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

$ go version
go version go1.11.3 darwin/amd64

Does this issue reproduce with the latest release?

Yes

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

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/stefanb/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/stefanb/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/Cellar/go/1.11.3/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.11.3/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/z2/3bdl__bs0xxd3kmf5c1pj0gm0000gn/T/go-build212726590=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

import (
	"net/http"
)

func main() {
	_, err := http.Get(" http://example.org")
	if err != nil {
		panic(err)
	}
}

https://play.golang.org/p/jkcYSD6ZRcO

What did you expect to see?

Either

• a generic error message of invalid URL or
• a detailed error of invalid URL scheme or
• a detailed error of leading space in URL

What did you see instead?

A misleading detailed error message:

parse  http://example.org: first path segment in URL cannot contain colon

In #24246 the proposed solution was to trim the URLs before using them, but from the given error message it is very hard to see what the real problem is.

I propose to either:

• adjust the error message to eg:

parse  http://example.org: URL scheme cannot contain spaces

or

• quote the problematic URL in the error message, so that it is more obvious even if the message itself remains misleading:

parse " http://example.org": first path segment in URL cannot contain colon

or

• ideally both adjust the error message + quote the URL:

parse " http://example.org": URL scheme cannot contain spaces

The cannot contain spaces in error message can be changed for cannot contain whitespace or even contains invalid characters, depending how the check is implemented.

Current implementation: