cmd/go: clarify error for invalid proxy responses #38680
Description
What version of Go are you using (go version)?
$ go version go version go1.14.2 darwin/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 GO111MODULE="" GOARCH="amd64" GOBIN="" GOCACHE="/Users/hennadii/Library/Caches/go-build" GOENV="/Users/hennadii/Library/Application Support/go/env" GOEXE="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="darwin" GOINSECURE="" GONOPROXY="" GONOSUMDB= GOOS="darwin" GOPATH="/Users/hennadii/code/golang" GOPRIVATE="" GOPROXY= GOROOT="/usr/local/Cellar/go/1.14.2_1/libexec" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/Cellar/go/1.14.2_1/libexec/pkg/tool/darwin_amd64" GCCGO="gccgo" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" 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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/2j/23_h2scj481d4l34mjxwpsyr0000gn/T/go-build221808420=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
Originally, tried to install tools in VS Code, but later narrowed it down to installing this package
go get rsc.io/quote
(in module, not on GOPATH)
I do have GOPROXY pointing at 'private' server, and I get the error when that server is not reachable due to networking. Go commands start working again as expected when connectivity is restored
What did you expect to see?
Some error hinting at problems with proxy accessibility
What did you see instead?
go get rsc.io/quote: module rsc.io/quote: invalid character 'e' looking for beginning of value