cmd/go: clarify error for invalid proxy responses

[homelchenko]

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

[smasher164]

@bcmills @jayconrod @matloob

[jayconrod]

I couldn't reproduce this. Tried a few different things:

When offline, with default GOPROXY:

go get rsc.io/quote: module rsc.io/quote: Get "https://proxy.golang.org/rsc.io/quote/@v/list": dial tcp: lookup proxy.golang.org: no such host

When offline, with GOPROXY=direct:

go get rsc.io/quote: unrecognized import path "rsc.io/quote": https fetch: Get "https://rsc.io/quote?go-get=1": dial tcp: lookup rsc.io: no such host

Online, with GOPROXY referring to a non-existent host:

go get rsc.io/quote: module rsc.io/quote: Get "https://does.not.exist/rsc.io/quote/@v/list": dial tcp: lookup does.not.exist: no such host

@homelchenko Could you post your GOPROXY setting? It wasn't included in the go env output. Could you tell us more about the proxy itself, too?

The string looking for beginning of value appears in encoding/json. Just taking a wild guess, the proxy may have served invalid JSON on the $module/@v/$version.info or $module/@latest endpoints.

[homelchenko]

Right, I specifically cut off GOPROXY settings as it contains a reference to 'private' goproxy based on athens, and I'd rather not post it on public issue tracker :sorry:

To add to my setup: there's this Athens instance, which is on internal network, and my GOPROXY points to it via some subdomain. When I am not on VPN these days, I get the error I described above. However, now that I pinged the proxy, it looks like it is reachable, it might be I get some 'other' response from athens while not on VPN

[homelchenko]

Okay, having done a few more experiments, I seem to understand more why i can see that 'e' letter in the error. So, under those circumstances when I am not on vpn, what server responds to '< proxy >/rsc.io/quote/@v/list/ is not html containing list of available versions, but with some dummy text starting with 'e'.

Looks like the root cause

[jayconrod]

Ok cool, I've changed the issue title to indicate we should clarify these error messages.

Out of curiosity, could you post the proxy response containing the dummy text?

[homelchenko]

HTTP/1.1 0 Unknown
content-length: 11
content-type: text/plain
date: Mon, 27 Apr 2020 16:59:09 GMT
server: envoy

empty token

[mlowicki]

I'll take a look at this issue.

[mlowicki]

I was able to reproduce it on my machine with:

$ GOPROXY=http://localhost:8000 go get rsc.io/quote
go get rsc.io/quote: module rsc.io/quote: invalid character 'x' looking for beginning of value

server:

package main

import (
        "fmt"
        "net/http"
)

func main() {
        http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
                fmt.Fprintf(w, "x")
        })
        err := http.ListenAndServe("localhost:8000", nil)
        if err != nil {
                panic(err)
        }
}

For the record, returning status code 0 as mentioned in #38680 (comment) triggers other error:

$ GOPROXY=http://localhost:8000 go get rsc.io/quote
go get rsc.io/quote: module rsc.io/quote: Get "http://localhost:8000/rsc.io/quote/@v/list": net/http: HTTP/1.x transport connection broken: malformed HTTP status code "0"

I'll work now on improving error messages.

[gopherbot]

Change https://golang.org/cl/233437 mentions this issue: cmd/go: clarify error for invalid proxy responses