was forced to grab a 3rd party library (e.g. github.com/deiu/linkheader, github.com/tomnomnom/linkheader), or implement the parser myself.

[julieqiu]

/cc @bradfitz

[bradfitz]

net/http doesn't aim to be everything to everybody. It's perfectly acceptable to use third-party packages. If somebody wants to add something to x/net/http/httpguts, that's fine too.

[arnottcr]

sgtm; is there opposition to merging in something that has stabilized in golang.org/x/net, considering this is an RFC, or is the API bloat not worth the cost?

[bradfitz]

I don't think it ever needs to live in net/http.

[smasher164]

Is there still demand for this feature? I see NeedsFix on this issue, but there isn't a proposed API.

[bradfitz]

Changed it to NeedsInvestigation then.