net/http: ReadRequest should return error or not delete Host Header

[ianwoolf]

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

$ go version
go version go1.16.2 darwin/amd64

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

go env Output

$ go env
GO111MODULE="auto"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/xx/Library/Caches/go-build"
GOENV="/Users/xx/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/xx/code/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/xx/code/go"
GOPRIVATE=""
GOPROXY="https://goproxy.io,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.16.2"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/xx/code/go/src/go/src/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/3f/x8jl0lgx629d_5bz0537gxnm0000gn/T/go-build908271374=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I noticed that http.readRequest has a param called deleteHostHeader to control whether to delete the Host of Request.Header. It seems to be designed so that http.ReadRequest can skip the Host check.

But if http.ReadRequest sets deleteHostHeader to true, the first Host Header is read in readRequest and the Host Header is deleted, which makes http.ReadRequest lose the rest of the Host Header.

I don't understand whether the processing of the Host Header is to be skipped, or the Host Header needs to be check and return error when there is multi Host Header. So I think the processing here can be more clear.

related to #45463

What did you expect to see?

Clear processing strategy for multiple Host Headers. For example, http.Request do not delete the Host Header, or reject multiple Host Header Requests

What did you see instead?

http.Request do not check the Host Header and delete the Host in the Header after getting the first Host Header

[gopherbot]

Change https://golang.org/cl/308952 mentions this issue: net/http: ReadRequest return error when requests has multiple Host headers

[mknyszek]

CC @bradfitz @rsc @empijei via https://dev.golang.org/owners

[mknyszek]

If I understand correctly, this is more of just a cleanup, right? Are there any functional changes that your CL makes?

[ianwoolf]

There is a function called http.ReadRequest that is not called by other functions. It is exposed for specialized applications. I made a small change. When the Header has multiple Host, the return is changed from nil to error.

In fact, this function does not allow multiple Host Headers. Because this function only read the first Host Header, and directly discards the rest Host Header. So I agree with what Dave said in #45463, it is more appropriate to return an error when there are multiple Host Headers.

[networkimprov]

@dmitshur we have a request to backport this, see #45463