net/mail: ParseAddress doesn't support using a domain-literal in the domain of an email address

[robplee]

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

$ go version
go version go1.19.5 darwin/amd64

Does this issue reproduce with the latest release?

Yes, confirmed against 1.20 and "Go dev branch" using The Go Playground

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/robertlee/Library/Caches/go-build"
GOENV="/Users/robertlee/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/robertlee/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/robertlee/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.19.5/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.19.5/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.19.5"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/robertlee/go/src/go.mod"
GOWORK=""
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/g9/kjpfy6dn3f3gr60k0j5f5j9r0000gn/T/go-build2238133857=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I used mail.ParseAddress to try to parse an email address containing an IP address.

package main

import (
	"fmt"
	"net/mail"
)

func main() {
	_, err := mail.ParseAddress("me@[192.168.0.1]")
	if err != nil {
		fmt.Println("mail is complaining incorrectly")
	}
}

Go playground: https://go.dev/play/p/rZW6QPqVZC6

What did you expect to see?

mail.ParseAddress shouldn't have returned an error and the program should not have printed any output

This format, me@[192.168.0.1], is how email addresses are supposed to be formatted according to Section 3.4.1 of RFC 5322, so this email address should have been parsed correctly without any error being returned.

What did you see instead?

mail.Parse address did return an error so the message "mail is complaining incorrectly" was printed

[heschi]

cc @bradfitz

[seankhliao]

It's a valid (according to RFC) formatting of an address, but it would also be valid to format it as me@192.168.0.1.

The RFC also notes

Note: A liberal syntax for the domain portion of addr-spec is
given here. However, the domain portion contains addressing
information specified by and used in other protocols (e.g.,
[RFC1034], [RFC1035], [RFC1123], [RFC5321]). It is therefore
incumbent upon implementations to conform to the syntax of
addresses for the context in which they are used.

Which sounds like we'd have to decide on address formats to support.

[nunogoncalves03]

I have reproduced the issue and investigated both the RFC specification and the code itself. Upon inspecting the code, I found a relevant TODO:

go/src/net/mail/message.go

Lines 550 to 562 in ef84d62

	// domain = dot-atom / domain-literal
	var domain string
	p.skipSpace()
	if p.empty() {
	return "", errors.New("mail: no domain in addr-spec")
	}
	// TODO(dsymonds): Handle domain-literal
	domain, err = p.consumeAtom(true, false)
	if err != nil {
	return "", err
	}
	return localPart + "@" + domain, nil

Based on this, it seems like there's a need to implement handling for domain literals in the email parsing logic. I'll be working on a fix.

[gopherbot]

Change https://go.dev/cl/567777 mentions this issue: net/mail: enhance address parser to include support for domain literals

[gopherbot]

Change https://go.dev/cl/613335 mentions this issue: net/mail: enhance address parser to include IPv6 address tags